Patent Application
20200385763
The present invention relates generally to biosynthetic processes, and more specifically to organisms having 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic capability.
Over 25 billion pounds of butadiene (1,3-butadiene, BD) are produced annually and is applied in the manufacture of polymers such as synthetic rubbers and ABS resins, and chemicals such as hexamethylenediamine and 1,4-butanediol. Butadiene is typically produced as a by-product of the steam cracking process for conversion of petroleum feedstocks such as naphtha, liquefied petroleum gas, ethane or natural gas to ethylene and other olefins. The ability to manufacture butadiene from alternative and/or renewable feedstocks would represent a major advance in the quest for more sustainable chemical production processes
One possible way to produce butadiene renewably involves fermentation of sugars or other feedstocks to produce diols, such as 1,4-butanediol or 1,3-butanediol, which are separated, purified, and then dehydrated to butadiene in a second step involving metal-based catalysis. Direct fermentative production of butadiene from renewable feedstocks would obviate the need for dehydration steps and butadiene gas (bp −4.4° C.) would be continuously emitted from the fermenter and readily condensed and collected. Developing a fermentative production process would eliminate the need for fossil-based butadiene and would allow substantial savings in cost, energy, and harmful waste and emissions relative to petrochemically-derived butadiene.
2,4-Pentadienoate is a useful substituted butadiene derivative in its own right and a valuable intermediate en route to other substituted 1,3-butadiene derivatives, including, for example, 1-carbamoyl-1,3-butadienes which are accessible via Curtius rearrangement. The resultant N-protected-1,3-butadiene derivatives can be used in Diels alder reactions for the preparation of substituted anilines. 2,4-Pentadienoate can be used in the preparation of various polymers and co-polymers.
1,3-butanediol (1,3-BDO) is a four carbon diol traditionally produced from acetylene via its hydration. The resulting acetaldehyde is then converted to 3-hydroxybutyraldehdye which is subsequently reduced to form 1,3-BDO. In more recent years, acetylene has been replaced by the less expensive ethylene as a source of acetaldehyde. 1,3-BDO is commonly used as an organic solvent for food flavoring agents. It is also used as a co-monomer for polyurethane and polyester resins and is widely employed as a hypoglycaemic agent. Optically active 1,3-BDO is a useful starting material for the synthesis of biologically active compounds and liquid crystals. A commercial use of 1,3-butanediol is subsequent dehydration to afford 1,3-butadiene (Ichikawa et al., J. of Molecular Catalysis A-Chemical, 256:106-112 (2006); Ichikawa et al., J. of Molecular Catalysis A-Chemical, 231:181-189 (2005)), a 25 billion lb/yr petrochemical used to manufacture synthetic rubbers (e.g., tires), latex, and resins. The reliance on petroleum based feedstocks for either acetylene or ethylene warrants the development of a renewable feedstock based route to 1,3-butanediol and to butadiene.
3-Buten-1-ol is a raw material used in pharmaceuticals, agrochemicals, perfumes and resins. The palladium-catalyzed coupling of 3-buten-1-ol with aryl halides is a valuable process for the preparation of aryl-substituted aldehydes such as, for example, the antifolate compound Pemetrexed disodium (R. C. Larock et al., Tetrahedron Letters, 30, 6629 (1989) and U.S. Pat. No. 6,262,262). 3-Buten-1-ol is commonly prepared from propylene and formaldehyde in the presence of a catalyst at high temperature and pressure. Alternately, it is prepared from 3,4-epoxy-1-butene. Preparation of 3-buten-1-ol from renewable feedstocks has not been demonstrated to date.
Propylene is produced primarily as a by-product of petroleum refining and of ethylene production by steam cracking of hydrocarbon feedstocks. Propene is separated by fractional distillation from hydrocarbon mixtures obtained from cracking and other refining processes. Typical hydrocarbon feedstocks are from non-renewable fossil fuels, such as petroleum, natural gas and to a much lesser extent coal. Over 75 billion pounds of propylene are manufactured annually, making it the second largest fossil-based chemical produced behind ethylene. Propylene is a base chemical that is converted into a wide range of polymers, polymer intermediates and chemicals. Some of the most common derivatives of chemical and polymer grade propylene are polypropylene, acrylic acid, butanol, butanediol, acrylonitrile, propylene oxide, isopropanol and cumene. The use of the propylene derivative, polypropylene, in the production of plastics, such as injection moulding, and fibers, such as carpets, accounts for over one-third of U.S. consumption for this derivative. Propylene is also used in the production of synthetic rubber and as a propellant or component in aerosols.
The ability to manufacture propylene from alternative and/or renewable feedstocks would represent a major advance in the quest for more sustainable chemical production processes. One possible way to produce propylene renewably involves fermentation of sugars or other feedstocks to produce the alcohols 2-propanol (isopropanol) or 1-propanol, which is separated, purified, and then dehydrated to propylene in a second step involving metal-based catalysis. Direct fermentative production of propylene from renewable feedstocks would obviate the need for dehydration. During fermentative production, propylene gas would be continuously emitted from the fermenter, which could be readily collected and condensed. Developing a fermentative production process would also eliminate the need for fossil-based propylene and would allow substantial savings in cost, energy, and harmful waste and emissions relative to petrochemically-derived propylene.
Crotyl alcohol, also referred to as 2-buten-1-ol, is a valuable chemical intermediate. It serves as a precursor to crotyl halides, esters, and ethers, which in turn are chemical intermediates in the production of monomers, fine chemicals, agricultural chemicals, and pharmaceuticals. Exemplary fine chemical products include sorbic acid, trimethylhydroquinone, crotonic acid and 3-methoxybutanol. Crotyl alcohol is also a precursor to 1,3-butadiene. Crotyl alcohol is currently produced exclusively from petroleum feedstocks. For example Japanese Patent 47-013009 and U.S. Pat. Nos. 3,090,815, 3,090,816, and 3,542,883 describe a method of producing crotyl alcohol by isomerization of 1,2-epoxybutane. The ability to manufacture crotyl alcohol from alternative and/or renewable feedstocks would represent a major advance in the quest for more sustainable chemical production processes.
Thus, there exists a need for alternative methods for effectively producing commercial quantities of compounds such as 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. The present invention satisfies this need and provides related advantages as well.
The invention provides non-naturally occurring microbial organisms containing 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathways having at least one exogenous nucleic acid encoding a butadiene pathway enzyme expressed in a sufficient amount to produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. The invention additionally provides methods of using such microbial organisms to produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol, by culturing a non-naturally occurring microbial organism containing 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathways as described herein under conditions and for a sufficient period of time to produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
The present invention is directed to the design and production of cells and organisms having biosynthetic production capabilities for 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. The invention, in particular, relates to the design of microbial organisms capable of producing 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol by introducing one or more nucleic acids encoding a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway enzyme.
In one embodiment, the invention utilizes in silico stoichiometric models of Escherichia coli metabolism that identify metabolic designs for biosynthetic production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. The results described herein indicate that metabolic pathways can be designed and recombinantly engineered to achieve the biosynthesis of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol in Escherichia coli and other cells or organisms. Biosynthetic production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol, for example, for the in silico designs can be confirmed by construction of strains having the designed metabolic genotype. These metabolically engineered cells or organisms also can be subjected to adaptive evolution to further augment butadiene biosynthesis, including under conditions approaching theoretical maximum growth.
In certain embodiments, the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthesis characteristics of the designed strains make them genetically stable and particularly useful in continuous bioprocesses. Separate strain design strategies were identified with incorporation of different non-native or heterologous reaction capabilities into E. coli or other host organisms leading to 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producing metabolic pathways from 2-aminoadipate, 5-aminopentanoate, 2-oxoadipate, glutaryl-CoA, acetyl-CoA, propionyl-CoA, 3-hydroxypropionyl-CoA or pyruvate. In silico metabolic designs were identified that resulted in the biosynthesis of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol in microorganisms from each of these substrates or metabolic intermediates.
Strains identified via the computational component of the platform can be put into actual production by genetically engineering any of the predicted metabolic alterations, which lead to the biosynthetic production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or other intermediate and/or downstream products. In yet a further embodiment, strains exhibiting biosynthetic production of these compounds can be further subjected to adaptive evolution to further augment product biosynthesis. The levels of product biosynthesis yield following adaptive evolution also can be predicted by the computational component of the system.
The maximum theoretical 2,4-pentadienoate yield from glucose is 1.09 mol/mol (0.59 g/g).
11C6H12O6=12C5H6O2+6CO2+30H2O
The pathways presented in
The maximum theoretical butadiene yield from glucose is 1.09 mol/mol (0.327 g/g).
11C6H12O6=12C4H6+18CO2+30H2O
The pathways presented in
The maximum theoretical 1,3-butanediol yield from glucose is 1.09 mol/mol (0.54 g/g).
11C6H12O6=12C4H10O2+18CO2+6H2O
The pathways presented in
The maximum theoretical 3-buten-1-ol yield from glucose is 1.09 mol/mol (0.437 g/g).
11C6H12O6=12C4H8O+18CO2+18H2O
The pathways presented in
The maximum theoretical crotyl alcohol yield from glucose is 1.09 mol/mol (0.436 g/g).
11C6H12O6=12C4H8O+18CO2+18H2O
The pathways presented in
The maximum theoretical propylene yield from glucose is 1.33 mol/mol (0.31 g/g).
3C6H12O6=4C4H8O+6CO2+6H2O
The pathways presented in
As used herein, the term “non-naturally occurring” when used in reference to a microbial organism or microorganism of the invention is intended to mean that the microbial organism has at least one genetic alteration not normally found in a naturally occurring strain of the referenced species, including wild-type strains of the referenced species. Genetic alterations include, for example, modifications introducing expressible nucleic acids encoding metabolic polypeptides, other nucleic acid additions, nucleic acid deletions and/or other functional disruption of the microbial organism's genetic material. Such modifications include, for example, coding regions and functional fragments thereof, for heterologous, homologous or both heterologous and homologous polypeptides for the referenced species. Additional modifications include, for example, non-coding regulatory regions in which the modifications alter expression of a gene or operon. Exemplary metabolic polypeptides include enzymes or proteins within a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway.
A metabolic modification refers to a biochemical reaction that is altered from its naturally occurring state. Therefore, non-naturally occurring microorganisms can have genetic modifications to nucleic acids encoding metabolic polypeptides, or functional fragments thereof. Exemplary metabolic modifications are disclosed herein.
As used herein, the term “isolated” when used in reference to a microbial organism is intended to mean an organism that is substantially free of at least one component as the referenced microbial organism is found in nature. The term includes a microbial organism that is removed from some or all components as it is found in its natural environment. The term also includes a microbial organism that is removed from some or all components as the microbial organism is found in non-naturally occurring environments. Therefore, an isolated microbial organism is partly or completely separated from other substances as it is found in nature or as it is grown, stored or subsisted in non-naturally occurring environments. Specific examples of isolated microbial organisms include partially pure microbes, substantially pure microbes and microbes cultured in a medium that is non-naturally occurring.
As used herein, the terms “microbial,” “microbial organism” or “microorganism” are intended to mean any organism that exists as a microscopic cell that is included within the domains of archaea, bacteria or eukarya. Therefore, the term is intended to encompass prokaryotic or eukaryotic cells or organisms having a microscopic size and includes bacteria, archaea and eubacteria of all species as well as eukaryotic microorganisms such as yeast and fungi. The term also includes cell cultures of any species that can be cultured for the production of a biochemical.
As used herein, the term “CoA” or “coenzyme A” is intended to mean an organic cofactor or prosthetic group (nonprotein portion of an enzyme) whose presence is required for the activity of many enzymes (the apoenzyme) to form an active enzyme system. Coenzyme A functions in certain condensing enzymes, acts in acetyl or other acyl group transfer and in fatty acid synthesis and oxidation, pyruvate oxidation and in other acetylation.
As used herein, the term “ACP” or “acyl carrier protein” refers to any of the relatively small acidic proteins that are associated with the fatty acid synthase system of many organisms, from bacteria to plants. ACPs can contain one 4′-phosphopantetheine prosthetic group bound covalently by a phosphate ester bond to the hydroxyl group of a serine residue. The sulfhydryl group of the 4′-phosphopantetheine moiety serves as an anchor to which acyl intermediates are (thio)esterified during fatty-acid synthesis. An example of an ACP is Escherichia coli ACP, a separate single protein, containing 77 amino-acid residues (8.85 kDa), wherein the phosphopantetheine group is linked to serine 36.
As used herein, the term “butadiene,” having the molecular formula C4H6 and a molecular mass of 54.09 g/mol (see
As used herein, the term “substantially anaerobic” when used in reference to a culture or growth condition is intended to mean that the amount of oxygen is less than about 10% of saturation for dissolved oxygen in liquid media. The term also is intended to include sealed chambers of liquid or solid medium maintained with an atmosphere of less than about 1% oxygen.
“Exogenous” as it is used herein is intended to mean that the referenced molecule or the referenced activity is introduced into the host microbial organism. The molecule can be introduced, for example, by introduction of an encoding nucleic acid into the host genetic material such as by integration into a host chromosome or as non-chromosomal genetic material such as a plasmid. Therefore, the term as it is used in reference to expression of an encoding nucleic acid refers to introduction of the encoding nucleic acid in an expressible form into the microbial organism. When used in reference to a biosynthetic activity, the term refers to an activity that is introduced into the host reference organism. The source can be, for example, a homologous or heterologous encoding nucleic acid that expresses the referenced activity following introduction into the host microbial organism. Therefore, the term “endogenous” refers to a referenced molecule or activity that is present in the host. Similarly, the term when used in reference to expression of an encoding nucleic acid refers to expression of an encoding nucleic acid contained within the microbial organism. The term “heterologous” refers to a molecule or activity derived from a source other than the referenced species whereas “homologous” refers to a molecule or activity derived from the host microbial organism. Accordingly, exogenous expression of an encoding nucleic acid of the invention can utilize either or both a heterologous or homologous encoding nucleic acid.
It is understood that when more than one exogenous nucleic acid is included in a microbial organism that the more than one exogenous nucleic acids refers to the referenced encoding nucleic acid or biosynthetic activity, as discussed above. It is further understood, as disclosed herein, that such more than one exogenous nucleic acids can be introduced into the host microbial organism on separate nucleic acid molecules, on polycistronic nucleic acid molecules, or a combination thereof, and still be considered as more than one exogenous nucleic acid. For example, as disclosed herein a microbial organism can be engineered to express two or more exogenous nucleic acids encoding a desired pathway enzyme or protein. In the case where two exogenous nucleic acids encoding a desired activity are introduced into a host microbial organism, it is understood that the two exogenous nucleic acids can be introduced as a single nucleic acid, for example, on a single plasmid, on separate plasmids, can be integrated into the host chromosome at a single site or multiple sites, and still be considered as two exogenous nucleic acids. Similarly, it is understood that more than two exogenous nucleic acids can be introduced into a host organism in any desired combination, for example, on a single plasmid, on separate plasmids, can be integrated into the host chromosome at a single site or multiple sites, and still be considered as two or more exogenous nucleic acids, for example three exogenous nucleic acids. Thus, the number of referenced exogenous nucleic acids or biosynthetic activities refers to the number of encoding nucleic acids or the number of biosynthetic activities, not the number of separate nucleic acids introduced into the host organism.
The non-naturally occurring microbal organisms of the invention can contain stable genetic alterations, which refers to microorganisms that can be cultured for greater than five generations without loss of the alteration. Generally, stable genetic alterations include modifications that persist greater than 10 generations, particularly stable modifications will persist more than about 25 generations, and more particularly, stable genetic modifications will be greater than 50 generations, including indefinitely.
Those skilled in the art will understand that the genetic alterations, including metabolic modifications exemplified herein, are described with reference to a suitable host organism such as E. coli and their corresponding metabolic reactions or a suitable source organism for desired genetic material such as genes for a desired metabolic pathway. However, given the complete genome sequencing of a wide variety of organisms and the high level of skill in the area of genomics, those skilled in the art will readily be able to apply the teachings and guidance provided herein to essentially all other organisms. For example, the E. coli metabolic alterations exemplified herein can readily be applied to other species by incorporating the same or analogous encoding nucleic acid from species other than the referenced species. Such genetic alterations include, for example, genetic alterations of species homologs, in general, and in particular, orthologs, paralogs or nonorthologous gene displacements.
An ortholog is a gene or genes that are related by vertical descent and are responsible for substantially the same or identical functions in different organisms. For example, mouse epoxide hydrolase and human epoxide hydrolase can be considered orthologs for the biological function of hydrolysis of epoxides. Genes are related by vertical descent when, for example, they share sequence similarity of sufficient amount to indicate they are homologous, or related by evolution from a common ancestor. Genes can also be considered orthologs if they share three-dimensional structure but not necessarily sequence similarity, of a sufficient amount to indicate that they have evolved from a common ancestor to the extent that the primary sequence similarity is not identifiable. Genes that are orthologous can encode proteins with sequence similarity of about 25% to 100% amino acid sequence identity. Genes encoding proteins sharing an amino acid similarity less that 25% can also be considered to have arisen by vertical descent if their three-dimensional structure also shows similarities. Members of the serine protease family of enzymes, including tissue plasminogen activator and elastase, are considered to have arisen by vertical descent from a common ancestor.
Orthologs include genes or their encoded gene products that through, for example, evolution, have diverged in structure or overall activity. For example, where one species encodes a gene product exhibiting two functions and where such functions have been separated into distinct genes in a second species, the three genes and their corresponding products are considered to be orthologs. For the production of a biochemical product, those skilled in the art will understand that the orthologous gene harboring the metabolic activity to be introduced or disrupted is to be chosen for construction of the non-naturally occurring microorganism. An example of orthologs exhibiting separable activities is where distinct activities have been separated into distinct gene products between two or more species or within a single species. A specific example is the separation of elastase proteolysis and plasminogen proteolysis, two types of serine protease activity, into distinct molecules as plasminogen activator and elastase. A second example is the separation of mycoplasma 5′-3′ exonuclease and Drosophila DNA polymerase III activity. The DNA polymerase from the first species can be considered an ortholog to either or both of the exonuclease or the polymerase from the second species and vice versa.
In contrast, paralogs are homologs related by, for example, duplication followed by evolutionary divergence and have similar or common, but not identical functions. Paralogs can originate or derive from, for example, the same species or from a different species. For example, microsomal epoxide hydrolase (epoxide hydrolase I) and soluble epoxide hydrolase (epoxide hydrolase II) can be considered paralogs because they represent two distinct enzymes, co-evolved from a common ancestor, that catalyze distinct reactions and have distinct functions in the same species. Paralogs are proteins from the same species with significant sequence similarity to each other suggesting that they are homologous, or related through co-evolution from a common ancestor. Groups of paralogous protein families include HipA homologs, luciferase genes, peptidases, and others.
A nonorthologous gene displacement is a nonorthologous gene from one species that can substitute for a referenced gene function in a different species. Substitution includes, for example, being able to perform substantially the same or a similar function in the species of origin compared to the referenced function in the different species. Although generally, a nonorthologous gene displacement will be identifiable as structurally related to a known gene encoding the referenced function, less structurally related but functionally similar genes and their corresponding gene products nevertheless will still fall within the meaning of the term as it is used herein. Functional similarity requires, for example, at least some structural similarity in the active site or binding region of a nonorthologous gene product compared to a gene encoding the function sought to be substituted. Therefore, a nonorthologous gene includes, for example, a paralog or an unrelated gene.
Therefore, in identifying and constructing the non-naturally occurring microbial organisms of the invention having 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic capability, those skilled in the art will understand with applying the teaching and guidance provided herein to a particular species that the identification of metabolic modifications can include identification and inclusion or inactivation of orthologs. To the extent that paralogs and/or nonorthologous gene displacements are present in the referenced microorganism that encode an enzyme catalyzing a similar or substantially similar metabolic reaction, those skilled in the art also can utilize these evolutionally related genes.
Orthologs, paralogs and nonorthologous gene displacements can be determined by methods well known to those skilled in the art. For example, inspection of nucleic acid or amino acid sequences for two polypeptides will reveal sequence identity and similarities between the compared sequences. Based on such similarities, one skilled in the art can determine if the similarity is sufficiently high to indicate the proteins are related through evolution from a common ancestor. Algorithms well known to those skilled in the art, such as Align, BLAST, Clustal W and others compare and determine a raw sequence similarity or identity, and also determine the presence or significance of gaps in the sequence which can be assigned a weight or score. Such algorithms also are known in the art and are similarly applicable for determining nucleotide sequence similarity or identity. Parameters for sufficient similarity to determine relatedness are computed based on well known methods for calculating statistical similarity, or the chance of finding a similar match in a random polypeptide, and the significance of the match determined. A computer comparison of two or more sequences can, if desired, also be optimized visually by those skilled in the art. Related gene products or proteins can be expected to have a high similarity, for example, 25% to 100% sequence identity. Proteins that are unrelated can have an identity which is essentially the same as would be expected to occur by chance, if a database of sufficient size is scanned (about 5%). Sequences between 5% and 24% may or may not represent sufficient homology to conclude that the compared sequences are related. Additional statistical analysis to determine the significance of such matches given the size of the data set can be carried out to determine the relevance of these sequences.
Exemplary parameters for determining relatedness of two or more sequences using the BLAST algorithm, for example, can be as set forth below. Briefly, amino acid sequence alignments can be performed using BLASTP version 2.0.8 (Jan. 5, 1999) and the following parameters: Matrix: 0 BLOSUM62; gap open: 11; gap extension: 1; x_dropoff: 50; expect: 10.0; wordsize: 3; filter: on. Nucleic acid sequence alignments can be performed using BLASTN version 2.0.6 (Sep. 16, 1998) and the following parameters: Match: 1; mismatch: −2; gap open: 5; gap extension: 2; x_dropoff: 50; expect: 10.0; wordsize: 11; filter: off. Those skilled in the art will know what modifications can be made to the above parameters to either increase or decrease the stringency of the comparison, for example, and determine the relatedness of two or more sequences.
In some embodiments, the invention provides a non-naturally occurring microbial organism, having a microbial organism having a 2,4-pentadienoate pathway having at least one exogenous nucleic acid encoding a 2,4-pentadienoate pathway enzyme expressed in a sufficient amount to produce 2,4-pentadienoate, wherein the 2,4-pentadienoate pathway includes a pathway shown in
In some aspects of the invention, the microbial organism can include two, three, four, five, six, seven, eight, nine or ten exogenous nucleic acids each encoding a 2,4-pentadienoate pathway enzyme. In some aspects of the invention, the microbial organism can include exogenous nucleic acids encoding each of the enzymes of at least one of the pathways selected from (1)-(24) as described above. In some aspects, the at least one exogenous nucleic acid is a heterologous nucleic acid. In some aspects, the non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
In some embodiments, the invention provides a non-naturally occurring microbial organism as described herein, wherein the non-naturally occuring microbial organism having a 2,4-pentadienoate pathway selected from (9)-(15) as described above further includes a glutaryl-CoA pathway having at least one exogenous nucleic acid encoding a glutaryl-CoA pathway enzyme expressed in a sufficient amount to produce glutaryl-CoA, the glutaryl-CoA pathway having a pathway selected from: an acetoacetyl-CoA thiolase or an acetoacetyl-CoA synthase; an acetoacetyl-CoA reductase; a 3-hydroxybutyryl-CoA dehydratase; and a glutaryl-CoA dehydrogenase; or a 2-aminoadipate aminotransferase, a 2-aminoadipate dehydrogenase or a 2-aminoadipate amine oxidase; and a 2-oxoadipate dehydrogenase, a 2-oxoadipate:ferridoxin oxidoreductase or a 2-oxoadipate formate lyase.
In some embodiments, the invention provides a non-naturally occurring microbial organism as described herein, wherein the non-naturally occuring microbial organism having a 2,4-pentadienoate pathway selected from (16)-(22) as described above further includes a 5-aminopentanoate pathway having at least one exogenous nucleic acid encoding a 5-aminopentanoate pathway enzyme expressed in a sufficient amount to produce 5-aminopentanoate, the 5-aminopentanoate pathway having a 2-aminoadipate decarboxylase; or a 2-aminoadipate decarboxylase and a 2-aminoadipate aminotransferase, a 2-aminoadipate dehydrogenase or a 2-aminoadipate amine oxidase.
In some embodiments, the invention provides a non-naturally occurring microbial organism as described herein, wherein the non-naturally occuring microbial organism having a 2,4-pentadienoate pathway selected from (1)-(8) as described above further includes a 2-oxoadipate pathway having an exogenous nucleic acid encoding a 2-oxoadipate pathway enzyme expressed in a sufficient amount to produce a 2-oxoadipate, the 2-oxoadipate pathway having a 2-aminoadipate aminotransferase, a 2-aminoadipate dehydrogenase or a 2-aminoadipate amine oxidase.
In some embodiments, the invention provides a non-naturally occurring microbial organism having a 2,4-pentadienoate pathway having at least one exogenous nucleic acid encoding a 2,4-pentadienoate pathway enzyme expressed in a sufficient amount to produce 2,4-pentadienoate, wherein the 2,4-pentadienoate pathway includes a pathway as described above, further having: (i) a reductive TCA pathway having at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; (ii) a reductive TCA pathway having at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or (iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H2 hydrogenase, and combinations thereof.
In some aspects, the microbial organism having (i) as described above further includes an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof. In some aspects, the microbial organism having (ii) further includes an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof. In some aspects, the microbial organism having (i) as described above includes four exogenous nucleic acids encoding an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; wherein the microbial organism having (ii) as described above includes five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or wherein the microbial organism having (iii) as described above includes two exogenous nucleic acids encoding a CO dehydrogenase and an H2 hydrogenase.
In some embodiments, the invention provides a method for producing 2,4-pentadienoate, having culturing the non-naturally occurring microbial organism as described herein under conditions and for a sufficient period of time to produce 2,4-pentadienoate.
In some embodiments, the invention provides a non-naturally occurring microbial organism, having a microbial organism having a butadiene pathway having at least one exogenous nucleic acid encoding a butadiene pathway enzyme expressed in a sufficient amount to produce butadiene, wherein the butadiene pathway includes a pathway shown in
In some aspects of the invention, the microbial organism can include two, three, four, five, six, seven, eight, nine, ten or eleven exogenous nucleic acids each encoding a butadiene pathway enzyme. In some aspects, the microbial organism includes exogenous nucleic acids encoding each of the enzymes of at least one of the pathways selected from (1)-(221). In some aspects, the at least one exogenous nucleic acid is a heterologous nucleic acid. In some aspects, the non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
In some embodiments, the invention provides a non-naturally occurring microbial organism as described herein, wherein the non-naturally occuring microbial organism having a butadiene pathway selected from (43)-(79) as described above further includes a glutaryl-CoA pathway having at least one exogenous nucleic acid encoding a glutaryl-CoA pathway enzyme expressed in a sufficient amount to produce glutaryl-CoA, the glutaryl-CoA pathway having a pathway selected from: an acetoacetyl-CoA thiolase or acetoacetyl-CoA synthase; an acetoacetyl-CoA reductase; a 3-hydroxybutyryl-CoA dehydratase; and a glutaryl-CoA dehydrogenase; or a 2-aminoadipate aminotransferase, a 2-aminoadipate dehydrogenase or a 2-aminoadipate amine oxidase; and a 2-oxoadipate dehydrogenase, a 2-oxoadipate:ferridoxin oxidoreductase or a 2-oxoadipate formate lyase.
In some embodiments, the invention provides a non-naturally occurring microbial organism as described herein, wherein the non-naturally occuring microbial organism having a butadiene pathway selected from (80)-(116) as described above further includes a 5-aminopentanoate pathway having at least one exogenous nucleic acid encoding a 5-aminopentanoate pathway enzyme expressed in a sufficient amount to produce 5-aminopentanoate, the 5-aminopentanoate pathway having a 2-aminoadipate decarboxylase; or a 2-aminoadipate decarboxylase and a 2-aminoadipate aminotransferase, a 2-aminoadipate dehydrogenase or a 2-aminoadipate amine oxidase.
In some embodiments, the invention provides a non-naturally occurring microbial organism as described herein, wherein the non-naturally occuring microbial organism having a butadiene pathway selected from (1)-(42) as described above further includes a 2-oxoadipate pathway having an exogenous nucleic acid encoding a 2-oxoadipate pathway enzyme expressed in a sufficient amount to produce a 2-oxoadipate, the 2-oxoadipate pathway having a 2-aminoadipate aminotransferase, a 2-aminoadipate dehydrogenase or a 2-aminoadipate amine oxidase.
In some embodiments, the invention provides a non-naturally occurring microbial organism having a butadiene pathway having at least one exogenous nucleic acid encoding a butadiene pathway enzyme expressed in a sufficient amount to produce butadiene, wherein the butadiene pathway includes a pathway as described above, further having: (i) a reductive TCA pathway having at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; (ii) a reductive TCA pathway having at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or (iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H2 hydrogenase, and combinations thereof.
In some aspects, the microbial organism having (i) as described above further includes an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof. In some aspect, the microbial organism having (ii) as described above further includes an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof. In some aspects, the microbial organism having (i) as described above includes four exogenous nucleic acids encoding an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; wherein the microbial organism having (ii) as described above includes five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or wherein the microbial organism having (iii) as described above includes two exogenous nucleic acids encoding a CO dehydrogenase and an H2 hydrogenase.
In some embodiments, the invention provides a method for producing butadiene, having culturing the non-naturally occurring microbial organism as described herein under conditions and for a sufficient period of time to produce butadiene.
In some embodiments, the invention provides a non-naturally occurring microbial organism, having a microbial organism having a 1,3-butanediol pathway having at least one exogenous nucleic acid encoding a 1,3-butanediol pathway enzyme expressed in a sufficient amount to produce 1,3-butanediol, wherein the 1,3-butanediol pathway includes a pathway shown in
In some aspects, the microbial organism includes two, three, four or five exogenous nucleic acids each encoding a 1,3-butanediol pathway enzyme. In some aspects, the microbial organism includes exogenous nucleic acids encoding each of the enzymes of at least one of the pathways selected from (1)-(37) as described above. In some aspects, the at least one exogenous nucleic acid is a heterologous nucleic acid. In some aspects, the non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
In some embodiments, the invention provides a non-naturally occurring microbial organism having a 1,3-butanediol pathway having at least one exogenous nucleic acid encoding a 1,3-butanediol pathway enzyme expressed in a sufficient amount to produce 1,3-butanediol, wherein the 1,3-butanediol pathway includes a pathway as described above, further having: (i) a reductive TCA pathway having at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; (ii) a reductive TCA pathway having at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or (iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H2 hydrogenase, and combinations thereof.
In some aspects, the microbial organism having (i) as described above further includes an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof. In some aspects, the microbial organism having (ii) as described above further includes an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof. In some aspects, the microbial organism having (i) as described herein includes four exogenous nucleic acids encoding an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; wherein the microbial organism having (ii) includes five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or wherein the microbial organism having (iii) includes two exogenous nucleic acids encoding a CO dehydrogenase and an H2 hydrogenase.
In some embodiments, the invention provides a method for producing 1,3-butanediol, having culturing the non-naturally occurring microbial organism as described herein under conditions and for a sufficient period of time to produce 1,3-butanediol.
In some embodiments, the invention provides a non-naturally occurring microbial organism, having a microbial organism having a 3-buten-1-ol pathway having at least one exogenous nucleic acid encoding a 3-buten-1-ol pathway enzyme expressed in a sufficient amount to produce 3-buten-1-ol, wherein the 3-buten-1-ol pathway includes a pathway shown in
In some aspects, the microbial organism includes two, three, four, five or six exogenous nucleic acids each encoding a 3-buten-1-ol pathway enzyme. In some aspects, the microbial organism includes exogenous nucleic acids encoding each of the enzymes of at least one of the pathways selected from (1)-(13) as described above. In some aspects, the at least one exogenous nucleic acid is a heterologous nucleic acid. In some aspects, the non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
In some embodiments, the invention provides a non-naturally occurring microbial organism having a 3-buten-1-ol pathway having at least one exogenous nucleic acid encoding a 3-buten-1-ol pathway enzyme expressed in a sufficient amount to produce 3-buten-1-ol, wherein the 3-buten-1-ol pathway includes a pathway as described above, further having: (i) a reductive TCA pathway having at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; (ii) a reductive TCA pathway having at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or (iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H2 hydrogenase, and combinations thereof.
In some aspects, the microbial organism having (i) as described above further includes an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof. In some aspects, the microbial organism having (ii) as described above further includes an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof. In some aspects the microbial organism having (i) as described above includes four exogenous nucleic acids encoding an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; wherein the microbial organism having (ii) as described above includes five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or wherein the microbial organism having (iii) as described above includes two exogenous nucleic acids encoding a CO dehydrogenase and an H2 hydrogenase.
In some embodiments, the invention provides a method for producing 3-buten-1-ol, having culturing the non-naturally occurring microbial organism as described above under conditions and for a sufficient period of time to produce 3-buten-1-ol.
In some embodiments, the invention provides a method for producing butadiene, having culturing the non-naturally occurring microbial organism as described above under conditions and for a sufficient to produce 3-buten-1-ol, and chemically dehydrating the 3-buten-1-ol to produce butadiene.
In some embodiments, the invention provides a non-naturally occurring microbial organism, including a microbial organism having a crotyl alcohol pathway including at least one exogenous nucleic acid encoding a crotyl alcohol pathway enzyme expressed in a sufficient amount to produce crotyl alcohol, wherein the crotyl alcohol pathway includes a pathway shown in
In some aspects, the invention provides that the microbial organism having a crotyl alcohol pathway as described above, wherein the microbial organism includes two, three, four, five, six or seven exogenous nucleic acids each encoding a crotyl alcohol pathway enzyme. In some aspects, the microbial organism includes exogenous nucleic acids encoding each of the enzymes of at least one of the crotyl alcohol pathways selected from (1)-(47) as described above. In some aspects, the at least one exogenous nucleic acid is a heterologous nucleic acid. In som aspects, the non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
In some embodiments, the invention provides a non-naturally occurring microbial organism having a crotyl alcohol pathway having at least one exogenous nucleic acid encoding a crotyl alcohol pathway enzyme expressed in a sufficient amount to produce crotyl alcohol, wherein the crotyl alcohol pathway includes a pathway as described above, and further includes: (i) a reductive TCA pathway including at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; (ii) a reductive TCA pathway including at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or (iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H2 hydrogenase, and combinations thereof.
In some aspects, the microbial organism including (i) as described above further includes an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof. In some aspects, the microbial organism including (ii) as described above further includes an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof. In some aspects, the microbial organism including (i) as described above includes four exogenous nucleic acids encoding an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; wherein the microbial organism including (ii) includes five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or wherein the microbial organism including (iii) includes two exogenous nucleic acids encoding a CO dehydrogenase and an H2 hydrogenase.
In some embodiments, the invention provides a method for producing crotyl alcohol, including culturing the non-naturally occurring microbial organism as described above under conditions and for a sufficient period of time to produce crotyl alcohol.
In some embodiments, access to butadiene can be accomplished by biosynthetic production of crotyl alcohol and subsequent chemical dehydration to butadiene. In some embodiments, the invention provides a process for the production of butadiene that includes (a) culturing by fermentation in a sufficient amount of nutrients and media a non-naturally occurring microbial organism as described herein that produces crotyl alcohol; and (b) converting crotyl alcohol produced by culturing the non-naturally occurring microbial organism to butadiene.
The dehydration of alcohols are known in the art and can include various thermal processes, both catalyzed and non-catalyzed. In some embodiments, a catalyzed thermal dehydration employs a metal oxide catalyst or silica. In some embodiments, step (b) of the process is performed by chemical dehydration in the presence of a catalyst. For example, it has been indicated that crotyl alcohol can be dehydrated over bismuth molybdate (Adams, C. R. J. Catal. 10:355-361, 1968) to afford 1,3-butadiene.
Dehydration can be achieved via activation of the alcohol group and subsequent elimination by standard elimination mechanisms such as E1 or E2 elimination. Activation can be achieved by way of conversion of the alcohol group to a halogen such as iodide, chloride, or bromide. Activation can also be accomplished by way of a sulfonyl, phosphate or other activating functionality that convert the alcohol into a good leaving group. In some embodiments, the activating group is a sulfate or sulfate ester selected from a tosylate, a mesylate, a nosylate, a brosylate, and a triflate. In some embodiments, the leaving group is a phosphate or phosphate ester. In some such embodiments, the dehydrating agent is phosphorus pentoxide.
In some embodiments, the invention provides a non-naturally occurring microbial organism, including a microbial organism having a propylene pathway including at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, wherein the propylene pathway includes a pathway shown in
In some aspects, the invention provides that the microbial organism having a propylene pathway as described above, wherein the microbial organism includes two, three, four, five, six, seven or eight exogenous nucleic acids each encoding a propylene pathway enzyme. In some aspects, the microbial organism includes exogenous nucleic acids encoding each of the enzymes of at least one of the pathways selected from (1)-(91) as described above. In some aspects, the at least one exogenous nucleic acid is a heterologous nucleic acid. In some aspects, the non-naturally occurring microbial organism is in a substantially anaerobic culture medium.
In some embodiments, the invention provides a non-naturally occurring microbial organism having a propylene pathway having at least one exogenous nucleic acid encoding a propylene pathway enzyme expressed in a sufficient amount to produce propylene, wherein the propylene pathway includes a pathway as described above, and further includes: (i) a reductive TCA pathway including at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; (ii) a reductive TCA pathway including at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme, wherein the at least one exogenous nucleic acid is selected from a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or (iii) at least one exogenous nucleic acid encodes an enzyme selected from a CO dehydrogenase, an H2 hydrogenase, and combinations thereof.
In some aspects, the microbial organism including (i) as described above further includes an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, ferredoxin, and combinations thereof. In some aspects, the microbial organism including (ii) as described above further includes an exogenous nucleic acid encoding an enzyme selected from an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, and combinations thereof. In some aspects, the microbial organism including (i) as described above includes four exogenous nucleic acids encoding an ATP-citrate lyase, citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; wherein the microbial organism including (ii) as described above includes five exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase, a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a CO dehydrogenase, and an H2 hydrogenase; or wherein the microbial organism including (iii) as described above includes two exogenous nucleic acids encoding a CO dehydrogenase and an H2 hydrogenase.
In some embodiments, the invention provides a method for producing propylene, including culturing the non-naturally occurring microbial organism of as described above under conditions and for a sufficient period of time to produce propylene.
In an additional embodiment, the invention provides a non-naturally occurring microbial organism having a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway, wherein the non-naturally occurring microbial organism includes at least one exogenous nucleic acid encoding an enzyme or protein that converts a substrate to a product selected from the group consisting of 2-aminoadipate to 5-aminopentanoate, 2-aminoadipate to 2-oxoadipate, 5-aminopentanoate to glutarate semialdehyde, 2-oxoadipate to glutarate semialdehyde, 2-oxoadipate to glutaryl-CoA, glutaryl-CoA to glutarate semialdehyde, glutarate semialdehyde to 5-hydroxyvalerate, 5-aminopentanoate to 5-aminopent-2enoate, 5-aminopent-2enoate to 5-hydroxypent-2-enoate, 5-hydroxypent-2-enoate to 5-hydroxypent-2-enoate, 5-hydroxyvalerate to 5-hydroxypent-2-enoate, 5-hydroxyvalerate to 5-hydroxyvaleryl-CoA, 5-hydroxyvalerate to 3-buten-1-ol, 5-aminopent-2-enoate to 2,4-pentadienoate, 5-hydroxypent-2-enoate to 3-buten-1-ol, 5-hydroxypent-2-enoate to 2,4-pentadienoate, 5-hydroxypent-2-enoate to 5-hydroxypent-2-enoyl-CoA, 5-hydroxypent-2-enoyl-CoA to 5-hydroxypent-2-enoate, glutarate semialdehyde to 5-aminopentanoate, 2-oxoadipate to 2-aminoadipate, 5-hydroxyvaleryl-CoA to 5-hydroxypent-2-enoyl-CoA, 5-hydroxyvaleryl-CoA to 2,4-pentadienoyl-CoA, 5-hydroxypent-2-enoyl-CoA to 2,4-pentadienoyl-CoA, 2,4-pentadienoyl-CoA to 2,4-pentadienoate, 2,4-pendienoate to butadiene, 3-buten-1-ol to butadiene, acetyl-CoA to acetoacetyl-CoA, acetoacetyl-CoA to 3-hydroxybutyryl-CoA, 3-hydroxybutyryl-CoA to crotonyl-CoA, crotonyl-CoA, glutaryl-CoA, propionyl-CoA and acetyl-CoA to 3-oxopentanoyl-CoA, propionyl-CoA and malonyl-CoA to 3-oxopentanoyl-CoA, 3-oxopentanoyl-CoA to 3-hydroxypentanoyl-CoA, 3-hydroxypentanoyl-CoA to pent-2-onoyl-CoA, pent-2-onoyl-CoA to pent-3-enoyl-CoA, pent-3-enoyl-CoA to 2,4-pentadienoyl-CoA, 3-hydroxypropionyl-CoA and acetyl-CoA to 3-oxo-5-hydroxypentanoyl-CoA, 3-oxo-5-hydroxypentanoyl-CoA to 3-oxo-5-hydroxypentanoate, 3-oxo-5-hydroxypentanoate to 3-oxobutanol, 3-oxobutanol to 1,3-butanediol, pyruvate and acetaldehyde to 4-hydroxy-2-oxovalerate, 4-hydroxy-2-oxovalerate to 2-oxopentenoate, 2-oxopentenoate to 3-buten-1-al, 3-buten-1-al to 3-buten-1-ol, 4-hydroxy-2-oxovalerate to 3-hydroxybutyryl-CoA, 4-hydroxy-2-oxovalerate to 3-hydroxybutanal, 3-hydroxybutyryl-CoA to 3-hydroxybutanal, 3-hydroxybutanal to 1,3-butanediol, 3-hydroxybutyryl-CoA to 3-hydroxybutyrate, 3-hydroxybutyrate to 3-hydroxybutyrate to 3-hydroxybutanal, 3-hydroxybutyryl-CoA to 1,3-butanediol, 2,4-pentadienoate to 2,4-pentadienoyl-CoA, 2,4-pentadienoate to penta-2,4-dienal, penta-2,4-dienal to butadiene, 2,4-pentadienoate to 2,4-pentadienoyl-phosphate, 2,4-pentadienoyl-phosphate to penta-2,4-dienal, 2,4-pentadienoyl-CoA to 2,4-pentadienoyl-phosphate, 2,4-pentadienoyl-CoA to penta-2,4-dienal, malonyl-ACP and acetyl-CoA or acetyl-ACP to acetoacetyl-ACP, acetoacetyl-ACP to 3-hydroxybutyryl-ACP, 3-hydroxybutyryl-ACP to crotonyl-ACP, acetoacetyl-ACP to acetoacetyl-CoA, malonyl-CoA and acetyl-CoA to acetoacetyl-CoA, acetoacetyl-CoA to acetoacetate, acetoacetate to 3-oxobutyraldehyde, 3-oxobutyraldehyde to 4-hydroxy-2-butanone, acetoacetyl-ACP to acetoacetate, acetoacetyl-CoA to 3-oxobutyraldehyde, acetoacetyl-ACP to 3-oxobutyraldehyde, acetoacetyl-CoA to 4-hydroxy-2-butanone, 3-hydroxybutyryl-ACP to 3-hydroxybutyrate, 3-hydroxybutyryl-ACP to 3-hydroxybutyraldehyde, 3-hydroxybutyryl-CoA to 3-hydroxybutyraldehyde, 3-hydroxybutyryl-CoA to 1,3-butanediol, acetoacetyl-CoA to 3-hydroxybutyryl-CoA, acetoacetate to 3-hydroxybutyrate, 3-oxobutyraldehyde to 3-hydroxybutyraldehyde, 4-hydroxy-2-butanone to 1,3-butanediol, crotonyl-ACP to crotonate, crotonyl-ACP to crotonaldehyde, crotonyl-CoA to crotonaldehyde, crotonyl-CoA to crotyl alcohol, 3-hydroxybutyryl-ACP to 3-hydroxybutyryl-CoA, 3-hydroxybutyryl-CoA to 3-hydroxybutyrate, 3-hydroxybutyrate to 3-hydroxybutyraldehyde, 3-hydroxybutyraldehyde to 1,3-butanediol, 3-hydroxybutyryl-CoA to crotonyl-CoA, 3-hydroxybutyrate to crotonate, 3-hydroxybutyraldehyde to crotonaldehyde, crotonyl-ACP to crotonyl-CoA, crotonyl-CoA to crotonate, crotonate to crotonaldehyde, crotonaldehyde to crotyl alcohol, butyryl-ACP to butyryl-CoA, butyryl-CoA to butyrate, butyrate to propylene, crotonyl-ACP to butyryl-ACP, crotonyl-CoA to butyryl-CoA, crotonate to butyrate, crotonaldehyde to propylene, butyryl-ACP to butyrate, crotonate to propylene, 3-hydroxybutyrate to propylene, crotyl alcohol to 2-butenyl-4-phosphate, 2-butenyl-4-phosphate to 2-butenyl-4-diphosphate, crotyl alcohol to 2-butenyl-4-diphosphate and 2-butenyl-4-diphosphate to butadiene. One skilled in the art will understand that these are merely exemplary and that any of the substrate-product pairs disclosed herein suitable to produce a desired product and for which an appropriate activity is available for the conversion of the substrate to the product can be readily determined by one skilled in the art based on the teachings herein. Thus, the invention provides a non-naturally occurring microbial organism containing at least one exogenous nucleic acid encoding an enzyme or protein, where the enzyme or protein converts the substrates and products of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway, such as that shown in
While generally described herein as a microbial organism that contains a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway, it is understood that the invention additionally provides a non-naturally occurring microbial organism having at least one exogenous nucleic acid encoding a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway enzyme expressed in a sufficient amount to produce an intermediate of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway. For example, as disclosed herein, a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway is exemplified in
It is understood that any of the pathways disclosed herein, as described in the Examples and exemplified in the Figures, including the pathways of
The invention is described herein with general reference to the metabolic reaction, reactant or product thereof, or with specific reference to one or more nucleic acids or genes encoding an enzyme associated with or catalyzing, or a protein associated with, the referenced metabolic reaction, reactant or product. Unless otherwise expressly stated herein, those skilled in the art will understand that reference to a reaction also constitutes reference to the reactants and products of the reaction. Similarly, unless otherwise expressly stated herein, reference to a reactant or product also references the reaction, and reference to any of these metabolic constituents also references the gene or genes encoding the enzymes that catalyze or proteins involved in the referenced reaction, reactant or product. Likewise, given the well known fields of metabolic biochemistry, enzymology and genomics, reference herein to a gene or encoding nucleic acid also constitutes a reference to the corresponding encoded enzyme and the reaction it catalyzes or a protein associated with the reaction as well as the reactants and products of the reaction.
As disclosed herein, the product 2,4-pentadienoate and intermediates 5-aminopentanoate, 5-aminopent-2-enoate, 5-hydroxypent-2-enoate, 5-hydroxyvalerate, 5-hydroxypent-2-enoate, 3-oxo-5-hydroxypentanoate, 3-hydroxybutyrate, 4-hydroxy-2-exovalerate, 2-oxopentenoate, acetoacetate, crotonate, butyrate, as well as other intermediates, are carboxylic acids, which can occur in various ionized forms, including fully protonated, partially protonated, and fully deprotonated forms. Accordingly, the suffix “-ate,” or the acid form, can be used interchangeably to describe both the free acid form as well as any deprotonated form, in particular since the ionized form is known to depend on the pH in which the compound is found. It is understood that carboxylate products or intermediates includes ester forms of carboxylate products or pathway intermediates, such as O-carboxylate and S-carboxylate esters. O- and S-carboxylates can include lower alkyl, that is C1 to C6, branched or straight chain carboxylates. Some such O- or S-carboxylates include, without limitation, methyl, ethyl, n-propyl, n-butyl, i-propyl, sec-butyl, and tert-butyl, pentyl, hexyl O- or S-carboxylates, any of which can further possess an unsaturation, providing for example, propenyl, butenyl, pentyl, and hexenyl O- or S-carboxylates. O-carboxylates can be the product of a biosynthetic pathway. Exemplary O-carboxylates accessed via biosynthetic pathways can include, without limitation, methyl 2,4-pentadienoate, ethyl 2,4-pentadienoate, and n-propyl 2,4-pentadienoate. Other biosynthetically accessible O-carboxylates can include medium to long chain groups, that is C7-C22, O-carboxylate esters derived from fatty alcohols, such heptyl, octyl, nonyl, decyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl, cetyl, palmitolyl, heptadecyl, stearyl, nonadecyl, arachidyl, heneicosyl, and behenyl alcohols, any one of which can be optionally branched and/or contain unsaturations. O-carboxylate esters can also be accessed via a biochemical or chemical process, such as esterification of a free carboxylic acid product or transesterification of an O- or S-carboxylate. S-carboxylates are exemplified by CoA S-esters, cysteinyl S-esters, alkylthioesters, and various aryl and heteroaryl thioesters. The non-naturally occurring microbial organisms of the invention can be produced by introducing expressible nucleic acids encoding one or more of the enzymes or proteins participating in one or more 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathways. Depending on the host microbial organism chosen for biosynthesis, nucleic acids for some or all of a particular 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway can be expressed. For example, if a chosen host is deficient in one or more enzymes or proteins for a desired biosynthetic pathway, then expressible nucleic acids for the deficient enzyme(s) or protein(s) are introduced into the host for subsequent exogenous expression. Alternatively, if the chosen host exhibits endogenous expression of some pathway genes, but is deficient in others, then an encoding nucleic acid is needed for the deficient enzyme(s) or protein(s) to achieve 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthesis. Thus, a non-naturally occurring microbial organism of the invention can be produced by introducing exogenous enzyme or protein activities to obtain a desired biosynthetic pathway or a desired biosynthetic pathway can be obtained by introducing one or more exogenous enzyme or protein activities that, together with one or more endogenous enzymes or proteins, produces a desired product such as 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
Host microbial organisms can be selected from, and the non-naturally occurring microbial organisms generated in, for example, bacteria, yeast, fungus or any of a variety of other microorganisms applicable to fermentation processes. Exemplary bacteria include species selected from Escherichia coli, Klebsiella oxytoca, Anaerobiospirillum succiniciproducens, Actinobacillus succinogenes, Mannheimia succiniciproducens, Rhizobium etli, Bacillus subtilis, Corynebacterium glutamicum, Cupriavidus necator, Gluconobacter oxydans, Zymomonas mobilis, Lactococcus lactis, Lactobacillus plantarum, Streptomyces coelicolor, Clostridium acetobutylicum, Pseudomonas fluorescens, and Pseudomonas putida. Exemplary yeasts or fungi include species selected from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces marxianus, Aspergillus terreus, Aspergillus niger, Pichia pastoris, Rhizopus arrhizus, Rhizopus oryzae, Yarrowia lipolytica, Candida albicans and the like. E. coli is a particularly useful host organism since it is a well characterized microbial organism suitable for genetic engineering. Other particularly useful host organisms include yeast such as Saccharomyces cerevisiae. It is understood that any suitable microbial host organism can be used to introduce metabolic and/or genetic modifications to produce a desired product.
Depending on the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway constituents of a selected host microbial organism, the non-naturally occurring microbial organisms of the invention will include at least one exogenously expressed 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway-encoding nucleic acid and up to all encoding nucleic acids for one or more 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathways. For example, 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthesis can be established in a host deficient in a pathway enzyme or protein through exogenous expression of the corresponding encoding nucleic acid. In a host deficient in all enzymes or proteins of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway, exogenous expression of all enzymes or proteins in the pathway can be included, although it is understood that all enzymes or proteins of a pathway can be expressed even if the host contains at least one of the pathway enzymes or proteins. For example, exogenous expression of all enzymes or proteins in a pathway for production of butadiene can be included, such as, a glutaryl-CoA reductase, aglutarate semialdehyde reductase, a 5-hydroxyvaleryl-CoA transferase and/or synthetase, a 5-hydroxyvaleryl-CoA dehydratase/dehydrogenase, a 2,4-pentadienoyl-CoA transferase, synthetase or hydrolase and a 2,4-pentadienoate decarboxylase. As another example, exogenous expression of all enzymes or proteins in a pathway for production of 1,3-butanediol can be included, such as, a 3-ketoacyl-ACP synthase, an acetoacetyl-ACP reductase, a 3-hydroxybutyryl-CoA:ACP transferase, an 3-hydroxybutyryl-CoA hydrolase, transferase or synthetase, a 3-hydroxybutyrate reductase, and a 3-hydroxybutyraldehyde reductase. As yet another example, exogenous expression of all enzymes or proteins in a pathway for production of crotyl-alcohol can be included, such as, a 3-ketoacyl-ACP synthase, an acetoacetyl-ACP reductase, a 3-hydroxybutyryl-ACP dehydratase, a crotonyl-CoA:ACP transferase, a crotonyl-CoA hydrolase, transferase or synthetase, a crotonate reductase and a crotonaldehyde reductase.
Given the teachings and guidance provided herein, those skilled in the art will understand that the number of encoding nucleic acids to introduce in an expressible form will, at least, parallel the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway deficiencies of the selected host microbial organism. Therefore, a non-naturally occurring microbial organism of the invention can have one, two, three, four, five, six, seven, eight, nine, ten or eleven, up to all nucleic acids encoding the enzymes or proteins constituting a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway disclosed herein. In some embodiments, the non-naturally occurring microbial organisms also can include other genetic modifications that facilitate or optimize 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthesis or that confer other useful functions onto the host microbial organism. One such other functionality can include, for example, augmentation of the synthesis of one or more of the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway precursors such as 2-aminoadipate, 5-aminopentanoate, 2-oxoadipate, glutaryl-CoA, propionyl-CoA, acetyl-CoA, malonyl-CoA, 3-hydroxypropionyl-CoA, malonyl-ACP or pyruvate.
Generally, a host microbial organism is selected such that it produces the precursor of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway, either as a naturally produced molecule or as an engineered product that either provides de novo production of a desired precursor or increased production of a precursor naturally produced by the host microbial organism. For example, 2-aminoadipate, 5-aminopentanoate, 2-oxoadipate, glutaryl-CoA, propionyl-CoA, acetyl-CoA, malonyl-CoA, 3-hydroxypropionyl-CoA, pyruvate or malonyl-ACP is produced naturally in a host organism such as E. coli. A host organism can be engineered to increase production of a precursor, as disclosed herein. In addition, a microbial organism that has been engineered to produce a desired precursor can be used as a host organism and further engineered to express enzymes or proteins of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway.
In some embodiments, a non-naturally occurring microbial organism of the invention is generated from a host that contains the enzymatic capability to synthesize 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. In this specific embodiment it can be useful to increase the synthesis or accumulation of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway product to, for example, drive 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway reactions toward 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol production. Increased synthesis or accumulation can be accomplished by, for example, overexpression of nucleic acids encoding one or more of the above-described 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway enzymes or proteins. Overexpression of the enzyme or enzymes and/or protein or proteins of the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway can occur, for example, through exogenous expression of the endogenous gene or genes, or through exogenous expression of the heterologous gene or genes. Therefore, naturally occurring organisms can be readily generated to be non-naturally occurring microbial organisms of the invention, for example, producing 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol, through overexpression of one, two, three, four, five, six, seven, eight, nine, ten or eleven, that is, up to all nucleic acids encoding 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway enzymes or proteins. In addition, a non-naturally occurring organism can be generated by mutagenesis of an endogenous gene that results in an increase in activity of an enzyme in the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway.
In particularly useful embodiments, exogenous expression of the encoding nucleic acids is employed. Exogenous expression confers the ability to custom tailor the expression and/or regulatory elements to the host and application to achieve a desired expression level that is controlled by the user. However, endogenous expression also can be utilized in other embodiments such as by removing a negative regulatory effector or induction of the gene's promoter when linked to an inducible promoter or other regulatory element. Thus, an endogenous gene having a naturally occurring inducible promoter can be up-regulated by providing the appropriate inducing agent, or the regulatory region of an endogenous gene can be engineered to incorporate an inducible regulatory element, thereby allowing the regulation of increased expression of an endogenous gene at a desired time. Similarly, an inducible promoter can be included as a regulatory element for an exogenous gene introduced into a non-naturally occurring microbial organism.
It is understood that, in methods of the invention, any of the one or more exogenous nucleic acids can be introduced into a microbial organism to produce a non-naturally occurring microbial organism of the invention. The nucleic acids can be introduced so as to confer, for example, a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway onto the microbial organism. Alternatively, encoding nucleic acids can be introduced to produce an intermediate microbial organism having the biosynthetic capability to catalyze some of the required reactions to confer 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic capability. For example, a non-naturally occurring microbial organism having a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway can comprise at least two exogenous nucleic acids encoding desired enzymes or proteins, such as the combination of a 5-hydroxypentanoyl-CoA dehydrogenase and a 2,4-pentadienoyl-CoA transferase, or alternatively a 5-aminopentanoate reductase and a 5-aminopent-2-enoate deaminase, or alternatively a 2,4-pentadienoate decarboxylase and a 3-hydroxybutyryl-CoA dehydratase, or alternatively a 3-oxopentanoyl-CoA reductase and a 2,4-pentadienoyl-CoA hydrolase, or alternatively a 4-hydroxy-2-oxopentanoate dehydrogenase and a 3-hydroxybutyryl-CoA reductase (alcohol forming), or alternatively a 3-hydroxybutyrate reductase and a 3-hydroxybutyraldehyde reductase, and the like. Thus, it is understood that any combination of two or more enzymes or proteins of a biosynthetic pathway can be included in a non-naturally occurring microbial organism of the invention. Similarly, it is understood that any combination of three or more enzymes or proteins of a biosynthetic pathway can be included in a non-naturally occurring microbial organism of the invention, for example, a 5-hydroxyvalerate dehydrogenase, a 5-hydroxypent-2-enoyl-CoA transferase and a 5-hydroxypent-2-enoyl-CoA dehydratase, or alternavely a penta-2,4-dienal decarbonylase, a 2,4-pentadienoyl-CoA reductase (acid reducing) and a 5-hydroxyvaleryl-CoA dehydratase/dehydrogenase, or alternatively a 2-oxopentenoate decarboxylase, a 3-buten-1-al reductase and a 3-buten-1-ol dehydratase, or alternatively a crotonaldehyde reductase, a crotonate reductase and a crotonyl-CoA hydrolase, and so forth, as desired, so long as the combination of enzymes and/or proteins of the desired biosynthetic pathway results in production of the corresponding desired product. Similarly, any combination of four, five, six, seven, eight, nine, ten, eleven or more enzymes or proteins of a biosynthetic pathway as disclosed herein can be included in a non-naturally occurring microbial organism of the invention, as desired, so long as the combination of enzymes and/or proteins of the desired biosynthetic pathway results in production of the corresponding desired product.
In addition to the biosynthesis of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol as described herein, the non-naturally occurring microbial organisms and methods of the invention also can be utilized in various combinations with each other and with other microbial organisms and methods well known in the art to achieve product biosynthesis by other routes. For example, one alternative to produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol other than use of the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producers is through addition of another microbial organism capable of converting a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate to 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. One such procedure includes, for example, the fermentation of a microbial organism that produces a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate. The 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate can then be used as a substrate for a second microbial organism that converts the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate to 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. The 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate can be added directly to another culture of the second organism or the original culture of the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate producers can be depleted of these microbial organisms by, for example, cell separation, and then subsequent addition of the second organism to the fermentation broth can be utilized to produce the final product without intermediate purification steps.
In other embodiments, the non-naturally occurring microbial organisms and methods of the invention can be assembled in a wide variety of subpathways to achieve biosynthesis of, for example, 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. In these embodiments, biosynthetic pathways for a desired product of the invention can be segregated into different microbial organisms, and the different microbial organisms can be co-cultured to produce the final product. In such a biosynthetic scheme, the product of one microbial organism is the substrate for a second microbial organism until the final product is synthesized. For example, the biosynthesis of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol can be accomplished by constructing a microbial organism that contains biosynthetic pathways for conversion of one pathway intermediate to another pathway intermediate or the product. Alternatively, 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol also can be biosynthetically produced from microbial organisms through co-culture or co-fermentation using two organisms in the same vessel, where the first microbial organism produces a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol intermediate and the second microbial organism converts the intermediate to 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
Given the teachings and guidance provided herein, those skilled in the art will understand that a wide variety of combinations and permutations exist for the non-naturally occurring microbial organisms and methods of the invention together with other microbial organisms, with the co-culture of other non-naturally occurring microbial organisms having subpathways and with combinations of other chemical and/or biochemical procedures well known in the art to produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
Sources of encoding nucleic acids for a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway enzyme or protein can include, for example, any species where the encoded gene product is capable of catalyzing the referenced reaction. Such species include both prokaryotic and eukaryotic organisms including, but not limited to, bacteria, including archaea and eubacteria, and eukaryotes, including yeast, plant, insect, animal, and mammal, including human. Exemplary species for such sources include, for example, Escherichia coli, Acetobacter aceti, Acetobacter pasteurians, Achromobacter denitrificans, Acidaminococcus fermentans, Acinetobacter baumanii, Acinetobacter baylyi, Acinetobacter calcoaceticus, Acinetobacter sp. ADP 1, Acinetobacter sp. Strain M-1, Actinobacillus succinogenes, Acyrthosiphon pisum, Aeropyrum pernix, Agrobacterium tumefaciens, Allochromatium vinosum DSM 180, Anabaena variabilis, Anaerobiospirillum succiniciproducens, Anaerostipes caccae DSM 14662, Anaerotruncus colihominis, Antheraea yamamai, Aquifex aeolicus, Arabidopsis thaliana, Archaeglubus fulgidus, Archaeoglobus fulgidus, Aromatoleum aromaticum EbN1, Ascaris suum, Ascarius suum, Aspergillus nidulans, Aspergillus niger, Aspergillus oryzae, Aspergillus terreus, Aspergillus terreus NIH2624, Azoarcus sp. CIB, Azoarcus sp. T, Azotobacter vinelandii DJ, Anabaena variabilis, Bacillus anthracis, Bacillus amyloliquefaciens, Bacillus cereus, Bacillus coahuilensis, Bacillus megaterium, Bacillus pseudofirmus, Bacillus pumilus, Bacillus sphaericus, Bacillus subtilis,Bacteroides capillosus, Balnearium lithotrophicum, Bos taurus, Bradyrhizobium japonicum, Bradyrhizobium japonicum USDA110, Brassica napsus, Burkholderia ambifaria AMMD, Burkholderia phymatum, Burkholderia xenovorans, butyrate producing bacterium L2-50, butyrate producing bacterium L2-50, butyrate producing bacterium SS3/4, Campylobacter curvus 525.92, Campylobacter jejuni, Candida albicans, Candida parapsilosis, Candida tropicalis, Carboxydothermus hydrogenoformans, Chlamydomonas reinhardtii, Chlorobium limicola, Chlorobium phaeobacteroides DSM 266, Chlorobium tepidum, Chlorobium tepidum, Chloroflexus aurantiacus, Citrobacter amalonaticus, Citrobacter youngae ATCC 29220, Clostridium acetobutylicum, Clostridium aminobutyricum, Clostridium beijerinckii, Clostridium beijerinckii NRRL B593, Clostridium botulinum, Clostridium botulinum A3 str, Clostridium botulinum C str. Eklund, Clostridium carboxidivorans P7, Clostridium carboxidivorans P7, Clostridium cellulolyticum H10, Clostridium kluyveri, Clostridium kluyveri DSM 555, Clostridium novyi NT, Clostridium pasteurianum, Clostridium propionicum, Clostridium saccharoperbutylacetonicum, Clostridium sp. SS2/1, Clostridium tetani, Clostridium tetanomorphum,Clostridium tyrobutyricum, Comamonas sp. CNB-1, Corynebacterium glutamicum, Corynebacterium glutamicum ATCC 13032, Corynebacterium glutanicum, Cucumis sativus, Cupriavidus necator, Cupriavidus taiwanensis, Cyanobium PCC7001, Desulfovibrio africanus, DesulfoVibrio desulfuricans G20, Desulfovibrio desulfuricans subsp. desulfuricans str. ATCC 27774, Desulfovibrio fructosovorans JJ, Desulfovibrio vulgaris str. Hildenborough, Dictyostelium discoideum AX4, Drosophila melanogaster, Elizabethkingia meningoseptica, Erythrobacter sp. NAP 1, Escherichia coli C, Escherichia coli K12, Escherichia coli K12 subsp. MG1655, Escherichia coli O157:H7 str. Sakai, Escherichia coli str. K-12 substr. MG1655, Escherichia coli W, Eubacterium barkeri, Eubacterium rectale ATCC 33656, Eubacterium yurii, Euglena gracilis, Flavobacterium lutescens, Fusobacterium gonidiaformans, Fusobacterium nucleatum, Geobacillus stearothermophilus, Geobacillus thermoglucosidasius, Geobacter metallireducens GS-15, Geobacter sulfurreducens, Gibberella zeae, Haemophilus influenza, Haloarcula marismortui, Halobacillus dabanensis, Halobacterium salinarum, Haloferax mediterranei, Helicobacter pylori, Helicobacter pylori 26695, Helicoverpa zea, Heliobacter pylori, Homo sapiens, Hydrogenobacter thermophilus, Jeotgalicoccus sp. ATCC8456, Klebsiella oxytoca, Klebsiella pneumonia, Klebsiella pneumonia, Kluyveromyces lactis, Kocuria rosea, Lactobacillus plantarum, Lactobacillus sp. 30a, Lactococcus lactis, Leuconostoc mesenteroides, Macrococcus caseolyticus, Mannheimia succiniciproducens, marine gamma proteobacterium HTCC2080, Marinococcus halophilus, Marinomonas mediterranea, Medicago truncatula, Mesorhizobium loti, Metallosphaera sedula, Methanocaldococcus jannaschii, Methanosarcina thermophila, Methanothermobacter thermautotrophicus, Methylobacterium extorquens, Moorella thermoacetica, Mus musculus, Musca domestica, Mycobacterium avium, Mycobacterium avium subsp. paratuberculosis K-10, Mycobacterium avium subsp. Pratuberculosis, Mycobacterium bovis BCG, Mycobacterium marinum M Mycobacterium smegmatis, Mycobacterium smegmatis MC2 155, Mycobacterium tuberculosis, Natranaerobius thermophilus, Neosartorya fischeri, Nicotiana glutinosa, Nicotiana tabacum, Nocardia farcinica IFM 10152, Nocardia iowensis, Nostoc sp. PCC 7120, Oryctolagus cuniculus, Oryza sativa, Paracoccus denitrificans, Pedicoccus pentosaceus, Pelobacter carbinolicus DSM 2380, Pelotomaculum thermopropionicum, Penicillium chrysogenum, Peptoniphilus harei, Pichia stipitis, Porphyromonas gingivalis, Pseudoalteromonas tunicate, Pseudomonas aeruginosa, Pseudomonas aeruginosa PAO 1, Pseudomonas fluorescens, Pseudomonas fluorescens KU-7, Pseudomonas fluorescens Pf-5, Pseudomonas knackmussii (B13), Pseudomonas mendocina, Pseudomonas putida, Pseudomonas putida KT2440, Pseudomonas reinekei MT1, Pseudomonas sp, Pseudomonas sp. CF600, Pseudomonas sp. CF600, Pseudomonas sp. CF600, Pseudomonas sp. strain B13, Pseudomonas stutzeri, Pseudoramibacter alactolyticus, Psychroflexus torquis ATCC 700755, Pyrobaculum aerophilum str. IM2, Pyrococcus furiosus, Ralstonia eutropha, Ralstonia eutropha H16, Ralstonia eutropha JMP 134, Ralstonia metallidurans, Ralstonia pickettii, Rattus norvegicus, Rhizobium leguminosarum, Rhodobacter capsulates, Rhodobacter capsulatus, Rhodobacter sphaeroides, Rhodococcus opacus, Rhodococcus ruber, Rhodopseudomonas palustris, Rhodopseudomonas palustris CGA009, Rhodospirillum rubrum, Roseburia intestinalis L1-82, Roseburia inulinivorans, Roseburia sp. A2-183, Roseiflexus castenholzii, Saccharomyces cerevisae, Salinispora arenicola, Salmonella enteric, Salmonella enterica subsp. arizonae serovar, Salmonella typhimurium, Salmonella typhimurium LT2, Schizosaccharomyces pombe, Selenomonas ruminantium, Serratia marcescens, Simmondsia chinensis, Solibacillus silvestris, Sordaria macrospora, Sporosarcina newyorkensis, Staphylococcus pseudintermedius, Streptococcus mutans, Streptococcus oligofermentans, Streptococcus pyogenes ATCC 10782, Streptomyces clavuligenus, Streptomyces coelicolor, Streptomyces griseus, Streptomyces griseus subsp. griseus NBRC 13350, Sulfolobus acidocalarius, Sulfolobus sp. strain 7, Sulfolobus tokodaii, Sulfolobus tokodaii 7, Sulfurihydrogenibium subterraneum, Sulfurimonas denitrificans, Sus scrofa, Synechocystis str. PCC 6803, Syntrophus aciditrophicus, Thauera aromatic, Thauera aromatic, Thermoanaerobacter brockii HTD4, Thermocrinis albus, Thermoproteus neutrophilus, Thermotoga maritime, Thermus thermophilus, Thiobacillus denitrificans, Treponema denticola, Trichomonas vaginalis G3, Trypanosoma brucei, Tsukamurella paurometabola DSM 20162, Vibrio cholera, Vibrio parahaemolyticus, Vibrio vulnificus, Vitis vinifera, Yarrowia lipolytica, Yersinia intermedia ATCC 29909, Zea mays, Zoogloea ramigera, Zymomonas mobilis, Carthamus tinctorius, Cuphea hookeriana, Cuphea palustris, Cyanothece sp. PCC 7425, Elizabethkingia meningoseptica, Lyngbya sp. PCC 8106, Nodularia spumigena CCY9414, Nostoc azollae, Plasmodium falciparum, Prochlorococcus marinus, Streptococcus pneumoniae, Streptococcus pyogenes ATCC 10782, Streptomyces avermitillis, Synechococcus elongatus, Synechococcus elongatus PCC7942, Thermomyces lanuginosus, Umbellularia californica, Arabidopsis thaliana col, Enterococcus faecalis, Mycoplasma pneumoniae M129, Populus alba, Populus tremula, Pueraria montana, Staphylococcus aureus, Streptomyces sp. ACT-1, Thermotoga maritime MSB8, Streptomyces sp CL190, Streptomyces sp. KO-3988, Streptomyces cinnamonensis, Streptomyces anulatus, Nocardia brasiliensis as well as other exemplary species disclosed herein are available as source organisms for corresponding genes. However, with the complete genome sequence available for now more than 550 species (with more than half of these available on public databases such as the NCBI), including 395 microorganism genomes and a variety of yeast, fungi, plant, and mammalian genomes, the identification of genes encoding the requisite 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic activity for one or more genes in related or distant species, including for example, homologues, orthologs, paralogs and nonorthologous gene displacements of known genes, and the interchange of genetic alterations between organisms is routine and well known in the art. Accordingly, the metabolic alterations allowing biosynthesis of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol described herein with reference to a particular organism such as E. coli can be readily applied to other microorganisms, including prokaryotic and eukaryotic organisms alike. Given the teachings and guidance provided herein, those skilled in the art will know that a metabolic alteration exemplified in one organism can be applied equally to other organisms.
In some instances, such as when an alternative 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway exists in an unrelated species, 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthesis can be conferred onto the host species by, for example, exogenous expression of a paralog or paralogs from the unrelated species that catalyzes a similar, yet non-identical metabolic reaction to replace the referenced reaction. Because certain differences among metabolic networks exist between different organisms, those skilled in the art will understand that the actual gene usage between different organisms may differ. However, given the teachings and guidance provided herein, those skilled in the art also will understand that the teachings and methods of the invention can be applied to all microbial organisms using the cognate metabolic alterations to those exemplified herein to construct a microbial organism in a species of interest that will synthesize 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
Methods for constructing and testing the expression levels of a non-naturally occurring 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol-producing host can be performed, for example, by recombinant and detection methods well known in the art. Such methods can be found described in, for example, Sambrook et al., Molecular Cloning: A Laboratory Manual, Third Ed., Cold Spring Harbor Laboratory, New York (2001); and Ausubel et al., Current Protocols in Molecular Biology, John Wiley and Sons, Baltimore, Md. (1999).
Exogenous nucleic acid sequences involved in a pathway for production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol can be introduced stably or transiently into a host cell using techniques well known in the art including, but not limited to, conjugation, electroporation, chemical transformation, transduction, transfection, and ultrasound transformation. For exogenous expression in E. coli or other prokaryotic cells, some nucleic acid sequences in the genes or cDNAs of eukaryotic nucleic acids can encode targeting signals such as an N-terminal mitochondrial or other targeting signal, which can be removed before transformation into prokaryotic host cells, if desired. For example, removal of a mitochondrial leader sequence led to increased expression in E. coli (Hoffmeister et al., J. Biol. Chem. 280:4329-4338 (2005)). For exogenous expression in yeast or other eukaryotic cells, genes can be expressed in the cytosol without the addition of leader sequence, or can be targeted to mitochondrion or other organelles, or targeted for secretion, by the addition of a suitable targeting sequence such as a mitochondrial targeting or secretion signal suitable for the host cells. Thus, it is understood that appropriate modifications to a nucleic acid sequence to remove or include a targeting sequence can be incorporated into an exogenous nucleic acid sequence to impart desirable properties. Furthermore, genes can be subjected to codon optimization with techniques well known in the art to achieve optimized expression of the proteins.
An expression vector or vectors can be constructed to include one or more 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathway encoding nucleic acids as exemplified herein operably linked to expression control sequences functional in the host organism. Expression vectors applicable for use in the microbial host organisms of the invention include, for example, plasmids, phage vectors, viral vectors, episomes and artificial chromosomes, including vectors and selection sequences or markers operable for stable integration into a host chromosome. Additionally, the expression vectors can include one or more selectable marker genes and appropriate expression control sequences. Selectable marker genes also can be included that, for example, provide resistance to antibiotics or toxins, complement auxotrophic deficiencies, or supply critical nutrients not in the culture media. Expression control sequences can include constitutive and inducible promoters, transcription enhancers, transcription terminators, and the like which are well known in the art. When two or more exogenous encoding nucleic acids are to be co-expressed, both nucleic acids can be inserted, for example, into a single expression vector or in separate expression vectors. For single vector expression, the encoding nucleic acids can be operationally linked to one common expression control sequence or linked to different expression control sequences, such as one inducible promoter and one constitutive promoter. The transformation of exogenous nucleic acid sequences involved in a metabolic or synthetic pathway can be confirmed using methods well known in the art. Such methods include, for example, nucleic acid analysis such as Northern blots or polymerase chain reaction (PCR) amplification of mRNA, or immunoblotting for expression of gene products, or other suitable analytical methods to test the expression of an introduced nucleic acid sequence or its corresponding gene product. It is understood by those skilled in the art that the exogenous nucleic acid is expressed in a sufficient amount to produce the desired product, and it is further understood that expression levels can be optimized to obtain sufficient expression using methods well known in the art and as disclosed herein.
Suitable purification and/or assays to test for the production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol can be performed using well known methods. Suitable replicates such as triplicate cultures can be grown for each engineered strain to be tested. For example, product and byproduct formation in the engineered production host can be monitored. The final product and intermediates, and other organic compounds, can be analyzed by methods such as HPLC (High Performance Liquid Chromatography), GC-MS (Gas Chromatography-Mass Spectroscopy) and LC-MS (Liquid Chromatography-Mass Spectroscopy) or other suitable analytical methods using routine procedures well known in the art. The release of product in the fermentation broth can also be tested with the culture supernatant. Byproducts and residual glucose can be quantified by HPLC using, for example, a refractive index detector for glucose and alcohols, and a UV detector for organic acids (Lin et al., Biotechnol. Bioeng. 90:775-779 (2005)), or other suitable assay and detection methods well known in the art. The individual enzyme or protein activities from the exogenous DNA sequences can also be assayed using methods well known in the art.
The 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol can be separated from other components in the culture using a variety of methods well known in the art. Such separation methods include, for example, extraction procedures as well as methods that include continuous liquid-liquid extraction, pervaporation, membrane filtration, membrane separation, reverse osmosis, electrodialysis, distillation, crystallization, centrifugation, extractive filtration, ion exchange chromatography, size exclusion chromatography, adsorption chromatography, and ultrafiltration. All of the above methods are well known in the art.
Any of the non-naturally occurring microbial organisms described herein can be cultured to produce and/or secrete the biosynthetic products of the invention. For example, the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producers can be cultured for the biosynthetic production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
For the production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol, the recombinant strains are cultured in a medium with carbon source and other essential nutrients. It is sometimes desirable and can be highly desirable to maintain anaerobic conditions in the fermenter to reduce the cost of the overall process. Such conditions can be obtained, for example, by first sparging the medium with nitrogen and then sealing the flasks with a septum and crimp-cap. For strains where growth is not observed anaerobically, microaerobic or substantially anaerobic conditions can be applied by perforating the septum with a small hole for limited aeration. Exemplary anaerobic conditions have been described previously and are well-known in the art. Exemplary aerobic and anaerobic conditions are described, for example, in United State publication 2009/0047719, filed Aug. 10, 2007. Fermentations can be performed in a batch, fed-batch or continuous manner, as disclosed herein. Fermentations can also be conducted in two phases, if desired. The first phase can be aerobic to allow for high growth and therefore high productivity, followed by an anaerobic phase of high 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol yields.
If desired, the pH of the medium can be maintained at a desired pH, in particular neutral pH, such as a pH of around 7 by addition of a base, such as NaOH or other bases, or acid, as needed to maintain the culture medium at a desirable pH. The growth rate can be determined by measuring optical density using a spectrophotometer (600 nm), and the glucose uptake rate by monitoring carbon source depletion over time.
The growth medium can include, for example, any carbohydrate source which can supply a source of carbon to the non-naturally occurring microorganism. Such sources include, for example, sugars such as glucose, xylose, arabinose, galactose, mannose, fructose, sucrose and starch. Other sources of carbohydrate include, for example, renewable feedstocks and biomass. Exemplary types of biomasses that can be used as feedstocks in the methods of the invention include cellulosic biomass, hemicellulosic biomass and lignin feedstocks or portions of feedstocks. Such biomass feedstocks contain, for example, carbohydrate substrates useful as carbon sources such as glucose, xylose, arabinose, galactose, mannose, fructose and starch. Given the teachings and guidance provided herein, those skilled in the art will understand that renewable feedstocks and biomass other than those exemplified above also can be used for culturing the microbial organisms of the invention for the production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
In addition to renewable feedstocks such as those exemplified above, the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol microbial organisms of the invention also can be modified for growth on syngas as its source of carbon. In this specific embodiment, one or more proteins or enzymes are expressed in the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producing organisms to provide a metabolic pathway for utilization of syngas or other gaseous carbon source.
Synthesis gas, also known as syngas or producer gas, is the major product of gasification of coal and of carbonaceous materials such as biomass materials, including agricultural crops and residues. Syngas is a mixture primarily of H2 and CO and can be obtained from the gasification of any organic feedstock, including but not limited to coal, coal oil, natural gas, biomass, and waste organic matter. Gasification is generally carried out under a high fuel to oxygen ratio. Although largely H2 and CO, syngas can also include CO2 and other gases in smaller quantities. Thus, synthesis gas provides a cost effective source of gaseous carbon such as CO and, additionally, CO2.
The Wood-Ljungdahl pathway catalyzes the conversion of CO and H2 to acetyl-CoA and other products such as acetate. Organisms capable of utilizing CO and syngas also generally have the capability of utilizing CO2 and CO2/H2 mixtures through the same basic set of enzymes and transformations encompassed by the Wood-Ljungdahl pathway. H2-dependent conversion of CO2 to acetate by microorganisms was recognized long before it was revealed that CO also could be used by the same organisms and that the same pathways were involved. Many acetogens have been shown to grow in the presence of CO2 and produce compounds such as acetate as long as hydrogen is present to supply the necessary reducing equivalents (see for example, Drake, Acetogenesis, pp. 3-60 Chapman and Hall, New York, (1994)). This can be summarized by the following equation:
2CO2+4H2+nADP+nPi→CH3COOH+2H2O+nATP
Hence, non-naturally occurring microorganisms possessing the Wood-Ljungdahl pathway can utilize CO2 and H2 mixtures as well for the production of acetyl-CoA and other desired products.
The Wood-Ljungdahl pathway is well known in the art and consists of 12 reactions which can be separated into two branches: (1) methyl branch and (2) carbonyl branch. The methyl branch converts syngas to methyl-tetrahydrofolate (methyl-THF) whereas the carbonyl branch converts methyl-THF to acetyl-CoA. The reactions in the methyl branch are catalyzed in order by the following enzymes or proteins: ferredoxin oxidoreductase, formate dehydrogenase, formyltetrahydrofolate synthetase, methenyltetrahydrofolate cyclodehydratase, methylenetetrahydrofolate dehydrogenase and methylenetetrahydrofolate reductase. The reactions in the carbonyl branch are catalyzed in order by the following enzymes or proteins: methyltetrahydrofolate:corrinoid protein methyltransferase (for example, AcsE), corrinoid iron-sulfur protein, nickel-protein assembly protein (for example, AcsF), ferredoxin, acetyl-CoA synthase, carbon monoxide dehydrogenase and nickel-protein assembly protein (for example, CooC). Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the Wood-Ljungdahl enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains the complete Wood-Ljungdahl pathway will confer syngas utilization ability.
Additionally, the reductive (reverse) tricarboxylic acid cycle coupled with carbon monoxide dehydrogenase and/or hydrogenase activities can also be used for the conversion of CO, CO2 and/or H2 to acetyl-CoA and other products such as acetate. Organisms capable of fixing carbon via the reductive TCA pathway can utilize one or more of the following enzymes: ATP citrate-lyase, citrate lyase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate:ferredoxin oxidoreductase, succinyl-CoA synthetase, succinyl-CoA transferase, fumarate reductase, fumarase, malate dehydrogenase, NAD(P)H:ferredoxin oxidoreductase, carbon monoxide dehydrogenase, and hydrogenase. Specifically, the reducing equivalents extracted from CO and/or H2 by carbon monoxide dehydrogenase and hydrogenase are utilized to fix CO2 via the reductive TCA cycle into acetyl-CoA or acetate. Acetate can be converted to acetyl-CoA by enzymes such as acetyl-CoA transferase, acetate kinase/phosphotransacetylase, and acetyl-CoA synthetase. Acetyl-CoA can be converted to the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol precursors, glyceraldehyde-3-phosphate, phosphoenolpyruvate, and pyruvate, by pyruvate:ferredoxin oxidoreductase and the enzymes of gluconeogenesis. Following the teachings and guidance provided herein for introducing a sufficient number of encoding nucleic acids to generate a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway, those skilled in the art will understand that the same engineering design also can be performed with respect to introducing at least the nucleic acids encoding the reductive TCA pathway enzymes or proteins absent in the host organism. Therefore, introduction of one or more encoding nucleic acids into the microbial organisms of the invention such that the modified organism contains a reductive TCA pathway can confer syngas utilization ability.
Thus, this invention is also directed, in part to engineered biosynthetic pathways to improve carbon flux through a central metabolism intermediate en route to 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. The present invention provides non-naturally occurring microbial organisms having one or more exogenous genes encoding enzymes that can catalyze various enzymatic transformations en route to 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. In some embodiments, these enzymatic transformations are part of the reductive tricarboxylic acid (RTCA) cycle and are used to improve product yields, including but not limited to, from carbohydrate-based carbon feedstock.
In numerous engineered pathways, realization of maximum product yields based on carbohydrate feedstock is hampered by insufficient reducing equivalents or by loss of reducing equivalents and/or carbon to byproducts. In accordance with some embodiments, the present invention increases the yields of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol by (i) enhancing carbon fixation via the reductive TCA cycle, and/or (ii) accessing additional reducing equivalents from gaseous carbon sources and/or syngas components such as CO, CO2, and/or H2. In addition to syngas, other sources of such gases include, but are not limted to, the atmosphere, either as found in nature or generated.
The CO2-fixing reductive tricarboxylic acid (RTCA) cycle is an endergenic anabolic pathway of CO2 assimilation which uses reducing equivalents and ATP (
In some embodiments, the reductive TCA cycle, coupled with carbon monoxide dehydrogenase and/or hydrogenase enzymes, can be employed to allow syngas, CO2, CO, H2, and/or other gaseous carbon source utilization by microorganisms. Synthesis gas (syngas), in particular is a mixture of primarily H2 and CO, sometimes including some amounts of CO2, that can be obtained via gasification of any organic feedstock, such as coal, coal oil, natural gas, biomass, or waste organic matter. Numerous gasification processes have been developed, and most designs are based on partial oxidation, where limiting oxygen avoids full combustion, of organic materials at high temperatures (500-1500° C.) to provide syngas as a 0.5:1-3:1 H2/CO mixture. In addition to coal, biomass of many types has been used for syngas production and represents an inexpensive and flexible feedstock for the biological production of renewable chemicals and fuels. Carbon dioxide can be provided from the atmosphere or in condensed from, for example, from a tank cylinder, or via sublimation of solid CO2. Similarly, CO and hydrogen gas can be provided in reagent form and/or mixed in any desired ratio. Other gaseous carbon forms can include, for example, methanol or similar volatile organic solvents.
The components of synthesis gas and/or other carbon sources can provide sufficient CO2, reducing equivalents, and ATP for the reductive TCA cycle to operate. One turn of the RTCA cycle assimilates two moles of CO2 into one mole of acetyl-CoA and requires 2 ATP and 4 reducing equivalents. CO and/or H2 can provide reducing equivalents by means of carbon monoxide dehydrogenase and hydrogenase enzymes, respectively. Reducing equivalents can come in the form of NADH, NADPH, FADH, reduced quinones, reduced ferredoxins, reduced flavodoxins and thioredoxins. The reducing equivalents, particularly NADH, NADPH, and reduced ferredoxin, can serve as cofactors for the RTCA cycle enzymes, for example, malate dehydrogenase, fumarate reductase, alpha-ketoglutarate:ferredoxin oxidoreductase (alternatively known as 2-oxoglutarate:ferredoxin oxidoreductase, alpha-ketoglutarate synthase, or 2-oxoglutarate synthase), pyruvate:ferredoxin oxidoreductase and isocitrate dehydrogenase. The electrons from these reducing equivalents can alternatively pass through an ion-gradient producing electron transport chain where they are passed to an acceptor such as oxygen, nitrate, oxidized metal ions, protons, or an electrode. The ion-gradient can then be used for ATP generation via an ATP synthase or similar enzyme.
The reductive TCA cycle was first reported in the green sulfur photosynthetic bacterium Chlorobium limicola (Evans et al., Proc. Natl. Acad. Sci. U.S.A. 55:928-934 (1966)). Similar pathways have been characterized in some prokaryotes (proteobacteria, green sulfur bacteria and thermophillic Knallgas bacteria) and sulfur-dependent archaea (Hugler et al., J. Bacteriol. 187:3020-3027 (2005; Hugler et al., Environ. Microbiol. 9:81-92 (2007). In some cases, reductive and oxidative (Krebs) TCA cycles are present in the same organism (Hugler et al., supra (2007); Siebers et al., J. Bacteriol. 186:2179-2194 (2004)). Some methanogens and obligate anaerobes possess incomplete oxidative or reductive TCA cycles that may function to synthesize biosynthetic intermediates (Ekiel et al., J. Bacteriol. 162:905-908 (1985); Wood et al., FEMS Microbiol. Rev. 28:335-352 (2004)).
The key carbon-fixing enzymes of the reductive TCA cycle are alpha-ketoglutarate:ferredoxin oxidoreductase, pyruvate:ferredoxin oxidoreductase and isocitrate dehydrogenase. Additional carbon may be fixed during the conversion of phosphoenolpyruvate to oxaloacetate by phosphoenolpyruvate carboxylase or phosphoenolpyruvate carboxykinase or by conversion of pyruvate to malate by malic enzyme.
Many of the enzymes in the TCA cycle are reversible and can catalyze reactions in the reductive and oxidative directions. However, some TCA cycle reactions are irreversible in vivo and thus different enzymes are used to catalyze these reactions in the directions required for the reverse TCA cycle. These reactions are: (1) conversion of citrate to oxaloacetate and acetyl-CoA, (2) conversion of fumarate to succinate, and (3) conversion of succinyl-CoA to alpha-ketoglutarate. In the TCA cycle, citrate is formed from the condensation of oxaloacetate and acetyl-CoA. The reverse reaction, cleavage of citrate to oxaloacetate and acetyl-CoA, is ATP-dependent and catalyzed by ATP-citrate lyase, or citryl-CoA synthetase and citryl-CoA lyase. Alternatively, citrate lyase can be coupled to acetyl-CoA synthetase, an acetyl-CoA transferase, or phosphotransacetylase and acetate kinase to form acetyl-CoA and oxaloacetate from citrate. The conversion of succinate to fumarate is catalyzed by succinate dehydrogenase while the reverse reaction is catalyzed by fumarate reductase. In the TCA cycle succinyl-CoA is formed from the NAD(P)+ dependent decarboxylation of alpha-ketoglutarate by the alpha-ketoglutarate dehydrogenase complex. The reverse reaction is catalyzed by alpha-ketoglutarate:ferredoxin oxidoreductase.
An organism capable of utilizing the reverse tricarboxylic acid cycle to enable production of acetyl-CoA-derived products on 1) CO, 2) CO2 and H2, 3) CO and CO2, 4) synthesis gas comprising CO and H2, and 5) synthesis gas or other gaseous carbon sources comprising CO, CO2, and H2 can include any of the following enzyme activities: ATP-citrate lyase, citrate lyase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate:ferredoxin oxidoreductase, succinyl-CoA synthetase, succinyl-CoA transferase, fumarate reductase, fumarase, malate dehydrogenase, acetate kinase, phosphotransacetylase, acetyl-CoA synthetase, acetyl-CoA transferase, pyruvate:ferredoxin oxidoreductase, NAD(P)H:ferredoxin oxidoreductase, carbon monoxide dehydrogenase, hydrogenase, and ferredoxin (see
Carbon from syngas or other gaseous carbon sources can be fixed via the reverse TCA cycle and components thereof. Specifically, the combination of certain carbon gas-utilization pathway components with the pathways for formation of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol from acetyl-CoA results in high yields of these products by providing an efficient mechanism for fixing the carbon present in carbon dioxide, fed exogenously or produced endogenously from CO, into acetyl-CoA.
In some embodiments, a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway in a non-naturally occurring microbial organism of the invention can utilize any combination of (1) CO, (2) CO2, (3) H2, or mixtures thereof to enhance the yields of biosynthetic steps involving reduction, including addition to driving the reductive TCA cycle.
In some embodiments a non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway includes at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme. The at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, isocitrate dehydrogenase, aconitase, and an alpha-ketoglutarate:ferredoxin oxidoreductase; and at least one exogenous enzyme selected from a carbon monoxide dehydrogenase, a hydrogenase, a NAD(P)H:ferredoxin oxidoreductase, and a ferredoxin, expressed in a sufficient amount to allow the utilization of (1) CO, (2) CO2, (3) H2, (4) CO2 and H2, (5) CO and CO2, (6) CO and H2, or (7) CO, CO2, and H2.
In some embodiments a method includes culturing a non-naturally occurring microbial organism having a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway also comprising at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme. The at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, isocitrate dehydrogenase, aconitase, and an alpha-ketoglutarate:ferredoxin oxidoreductase. Additionally, such an organism can also include at least one exogenous enzyme selected from a carbon monoxide dehydrogenase, a hydrogenase, a NAD(P)H:ferredoxin oxidoreductase, and a ferredoxin, expressed in a sufficient amount to allow the utilization of (1) CO, (2) CO2, (3) H2, (4) CO2 and H2, (5) CO and CO2, (6) CO and H2, or (7) CO, CO2, and H2 to produce a product.
In some embodiments a non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway further includes at least one exogenous nucleic acid encoding a reductive TCA pathway enzyme expressed in a sufficient amount to enhance carbon flux through acetyl-CoA. The at least one exogenous nucleic acid is selected from an ATP-citrate lyase, citrate lyase, a fumarate reductase, a pyruvate:ferredoxin oxidoreductase, isocitrate dehydrogenase, aconitase and an alpha-ketoglutarate:ferredoxin oxidoreductase.
In some embodiments a non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway includes at least one exogenous nucleic acid encoding an enzyme expressed in a sufficient amount to enhance the availability of reducing equivalents in the presence of carbon monoxide and/or hydrogen, thereby increasing the yield of redox-limited products via carbohydrate-based carbon feedstock. The at least one exogenous nucleic acid is selected from a carbon monoxide dehydrogenase, a hydrogenase, an NAD(P)H:ferredoxin oxidoreductase, and a ferredoxin. In some embodiments, the present invention provides a method for enhancing the availability of reducing equivalents in the presence of carbon monoxide or hydrogen thereby increasing the yield of redox-limited products via carbohydrate-based carbon feedstock, such as sugars or gaseous carbon sources, the method includes culturing this non-naturally occurring microbial organism under conditions and for a sufficient period of time to produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway includes two exogenous nucleic acids, each encoding a reductive TCA pathway enzyme. In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway includes three exogenous nucleic acids each encoding a reductive TCA pathway enzyme. In some embodiments, the non-naturally occurring microbial organism includes three exogenous nucleic acids encoding an ATP-citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase. In some embodiments, the non-naturally occurring microbial organism includes three exogenous nucleic acids encoding a citrate lyase, a fumarate reductase, and an alpha-ketoglutarate:ferredoxin oxidoreductase. In some embodiments, the non-naturally occurring microbial organism includes four exogenous nucleic acids encoding a pyruvate:ferredoxin oxidoreductase; a phosphoenolpyruvate carboxylase or a phosphoenolpyruvate carboxykinase, a CO dehydrogenase; and an H2 hydrogenase. In some embodiments, the non-naturally occurring microbial organism includes two exogenous nucleic acids encoding a CO dehydrogenase and an H2 hydrogenase.
In some embodiments, the non-naturally occurring microbial organisms having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway further include an exogenous nucleic acid encoding an enzyme selected from a pyruvate:ferredoxin oxidoreductase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, an NAD(P)H:ferredoxin oxidoreductase, and combinations thereof.
In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway further includes an exogenous nucleic acid encoding an enzyme selected from carbon monoxide dehydrogenase, acetyl-CoA synthase, ferredoxin, NAD(P)H:ferredoxin oxidoreductase and combinations thereof.
In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway utilizes a carbon feedstock selected from (1) CO, (2) CO2, (3) CO2 and H2, (4) CO and H2, or (5) CO, CO2, and H2. In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway utilizes hydrogen for reducing equivalents. In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway utilizes CO for reducing equivalents. In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway utilizes combinations of CO and hydrogen for reducing equivalents.
In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway further includes one or more nucleic acids encoding an enzyme selected from a phosphoenolpyruvate carboxylase, a phosphoenolpyruvate carboxykinase, a pyruvate carboxylase, and a malic enzyme.
In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway further includes one or more nucleic acids encoding an enzyme selected from a malate dehydrogenase, a fumarase, a fumarate reductase, a succinyl-CoA synthetase, and a succinyl-CoA transferase.
In some embodiments, the non-naturally occurring microbial organism having an 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway further includes at least one exogenous nucleic acid encoding a citrate lyase, an ATP-citrate lyase, a citryl-CoA synthetase, a citryl-CoA lyase, an aconitase, an isocitrate dehydrogenase, a succinyl-CoA synthetase, a succinyl-CoA transferase, a fumarase, a malate dehydrogenase, an acetate kinase, a phosphotransacetylase, an acetyl-CoA synthetase, and a ferredoxin.
Accordingly, given the teachings and guidance provided herein, those skilled in the art will understand that a non-naturally occurring microbial organism can be produced that secretes the biosynthesized compounds of the invention when grown on a carbon source such as a carbohydrate. Such compounds include, for example, 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol and any of the intermediate metabolites in the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway. All that is required is to engineer in one or more of the required enzyme or protein activities to achieve biosynthesis of the desired compound or intermediate including, for example, inclusion of some or all of the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol biosynthetic pathways. Accordingly, the invention provides a non-naturally occurring microbial organism that produces and/or secretes 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol when grown on a carbohydrate or other carbon source and produces and/or secretes any of the intermediate metabolites shown in the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway when grown on a carbohydrate or other carbon source. The 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producing microbial organisms of the invention can initiate synthesis from an intermediate, for example, 5-aminopent-2-enoate, glutarate semialdehyde, 5-hydroxyvalerate, 5-hydroxyvaleryl-CoA, 5-hydroxypent-2-enoyl-CoA, 2,4-pentadienoyl-CoA, 5-hydroxypent-2-enoate, 5-hydroxypent-2-enoate, acetoacetyl-CoA, 3-hydroxybutyryl-CoA, crotoyl-CoA, glutaryl-CoA, 3-oxopentanoyl-CoA, 3-hydroxypentanoyl-CoA, pent-2-enoyl-CoA, pent-3-enoyl-CoA, 3-oxo-5-hydroxypentanoyl-CoA, 3-oxo-5-hydroxypentanoate, 3-oxobutanol, 4-hydroxy-2-oxovalerate, 2-oxopentenoate, 3-buten-1-al, 3-hydroxybutyryl-CoA, 3-hydroxybutyrate, 3-hydroxybutanal, 2,4-pentadienoyl-phosphate, or penta-2,4-dienal.
The non-naturally occurring microbial organisms of the invention are constructed using methods well known in the art as exemplified herein to exogenously express at least one nucleic acid encoding a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway enzyme or protein in sufficient amounts to produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. It is understood that the microbial organisms of the invention are cultured under conditions sufficient to produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. Following the teachings and guidance provided herein, the non-naturally occurring microbial organisms of the invention can achieve biosynthesis of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol resulting in intracellular concentrations between about 0.1-200 mM or more. Generally, the intracellular concentration of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol is between about 3-150 mM, particularly between about 5-125 mM and more particularly between about 8-100 mM, including about 10 mM, 20 mM, 50 mM, 80 mM, or more. Intracellular concentrations between and above each of these exemplary ranges also can be achieved from the non-naturally occurring microbial organisms of the invention.
In some embodiments, culture conditions include anaerobic or substantially anaerobic growth or maintenance conditions. Exemplary anaerobic conditions have been described previously and are well known in the art. Exemplary anaerobic conditions for fermentation processes are described herein and are described, for example, in U.S. publication 2009/0047719, filed Aug. 10, 2007. Any of these conditions can be employed with the non-naturally occurring microbial organisms as well as other anaerobic conditions well known in the art. Under such anaerobic or substantially anaerobic conditions, the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producers can synthesize 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol at intracellular concentrations of 5-10 mM or more as well as all other concentrations exemplified herein. It is understood that, even though the above description refers to intracellular concentrations, 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producing microbial organisms can produce 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol intracellularly and/or secrete the product into the culture medium.
In addition to the culturing and fermentation conditions disclosed herein, growth condition for achieving biosynthesis of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol can include the addition of an osmoprotectant to the culturing conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented as described herein in the presence of an osmoprotectant. Briefly, an osmoprotectant refers to a compound that acts as an osmolyte and helps a microbial organism as described herein survive osmotic stress. Osmoprotectants include, but are not limited to, betaines, amino acids, and the sugar trehalose. Non-limiting examples of such are glycine betaine, praline betaine, dimethylthetin, dimethyl slfonioproprionate, 3-dimethylsulfonio-2-methylproprionate, pipecolic acid, dimethylsulfonioacetate, choline, L-carnitine and ectoine. In one aspect, the osmoprotectant is glycine betaine. It is understood to one of ordinary skill in the art that the amount and type of osmoprotectant suitable for protecting a microbial organism described herein from osmotic stress will depend on the microbial organism used. The amount of osmoprotectant in the culturing conditions can be, for example, no more than about 0.1 mM, no more than about 0.5 mM, no more than about 1.0 mM, no more than about 1.5 mM, no more than about 2.0 mM, no more than about 2.5 mM, no more than about 3.0 mM, no more than about 5.0 mM, no more than about 7.0 mM, no more than about 10 mM, no more than about 50 mM, no more than about 100 mM or no more than about 500 mM.
In some embodiments, the carbon feedstock and other cellular uptake sources such as phosphate, ammonia, sulfate, chloride and other halogens can be chosen to alter the isotopic distribution of the atoms present in 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or any 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate. The various carbon feedstock and other uptake sources enumerated above will be referred to herein, collectively, as “uptake sources.” Uptake sources can provide isotopic enrichment for any atom present in the product 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate, or for side products generated in reactions diverging away from a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway. Isotopic enrichment can be achieved for any target atom including, for example, carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, chloride or other halogens.
In some embodiments, the uptake sources can be selected to alter the carbon-12, carbon-13, and carbon-14 ratios. In some embodiments, the uptake sources can be selected to alter the oxygen-16, oxygen-17, and oxygen-18 ratios. In some embodiments, the uptake sources can be selected to alter the hydrogen, deuterium, and tritium ratios. In some embodiments, the uptake sources can be selected to alter the nitrogen-14 and nitrogen-15 ratios. In some embodiments, the uptake sources can be selected to alter the sulfur-32, sulfur-33, sulfur-34, and sulfur-35 ratios. In some embodiments, the uptake sources can be selected to alter the phosphorus-31, phosphorus-32, and phosphorus-33 ratios. In some embodiments, the uptake sources can be selected to alter the chlorine-35, chlorine-36, and chlorine-37 ratios.
In some embodiments, the isotopic ratio of a target atom can be varied to a desired ratio by selecting one or more uptake sources. An uptake source can be derived from a natural source, as found in nature, or from a man-made source, and one skilled in the art can select a natural source, a man-made source, or a combination thereof, to achieve a desired isotopic ratio of a target atom. An example of a man-made uptake source includes, for example, an uptake source that is at least partially derived from a chemical synthetic reaction. Such isotopically enriched uptake sources can be purchased commercially or prepared in the laboratory and/or optionally mixed with a natural source of the uptake source to achieve a desired isotopic ratio. In some embodiments, a target atom isotopic ratio of an uptake source can be achieved by selecting a desired origin of the uptake source as found in nature. For example, as discussed herein, a natural source can be a biobased derived from or synthesized by a biological organism or a source such as petroleum-based products or the atmosphere. In some such embodiments, a source of carbon, for example, can be selected from a fossil fuel-derived carbon source, which can be relatively depleted of carbon-14, or an environmental or atmospheric carbon source, such as CO2, which can possess a larger amount of carbon-14 than its petroleum-derived counterpart.
The unstable carbon isotope carbon-14 or radiocarbon makes up for roughly 1 in 1012 carbon atoms in the earth's atmosphere and has a half-life of about 5700 years. The stock of carbon is replenished in the upper atmosphere by a nuclear reaction involving cosmic rays and ordinary nitrogen (14N). Fossil fuels contain no carbon-14, as it decayed long ago. Burning of fossil fuels lowers the atmospheric carbon-14 fraction, the so-called “Suess effect”.
Methods of determining the isotopic ratios of atoms in a compound are well known to those skilled in the art. Isotopic enrichment is readily assessed by mass spectrometry using techniques known in the art such as accelerated mass spectrometry (AMS), Stable Isotope Ratio Mass Spectrometry (SIRMS) and Site-Specific Natural Isotopic Fractionation by Nuclear Magnetic Resonance (SNIF-NMR). Such mass spectral techniques can be integrated with separation techniques such as liquid chromatography (LC), high performance liquid chromatography (HPLC) and/or gas chromatography, and the like.
In the case of carbon, ASTM D6866 was developed in the United States as a standardized analytical method for determining the biobased content of solid, liquid, and gaseous samples using radiocarbon dating by the American Society for Testing and Materials (ASTM) International. The standard is based on the use of radiocarbon dating for the determination of a product's biobased content. ASTM D6866 was first published in 2004, and the current active version of the standard is ASTM D6866-11 (effective Apr. 1, 2011). Radiocarbon dating techniques are well known to those skilled in the art, including those described herein.
The biobased content of a compound is estimated by the ratio of carbon-14 (14C) to carbon-12 (12C). Specifically, the Fraction Modern (Fm) is computed from the expression: Fm=(S−B)/(M−B), where B, S and M represent the 14C/12C ratios of the blank, the sample and the modern reference, respectively. Fraction Modern is a measurement of the deviation of the 14C/12C ratio of a sample from “Modern.” Modern is defined as 95% of the radiocarbon concentration (in AD 1950) of National Bureau of Standards (NBS) Oxalic Acid I (i.e., standard reference materials (SRM) 4990b) normalized to δ13CVPDB=−19 per mil (Olsson, The use of Oxalic acid as a Standard. in, Radiocarbon Variations and Absolute Chronology, Nobel Symposium, 12th Proc., John Wiley & Sons, New York (1970)). Mass spectrometry results, for example, measured by ASM, are calculated using the internationally agreed upon definition of 0.95 times the specific activity of NBS Oxalic Acid I (SRM 4990b) normalized to δ13CVPDB=19 per mil. This is equivalent to an absolute (AD 1950) 14C/12C ratio of 1.176±0.010×1012 (Karlen et al., Arkiv Geofysik, 4:465-471 (1968)). The standard calculations take into account the differential uptake of one istope with respect to another, for example, the preferential uptake in biological systems of C12 over C13 over C14, and these corrections are reflected as a Fm corrected for δ13.
An oxalic acid standard (SRM 4990b or HOx 1) was made from a crop of 1955 sugar beet. Although there were 1000 lbs made, this oxalic acid standard is no longer commercially available. The Oxalic Acid II standard (HOx 2; N.I.S.T designation SRM 4990 C) was made from a crop of 1977 French beet molasses. In the early 1980's, a group of 12 laboratories measured the ratios of the two standards. The ratio of the activity of Oxalic acid II to 1 is 1.2933±0.001 (the weighted mean). The isotopic ratio of HOx II is −17.8 per mille. ASTM D6866-11 suggests use of the available Oxalic Acid II standard SRM 4990 C (Hox2) for the modern standard (see discussion of original vs. currently available oxalic acid standards in Mann, Radiocarbon, 25(2):519-527 (1983)). A Fm=0% represents the entire lack of carbon-14 atoms in a material, thus indicating a fossil (for example, petroleum based) carbon source. A Fm=100%, after correction for the post-1950 injection of carbon-14 into the atmosphere from nuclear bomb testing, indicates an entirely modern carbon source. As described herein, such a “modern” source includes biobased sources.
As described in ASTM D6866, the percent modern carbon (pMC) can be greater than 100% because of the continuing but diminishing effects of the 1950s nuclear testing programs, which resulted in a considerable enrichment of carbon-14 in the atmosphere as described in ASTM D6866-11. Because all sample carbon-14 activities are referenced to a “pre-bomb” standard, and because nearly all new biobased products are produced in a post-bomb environment, all pMC values (after correction for isotopic fraction) must be multiplied by 0.95 (as of 2010) to better reflect the true biobased content of the sample. A biobased content that is greater than 103% suggests that either an analytical error has occurred, or that the source of biobased carbon is more than several years old.
ASTM D6866 quantifies the biobased content relative to the material's total organic content and does not consider the inorganic carbon and other non-carbon containing substances present. For example, a product that is 50% starch-based material and 50% water would be considered to have a Biobased Content=100% (50% organic content that is 100% biobased) based on ASTM D6866. In another example, a product that is 50% starch-based material, 25% petroleum-based, and 25% water would have a Biobased Content=66.7% (75% organic content but only 50% of the product is biobased). In another example, a product that is 50% organic carbon and is a petroleum-based product would be considered to have a Biobased Content=0% (50% organic carbon but from fossil sources). Thus, based on the well known methods and known standards for determining the biobased content of a compound or material, one skilled in the art can readily determine the biobased content and/or prepared downstream products that utilize of the invention having a desired biobased content.
Applications of carbon-14 dating techniques to quantify bio-based content of materials are known in the art (Currie et al., Nuclear Instruments and Methods in Physics Research B, 172:281-287 (2000)). For example, carbon-14 dating has been used to quantify bio-based content in terephthalate-containing materials (Colonna et al., Green Chemistry, 13:2543-2548 (2011)). Notably, polypropylene terephthalate (PPT) polymers derived from renewable 1,3-propanediol and petroleum-derived terephthalic acid resulted in Fm values near 30% (i.e., since 3/11 of the polymeric carbon derives from renewable 1,3-propanediol and 8/11 from the fossil end member terephthalic acid) (Currie et al., supra, 2000). In contrast, polybutylene terephthalate polymer derived from both renewable 1,4-butanediol and renewable terephthalic acid resulted in bio-based content exceeding 90% (Colonna et al., supra, 2011).
Accordingly, in some embodiments, the present invention provides 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate that has a carbon-12, carbon-13, and carbon-14 ratio that reflects an atmospheric carbon, also referred to as environmental carbon, uptake source. For example, in some aspects the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate can have an Fm value of at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98% or as much as 100%. In some such embodiments, the uptake source is CO2. In some embodiments, the present invention provides 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol intermediate that has a carbon-12, carbon-13, and carbon-14 ratio that reflects petroleum-based carbon uptake source. In this aspect, the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate can have an Fm value of less than 95%, less than 90%, less than 85%, less than 80%, less than 75%, less than 70%, less than 65%, less than 60%, less than 55%, less than 50%, less than 45%, less than 40%, less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, less than 5%, less than 2% or less than 1%. In some embodiments, the present invention provides 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol intermediate that has a carbon-12, carbon-13, and carbon-14 ratio that is obtained by a combination of an atmospheric carbon uptake source with a petroleum-based uptake source. Using such a combination of uptake sources is one way by which the carbon-12, carbon-13, and carbon-14 ratio can be varied, and the respective ratios would reflect the proportions of the uptake sources.
Further, the present invention relates to the biologically produced 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate as disclosed herein, and to the products derived therefrom, wherein the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate has a carbon-12, carbon-13, and carbon-14 isotope ratio of about the same value as the CO2 that occurs in the environment. For example, in some aspects the invention provides: bioderived 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a bioderived 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway intermediate having a carbon-12 versus carbon-13 versus carbon-14 isotope ratio of about the same value as the CO2 that occurs in the environment, or any of the other ratios disclosed herein. It is understood, as disclosed herein, that a product can have a carbon-12 versus carbon-13 versus carbon-14 isotope ratio of about the same value as the CO2 that occurs in the environment, or any of the ratios disclosed herein, wherein the product is generated from bioderived 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a bioderived 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol intermediate as disclosed herein, wherein the bioderived product is chemically modified to generate a final product. Methods of chemically modifying a bioderived product of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol, or an intermediate thereof, to generate a desired product are well known to those skilled in the art, as described herein. The invention further provides polyurethane, polymer, co-polymer, synthetic rubber, resin, chemical, polymer intermediate, organic solvent, hypoglycaemic agent, polyester resin, latex, monomer, fine chemical, agricultural chemical, pharmaceutical, or perfume having a carbon-12 versus carbon-13 versus carbon-14 isotope ratio of about the same value as the CO2 that occurs in the environment, wherein the polyurethane, polymer, co-polymer, synthetic rubber, resin, chemical, polymer intermediate, organic solvent, hypoglycaemic agent, polyester resin, latex, monomer, fine chemical, agricultural chemical, pharmaceutical, or perfume is generated directly from or in combination with bioderived 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol or a bioderived 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol intermediate as disclosed herein.
2,4-Pentadienoate is a useful substituted butadiene derivative and a valuable intermediate en route to other substituted 1,3-butadiene derivatives, including, for example, 1-carbamoyl-1,3-butadienes. Non-limiting examples of applications of 2,4-pentadienoate include production of N-protected-1,3-butadiene derivatives that can be used in the preparation of anilines, a precursor to many inductrial chemicals, such as polyurethane and production of various polymers and co-polymers. Accordingly, in some embodiments, the invention provides a biobased polyurethane, polymer or co-polymer comprising one or more bioderived 2,4-pentadienoate or bioderived 2,4-pentadienoate intermediate produced by a non-naturally occurring microorganism of the invention or produced using a method disclosed herein.
Butadiene is a chemical commonly used in many commercial and industrial applications. Non-limiting examples of such applications include production of polymers, such as synthetic rubbers and ABS resins, and chemicals, such as hexamethylenediamine and 1,4-butanediol. Accordingly, in some embodiments, the invention provides a biobased polymer, synthetic rubber, resin, or chemical comprising one or more bioderived butadiene or bioderived butadiene intermediate produced by a non-naturally occurring microorganism of the invention or produced using a method disclosed herein.
Propylene is a chemical commonly used in many commercial and industrial applications. Non-limiting examples of such applications include production of polymers, polymer intermediates and chemicals, such as polypropylene, acrylic acid, butanol, butanediol, acrylonitrile, propylene oxide, isopropanol and cumene. Moreover, these propylene derivatives, such as polypropylene, are used in the production of a wide range of products including plastics, such as injection moulding, and fibers, such as carpets. Accordingly, in some embodiments, the invention provides a biobased polymer, polymer intermediate, or chemical comprising one or more bioderived propylene or bioderived propylene intermediate produced by a non-naturally occurring microorganism of the invention or produced using a method disclosed herein.
1,3-Butanediol is a chemical commonly used in many commercial and industrial applications. Non-limiting examples of such applications include its use as an organic solvent for food flavoring agents or as a hypoglycaemic agent and its use in the production of polyurethane and polyester resins. Moreover, optically active 1,3-butanediol is also used in the synthesis of biologically active compounds and liquid crystals. Still further, 1,3-butanediol can be used in commercial production of 1,3-butadiene, a compound used in the manufacture of synthetic rubbers (e.g., tires), latex, and resins. Accordingly, in some embodiments, the invention provides a biobased organic solvent, hypoglycaemic agent, polyurethane, polyester resin, synthetic rubber, latex, or resin comprising one or more bioderived 1,3-butanediol or bioderived 1,3-butanediolintermediate produced by a non-naturally occurring microorganism of the invention or produced using a method disclosed herein.
Crotyl alcohol is a chemical commonly used in many commercial and industrial applications. Non-limiting examples of such applications include production of crotyl halides, esters, and ethers, which in turn are chemical are chemical intermediates in the production of monomers, fine chemicals, such as sorbic acid, trimethylhydroquinone, crotonic acid and 3-methoxybutanol, agricultural chemicals, and pharmaceuticals. Crotyl alcohol can also be used as a precursor in the production of 1,3-butadiene. Accordingly, in some embodiments, the invention provides a biobased monomer, fine chemical, agricultural chemical, or pharmaceutical comprising one or more bioderived crotyl alcohol or bioderived crotyl alcohol intermediate produced by a non-naturally occurring microorganism of the invention or produced using a method disclosed herein.
3-Buten-1-ol is a chemical commonly used in many commercial and industrial applications. Non-limiting examples of such applications include production of pharmaceuticals, agrochemicals, perfumes and resins. Accordingly, in some embodiments, the invention provides a biobased pharmaceutical, agrochemical, perfume or resin comprising one or more bioderived 3-buten-1-ol or bioderived 3-buten-1-ol intermediate produced by a non-naturally occurring microorganism of the invention or produced using a method disclosed herein.
As used herein, the term “bioderived” means derived from or synthesized by a biological organism and can be considered a renewable resource since it can be generated by a biological organism. Such a biological organism, in particular the microbial organisms of the invention disclosed herein, can utilize feedstock or biomass, such as, sugars or carbohydrates obtained from an agricultural, plant, bacterial, or animal source. Alternatively, the biological organism can utilize atmospheric carbon. As used herein, the term “biobased” means a product as described above that is composed, in whole or in part, of a bioderived compound of the invention. A biobased or bioderived product is in contrast to a petroleum derived product, wherein such a product is derived from or synthesized from petroleum or a petrochemical feedstock.
In some embodiments, the invention provides polyurethane, polymer or co-polymer comprising bioderived 2,4-pentadienoate or bioderived 2,4-pentadienoate pathway intermediate, wherein the bioderived 2,4-pentadienoate or bioderived 2,4-pentadienoate pathway intermediate includes all or part of the 2,4-pentadienoate or 2,4-pentadienoate pathway intermediate used in the production of polyurethane, polymer or co-polymer. Thus, in some aspects, the invention provides a biobased polyurethane, polymer or co-polymer comprising at least 2%, at least 3%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98% or 100% bioderived 2,4-pentadienoate or bioderived 2,4-pentadienoate pathway intermediate as disclosed herein. Additionally, in some aspects, the invention provides a biobased polyurethane, polymer or co-polymer wherein the 2,4-pentadienoate or 2,4-pentadienoate pathway intermediate used in its production is a combination of bioderived and petroleum derived 2,4-pentadienoate or 2,4-pentadienoate pathway intermediate. For example, a biobased polyurethane, polymer or co-polymer can be produced using 50% bioderived 2,4-pentadienoate and 50% petroleum derived 2,4-pentadienoate or other desired ratios such as 60%/40%, 70%/30%, 80%/20%, 90%/10%, 95%/5%, 100%/0%, 40%/60%, 30%/70%, 20%/80%, 10%/90% of bioderived/petroleum derived precursors, so long as at least a portion of the product comprises a bioderived product produced by the microbial organisms disclosed herein. It is understood that methods for producing polyurethane, polymer or co-polymer using the bioderived 2,4-pentadienoate or bioderived 2,4-pentadienoate pathway intermediate of the invention are well known in the art.
In some embodiments, the invention provides polymer, synthetic rubber, resin, or chemical comprising bioderived butadiene or bioderived butadiene pathway intermediate, wherein the bioderived butadiene or bioderived butadiene pathway intermediate includes all or part of the butadiene or butadiene pathway intermediate used in the production of polymer, synthetic rubber, resin, or chemical. Thus, in some aspects, the invention provides a biobased polymer, synthetic rubber, resin, or chemical comprising at least 2%, at least 3%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98% or 100% bioderived butadiene or bioderived butadiene pathway intermediate as disclosed herein. Additionally, in some aspects, the invention provides a biobased polymer, synthetic rubber, resin, or chemical wherein the butadiene or butadiene pathway intermediate used in its production is a combination of bioderived and petroleum derived butadiene or butadiene pathway intermediate. For example, a biobased polymer, synthetic rubber, resin, or chemical can be produced using 50% bioderived butadiene and 50% petroleum derived butadiene or other desired ratios such as 60%/40%, 70%/30%, 80%/20%, 90%/10%, 95%/5%, 100%/0%, 40%/60%, 30%/70%, 20%/80%, 10%/90% of bioderived/petroleum derived precursors, so long as at least a portion of the product comprises a bioderived product produced by the microbial organisms disclosed herein. It is understood that methods for producing polymer, synthetic rubber, resin, or chemical using the bioderived butadiene or bioderived butadiene pathway intermediate of the invention are well known in the art.
In some embodiments, the invention provides polymer, polymer intermediate, or chemical comprising bioderived propylene or bioderived propylene pathway intermediate, wherein the bioderived propylene or bioderived propylene pathway intermediate includes all or part of the propylene or propylene pathway intermediate used in the production of polymer, polymer intermediate, or chemical. Thus, in some aspects, the invention provides a biobased polymer, polymer intermediate, or chemical comprising at least 2%, at least 3%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98% or 100% bioderived propylene or bioderived propylene pathway intermediate as disclosed herein. Additionally, in some aspects, the invention provides a biobased polymer, polymer intermediate, or chemical wherein the propylene or propylene pathway intermediate used in its production is a combination of bioderived and petroleum derived propylene or propylene pathway intermediate. For example, a biobased polymer, polymer intermediate, or chemical can be produced using 50% bioderived propylene and 50% petroleum derived propylene or other desired ratios such as 60%/40%, 70%/30%, 80%/20%, 90%/10%, 95%/5%, 100%/0%, 40%/60%, 30%/70%, 20%/80%, 10%/90% of bioderived/petroleum derived precursors, so long as at least a portion of the product comprises a bioderived product produced by the microbial organisms disclosed herein. It is understood that methods for producing polymer, polymer intermediate, or chemical using the bioderived propylene or bioderived propylene pathway intermediate of the invention are well known in the art.
In some embodiments, the invention provides organic solvent, hypoglycaemic agent, polyurethane, polyester resin, synthetic rubber, latex, or resin comprising bioderived 1,3-butanediol or bioderived 1,3-butanediol pathway intermediate, wherein the bioderived 1,3-butanediol or bioderived 1,3-butanediol pathway intermediate includes all or part of the 1,3-butanediol or 1,3-butanediol pathway intermediate used in the production of organic solvent, hypoglycaemic agent, polyurethane, polyester resin, synthetic rubber, latex, or resin. Thus, in some aspects, the invention provides a biobased organic solvent, hypoglycaemic agent, polyurethane, polyester resin, synthetic rubber, latex, or resin comprising at least 2%, at least 3%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98% or 100% bioderived 1,3-butanediol or bioderived 1,3-butanediol pathway intermediate as disclosed herein. Additionally, in some aspects, the invention provides a biobased organic solvent, hypoglycaemic agent, polyurethane, polyester resin, synthetic rubber, latex, or resin wherein the 1,3-butanediol or 1,3-butanediol pathway intermediate used in its production is a combination of bioderived and petroleum derived 1,3-butanediol or 1,3-butanediol pathway intermediate. For example, a biobased organic solvent, hypoglycaemic agent, polyurethane, polyester resin, synthetic rubber, latex, or resin can be produced using 50% bioderived 1,3-butanediol and 50% petroleum derived 1,3-butanediol or other desired ratios such as 60%/40%, 70%/30%, 80%/20%, 90%/10%, 95%/5%, 100%/0%, 40%/60%, 30%/70%, 20%/80%, 10%/90% of bioderived/petroleum derived precursors, so long as at least a portion of the product comprises a bioderived product produced by the microbial organisms disclosed herein. It is understood that methods for producing organic solvent, hypoglycaemic agent, polyurethane, polyester resin, synthetic rubber, latex, or resin using the bioderived 1,3-butanediol or bioderived 1,3-butanediol pathway intermediate of the invention are well known in the art.
In some embodiments, the invention provides monomer, fine chemical, agricultural chemical, or pharmaceutical comprising bioderived crotyl alcohol or bioderived crotyl alcohol pathway intermediate, wherein the bioderived crotyl alcohol or bioderived crotyl alcohol pathway intermediate includes all or part of the crotyl alcohol or crotyl alcohol pathway intermediate used in the production of monomer, fine chemical, agricultural chemical, or pharmaceutical. Thus, in some aspects, the invention provides a biobased monomer, fine chemical, agricultural chemical, or pharmaceutical comprising at least 2%, at least 3%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98% or 100% bioderived crotyl alcohol or bioderived crotyl alcohol pathway intermediate as disclosed herein. Additionally, in some aspects, the invention provides a biobased monomer, fine chemical, agricultural chemical, or pharmaceutical wherein the crotyl alcohol or crotyl alcohol pathway intermediate used in its production is a combination of bioderived and petroleum derived crotyl alcohol or crotyl alcohol pathway intermediate. For example, a biobased monomer, fine chemical, agricultural chemical, or pharmaceutical can be produced using 50% bioderived crotyl alcohol and 50% petroleum derived crotyl alcohol or other desired ratios such as 60%/40%, 70%/30%, 80%/20%, 90%/10%, 95%/5%, 100%/0%, 40%/60%, 30%/70%, 20%/80%, 10%/90% of bioderived/petroleum derived precursors, so long as at least a portion of the product comprises a bioderived product produced by the microbial organisms disclosed herein. It is understood that methods for producing monomer, fine chemical, agricultural chemical, or pharmaceutical using the bioderived crotyl alcohol or bioderived crotyl alcohol pathway intermediate of the invention are well known in the art.
In some embodiments, the invention provides pharmaceutical, agrochemical, perfume, or resin comprising bioderived 3-buten-1-ol or bioderived 3-buten-1-ol pathway intermediate, wherein the bioderived 3-buten-1-ol or bioderived 3-buten-1-ol pathway intermediate includes all or part of the 3-buten-1-ol or 3-buten-1-ol pathway intermediate used in the production of pharmaceutical, agrochemical, perfume, or resin. Thus, in some aspects, the invention provides a biobased pharmaceutical, agrochemical, perfume, or resin comprising at least 2%, at least 3%, at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98% or 100% bioderived 3-buten-1-ol or bioderived 3-buten-1-ol pathway intermediate as disclosed herein. Additionally, in some aspects, the invention provides a biobased pharmaceutical, agrochemical, perfume, or resin wherein the 3-buten-1-ol or 3-buten-1-ol pathway intermediate used in its production is a combination of bioderived and petroleum derived 3-buten-1-ol or 3-buten-1-ol pathway intermediate. For example, a biobased pharmaceutical, agrochemical, perfume, or resin can be produced using 50% bioderived 3-buten-1-ol and 50% petroleum derived 3-buten-1-ol or other desired ratios such as 60%/40%, 70%/30%, 80%/20%, 90%/10%, 95%/5%, 100%/0%, 40%/60%, 30%/70%, 20%/80%, 10%/90% of bioderived/petroleum derived precursors, so long as at least a portion of the product comprises a bioderived product produced by the microbial organisms disclosed herein. It is understood that methods for producing pharmaceutical, agrochemical, perfume, or resin using the bioderived 3-buten-1-ol or bioderived 3-buten-1-ol pathway intermediate of the invention are well known in the art.
The culture conditions can include, for example, liquid culture procedures as well as fermentation and other large scale culture procedures. As described herein, particularly useful yields of the biosynthetic products of the invention can be obtained under anaerobic or substantially anaerobic culture conditions.
As described herein, one exemplary growth condition for achieving biosynthesis of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol includes anaerobic culture or fermentation conditions. In certain embodiments, the non-naturally occurring microbial organisms of the invention can be sustained, cultured or fermented under anaerobic or substantially anaerobic conditions. Briefly, anaerobic conditions refers to an environment devoid of oxygen. Substantially anaerobic conditions include, for example, a culture, batch fermentation or continuous fermentation such that the dissolved oxygen concentration in the medium remains between 0 and 10% of saturation. Substantially anaerobic conditions also includes growing or resting cells in liquid medium or on solid agar inside a sealed chamber maintained with an atmosphere of less than 1% oxygen. The percent of oxygen can be maintained by, for example, sparging the culture with an N2/CO2 mixture or other suitable non-oxygen gas or gases.
The culture conditions described herein can be scaled up and grown continuously for manufacturing of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. Exemplary growth procedures include, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. All of these processes are well known in the art. Fermentation procedures are particularly useful for the biosynthetic production of commercial quantities of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. Generally, and as with non-continuous culture procedures, the continuous and/or near-continuous production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol will include culturing a non-naturally occurring 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producing organism of the invention in sufficient nutrients and medium to sustain and/or nearly sustain growth in an exponential phase. Continuous culture under such conditions can include, for example, growth for 1 day, 2, 3, 4, 5, 6 or 7 days or more. Additionally, continuous culture can include longer time periods of 1 week, 2, 3, 4 or 5 or more weeks and up to several months. Alternatively, organisms of the invention can be cultured for hours, if suitable for a particular application. It is to be understood that the continuous and/or near-continuous culture conditions also can include all time intervals in between these exemplary periods. It is further understood that the time of culturing the microbial organism of the invention is for a sufficient period of time to produce a sufficient amount of product for a desired purpose.
Fermentation procedures are well known in the art. Briefly, fermentation for the biosynthetic production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol can be utilized in, for example, fed-batch fermentation and batch separation; fed-batch fermentation and continuous separation, or continuous fermentation and continuous separation. Examples of batch and continuous fermentation procedures are well known in the art.
In addition to the above fermentation procedures using the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producers of the invention for continuous production of substantial quantities of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol, the 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol producers also can be, for example, simultaneously subjected to chemical synthesis procedures to convert the product to other compounds or the product can be separated from the fermentation culture and sequentially subjected to chemical or enzymatic conversion to convert the product to other compounds, if desired.
To generate better producers, metabolic modeling can be utilized to optimize growth conditions. Modeling can also be used to design gene knockouts that additionally optimize utilization of the pathway (see, for example, U.S. patent publications US 2002/0012939, US 2003/0224363, US 2004/0029149, US 2004/0072723, US 2003/0059792, US 2002/0168654 and US 2004/0009466, and U.S. Pat. No. 7,127,379). Modeling analysis allows reliable predictions of the effects on cell growth of shifting the metabolism towards more efficient production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol.
One computational method for identifying and designing metabolic alterations favoring biosynthesis of a desired product is the OptKnock computational framework (Burgard et al., Biotechnol. Bioeng. 84:647-657 (2003)). OptKnock is a metabolic modeling and simulation program that suggests gene deletion or disruption strategies that result in genetically stable microorganisms which overproduce the target product. Specifically, the framework examines the complete metabolic and/or biochemical network of a microorganism in order to suggest genetic manipulations that force the desired biochemical to become an obligatory byproduct of cell growth. By coupling biochemical production with cell growth through strategically placed gene deletions or other functional gene disruption, the growth selection pressures imposed on the engineered strains after long periods of time in a bioreactor lead to improvements in performance as a result of the compulsory growth-coupled biochemical production. Lastly, when gene deletions are constructed there is a negligible possibility of the designed strains reverting to their wild-type states because the genes selected by OptKnock are to be completely removed from the genome. Therefore, this computational methodology can be used to either identify alternative pathways that lead to biosynthesis of a desired product or used in connection with the non-naturally occurring microbial organisms for further optimization of biosynthesis of a desired product.
Briefly, OptKnock is a term used herein to refer to a computational method and system for modeling cellular metabolism. The OptKnock program relates to a framework of models and methods that incorporate particular constraints into flux balance analysis (FBA) models. These constraints include, for example, qualitative kinetic information, qualitative regulatory information, and/or DNA microarray experimental data. OptKnock also computes solutions to various metabolic problems by, for example, tightening the flux boundaries derived through flux balance models and subsequently probing the performance limits of metabolic networks in the presence of gene additions or deletions. OptKnock computational framework allows the construction of model formulations that allow an effective query of the performance limits of metabolic networks and provides methods for solving the resulting mixed-integer linear programming problems. The metabolic modeling and simulation methods referred to herein as OptKnock are described in, for example, U.S. publication 2002/0168654, filed Jan. 10, 2002, in International Patent No. PCT/US02/00660, filed Jan. 10, 2002, and U.S. publication 2009/0047719, filed Aug. 10, 2007.
Another computational method for identifying and designing metabolic alterations favoring biosynthetic production of a product is a metabolic modeling and simulation system termed SimPheny®. This computational method and system is described in, for example, U.S. publication 2003/0233218, filed Jun. 14, 2002, and in International Patent Application No. PCT/US03/18838, filed Jun. 13, 2003. SimPheny® is a computational system that can be used to produce a network model in silico and to simulate the flux of mass, energy or charge through the chemical reactions of a biological system to define a solution space that contains any and all possible functionalities of the chemical reactions in the system, thereby determining a range of allowed activities for the biological system. This approach is referred to as constraints-based modeling because the solution space is defined by constraints such as the known stoichiometry of the included reactions as well as reaction thermodynamic and capacity constraints associated with maximum fluxes through reactions. The space defined by these constraints can be interrogated to determine the phenotypic capabilities and behavior of the biological system or of its biochemical components.
These computational approaches are consistent with biological realities because biological systems are flexible and can reach the same result in many different ways. Biological systems are designed through evolutionary mechanisms that have been restricted by fundamental constraints that all living systems must face. Therefore, constraints-based modeling strategy embraces these general realities. Further, the ability to continuously impose further restrictions on a network model via the tightening of constraints results in a reduction in the size of the solution space, thereby enhancing the precision with which physiological performance or phenotype can be predicted.
Given the teachings and guidance provided herein, those skilled in the art will be able to apply various computational frameworks for metabolic modeling and simulation to design and implement biosynthesis of a desired compound in host microbial organisms. Such metabolic modeling and simulation methods include, for example, the computational systems exemplified above as SimPheny® and OptKnock. For illustration of the invention, some methods are described herein with reference to the OptKnock computation framework for modeling and simulation. Those skilled in the art will know how to apply the identification, design and implementation of the metabolic alterations using OptKnock to any of such other metabolic modeling and simulation computational frameworks and methods well known in the art.
The methods described above will provide one set of metabolic reactions to disrupt. Elimination of each reaction within the set or metabolic modification can result in a desired product as an obligatory product during the growth phase of the organism. Because the reactions are known, a solution to the bilevel OptKnock problem also will provide the associated gene or genes encoding one or more enzymes that catalyze each reaction within the set of reactions. Identification of a set of reactions and their corresponding genes encoding the enzymes participating in each reaction is generally an automated process, accomplished through correlation of the reactions with a reaction database having a relationship between enzymes and encoding genes.
Once identified, the set of reactions that are to be disrupted in order to achieve production of a desired product are implemented in the target cell or organism by functional disruption of at least one gene encoding each metabolic reaction within the set. One particularly useful means to achieve functional disruption of the reaction set is by deletion of each encoding gene. However, in some instances, it can be beneficial to disrupt the reaction by other genetic aberrations including, for example, mutation, deletion of regulatory regions such as promoters or cis binding sites for regulatory factors, or by truncation of the coding sequence at any of a number of locations. These latter aberrations, resulting in less than total deletion of the gene set can be useful, for example, when rapid assessments of the coupling of a product are desired or when genetic reversion is less likely to occur.
To identify additional productive solutions to the above described bilevel OptKnock problem which lead to further sets of reactions to disrupt or metabolic modifications that can result in the biosynthesis, including growth-coupled biosynthesis of a desired product, an optimization method, termed integer cuts, can be implemented. This method proceeds by iteratively solving the OptKnock problem exemplified above with the incorporation of an additional constraint referred to as an integer cut at each iteration. Integer cut constraints effectively prevent the solution procedure from choosing the exact same set of reactions identified in any previous iteration that obligatorily couples product biosynthesis to growth. For example, if a previously identified growth-coupled metabolic modification specifies reactions 1, 2, and 3 for disruption, then the following constraint prevents the same reactions from being simultaneously considered in subsequent solutions. The integer cut method is well known in the art and can be found described in, for example, Burgard et al., Biotechnol. Prog. 17:791-797 (2001). As with all methods described herein with reference to their use in combination with the OptKnock computational framework for metabolic modeling and simulation, the integer cut method of reducing redundancy in iterative computational analysis also can be applied with other computational frameworks well known in the art including, for example, SimPheny®.
The methods exemplified herein allow the construction of cells and organisms that biosynthetically produce a desired product, including the obligatory coupling of production of a target biochemical product to growth of the cell or organism engineered to harbor the identified genetic alterations. Therefore, the computational methods described herein allow the identification and implementation of metabolic modifications that are identified by an in silico method selected from OptKnock or SimPheny®. The set of metabolic modifications can include, for example, addition of one or more biosynthetic pathway enzymes and/or functional disruption of one or more metabolic reactions including, for example, disruption by gene deletion.
As discussed above, the OptKnock methodology was developed on the premise that mutant microbial networks can be evolved towards their computationally predicted maximum-growth phenotypes when subjected to long periods of growth selection. In other words, the approach leverages an organism's ability to self-optimize under selective pressures. The OptKnock framework allows for the exhaustive enumeration of gene deletion combinations that force a coupling between biochemical production and cell growth based on network stoichiometry. The identification of optimal gene/reaction knockouts requires the solution of a bilevel optimization problem that chooses the set of active reactions such that an optimal growth solution for the resulting network overproduces the biochemical of interest (Burgard et al., Biotechnol. Bioeng. 84:647-657 (2003)).
An in silico stoichiometric model of E. coli metabolism can be employed to identify essential genes for metabolic pathways as exemplified previously and described in, for example, U.S. patent publications US 2002/0012939, US 2003/0224363, US 2004/0029149, US 2004/0072723, US 2003/0059792, US 2002/0168654 and US 2004/0009466, and in U.S. Pat. No. 7,127,379. As disclosed herein, the OptKnock mathematical framework can be applied to pinpoint gene deletions leading to the growth-coupled production of a desired product. Further, the solution of the bilevel OptKnock problem provides only one set of deletions. To enumerate all meaningful solutions, that is, all sets of knockouts leading to growth-coupled production formation, an optimization technique, termed integer cuts, can be implemented. This entails iteratively solving the OptKnock problem with the incorporation of an additional constraint referred to as an integer cut at each iteration, as discussed above.
As disclosed herein, a nucleic acid encoding a desired activity of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway can be introduced into a host organism. In some cases, it can be desirable to modify an activity of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway enzyme or protein to increase production of 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol. For example, known mutations that increase the activity of a protein or enzyme can be introduced into an encoding nucleic acid molecule. Additionally, optimization methods can be applied to increase the activity of an enzyme or protein and/or decrease an inhibitory activity, for example, decrease the activity of a negative regulator.
One such optimization method is directed evolution. Directed evolution is a powerful approach that involves the introduction of mutations targeted to a specific gene in order to improve and/or alter the properties of an enzyme. Improved and/or altered enzymes can be identified through the development and implementation of sensitive high-throughput screening assays that allow the automated screening of many enzyme variants (for example, >104). Iterative rounds of mutagenesis and screening typically are performed to afford an enzyme with optimized properties. Computational algorithms that can help to identify areas of the gene for mutagenesis also have been developed and can significantly reduce the number of enzyme variants that need to be generated and screened. Numerous directed evolution technologies have been developed (for reviews, see Hibbert et al., Biomol. Eng 22:11-19 (2005); Huisman and Lalonde, In Biocatalysis in the pharmaceutical and biotechnology industries pgs. 717-742 (2007), Patel (ed.), CRC Press; Otten and Quax. Biomol. Eng 22:1-9 (2005).; and Sen et al., Appl Biochem. Biotechnol 143:212-223 (2007)) to be effective at creating diverse variant libraries, and these methods have been successfully applied to the improvement of a wide range of properties across many enzyme classes. Enzyme characteristics that have been improved and/or altered by directed evolution technologies include, for example: selectivity/specificity, for conversion of non-natural substrates; temperature stability, for robust high temperature processing; pH stability, for bioprocessing under lower or higher pH conditions; substrate or product tolerance, so that high product titers can be achieved; binding (Km), including broadening substrate binding to include non-natural substrates; inhibition (Ki), to remove inhibition by products, substrates, or key intermediates; activity (kcat), to increases enzymatic reaction rates to achieve desired flux; expression levels, to increase protein yields and overall pathway flux; oxygen stability, for operation of air sensitive enzymes under aerobic conditions; and anaerobic activity, for operation of an aerobic enzyme in the absence of oxygen.
A number of exemplary methods have been developed for the mutagenesis and diversification of genes to target desired properties of specific enzymes. Such methods are well known to those skilled in the art. Any of these can be used to alter and/or optimize the activity of a 2,4-pentadienoate, butadiene, propylene, 1,3-butanediol, crotyl alcohol or 3-buten-1-ol pathway enzyme or protein. Such methods include, but are not limited to EpPCR, which introduces random point mutations by reducing the fidelity of DNA polymerase in PCR reactions (Pritchard et al., J Theor. Biol. 234:497-509 (2005)); Error-prone Rolling Circle Amplification (epRCA), which is similar to epPCR except a whole circular plasmid is used as the template and random 6-mers with exonuclease resistant thiophosphate linkages on the last 2 nucleotides are used to amplify the plasmid followed by transformation into cells in which the plasmid is re-circularized at tandem repeats (Fujii et al., Nucleic Acids Res. 32:e145 (2004); and Fujii et al., Nat. Protoc. 1:2493-2497 (2006)); DNA or Family Shuffling, which typically involves digestion of two or more variant genes with nucleases such as Dnase I or EndoV to generate a pool of random fragments that are reassembled by cycles of annealing and extension in the presence of DNA polymerase to create a library of chimeric genes (Stemmer, Proc Natl Acad Sci USA 91:10747-10751 (1994); and Stemmer, Nature 370:389-391 (1994)); Staggered Extension (StEP), which entails template priming followed by repeated cycles of 2 step PCR with denaturation and very short duration of annealing/extension (as short as 5 sec) (Zhao et al., Nat. Biotechnol. 16:258-261 (1998)); Random Priming Recombination (RPR), in which random sequence primers are used to generate many short DNA fragments complementary to different segments of the template (Shao et al., Nucleic Acids Res 26:681-683 (1998)).
Additional methods include Heteroduplex Recombination, in which linearized plasmid DNA is used to form heteroduplexes that are repaired by mismatch repair (Volkov et al, Nucleic Acids Res. 27:e18 (1999); and Volkov et al., Methods Enzymol. 328:456-463 (2000)); Random Chimeragenesis on Transient Templates (RACHITT), which employs Dnase I fragmentation and size fractionation of single stranded DNA (ssDNA) (Coco et al., Nat. Biotechnol. 19:354-359 (2001)); Recombined Extension on Truncated templates (RETT), which entails template switching of unidirectionally growing strands from primers in the presence of unidirectional ssDNA fragments used as a pool of templates (Lee et al., J. Molec. Catalysis 26:119-129 (2003)); Degenerate Oligonucleotide Gene Shuffling (DOGS), in which degenerate primers are used to control recombination between molecules; (Bergquist and Gibbs, Methods Mol. Biol 352:191-204 (2007); Bergquist et al., Biomol. Eng 22:63-72 (2005); Gibbs et al., Gene 271:13-20 (2001)); Incremental Truncation for the Creation of Hybrid Enzymes (ITCHY), which creates a combinatorial library with 1 base pair deletions of a gene or gene fragment of interest (Ostermeier et al., Proc. Natl. Acad. Sci. USA 96:3562-3567 (1999); and Ostermeier et al., Nat. Biotechnol. 17:1205-1209 (1999)); Thio-Incremental Truncation for the Creation of Hybrid Enzymes (THIO-ITCHY), which is similar to ITCHY except that phosphothioate dNTPs are used to generate truncations (Lutz et al., Nucleic Acids Res 29:E16 (2001)); SCRATCHY, which combines two methods for recombining genes, ITCHY and DNA shuffling (Lutz et al., Proc. Natl. Acad. Sci. USA 98:11248-11253 (2001)); Random Drift Mutagenesis (RNDM), in which mutations made via epPCR are followed by screening/selection for those retaining usable activity (Bergquist et al., Biomol. Eng. 22:63-72 (2005)); Sequence Saturation Mutagenesis (SeSaM), a random mutagenesis method that generates a pool of random length fragments using random incorporation of a phosphothioate nucleotide and cleavage, which is used as a template to extend in the presence of “universal” bases such as inosine, and replication of an inosine-containing complement gives random base incorporation and, consequently, mutagenesis (Wong et al., Biotechnol. J. 3:74-82 (2008); Wong et al., Nucleic Acids Res. 32:e26 (2004); and Wong et al., Anal. Biochem. 341:187-189 (2005)); Synthetic Shuffling, which uses overlapping oligonucleotides designed to encode “all genetic diversity in targets” and allows a very high diversity for the shuffled progeny (Ness et al., Nat. Biotechnol. 20:1251-1255 (2002)); Nucleotide Exchange and Excision Technology NexT, which exploits a combination of dUTP incorporation followed by treatment with uracil DNA glycosylase and then piperidine to perform endpoint DNA fragmentation (Muller et al., Nucleic Acids Res. 33:e117 (2005)).
Further methods include Sequence Homology-Independent Protein Recombination (SHIPREC), in which a linker is used to facilitate fusion between two distantly related or unrelated genes, and a range of chimeras is generated between the two genes, resulting in libraries of single-crossover hybrids (Sieber et al., Nat. Biotechnol. 19:456-460 (2001)); Gene Site Saturation Mutagenesis™ (GSSM™), in which the starting materials include a supercoiled double stranded DNA (dsDNA) plasmid containing an insert and two primers which are degenerate at the desired site of mutations (Kretz et al., Methods Enzymol. 388:3-11 (2004)); Combinatorial Cassette Mutagenesis (CCM), which involves the use of short oligonucleotide cassettes to replace limited regions with a large number of possible amino acid sequence alterations (Reidhaar-Olson et al. Methods Enzymol. 208:564-586 (1991); and Reidhaar-Olson et al. Science 241:53-57 (1988)); Combinatorial Multiple Cassette Mutagenesis (CMCM), which is essentially similar to CCM and uses epPCR at high mutation rate to identify hot spots and hot regions and then extension by CMCM to cover a defined region of protein sequence space (Reetz et al., Angew. Chem. Int. Ed Engl. 40:3589-3591 (2001)); the Mutator Strains technique, in which conditional is mutator plasmids, utilizing the mutD5 gene, which encodes a mutant subunit of DNA polymerase III, to allow increases of 20 to 4000-X in random and natural mutation frequency during selection and block accumulation of deleterious mutations when selection is not required (Selifonova et al., Appl. Environ. Microbiol. 67:3645-3649 (2001)); Low et al., J. Mol. Biol. 260:359-3680 (1996)).
Additional exemplary methods include Look-Through Mutagenesis (LTM), which is a multidimensional mutagenesis method that assesses and optimizes combinatorial mutations of selected amino acids (Rajpal et al., Proc. Natl. Acad. Sci. USA 102:8466-8471 (2005)); Gene Reassembly, which is a DNA shuffling method that can be applied to multiple genes at one time or to create a large library of chimeras (multiple mutations) of a single gene (Tunable GeneReassembly™ (TGR™) Technology supplied by Verenium Corporation), in Silico Protein Design Automation (PDA), which is an optimization algorithm that anchors the structurally defined protein backbone possessing a particular fold, and searches sequence space for amino acid substitutions that can stabilize the fold and overall protein energetics, and generally works most effectively on proteins with known three-dimensional structures (Hayes et al., Proc. Natl. Acad. Sci. USA 99:15926-15931 (2002)); and Iterative Saturation Mutagenesis (ISM), which involves using knowledge of structure/function to choose a likely site for enzyme improvement, performing saturation mutagenesis at chosen site using a mutagenesis method such as Stratagene QuikChange (Stratagene; San Diego Calif.), screening/selecting for desired properties, and, using improved clone(s), starting over at another site and continue repeating until a desired activity is achieved (Reetz et al., Nat. Protoc. 2:891-903 (2007); and Reetz et al., Angew. Chem. Int. Ed Engl. 45:7745-7751 (2006)).
Any of the aforementioned methods for mutagenesis can be used alone or in any combination. Additionally, any one or combination of the directed evolution methods can be used in conjunction with adaptive evolution techniques, as described herein.
It is understood that modifications which do not substantially affect the activity of the various embodiments of this invention are also provided within the definition of the invention provided herein. Accordingly, the following examples are intended to illustrate but not limit the present invention.
Several routes to 2,4-pentadienoate, 3-buten-1-ol and butadiene, are depicted in
Glutaryl-CoA is an intermediate in the degradation of numerous metabolites including benzoyl-CoA, lysine and tryptophan. Glutaryl-CoA can also be biosynthesized by means of, for example, the pathway shown in
Another starting metabolite for the pathways shown in
2-Aminoadipate and 2-oxoadipate (also called alpha-ketoadipate) are intermediates of lysine metabolism in organisms such as Saccharomyces cerevisiae. 2-Oxoadipate is also an intermediate of coenzyme B biosynethesis, where it is formed from alpha-ketoglutarate and acetyl-CoA by the enzymes homocitrate synthase, homoaconitase, and homoisocitrate dehydrogenase. 2-Oxoadipate and 2-aminoadipate are interconverted by aminotransferase, dehydrogenase or amine oxidase enzymes. Decarboxylation of 2-oxoadipate by a keto-acid decarboxylase yields glutarate semialdehyde (step D). Alternately, an acylating decarboxylase with alpha-ketoadipate dehydrogenase activity forms glutaryl-CoA from 2-oxoadipate (step R). Decarboxylation of 2-aminoadipate by an amino acid decarboxylase yields 5-aminopentanoate. Further transformation of the glutaryl-CoA, glutarate semialdehyde or 5-aminopentanoate intermediates to 2,4-pentadienoate, 3-buten-1-ol or butadiene proceeds as shown in
Enzyme candidates for the reactions shown in
This example describes a pathway for converting propionyl-CoA to 2,4-pentadienoate, shown in
Propionyl-CoA is formed as a metabolic intermediate in numerous biological pathways including the 3-hydroxypropionate/4-hydroxybutyrate and 3-hydroxypropionate cycles of CO2 fixation, conversion of succinate or pyruvate to propionate, glyoxylate assimilation and amino acid degradation. In the pathways of
This example describes a pathway for converting 3-hydroxypropionyl-CoA to 1,3-butanediol, shown in
3-Hydroxypropionyl-CoA is an intermediate of the 3-hydroxypropionate/4-hydroxybutyrate CO2 fixation cycle of autotrophs and a related 3-hydroxypropionate cycle discovered in phototrophic bacteria (Berg et al, Science 318(5857):1782-6 (2007); Strauss and Fuchs, Eur J Biochem 215(3):633-43 (1993)). In the pathway to 1,3-butanediol, 3-hydroxypropionyl-CoA and acetyl-CoA are condensed by a 3-oxo-5-hydroxypentanoyl-CoA thiolase to form 3-oxo-5-hydroxypentanoyl-CoA (step A). Alternately, the 3-oxo-5-hydroxypentanoyl-CoA intermediate is formed from 3-HP-CoA and malonyl-CoA by a 3-oxo-5-hydroxypentanoyl-CoA synthase. Removal of the CoA moiety by a CoA synthetase, transferase or hydrolase yields 3-oxo-5-hydroxypentanoate (step B). Decarboxylation of 3-oxo-5-hydroxypentanoate to 3-oxobutanol is catalyzed by a keto-acid decarboxylase (step C). In the final step of the pathway 3-oxobutanol is reduced to 1,3-butanol by an alcohol dehydrogenase or ketone reductase. Enzymes and gene candidates are described in further detail in Example VII.
This example describes pathways for converting pyruvate and acetaldehyde to 1,3-butanediol, 3-buten-1-ol and butadiene. The pathways are shown in
The conversion of pyruvate and acetaldehyde to 3-buten-1-ol is accomplished in four enzymatic steps. Pyruvate and acetaldehyde are first condensed to 4-hydroxy-2-oxovalerate by 4-hydroxy-2-ketovalerate aldolase (Step A of
The 4-hydroxy-2-oxovalerate intermediate can also be converted to 1,3-butanediol in two or more enzymatic steps. In one embodiment, 4-hydroxy-2-oxovalerate is decarboxylated to 3-hydroxybutanal (step F) and reduced to form 1,3-butanediol (step G). Alternately, 4-hydroxy-2-oxovalerate is converted to 3-hydroxybutyryl-CoA by an acylating and decarboxylating oxidoreductase or formate lyase (step H). The 3-hydroxybutyryl-CoA intermediate is further reduced to 3-hydroxybutanal in one or two enzymatic steps, by either an aldehyde-forming acyl-CoA reductase (step I) or the combined reaction of a 3-hydroxybutyryl-CoA hydrolase, transferase or synthetase and a 3-hydroxybutyrate reductase (steps J, K). 3-Hydroxybutanal is further reduced to 1,3-butanediol by 3-hydroxybutanal reductase (step G). In another embodiment, the 3-hydroxybutyryl-CoA intermediate is directly converted to 1,3-butanediol by an alcohol-forming bifunctional aldehyde/alcohol dehydrogenase (step L). Enzymes and gene candidates are described in further detail in Example VII.
Several reactions shown in
The reduction of glutarate semialdehyde to 5-hydroxyvalerate by glutarate semialdehyde reductase entails reduction of an aldehyde to its corresponding alcohol. Enzymes with glutarate semialdehyde reductase activity include the ATEG 00539 gene product of Aspergillus terreus and 4-hydroxybutyrate dehydrogenase of Arabidopsis thaliana, encoded by 4hbd (WO 2010/068953A2). The A. thaliana enzyme was cloned and characterized in yeast (Breitkreuz et al., J. Biol. Chem. 278:41552-41556 (2003)).
Aspergillus terreus NIH2624
Arabidopsis thaliana
Additional genes encoding enzymes that catalyze the reduction of an aldehyde to alcohol (i.e., alcohol dehydrogenase or equivalently aldehyde reductase) include alrA encoding a medium-chain alcohol dehydrogenase for C2-C14 (Tani et al., Appl. Environ. Microbiol. 66:5231-5235 (2000)), yqhD and fucO from E. coli (Sulzenbacher et al., 342:489-502 (2004)), and bdh I and bdh II from C. acetobutylicum which converts butyryaldehyde into butanol (Walter et al., 174:7149-7158 (1992)). YqhD catalyzes the reduction of a wide range of aldehydes using NADPH as the cofactor, with a preference for chain lengths longer than C(3) (Sulzenbacher et al., 342:489-502 (2004); Perez et al., J Biol. Chem. 283:7346-7353 (2008)). The adhA gene product from Zymomonas mobilis E has been demonstrated to have activity on a number of aldehydes including formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and acrolein (Kinoshita et al., Appl Microbiol Biotechnol 22:249-254 (1985)). Additional aldehyde reductase candidates are encoded by bdh in C. saccharoperbutylacetonicum and Cbei_1722, Cbei_2181 and Cbei_2421 in C. Beijerinckii. Additional aldehyde reductase gene candidates in Saccharomyces cerevisiae include the aldehyde reductases GRE3, ALD2-6 and HFD1, glyoxylate reductases GOR1 and YPL113C and glycerol dehydrogenase GCY1 (WO 2011/022651A1; Atsumi et al., Nature 451:86-89 (2008)). The enzyme candidates described previously for catalyzing the reduction of methylglyoxal to acetol or lactaldehyde are also suitable lactaldehyde reductase enzyme candidates.
Acinetobacter sp. strain M-1
Saccharomyces cerevisiae
Escherichia coli
Escherichia coli
Clostridium acetobutylicum
Clostridium acetobutylicum
Zymomonas mobilis
Clostridium saccharoperbutylacetonicum
Clostridium beijerinckii
Clostridium beijerinckii
Clostridium beijerinckii
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Enzymes exhibiting 4-hydroxybutyrate dehydrogenase activity (EC 1.1.1.61) also fall into this category. Such enzymes have been characterized in Ralstonia eutropha (Bravo et al., J Forens Sci, 49:379-387 (2004)) and Clostridium kluyveri (Wolff et al., Protein Expr. Purif. 6:206-212 (1995)). Yet another gene is the alcohol dehydrogenase adhl from Geobacillus thermoglucosidasius (Jeon et al., J Biotechnol 135:127-133 (2008)).
Ralstonia eutropha H16
Clostridium kluyveri DSM 555
Geobacillus thermoglucosidasius
Another exemplary aldehyde reductase is methylmalonate semialdehyde reductase, also known as 3-hydroxyisobutyrate dehydrogenase (EC 1.1.1.31). This enzyme participates in valine, leucine and isoleucine degradation and has been identified in bacteria, eukaryotes, and mammals. The enzyme encoded by P84067 from Thermus thermophilus HB8 has been structurally characterized (Lokanath et al., J Mol Biol, 352:905-17 (2005)). The reversibility of the human 3-hydroxyisobutyrate dehydrogenase was demonstrated using isotopically-labeled substrate (Manning et al., Biochem J, 231:481-4 (1985)). Additional genes encoding this enzyme include 3hidh in Homo sapiens (Hawes et al., Methods Enzymol, 324:218-228 (2000)) and Oryctolagus cuniculus (Hawes et al., supra; Chowdhury et al., Biosci. Biotechnol Biochem. 60:2043-2047 (1996)), mmsB in Pseudomonas aeruginosa and Pseudomonas putida, and dhat in Pseudomonas putida (Aberhart et al., J Chem.Soc. [Perkin 1] 6:1404-1406 (1979); Chowdhury et al., Biosci. Biotechnol Biochem. 60:2043-2047 (1996); Chowdhury et al., Biosci. Biotechnol Biochem. 67:438-441 (2003)). Several 3-hydroxyisobutyrate dehydrogenase enzymes have been characterized in the reductive direction, including mmsB from Pseudomonas aeruginosa (Gokarn et al., U.S. Pat. No. 739,676, (2008)) and mmsB from Pseudomonas putida.
Thermus thermophilus
Homo sapiens
Oryctolagus cuniculus
Pseudomonas putida
Pseudomonas aeruginosa
Pseudomonas putida
There exist several exemplary alcohol dehydrogenases that convert a ketone to a hydroxyl functional group. Two such enzymes from E. coli are encoded by malate dehydrogenase (mdh) and lactate dehydrogenase (ldhA). In addition, lactate dehydrogenase from Ralstonia eutropha has been shown to demonstrate high activities on 2-ketoacids of various chain lengths includings lactate, 2-oxobutyrate, 2-oxopentanoate and 2-oxoglutarate (Steinbuchel et al., Eur. J. Biochem. 130:329-334 (1983)). Conversion of alpha-ketoadipate into alpha-hydroxyadipate can be catalyzed by 2-ketoadipate reductase, an enzyme reported to be found in rat and in human placenta (Suda et al., Arch. Biochem. Biophys. 176:610-620 (1976); Suda et al., Biochem. Biophys. Res. Commun. 77:586-591 (1977)). An additional oxidoreductase is the mitochondrial 3-hydroxybutyrate dehydrogenase (bdh) from the human heart which has been cloned and characterized (Marks et al., J. Biol. Chem. 267:15459-15463 (1992)). Alcohol dehydrogenase enzymes of C. beijerinckii (Ismaiel et al., J. Bacteriol. 175:5097-5105 (1993)) and T. brockii (Lamed et al., Biochem.i 195:183-190 (1981); Peretz et al., Biochemistry. 28:6549-6555 (1989)) convert acetone to isopropanol. Methyl ethyl ketone reductase catalyzes the reduction of MEK to 2-butanol. Exemplary MEK reductase enzymes can be found in Rhodococcus ruber (Kosjek et al., Biotechnol Bioeng. 86:55-62 (2004)) and Pyrococcus furiosus (van der Oost et al., Eur. J. Biochem. 268:3062-3068 (2001)).
Escherichia coli
Escherichia coli
Ralstonia eutropha
Homo sapiens
Clostridium beijerinckii NRRL
Thermoanaerobacter brockii
Rhodococcus ruber
Pyrococcus furiosus
A number of organisms encode genes that catalyze the reduction of 3-oxobutanol to 1,3-butanediol, including those belonging to the genus Bacillus, Brevibacterium, Candida, and Klebsiella among others, as described by Matsuyama et al. J Mol Cat B Enz, 11:513-521 (2001). One of these enzymes, SADH from Candida parapsilosis, was cloned and characterized in E. coli. A mutated Rhodococcus phenylacetaldehyde reductase (Sar268) and a Leifonia alcohol dehydrogenase have also been shown to catalyze this transformation at high yields (Itoh et al., Appl. Microbiol Biotechnol. 75:1249-1256 (2007)).
Candida parapsilosis
Alcohol dehydrogenase enzymes that reduce 3-oxoacyl-CoA substrates to their corresponding 3-hydroxyacyl-CoA product are also relevant to the pathways depicted in
Acetoacetyl-CoA reductase (EC 1.1.1.36) catalyzes the reduction of acetoacetyl-CoA to 3-hydroxybutyryl-CoA. This enzyme participates in the acetyl-CoA fermentation pathway to butyrate in several species of Clostridia and has been studied in detail (Jones et al., Microbiol Rev. 50:484-524 (1986)). Acetoacetyl-CoA reducatse also participates in polyhydroxybutyrate biosynthesis in many organisms, and has also been used in metabolic engineering applications for overproducing PHB and 3-hydroxyisobutyrate (Liu et al., Appl. Microbiol. Biotechnol. 76:811-818 (2007); Qui et al., Appl. Microbiol. Biotechnol. 69:537-542 (2006)). The enzyme from Clostridium acetobutylicum, encoded by hbd, has been cloned and functionally expressed in E. coli (Youngleson et al., J Bacteriol. 171:6800-6807 (1989)). Additional gene candidates include phbB from Zoogloea ramigera (Ploux et al., Eur. J Biochem. 174:177-182 (1988)) and phaB from Rhodobacter sphaeroides (Alber et al., Mol. Microbiol 61:297-309 (2006)). The Z. ramigera gene is NADPH-dependent and the gene has been expressed in E. coli (Peoples et al., Mol. Microbiol 3:349-357 (1989)). Substrate specificity studies on the gene led to the conclusion that it could accept 3-oxopropionyl-CoA as a substrate besides acetoacetyl-CoA (Ploux et al., Eur. J Biochem. 174:177-182 (1988)). Additional genes include phaB in Paracoccus denitrificans, Hbd1 (C-terminal domain) and Hbd2 (N-terminal domain) in Clostridium kluyveri (Hillmer and Gottschalk, Biochim. Biophys. Acta 3334:12-23 (1974)) and HSD17B10 in Bos taurus (Wakil et al., J Biol. Chem. 207:631-638 (1954)). The enzyme from Paracoccus denitrificans has been functionally expressed and characterized in E. coli (Yabutani et al., FEMS Microbiol Lett. 133:85-90 (1995)). A number of similar enzymes have been found in other species of Clostridia and in Metallosphaera sedula (Berg et al., Science. 318:1782-1786 (2007)). The enzyme from Candida tropicalis is a component of the peroxisomal fatty acid beta-oxidation multifunctional enzyme type 2 (WE-2). The dehydrogenase B domain of this protein is catalytically active on acetoacetyl-CoA. The domain has been functionally expressed in E. coli, a crystal structure is available, and the catalytic mechanism is well-understood (Ylianttila et al., Biochem Biophys Res Commun 324:25-30 (2004); Ylianttila et al., J Mol Biol 358:1286-1295 (2006)).
Escherichia coli
Escherichia coli
Escherichia coli
Clostridium kluyveri
Clostridium kluyveri
Pseudomonas putida
Pseudomonas fluorescens
Bos taurus
Zoogloea ramigera
Rhodobacter sphaeroides
Paracoccus denitrificans
Clostridium acetobutylicum
Clostridium beijerinckii
Metallosphaera sedula
Metallosphaera sedula
Metallosphaera sedula
Metallosphaera sedula
Candida tropicalis
Bifunctional oxidoreductases convert an acyl-CoA to its corresponding alcohol. Enzymes with this activity are required to convert 3-hydroxybutyryl-CoA to 1,3-butanediol (Step L of
Exemplary bifunctional oxidoreductases that convert an acyl-CoA to alcohol include those that transform substrates such as acetyl-CoA to ethanol (e.g., adhE from E. coli (Kessler et al., FEBS. Lett. 281:59-63 (1991))) and butyryl-CoA to butanol (e.g. adhE2 from C. acetobutylicum (Fontaine et al., J. Bacteriol. 184:821-830 (2002))). The C. acetobutylicum enzymes encoded by bdh I and bdh II (Walter, et al., J. Bacteriol. 174:7149-7158 (1992)), reduce acetyl-CoA and butyryl-CoA to ethanol and butanol, respectively. In addition to reducing acetyl-CoA to ethanol, the enzyme encoded by adhE in Leuconostoc mesenteroides has been shown to oxide the branched chain compound isobutyraldehyde to isobutyryl-CoA (Kazahaya et al., J. Gen. Appl. Microbiol. 18:43-55 (1972); Koo et al., Biotechnol Lett, 27:505-510 (2005)). Another exemplary enzyme can convert malonyl-CoA to 3-HP. An NADPH-dependent enzyme with this activity has characterized in Chloroflexus aurantiacus where it participates in the 3-hydroxypropionate cycle (Hugler et al., J Bacteriol, 184:2404-2410 (2002); Strauss et al., Eur J Biochem, 215:633-643 (1993)). This enzyme, with a mass of 300 kDa, is highly substrate-specific and shows little sequence similarity to other known oxidoreductases (Hugler et al., supra). No enzymes in other organisms have been shown to catalyze this specific reaction; however there is bioinformatic evidence that other organisms may have similar pathways (Klatt et al., Env Microbiol, 9:2067-2078 (2007)). Enzyme candidates in other organisms including Roseiflexus castenholzii, Erythrobacter sp. NAP1 and marine gamma proteobacterium HTCC2080 can be inferred by sequence similarity.
Escherichia coli
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Leuconostoc mesenteroides
Chloroflexus aurantiacus
Roseiflexus castenholzii
Erythrobacter sp. NAP1
Longer chain acyl-CoA molecules can be reduced to their corresponding alcohols by enzymes such as the jojoba (Simmondsia chinensis) FAR which encodes an alcohol-forming fatty acyl-CoA reductase. Its overexpression in E. coli resulted in FAR activity and the accumulation of fatty alcohol (Metz et al., Plant Physiol, 122:635-644 (2000)).
Simmondsia chinensis
Another candidate for catalyzing these steps is 3-hydroxy-3-methylglutaryl-CoA reductase (or HMG-CoA reductase). This enzyme naturally reduces the CoA group in 3-hydroxy-3-methylglutaryl-CoA to an alcohol forming mevalonate. The hmgA gene of Sulfolobus solfataricus, encoding 3-hydroxy-3-methylglutaryl-CoA reductase, has been cloned, sequenced, and expressed in E. coli (Bochar et al., J Bacteriol. 179:3632-3638 (1997)). S. cerevisiae also has two HMG-CoA reductases in it (Basson et al., Proc. Natl. Acad. Sci. U.S.A 83:5563-5567 (1986)). The gene has also been isolated from Arabidopsis thaliana and has been shown to complement the HMG-COA reductase activity in S. cerevisiae (Learned et al., Proc. Natl. Acad. Sci. U.S.A 86:2779-2783 (1989)).
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Arabidopsis thaliana
Sulfolobus solfataricus
Acyl-CoA reductases in the 1.2.1 family reduce an acyl-CoA to its corresponding aldehyde. Such a conversion is required to catalyze the reduction of glutaryl-CoA to glutarate semialdehyde (step S of
Acyl-CoA reductases or acylating aldehyde dehydrogenases reduce an acyl-CoA to its corresponding aldehyde. Exemplary enzymes include fatty acyl-CoA reductase, succinyl-CoA reductase (EC 1.2.1.76), acetyl-CoA reductase, butyryl-CoA reductase and propionyl-CoA reductase (EC 1.2.1.3). Exemplary fatty acyl-CoA reductases enzymes are encoded by acr1 of Acinetobacter calcoaceticus (Reiser, Journal of Bacteriology 179:2969-2975 (1997)) and Acinetobacter sp. M-1 (Ishige et al., Appl. Environ. Microbiol. 68:1192-1195 (2002)). Enzymes with succinyl-CoA reductase activity are encoded by sucD of Clostridium kluyveri (Sohling, J Bacteriol. 178:871-880 (1996)) and sucD of P. gingivalis (Takahashi, J. Bacteriol 182:4704-4710 (2000)). Additional succinyl-CoA reductase enzymes participate in the 3-hydroxypropionate/4-hydroxybutyrate cycle of thermophilic archaea including Metallosphaera sedula (Berg et al., Science 318:1782-1786 (2007)) and Thermoproteus neutrophilus (Ramos-Vera et al., J Bacteriol., 191:4286-4297 (2009)). The M. sedula enzyme, encoded by Msed 0709, is strictly NADPH-dependent and also has malonyl-CoA reductase activity. The T. neutrophilus enzyme is active with both NADPH and NADH. The enzyme acylating acetaldehyde dehydrogenase in Pseudomonas sp, encoded by bphG, is yet another as it has been demonstrated to oxidize and acylate acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde and formaldehyde (Powlowski, J. Bacteriol. 175:377-385 (1993)). In addition to reducing acetyl-CoA to ethanol, the enzyme encoded by adhE in Leuconostoc mesenteroides has been shown to oxidize the branched chain compound isobutyraldehyde to isobutyryl-CoA (Kazahaya, J. Gen. Appl. Microbiol. 18:43-55 (1972); and Koo et al., Biotechnol Lett. 27:505-510 (2005)). Butyraldehyde dehydrogenase catalyzes a similar reaction, conversion of butyryl-CoA to butyraldehyde, in solventogenic organisms such as Clostridium saccharoperbutylacetonicum (Kosaka et al., Biosci Biotechnol Biochem., 71:58-68 (2007)). Exemplary propionyl-CoA reductase enzymes include pduP of Salmonella typhimurium LT2 (Leal, Arch. Microbiol. 180:353-361 (2003)) and eutE from E. coli (Skraly, WO Patent No. 2004/024876). The propionyl-CoA reductase of Salmonella typhimurium LT2, which naturally converts propionyl-CoA to propionaldehyde, also catalyzes the reduction of 5-hydroxyvaleryl-CoA to 5-hydroxypentanal (WO 2010/068953A2).
Acinetobacter calcoaceticus
Acinetobacter baylyi
Acinetobacter sp. Strain M-1
Metallosphaera sedula
Thermoproteus neutrophilus
Clostridium kluyveri
Porphyromonas gingivalis
Pseudomonas sp
Leuconostoc mesenteroides
Clostridium
saccharoperbutylace tonicum
Salmonella typhimurium LT2
Escherichia coli
An additional enzyme that converts an acyl-CoA to its corresponding aldehyde is malonyl-CoA reductase which transforms malonyl-CoA to malonic semialdehyde. Malonyl-CoA reductase is a key enzyme in autotrophic carbon fixation via the 3-hydroxypropionate cycle in thermoacidophilic archaeal bacteria (Berg, Science 318:1782-1786 (2007); and Thauer, Science 318:1732-1733 (2007)). The enzyme utilizes NADPH as a cofactor and has been characterized in Metallosphaera and Sulfolobus sp. (Alber et al., J. Bacteriol. 188:8551-8559 (2006); and Hugler, J. Bacteriol. 184:2404-2410 (2002)). The enzyme is encoded by Msed 0709 in Metallosphaera sedula (Alber et al., J. Bacteriol. 188:8551-8559 (2006); and Berg, Science 318:1782-1786 (2007)). A gene encoding a malonyl-CoA reductase from Sulfolobus tokodaii was cloned and heterologously expressed in E. coli (Alber et al., J. Bacteriol 188:8551-8559 (2006). This enzyme has also been shown to catalyze the conversion of methylmalonyl-CoA to its corresponding aldehyde (WO2007141208 (2007)). Although the aldehyde dehydrogenase functionality of these enzymes is similar to the bifunctional dehydrogenase from Chloroflexus aurantiacus, there is little sequence similarity. Both malonyl-CoA reductase enzyme candidates have high sequence similarity to aspartate-semialdehyde dehydrogenase, an enzyme catalyzing the reduction and concurrent dephosphorylation of aspartyl-4-phosphate to aspartate semialdehyde. Additional gene candidates can be found by sequence homology to proteins in other organisms including Sulfolobus solfataricus and Sulfolobus acidocaldarius and have been listed below. Yet another candidate for CoA-acylating aldehyde dehydrogenase is the ald gene from Clostridium beijerinckii (Toth, Appl. Environ. Microbiol. 65:4973-4980 (1999). This enzyme has been reported to reduce acetyl-CoA and butyryl-CoA to their corresponding aldehydes. This gene is very similar to eutE that encodes acetaldehyde dehydrogenase of Salmonella typhimurium and E. coli (Toth, Appl. Environ. Microbiol. 65:4973-4980 (1999).
Metallosphaera sedula
Sulfolobus tokodaii
Sulfolobus solfataricus
Sulfolobus
acidocaldarius
Clostridium beijerinckii
Salmonella typhimurium
Escherichia coli
The reductive decarboxylation and acylation of 2-oxoadipate to glutarate semialdehyde (step D of
Alpha-ketoglutarate dehydrogenase (AKGD) converts alpha-ketoglutarate to succinyl-CoA and is the primary site of control of metabolic flux through the TCA cycle (Hansford, Curr. Top. Bioenerg. 10:217-278 (1980)). Encoded by genes sucA, sucB and lpd in E. coli, AKGD gene expression is downregulated under anaerobic conditions and during growth on glucose (Park et al., 15:473-482 (1995)). Although the substrate range of AKGD is narrow, structural studies of the catalytic core of the E2 component pinpoint specific residues responsible for substrate specificity (Knapp et al., J. Mol. Biol. 280:655-668 (1998)). The Bacillus subtilis AKGD, encoded by odhAB (E1 and E2) and pdhD (E3, shared domain), is regulated at the transcriptional level and is dependent on the carbon source and growth phase of the organism (Resnekov et al., Mol. Gen. Genet. 234:285-296 (1992)). In yeast, the LPD1 gene encoding the E3 component is regulated at the transcriptional level by glucose (Roy et al., J. Gen. Microbiol. 133:925-933 (1987)). The E1 component, encoded by KGDJ, is also regulated by glucose and activated by the products of HAP2 and HAP3 (Repetto et al., Mol. Cell Biol. 9:2695-2705 (1989)). The AKGD enzyme complex, inhibited by products NADH and succinyl-CoA, is well-studied in mammalian systems, as impaired function of has been linked to several neurological diseases.
Escherichia coli
Escherichia coli
Escherichia coli
Bacillus subtilis
Bacillus subtilis
Bacillus subtilis
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Branched-chain 2-keto-acid dehydrogenase complex (BCKAD), also known as 2-oxoisovalerate dehydrogenase, participates in branched-chain amino acid degradation pathways, converting 2-keto acids derivatives of valine, leucine and isoleucine to their acyl-CoA derivatives and CO2. The complex has been studied in many organisms including Bacillus subtilis (Wang et al., Eur. J. Biochem. 213:1091-1099 (1993)), Rattus norvegicus (Namba et al., J. Biol. Chem. 244:4437-4447 (1969)) and Pseudomonas putida (Sokatch et al., 148:647-652 (1981)). In Bacillus subtilis the enzyme is encoded by genes pdhD (E3 component), bfm_BB (E2 component), bfmBAA and bfmBAB (E1 component) (Wang et al., Eur.1Biochem. 213:1091-1099 (1993)). In mammals, the complex is regulated by phosphorylation by specific phosphatases and protein kinases. The complex has been studied in rat hepatocites (Chicco et al., J. Biol. Chem. 269:19427-19434 (1994)) and is encoded by genes Bckdha (E1 alpha), Bckdhb (E1 beta), Dbt (E2), and Dld (E3). The E1 and E3 components of the Pseudomonas putida BCKAD complex have been crystallized (Aevarsson et al., Nat.Struct.Biol. 6:785-792 (1999); Mattevi et al., Science. 255:1544-1550 (1992)) and the enzyme complex has been studied (Sokatch et al., 148:647-652 (1981)). Transcription of the P. putida BCKAD genes is activated by the gene product of bkdR (Hester et al., 233:828-836 (1995)). In some organisms including Rattus norvegicus (Paxton et al., Biochem.i 234:295-303 (1986)) and Saccharomyces cerevisiae (Sinclair et al., Biochem. Mol. Biol. Int. 31:911-922 (1993)), this complex has been shown to have a broad substrate range that includes linear oxo-acids such as 2-oxobutanoate and alpha-ketoglutarate, in addition to the branched-chain amino acid precursors. The active site of the bovine BCKAD was engineered to favor alternate substrate acetyl-CoA (Meng et al., Biochemistry. 33:12879-12885 (1994)).
Bacillus subtilis
Bacillus subtilis
Bacillus subtilis
Bacillus subtilis
Pseudomonas putida
Pseudomonas putida
Pseudomonas putida
Pseudomonas putida
Rattus norvegicus
Rattus norvegicus
Rattus norvegicus
Rattus norvegicus
The pyruvate dehydrogenase complex, catalyzing the conversion of pyruvate to acetyl-CoA, has also been extensively studied. In the E. coli enzyme, specific residues in the E1 component are responsible for substrate specificity (Bisswanger, 256:815-822 (1981); Bremer, 8:535-540 (1969); Gong et al., 275:13645-13653 (2000)). As mentioned previously, enzyme engineering efforts have improved the E. coli PDH enzyme activity under anaerobic conditions (Kim et al., J. Bacteriol. 190:3851-3858 (2008); Kim et al., Appl. Environ. Microbiol. 73:1766-1771 (2007); Zhou et al., Biotechnol. Lett. 30:335-342 (2008)). In contrast to the E. coli PDH, the B. subtilis complex is active and required for growth under anaerobic conditions (Nakano et al., 179:6749-6755 (1997)). The Klebsiella pneumoniae PDH, characterized during growth on glycerol, is also active under anaerobic conditions (Menzel et al., 56:135-142 (1997)). Crystal structures of the enzyme complex from bovine kidney (Zhou et al., 98:14802-14807 (2001)) and the E2 catalytic domain from Azotobacter vinelandii are available (Mattevi et al., Science. 255:1544-1550 (1992)). Some mammalian PDH enzymes complexes can react on alternate substrates such as 2-oxobutanoate. Comparative kinetics of Rattus norvegicus PDH and BCKAD indicate that BCKAD has higher activity on 2-oxobutanoate as a substrate (Paxton et al., Biochem. J. 234:295-303 (1986)). The S. cerevisiae complex consists of an E2 (LAT1) core that binds E1 (PDA1, PDB1), E3 (LPD1), and Protein X (PDX1) components (Pronk et al., Yeast 12:1607-1633 (1996)).
Escherichia coli
Escherichia coli
Escherichia coli
Bacillus subtilis
Bacillus subtilis
Bacillus subtilis
Bacillus subtilis
Klebsiella pneumonia
Klebsiella pneumonia
Klebsiella pneumonia
Rattus norvegicus
Rattus norvegicus
Rattus norvegicus
Rattus norvegicus
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
As an alternative to the large multienzyme 2-keto-acid dehydrogenase complexes described above, some anaerobic organisms utilize enzymes in the 2-ketoacid oxidoreductase family (OFOR) to catalyze acylating oxidative decarboxylation of 2-keto-acids. Unlike the dehydrogenase complexes, these enzymes contain iron-sulfur clusters, utilize different cofactors, and use ferredoxin, flavodixin or FAD as electron donors in lieu of NAD(P)H. While most enzymes in this family are specific to pyruvate as a substrate (POR) some 2-keto-acid:ferredoxin oxidoreductases have been shown to accept a broad range of 2-ketoacids as substrates including alpha-ketoglutarate and 2-oxobutanoate (Zhang et al., J.Biochem. 120:587-599 (1996); Fukuda et al., Biochim. Biophys. Acta 1597:74-80 (2002)). One such enzyme is the OFOR from the thermoacidophilic archaeon Sulfolobus tokodaii 7, which contains an alpha and beta subunit encoded by gene ST2300 (Zhang et al., J.Biochem. 120:587-599 (1996); Fukuda and Wakagi, Biochim. Biophys. Acta 1597:74-80 (2002)). A plasmid-based expression system has been developed for efficiently expressing this protein in E. coli (Fukuda et al., Eur. J.Biochem. 268:5639-5646 (2001)) and residues involved in substrate specificity were determined (Fukuda and Wakagi, Biochim. Biophys. Acta 1597:74-80 (2002)). The 2-oxoacid:ferredoxin oxidoreductase from Sulfolobus solfataricus P1 is also active on a broad range of 2-oxoacids (Park et al., J. Biochem. Mol. Biol. 39:46-54 (2006)). The OFOR enzyme encoded by Ape1472/Ape1473 from Aeropyrum pernix str. K1 was recently cloned into E. coli, characterized, and found to react with 2-oxoglutarate and a broad range of 2-oxoacids (Nishizawa et al., FEBS Lett. 579:2319-2322 (2005)). There is bioinformatic evidence that similar enzymes are present in all archaea, some anaerobic bacteria and amitochondrial eukarya (Fukuda and Wakagi, supra). OFOR enzymes are also found in organisms that fix carbon by the RTCA cycle including Hydrogenobacter thermophilus, Desulfobacter hydrogenophilus and Chlorobium species (Shiba et al., Archives of Microbiology 141:198-203 (1985); Evans et al., Proc.Natl.Acad.Sci. U.S.A 55:928-934 (1966)). The two-subunit enzyme from H. thermophilus, encoded by korAB, was cloned and expressed in E. coli (Yun et al., Biochem. Biophys. Res. Commun. 282:589-594 (2001)).
Sulfolobus tokodaii 7
Aeropyrum pernix
Aeropyrum pernix
Hydrogenobacter
thermophilus
Hydrogenobacter
thermophilus
The reduction of a phosphonic acid to its corresponding aldehyde is catalyzed by an oxidoreductase or phosphate reductase in the EC class 1.2.1. Step E of
Escherichia coli
Haemophilus influenzae
Mycobacterium tuberculosis
Vibrio cholera
Heliobacter pylori
Saccharomyces cerevisiae
Bacillus subtilis
Escherichia coli
Escherichia coli
Escherichia coli
Salmonella typhimurium
Campylobacter jejuni
The conversion of an acid to an aldehyde is thermodynamically unfavorable and typically requires energy-rich cofactors and multiple enzymatic steps. Direct conversion of the acid to aldehyde by a single enzyme is catalyzed by an acid reductase enzyme in the 1.2.1 family. An enzyme in this EC class is required to convert 3-hydroxybutyrate to 3-hydroxybutanal (Step 5K of
Exemplary acid reductase enzymes include carboxylic acid reductase, alpha-aminoadipate reductase and retinoic acid reductase. Carboxylic acid reductase (CAR), found in Nocardia iowensis, catalyzes the magnesium, ATP and NADPH-dependent reduction of carboxylic acids to their corresponding aldehydes (Venkitasubramanian et al., J Biol. Chem. 282:478-485 (2007)). The natural substrate of this enzyme is benzoate and the enzyme exhibits broad acceptance of aromatic substrates including p-toluate (Venkitasubramanian et al., Biocatalysis in Pharmaceutical and Biotechnology Industries. CRC press (2006)). The enzyme from Nocardia iowensis, encoded by car, was cloned and functionally expressed in E. coli (Venkitasubramanian et al., J Biol. Chem. 282:478-485 (2007)). CAR requires post-translational activation by a phosphopantetheine transferase (PPTase) that converts the inactive apo-enzyme to the active holo-enzyme (Hansen et al., Appl. Environ. Microbiol 75:2765-2774 (2009)). Expression of the npt gene, encoding a specific PPTase, product improved activity of the enzyme. An additional enzyme candidate found in Streptomyces griseus is encoded by the griC and griD genes. This enzyme is believed to convert 3-amino-4-hydroxybenzoic acid to 3-amino-4-hydroxybenzaldehyde as deletion of either griC or griD led to accumulation of extracellular 3-acetylamino-4-hydroxybenzoic acid, a shunt product of 3-amino-4-hydroxybenzoic acid metabolism (Suzuki, et al., J Antibiot. 60(6):380-387 (2007)). Co-expression of griC and griD with SGR 665, an enzyme similar in sequence to the Nocardia iowensis npt, can be beneficial.
Nocardia iowensis
Nocardia iowensis
Streptomyces griseus
Streptomyces griseus
Additional car and npt genes can be identified based on sequence homology.
Mycobacterium bovis BCG
Mycobacterium bovis BCG
Nocardia farcinica IFM
Nocardia farcinica IFM
Streptomyces griseus subsp.
griseus NBRC 13350
Streptomyces griseus subsp.
griseus NBRC 13350
Mycobacterium smegmatis
Mycobacterium smegmatis
Mycobacterium smegmatis
Mycobacterium avium
Mycobacterium avium
Mycobacterium marinum M
Mycobacterium marinum M
Mycobacterium marinum M
Tsukamurella
paurometabola DSM 20162
Tsukamurella
paurometabola DSM 20162
Cyanobium PCC7001
Dictyostelium discoideum
An enzyme with similar characteristics, alpha-aminoadipate reductase (AAR, EC 1.2.1.31), participates in lysine biosynthesis pathways in some fungal species. This enzyme naturally reduces alpha-aminoadipate to alpha-aminoadipate semialdehyde. The carboxyl group is first activated through the ATP-dependent formation of an adenylate that is then reduced by NAD(P)H to yield the aldehyde and AMP. Like CAR, this enzyme utilizes magnesium and requires activation by a PPTase. Enzyme candidates for AAR and its corresponding PPTase are found in Saccharomyces cerevisiae (Morris et al., Gene 98:141-145 (1991)), Candida albicans (Guo et al., Mol. Genet. Genomics 269:271-279 (2003)), and Schizosaccharomyces pombe (Ford et al., Curr. Genet. 28:131-137 (1995)). The AAR from S. pombe exhibited significant activity when expressed in E. coli (Guo et al., Yeast 21:1279-1288 (2004)). The AAR from Penicillium chrysogenum accepts S-carboxymethyl-L-cysteine as an alternate substrate, but did not react with adipate, L-glutamate or diaminopimelate (Hijarrubia et al., J Biol. Chem. 278:8250-8256 (2003)). The gene encoding the P. chrysogenum PPTase has not been identified to date and no high-confidence hits were identified by sequence comparison homology searching.
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Candida albicans
Candida albicans
Schizosaccharomyces pombe
Schizosaccharomyces pombe
Penicillium chrysogenum
Several transformations in
The oxidation of pent-3-enoyl-CoA or pent-2-enoyl-CoA to 2,4-pentadienoyl-CoA is catalyzed by 2,4-pentadienoyl-CoA forming dehydrogenase enzymes. 2,4-Dienoyl-CoA reductase enzymes (EC 1.3.1.34) are suitable candidates for these transformations. Generally, bacterial 2,4-dienoyl-CoA reductases yield 2-enoyl-CoA products, whereas eukaryotic 2,4-dienoyl-CoA reductases yield 3-enoyl-CoA products (Dommes and Kunau, J Biol Chem, 259:1781-1788 (1984)). The fadH gene product of E. coli is an NADPH-dependent 2,4-dienoyl-CoA reductase, which participates in the beta-oxidation of unsaturated fatty acids (Tu et al, Biochem, 47:1167-1175 (2008). A series of mutant DCR enzymes were constructed and shown to yield both 2-enoyl-CoA and 3-enoyl-CoA products (Tu et al, supra). Eukaryotic DCR enzymes have been characterized in humans and the mouse (Koivuranta et al, Biochem J, 304:787-792 (1994); Geisbrecht et al, J Biol Chem 274:25814-20 (1999); Miinalainen et al, PLoS genet. 5: E1000543 (2009)). The 2,4-pentadienoyl-CoA reductase of Clostridium aminovalericum was shown to catalyze the oxidation of 3-pent-3-enoyl-CoA to 2,4-pentadienoyl-CoA. This enzyme has been purified, characterized and crystallized (Eikmanns, Acta Cryst, D 50: 913-914 (1994) and Eikmanns and Buckel, Eur J Biochem 198:263-266 (1991)). The electron carrier of this enzyme is not known; however, it is not NAD(P)H. The sequence of the enzyme has not been published to date.
Escherichia coli
Homo sapiens
Mus musculus
Mus musculus
2-Enoate reductase enzymes in the EC classes 1.3.* are known to catalyze the reversible reduction of a wide variety of α,β-unsaturated carboxylic acids and aldehydes (Rohdich et al., J Biol Chem 276:5779-5787 (2001)). In the recently published genome sequence of C. kluyveri, 9 coding sequences for enoate reductases were reported, out of which one has been characterized (Seedorf et al., PNAS 105:2128-2133 (2008)). The enr genes from both C. tyrobutyricum and Moorella thermoaceticum have been cloned and sequenced and show 59% identity to each other. The former gene is also found to have approximately 75% similarity to the characterized gene in C. kluyveri (Giesel et al., 135:51-57 (1983)). It has been reported based on these sequence results that the C. tyrobutyricum enr is very similar to the FadH dienoyl CoA reductase of E. coli (Rohdich et al., supra). The M. thermoaceticum enr gene was expressed in a catalytically active form in E. coli (Rohdich et al., supra). This enzyme exhibits activity on a broad range of alpha, beta-unsaturated carbonyl compounds.
Clostridium botulinum A3 str
Clostridium tyrobutyricum
Clostridium kluyveri
Moorella thermoacetica
Another candidate 2-enoate reductase is maleylacetate reductase (MAR, EC 1.3.1.32), an enzyme catalyzing the reduction of 2-maleylacetate (4-oxohex-2-enedioate) to 3-oxoadipate. MAR enzymes naturally participate in aromatic degradation pathways (Kaschabek et al., J Bacteriol. 175:6075-6081 (1993); Kaschabek et al., J Bacteriol. 177:320-325 (1995); Camara et al., J Bacteriol. (2009); Huang et al., Appl Environ.Microbiol 72:7238-7245 (2006)). The enzyme activity was identified and characterized in Pseudomonas sp. strain B13 (Kaschabek et al., 175:6075-6081 (1993); Kaschabek et al., 177:320-325 (1995)), and the coding gene was cloned and sequenced (Kasberg et al., J Bacteriol. 179:3801-3803 (1997)). Additional MAR gene candidates include cicE gene from Pseudomonas sp. strain B13 (Kasberg et al., J Bacteriol. 179:3801-3803 (1997)), macA gene from Rhodococcus opacus (Seibert et al., 180:3503-3508 (1998)), the macA gene from Ralstonia eutropha (also known as Cupriavidus necator) (Seibert et al., Microbiology 150:463-472 (2004)), tfdFll from Ralstonia eutropha (Seibert et al., J Bacteriol. 175:6745-6754 (1993)) and NCgl1112 in Corynebacterium glutamicum (Huang et al., Appl Environ.Microbiol 72:7238-7245 (2006)). A MAR in Pseudomonas reinekei MT1, encoded by ccaD, was recently identified (Camara et al., J Bacteriol. (2009)).
Pseudomonas sp. strain B13
Rhodococcus opacus
Cupriavidus necator
Ralstonia eutropha JMP134
Corynebacterium glutamicum
Pseudomonas reinekei MT1
An exemplary enoate reductase that favors the alkene-forming oxidative direction is succinate dehydrogenase (EC classes 1.3.99 or 1.3.5), also known as succinate-ubiquinone oxidoreductase and complex II. SDH is a membrane-bound enzyme complex that converts succinate to fumarate and transfers electrons to ubiquinone. The enzyme is composed of two catalytic subunits, encoded by sdhAB, and two membrane subunits encoded by sdhCD. Although the E. coli SDH is reversible, the enzyme is 50-fold more proficient in oxidizing succinate than reducing fumarate (Maklashina et al J Biol. Chem. 281:11357-11365 (2006)).
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
An exemplary acyl-CoA dehydrogenase or enoyl-CoA reductase is the gene product of bcd from Clostridium acetobutylicum (Atsumi et al., 10:305-311 (2008); Boynton et al., J Bacteriol. 178:3015-3024 (1996)), which naturally catalyzes the reduction of crotonyl-CoA to butyryl-CoA (EC 1.3.99.2). This enzyme participates in the acetyl-CoA fermentation pathway to butyrate in Clostridial species (Jones et al., Microbiol Rev. 50:484-524 (1986)). Activity of butyryl-CoA reductase can be enhanced by expressing bcd in conjunction with expression of the C. acetobutylicum etfAB genes, which encode an electron transfer flavoprotein. An additional candidate for the enoyl-CoA reductase step is the mitochondrial enoyl-CoA reductase (EC 1.3.1.44) from E. gracilis (Hoffmeister et al., J Biol. Chem 280:4329-4338 (2005)). A construct derived from this sequence following the removal of its mitochondrial targeting leader sequence was cloned in E. coli resulting in an active enzyme (Hoffmeister et al, supra). A close homolog of the protein from the prokaryote Treponema denticola, encoded by TDE0597, has also been cloned and expressed in E. coli (Tucci et al., FEBS Lett, 581:1561-1566 (2007)). Six genes in Syntrophus aciditrophicus were identified by sequence homology to the C. acetobutylicum bcd gene product. The S. aciditrophicus genes syn_02637 and syn_02636 bear high sequence homology to the etfAB genes of C. acetobutylicum, and are predicted to encode the alpha and beta subunits of an electron transfer flavoprotein.
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Euglena gracilis
Treponema denticola
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Additional enoyl-CoA reductase enzyme candidates are found in organisms that degrade aromatic compounds. Rhodopseudomonas palustris, a model organism for benzoate degradation, has the enzymatic capability to degrade pimelate via beta-oxidation of pimeloyl-CoA. Adjacent genes in the pim operon, pimC and pimD, bear sequence homology to C. acetobutylicum bcd and are predicted to encode a flavin-containing pimeloyl-CoA dehydrogenase (Harrison et al., 151:727-736 (2005)). The genome of nitrogen-fixing soybean symbiont Bradyrhizobium japonicum also contains a pim operon composed of genes with high sequence similarity to pimC and pimD of R. palustris (Harrison and Harwood, Microbiology 151:727-736 (2005)).
Rhodopseudomonas palustris
Rhodopseudomonas palustris
Bradyrhizobium japonicum
Bradyrhizobium japonicum
An additional candidate is 2-methyl-branched chain enoyl-CoA reductase (EC 1.3.1.52 and EC 1.3.99.12), an enzyme catalyzing the reduction of sterically hindered trans-enoyl-CoA substrates. This enzyme participates in branched-chain fatty acid synthesis in the nematode Ascarius suum and is capable of reducing a variety of linear and branched chain substrates including 2-methylvaleryl-CoA, 2-methylbutanoyl-CoA, 2-methylpentanoyl-CoA, octanoyl-CoA and pentanoyl-CoA (Duran et al., 268:22391-22396 (1993)). Two isoforms of the enzyme, encoded by genes acad1 and acad, have been characterized.
Ascarius suum
Ascarius suum
Enzymes in the EC class 1.4.1 catalyze the oxidative deamination of amines to aldehydes or ketones. Enzymes in this EC class typically employ NAD+, NADP+ or FAD as an electron acceptor, and the reactions are typically reversible. Steps C, H and J. of
Glutamate dehydrogenase (EC 1.4.1.2), leucine dehydrogenase (EC 1.4.1.9), and aspartate dehydrogenase (EC 1.4.1.21) convert amino acids to their corresponding 2-keto acids. The gdhA gene product from Escherichia coli (Korber et al., J Mol. Biol. 234:1270-1273 (1993); McPherson et al., Nucleic Acids Res. 11:5257-5266 (1983)), gdh from Thermotoga maritime (Kort et al., Extremophiles. 1:52-60 (1997); Lebbink et al., J Mol. Biol. 280:287-296 (1998); Lebbink et al., J Mol. Biol. 289:357-369 (1999)), and gdhAl from Halobacterium salinarum (Ingoldsby et al., Gene 349:237-244 (2005)) catalyze the reversible conversion of glutamate to 2-oxoglutarate and ammonia, while favoring NADP(H), NAD(H), or both, respectively. Additional glutamate dehydrogenase gene candidates are found in Bacillus subtilis (Khan et al., Biosci. Biotechnol Biochem. 69:1861-1870 (2005)), Nicotiana tabacum (Purnell et al., Planta 222:167-180 (2005)), Oryza sativa (Abiko et al., Plant Cell Physiol 46:1724-1734 (2005)), Haloferax mediterranei (Diaz et al., Extremophiles. 10:105-115 (2006)) and Halobacterium salinarum (Hayden et al., FEMS Microbiol Lett. 211:37-41 (2002)). The Nicotiana tabacum enzyme is composed of alpha and beta subunits encoded by gdh1 and gdh2 (Purnell et al., Planta 222:167-180 (2005)). Overexpression of the NADH-dependent glutamate dehydrogenase was found to improve ethanol production in engineered strains of S. cerevisiae (Roca et al., Appl Environ.Microbiol 69:4732-4736 (2003)). The ldh gene of Bacillus cereus encodes the LeuDH protein that accepts a wide of range of substrates including leucine, isoleucine, valine, and 2-aminobutanoate (Ansorge et al., Biotechnol Bioeng 68:557-562 (2000); Stoyan et al., J Biotechnol 54:77-80 (1997)). The nadX gene from Thermotoga maritima encodes aspartate dehydrogenase, involved in the biosynthesis of NAD (Yang et al., J Biol. Chem. 278:8804-8808 (2003)).
Escherichia coli
Thermotoga maritima
Halobacterium salinarum
Bacillus subtilis
Nicotiana tabacum
Nicotiana tabacum
Oryza sativa
Haloferax mediterranei
Halobactreium salinarum
Saccharomyces cerevisiae
Bacillus cereus
Thermotoga maritima
An exemplary enzyme for catalyzing the conversion of primary amines to their corresponding aldehydes is lysine 6-dehydrogenase (EC 1.4.1.18), encoded by the lysDH genes. This enzyme catalyzes the oxidative deamination of the 6-amino group of L-lysine to form 2-aminoadipate-6-semialdehyde (Misono et al., J Bacteriol. 150:398-401 (1982)). Exemplary lysine 6-dehydrogenase enzymes are found in Geobacillus stearothermophilus (Heydari et al., AEM 70:937-942 (2004)), Agrobacterium tumefaciens (Hashimoto et al., J Biochem. 106:76-80 (1989); Misono and Nagasaki, J Bacteriol. 150:398-401 (1982)), and Achromobacter denitrificans (Ruldeekulthamrong et al., BMB.Rep. 41:790-795 (2008)).
Geobacillus stearothermophilus
Agrobacterium tumefaciens
Achromobacter denitrificans
Amine oxidase enzymes in EC class 1.4.3 catalyze the oxidative deamination of amino groups to their corresponding aldehydes or ketones. This class of enzymes utilizes oxygen as the electron acceptor, converting an amine, O2 and water to an aldehyde or ketone, ammonia and hydrogen peroxide. L-Amino-acid oxidase catalyzes the oxidative deamination of a number of L-amino acids to their respective 2-oxoacids. The Streptococcus oligofermentans enzyme was overexpressed in E. coli (Tong et al, J Bacteriol 190:4716-21 (2008)). Other amine oxidase enzymes such as lysine-6-oxidase (EC 1.4.3.20) and putrescine oxidase (EC 1.4.3.10), are specific to terminal amines. Lysine-6-oxidase enzymes are encoded by lodA of Marinomonas mediterranea (Lucas-Elio et al, J Bacteriol 188:2493-501 (2006)) and alpP of Pseudoalteromonas tunicata (Mai-Prochnow et al, J Bacteriol 190:5493-501 (2008)). Putrescine oxidase enzymes are encoded by puo of Kocuria rosea (Ishizuka et al, J Gen Microbiol 139:425-32 (1993)) and ATAO 1 of Arabidopsis thaliana (Moller and McPherson, Plant J 13:781-91 (1998)).
Streptococcus oligofermentans
Marinomonas mediterranea
Pseudoalteromonas tunicata
Kocuria rosea
Arabidopsis thaliana
An enzyme with 2,4-pentadienoyl-CoA phosphotransferase activity is required to convert 2,4-pentadienoyl-CA to 2,4-pentadienoyl-phosphate (
Escherichia coli
Bacillus subtilis
Clostridium kluyveri
Thermotoga maritima
Clostridium acetobutylicum
Bacillus megaterium
Beta-ketothiolase enzymes in the EC class 2.3.1 catalyze the condensation of two acyl-CoA substrates. Several transforms in
Exemplary beta-ketothiolases with acetoacetyl-CoA thiolase activity include the gene products of atoB from E. coli (Martin et al., Nat.Biotechnol 21:796-802 (2003)), thlA and th1B from C. acetobutylicum (Hanai et al., Appl Environ Microbiol 73:7814-7818 (2007); Winzer et al., J. Mol. Microbiol Biotechnol 2:531-541 (2000)), and ERG10 from S. cerevisiae (Hiser et al., J. Biol. Chem. 269:31383-31389 (1994)).
Escherichia coli
Clostridium acetobutylicum
Clostridium acetobutylicum
Saccharomyces cerevisiae
Beta-ketothiolase enzymes catalyzing the formation of beta-ketovalerate from acetyl-CoA and propionyl-CoA are also suitable candidates. Zoogloea ramigera possesses two ketothiolases that can form 3-ketovaleryl-CoA from propionyl-CoA and acetyl-CoA and R. eutropha has a beta-oxidation ketothiolase that is also capable of catalyzing this transformation (Gruys et al., U.S. Pat. No. 5,958,745 (1999)). The sequences of these genes or their translated proteins have not been reported, but several candidates in R. eutropha, Z. ramigera, or other organisms can be identified based on sequence homology to bktB from R. eutropha. These include:
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Ralstonia eutropha
Zoogloea ramigera
Cupriavidus taiwanensis
Ralstonia metallidurans
Burkholderia phymatum
Another suitable candidate is 3-oxoadipyl-CoA thiolase (EC 2.3.1.174), which converts beta-ketoadipyl-CoA to succinyl-CoA and acetyl-CoA, and is a key enzyme of the beta-ketoadipate pathway for aromatic compound degradation. The enzyme is widespread in soil bacteria and fungi including Pseudomonas putida (Harwood et al., J Bacteriol. 176:6479-6488 (1994)) and Acinetobacter calcoaceticus (Doten et al., J Bacteriol. 169:3168-3174 (1987)). The gene products encoded by pcaF in Pseudomonas strain B 13 (Kaschabek et al., J Bacteriol. 184:207-215 (2002)), phaD in Pseudomonas putida U (Olivera et al., Proc. Natl. Acad. Sci USA 95:6419-6424 (1998)), paaE in Pseudomonas fluorescens ST (Di et al., Arch. Microbiol 188:117-125 (2007)), and paaJ from E. coli (Nogales et al., Microbiology 153:357-365 (2007)) also catalyze this transformation. Several beta-ketothiolases exhibit significant and selective activities in the oxoadipyl-CoA forming direction including bkt from Pseudomonas putida, pcaF and bkt from Pseudomonas aeruginosa PAO 1, bkt from Burkholderia ambifaria AMMD, paaJ from E. coli, and phaD from P. putida.
Escherichia coli
Pseudomonas knackmussii (B13)
Pseudomonas putida
Pseudomonas putida
Acinetobacter calcoaceticus
Pseudomonasfluorescens
Burkholderia ambifaria AMMD
Pseudomonas aeruginosa PAO1
Pseudomonas aeruginosa PAO1
Formate C-acyltransferase enzymes in the EC class 2.3.1 catalyze the acylation of ketoacids and concurrent release of formate. Such an enzyme is suitable for the conversion of 2-oxoadipate to glutaryl-CoA in
Enzymes in this class include pyruvate formate-lyase and ketoacid formate-lyase. Pyruvate formate-lyase (PFL, EC 2.3.1.54), encoded by pflB in E. coli, converts pyruvate into acetyl-CoA and formate. The active site of PFL contains a catalytically essential glycyl radical that is posttranslationally activated under anaerobic conditions by PFL-activating enzyme (PFL-AE, EC 1.97.1.4) encoded by pflA (Knappe et al., Proc. Natl. Acad. Sci US.A 81:1332-1335 (1984); Wong et al., Biochemistry 32:14102-14110 (1993)). Keto-acid formate-lyase (EC 2.3.1.-), also known as 2-ketobutyrate formate-lyase (KFL) and pyruvate formate-lyase 4, is the gene product of tdcE in E. coli. This enzyme catalyzes the conversion of 2-ketobutyrate to propionyl-CoA and formate during anaerobic threonine degradation, and can also substitute for pyruvate formate-lyase in anaerobic catabolism (Simanshu et al., J Biosci. 32:1195-1206 (2007)). The enzyme is oxygen-sensitive and, like PflB, requires post-translational modification by PFL-AE to activate a glycyl radical in the active site (Hesslinger et al., Mol. Microbiol 27:477-492 (1998)). A pyruvate formate-lyase from Archaeglubus fulgidus encoded by pflD has been cloned, expressed in E. coli and characterized (Lehtio et al., Protein Eng Des Sel 17:545-552 (2004)). The crystal structures of the A. fulgidus and E. coli enzymes have been resolved (Lehtio et al., J Mol. Biol. 357:221-235 (2006); Leppanen et al., Structure. 7:733-744 (1999)). Additional PFL and PFL-AE candidates are found in Lactococcus lactis (Melchiorsen et al., Appl Microbiol Biotechnol 58:338-344 (2002)), and Streptococcus mutans (Takahashi-Abbe et al., Oral.Microbiol Immunol. 18:293-297 (2003)), Chlamydomonas reinhardtii (Hemschemeier et al., Eukaryot.Cell 7:518-526 (2008b); Atteia et al., J. Biol. Chem. 281:9909-9918 (2006)) and Clostridium pasteurianum (Weidner et al., J Bacteriol. 178:2440-2444 (1996)).
Escherichia coli
Escherichia coli
Escherichia coli
Archaeghibus fulgidus
Lactococcus lactis
Streptococcus mutans
Chlamydomonas reinhardtii
Chlamydomonas reinhardtii
Clostridium pasteurianum
Clostridium pasteurianum
3-Oxoacyl-CoA products such as acetoacetyl-CoA, 3-oxopentanoyl-CoA, 3-oxo-5-hydroxypentanoyl-CoA can be synthesized from acyl-CoA and malonyl-CoA substrates by 3-oxoacyl-CoA synthases (Steps 2A, 3A, 4A, 7AS). As enzymes in this class catalyze an essentially irreversible reaction, they are particularly useful for metabolic engineering applications for overproducing metabolites, fuels or chemicals derived from 3-oxoacyl-CoA intermediates such as acetoacetyl-CoA. Acetoacetyl-CoA synthase, for example, has been heterologously expressed in organisms that biosynthesize butanol (Lan et al, PNAS USA (2012)) and poly-(3-hydroxybutyrate) (Matsumoto et al, Biosci Biotech Biochem, 75:364-366 (2011). An acetoacetyl-CoA synthase (EC 2.3.1.194) enzyme (FhsA) has been characterized in the soil bacterium Streptomyces sp. CL190 where it participates in mevalonate biosynthesis (Okamura et al, PNAS USA 107:11265-70 (2010)). Other acetoacetyl-CoA synthase genes can be identified by sequence homology to fhsA.
Streptomyces sp CL190
Streptomyces sp. KO-3988
Streptomyces cinnamonensis
Streptomyces anulatus
Nocardia brasiliensis
Aminotransferases reversibly convert an amino group to an aldehyde or ketone. Exemplary enzymes for converting aldehydes to primary amines include lysine-6-aminotransferase (EC 2.6.1.36), 5-aminovalerate aminotransferase (EC 2.6.1.48), gamma-aminobutyrate aminotransferase and diamine aminotransferases such as putrescine aminotransferase (EC 2.6.1.82 and 2.6.1.29). These enzymes are suitable for catalyzing steps C and J. of
Lysine-6-aminotransferase (EC 2.6.1.36) converts lysine to alpha-aminoadipate semialdehyde, and has been charactierized in yeast and bacteria. Candidates from Candida utilis (Hammer et al., J Basic Microbiol 32:21-27 (1992)), Flavobacterium lutescens (Fujii et al., J Biochem. 128:391-397 (2000)) and Streptomyces clavuligenus (Romero et al., J Ind. Microbiol Biotechnol 18:241-246 (1997)) have been characterized. A recombinant lysine-6-aminotransferase from S. clavuligenus was functionally expressed in E. coli (Tobin et al., J Bacteriol. 173:6223-6229 (1991)). The F. lutescens enzyme is specific to alpha-ketoglutarate as the amino acceptor (Soda et al., Biochemistry 7:4110-4119 (1968)). A related enzyme, diaminobutyrate aminotransferase (EC 2.6.1.46 and EC 2.6.1.76), is encoded by the dat gene products in Acinetobacter baumanii and Haemophilus influenza (Ikai et al., J Bacteriol. 179:5118-5125 (1997); Ikai et al., Biol Pharm.Bull. 21:170-173 (1998)). In addition to its natural substrate, 2,4-diaminobutyrate, the A. baumanii DAT transaminates the terminal amines of lysine, 4-aminobutyrate and ornithine. Additional diaminobutyrate aminotransferase gene candidates include the ectB gene products of Marinococcus halophilus and Halobacillus dabanensis (Zhao et al., Curr Microbiol 53:183-188 (2006); Louis et al., Microbiology 143 (Pt 4):1141-1149 (1997)) and the pvdH gene product of Pseudomonas aeruginosa (Vandenende et al., J Bacteriol. 186:5596-5602 (2004)). The beta-alanine aminotransferase of Pseudomonas fluorescens also accepts 2,4-diaminobutyrate as a substrate (Hayaishi et al., J Biol Chem 236:781-790 (1961)); however, this activity has not been associated with a gene to date.
Flavobacterium lutescens
Streptomyces clavuligenus
Acinetobacter baumanii
Haemophilus influenzae
Marinococcus halophilus
Halobacillus dabanensis
Pseudomonas aeruginosa
The conversion of an aldehyde to a terminal amine can also be catalyzed by gamma-aminobutyrate (GABA) transaminase (EC 2.6.1.19) or 5-aminovalerate transaminase. GABA aminotransferase interconverts succinic semialdehyde and glutamate to 4-aminobutyrate and alpha-ketoglutarate and is known to have a broad substrate range (Schulz et al., 56:1-6 (1990); Liu et al., 43:10896-10905 (2004)). The two GABA transaminases in E. coli are encoded by gabT (Bartsch et al., J Bacteriol. 172:7035-7042 (1990)) and puuE (Kurihara et al., J. Biol. Chem. 280:4602-4608 (2005)). GABA transaminases in Mus musculus and Sus scrofa also catalyze the transamination of alternate substrates including 6-aminocaproic acid (Cooper, Methods Enzymol. 113:80-82 (1985)). 5-Aminovalerate aminotransferase (EC 2.6.1.48) converts 5-aminovalerate to 5-oxovalerate during lysine degradation. The enzyme is encoded by davT of Pseudomonas putida (Espinosa-Urgel et al, Appl Env Microbiol, 67:5219-24 (2001)) and PA0266 of Pseudomonas aeruginosa (Yamanishi et al, FEBS J. 274:2262-73 (2007)). A 5-aminovalerate aminotransferase from Clostridium aminovalericum was purified and characterized but the sequence has not been published to date (Barker et al, J Biol Chem, 262:8994-9003 (1987)).
Escherichia coli
Escherichia coli
Mus musculus
Pseudomonas fluorescens
Sus scrofa
Pseudomonas putida
Pseudomonas aeruginosa
Putrescine aminotransferase (EC 2.6.1.82) and other diamine aminotransferases (EC 2.6.1.29) also catalyze the interconversion of aldehydes and primary amines. The E. coli putrescine aminotransferase is encoded by the ygjG gene and the purified enzyme transaminates the alternative substrates cadaverine, spermidine and 1,7-diaminoheptane (Samsonova et al., BMC. Microbiol 3:2 (2003)). Activity of this enzyme with amino acceptors other than 2-oxoglutarate (e.g., pyruvate, 2-oxobutanoate) has been reported (Samsonova et al., BMC. Microbiol 3:2 (2003); KIM, J Biol. Chem. 239:783-786 (1964)). Another putrescine aminotransferase enzyme is encoded by spuC gene of Pseudomonas aeruginosa (Lu et al., J Bacteriol. 184:3765-3773 (2002)).
Escherichia coli
Pseudomonas aeruginosa
Several aminotransferases transaminate the amino groups of amino acid groups to form 2-oxoacids. Aspartate aminotransferase is an enzyme that naturally transfers an oxo group from oxaloacetate to glutamate, forming alpha-ketoglutarate and aspartate. Aspartate aminotransferase activity is catalyzed by, for example, the gene products of aspC from Escherichia coli (Yagi et al., 100:81-84 (1979); Yagi et al., 113:83-89 (1985)), AAT2 from Saccharomyces cerevisiae (Yagi et al., 92:35-43 (1982)) and ASPS from Arabidopsis thaliana (Kwok et al., 55:595-604 (2004); de la et al., 46:414-425 (2006); Wilkie et al., Protein Expr. Purif. 12:381-389 (1998)). The enzyme from Rattus norvegicus has been shown to transaminate alternate substrates such as 2-aminohexanedioic acid and 2,4-diaminobutyric acid (Recasens et al., Biochemistry 19:4583-4589 (1980)). Aminotransferases that work on other amino-acid substrates may also be able to catalyze these transformations. Valine aminotransferase catalyzes the conversion of valine and pyruvate to 2-ketoisovalerate and alanine. The E. coli gene, avtA, encodes one such enzyme (Whalen et al., J. Bacteriol. 150:739-746 (1982)). This gene product also catalyzes the transamination of α-ketobutyrate to generate α-aminobutyrate, although the amine donor in this reaction has not been identified (Whalen et al., J. Bacteriol. 158:571-574 (1984)). The gene product of the E. coli serC catalyzes two reactions, phosphoserine aminotransferase and phosphohydroxythreonine aminotransferase (Lam et al., J. Bacteriol. 172:6518-6528 (1990)), and activity on non-phosphorylated substrates could not be detected (Drewke et al., FEBS. Lett. 390:179-182 (1996)). Another enzyme candidate is alpha-aminoadipate aminotransferase (EC 2.6.1.39), an enzyme that participates in lysine biosynthesis and degradation in some organisms. This enzyme interconverts 2-aminoadipate and 2-oxoadipate, using alpha-ketoglutarate as the amino acceptor. Gene candidates are found in Homo sapiens (Okuno et al., Enzyme Protein 47:136-148 (1993)) and Thermus thermophilus (Miyazaki et al., Microbiology 150:2327-2334 (2004)). The Thermus thermophilus enzyme, encoded by lysN, is active with several alternate substrates including oxaloacetate, 2-oxoisocaproate, 2-oxoisovalerate, and 2-oxo-3-methylvalerate.
Escherichia coli
Saccharomyces cerevisiae
Arabidopsis thaliana
Rattus norvegicus
Escherichia coli
Thermus thermophilus
Homo sapiens
Kinase or phosphotransferase enzymes in the EC class 2.7.2 transform carboxylic acids to phosphonic acids with concurrent hydrolysis of one ATP. An enzyme with 2,4-pentadienoate kinase activity is required in step H of
Clostridium acetobutylicum
Clostridium acetobutylicum
Thermotoga maritima
Escherichia coli
Escherichia coli
Escherichia coli
Glycerate kinase (EC 2.7.1.31) activates glycerate to glycerate-2-phosphate or glycerate-3-phosphate. Three classes of glycerate kinase have been identified. Enzymes in class I and II produce glycerate-2-phosphate, whereas the class III enzymes found in plants and yeast produce glycerate-3-phosphate (Bartsch et al., FEBSLett. 582:3025-3028 (2008)). In a recent study, class III glycerate kinase enzymes from Saccharomyces cerevisiae, Oryza sativa and Arabidopsis thaliana were heterologously expressed in E. coli and characterized (Bartsch et al., FEBSLett. 582:3025-3028 (2008)). This study also assayed the glxK gene product of E. coli for ability to form glycerate-3-phosphate and found that the enzyme can only catalyze the formation of glycerate-2-phosphate, in contrast to previous work (Doughty et al., J Biol. Chem. 241:568-572 (1966)).
Escherichia coli
Saccharomyces cerevisiae
Oryza sativa
Arabidopsis thaliana
Enzymes in the 2.8.3 family catalyze the reversible transfer of a CoA moiety from one molecule to another. Such a transformation is required by steps L, P and O of
Many transferases have broad specificity and thus can utilize CoA acceptors as diverse as acetate, succinate, propionate, butyrate, 2-methylacetoacetate, 3-ketohexanoate, 3-ketopentanoate, valerate, crotonate, 3-mercaptopropionate, propionate, vinylacetate, butyrate, among others. For example, an enzyme from Roseburia sp. A2-183 was shown to have butyryl-CoA:acetate:CoA transferase and propionyl-CoA: acetate: CoA transferase activity (Charrier et al., Microbiology 152, 179-185 (2006)). Close homologs can be found in, for example, Roseburia intestinalis L1-82, Roseburia inulinivorans DSM 16841, Eubacterium rectale ATCC 33656. Another enzyme with propionyl-CoA transferase activity can be found in Clostridium propionicum (Selmer et al., Eur J Biochem 269, 372-380 (2002)). This enzyme can use acetate, (R)-lactate, (S)-lactate, acrylate, and butyrate as the CoA acceptor (Selmer et al., Eur J Biochem 269, 372-380 (2002); Schweiger and Buckel, FEBS Letters, 171(1) 79-84 (1984)). Close homologs can be found in, for example, Clostridium novyi NT, Clostridium beijerinckii NCIMB 8052, and Clostridium botulinum C str. Eklund. YgfH encodes a propionyl CoA:succinate CoA transferase in E. coli (Haller et al., Biochemistry, 39(16) 4622-4629). Close homologs can be found in, for example, Citrobacter youngae ATCC 29220, Salmonella enterica subsp. arizonae serovar, and Yersinia intermedia ATCC 29909. These proteins are identified below.
Roseburia sp. A2-183
Roseburia intestinalis L1-82
Roseburia inulinivorans
Eubacterium rectale ATCC
Clostridium propionicum
Clostridium novyi NT
Clostridium beijerinckii
Clostridium botulinum C str.
Escherichia coli
Citrobacter youngae ATCC
Salmonella enterica subsp.
arizonae serovar
Yersinia intermedia ATCC
An additional candidate enzyme is the two-unit enzyme encoded by pcaI and pcaJ in Pseudomonas, which has been shown to have 3-oxoadipyl-CoA/succinate transferase activity (Kaschabek et al., supra). Similar enzymes based on homology exist in Acinetobacter sp. ADP1 (Kowalchuk et al., Gene 146:23-30 (1994)) and Streptomyces coelicolor. Additional exemplary succinyl-CoA:3:oxoacid-CoA transferases are present in Helicobacter pylori (Corthesy-Theulaz et al., J. Biol. Chem. 272:25659-25667 (1997)) and Bacillus subtilis (Stols et al., Protein. Expr. Purif. 53:396-403 (2007)). These proteins are identified below.
Pseudomonas putida
Pseudomonas putida
Acinetobacter sp. ADP1
Acinetobacter sp. ADP1
Streptomyces coelicolor
Streptomyces coelicolor
Helicobacter pylori
Helicobacter pylori
Bacillus subtilis
Bacillus subtilis
A CoA transferase that can utilize acetate as the CoA acceptor is acetoacetyl-CoA transferase, encoded by the E. coli atoA (alpha subunit) and atoD (beta subunit) genes (Vanderwinkel et al., Biochem. Biophys. Res Commun. 33:902-908 (1968); Korolev et al., Acta Crystallogr. D Biol Crystallogr. 58:2116-2121 (2002)). This enzyme has also been shown to transfer the CoA moiety to acetate from a variety of branched and linear acyl-CoA substrates, including isobutyrate (Matthies et al., Appl Environ Microbiol 58:1435-1439 (1992)), valerate (Vanderwinkel et al., supra) and butanoate (Vanderwinkel et al., supra). Similar enzymes exist in Corynebacterium glutamicum ATCC 13032 (Duncan et al., Appl Environ Microbiol 68:5186-5190 (2002)), Clostridium acetobutylicum (Cary et al., Appl Environ Microbiol 56:1576-1583 (1990)), and Clostridium saccharoperbutylacetonicum (Kosaka et al., Biosci. Biotechnol Biochem. 71:58-68 (2007)). These proteins are identified below.
Escherichia coli K12
Escherichia coli K12
Corynebacterium glutamicum
Corynebacterium glutamicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium
saccharoperbutylacetonicum
Clostridium
saccharoperbutylacetonicum
Additional exemplary transferase candidates are catalyzed by the gene products of cat1, cat2, and cat3 of Clostridium kluyveri which have been shown to exhibit succinyl-CoA, 4-hydroxybutyryl-CoA, and butyryl-CoA transferase activity, respectively (Seedorf et al., supra; Sohling et al., Eur. J Biochem. 212:121-127 (1993); Sohling et al., J Bacteriol. 178:871-880 (1996)). Similar CoA transferase activities are also present in Trichomonas vaginalis (van Grinsven et al., J. Biol. Chem. 283:1411-1418 (2008)) and Trypanosoma brucei (Riviere et al., J. Biol. Chem. 279:45337-45346 (2004)). These proteins are identified below.
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
Trichomonas vaginalis G3
Trypanosoma brucei
The glutaconate-CoA-transferase (EC 2.8.3.12) enzyme from anaerobic bacterium Acidaminococcus fermentans reacts with diacid glutaconyl-CoA and 3-butenoyl-CoA (Mack et al., FEBS Lett. 405:209-212 (1997)). The genes encoding this enzyme are gctA and gctB. This enzyme has reduced but detectable activity with other CoA derivatives including glutaryl-CoA, 2-hydroxyglutaryl-CoA, adipyl-CoA and acrylyl-CoA (Buckel et al., Eur. J. Biochem. 118:315-321 (1981)). The enzyme has been cloned and expressed in E. coli (Mack et al., Eur. J. Biochem. 226:41-51 (1994)). These proteins are identified below.
Acidaminococcus fermentans
Acidaminococcus fermentans
Enzymes in the 3.1.2 family hydrolyze acyl-CoA molecules to their corresponding acids. Such a transformation is required by step O of
For example, the enzyme encoded by acot12 from Rattus norvegicus brain (Robinson et al., Biochem. Biophys. Res. Commun. 71:959-965 (1976)) can react with butyryl-CoA, hexanoyl-CoA and malonyl-CoA. The human dicarboxylic acid thioesterase, encoded by acot8, exhibits activity on glutaryl-CoA, adipyl-CoA, suberyl-CoA, sebacyl-CoA, and dodecanedioyl-CoA (Westin et al., J. Biol. Chem. 280:38125-38132 (2005)). The closest E. coli homolog to this enzyme, tesB, can also hydrolyze a range of CoA thiolesters (Naggert et al., J Biol Chem 266:11044-11050 (1991)). A similar enzyme has also been characterized in the rat liver (Deana R., Biochem Int 26:767-773 (1992)). Additional enzymes with hydrolase activity in E. coli include ybgC, paal, and ybdB (Kuznetsova, et al., FEMS Microbiol Rev, 2005, 29(2):263-279; Song et al., J Biol Chem, 2006, 281(16):11028-38). Though its sequence has not been reported, the enzyme from the mitochondrion of the pea leaf has a broad substrate specificity, with demonstrated activity on acetyl-CoA, propionyl-CoA, butyryl-CoA, palmitoyl-CoA, oleoyl-CoA, succinyl-CoA, and crotonyl-CoA (Zeiher et al., Plant.Physiol. 94:20-27 (1990)) The acetyl-CoA hydrolase, ACH1, from S. cerevisiae represents another candidate hydrolase (Buu et al., J. Biol. Chem. 278:17203-17209 (2003)).
Rattus norvegicus
Escherichia coli
Homo sapiens
Rattus norvegicus
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Saccharomyces cerevisiae
Additional hydrolase enzymes include 3-hydroxyisobutyryl-CoA hydrolase which has been described to efficiently catalyze the conversion of 3-hydroxyisobutyryl-CoA to 3-hydroxyisobutyrate during valine degradation (Shimomura et al., J Biol Chem. 269:14248-14253 (1994)). Genes encoding this enzyme include hibch of Rattus norvegicus (Shimomura et al., Methods Enzymol. 324:229-240 (2000)) and Homo sapiens (Shimomura et al., supra). Similar gene candidates can also be identified by sequence homology, including hibch of Saccharomyces cerevisiae and BC 2292 of Bacillus cereus.
Rattus norvegicus
Homo sapiens
Saccharomyces cerevisiae
Bacillus cereus
Yet another candidate hydrolase is the glutaconate CoA-transferase from Acidaminococcus fermentans. This enzyme was transformed by site-directed mutagenesis into an acyl-CoA hydrolase with activity on glutaryl-CoA, acetyl-CoA and 3-butenoyl-CoA (Mack et al., FEBS. Lett. 405:209-212 (1997)).This suggests that the enzymes encoding succinyl-CoA:3-ketoacid-CoA transferases and acetoacetyl-CoA:acetyl-CoA transferases may also serve as candidates for this reaction step but would require certain mutations to change their function. GeneBank accession numbers for the gctA and gctB genes are listed above.
Decarboxylase enzymes in the EC class 4.1.1 are required to catalyze steps A, D, T and U of
The decarboxylation reactions of 2,4-pentadienoate to butadiene (step T of
Aspergillus niger
Aspergillus niger
Aspergillus niger
Aspergillus oryzae
Aspergillus oryzae
Aspergillus oryzae
Neosartorya fischeri
Neosartorya fischeri
Neosartorya fischeri
Aconitate decarboxylase (EC 4.1.1.6) catalyzes the final step in itaconate biosynthesis in a strain of Candida and also in the filamentous fungus Aspergillus terreus (Bonnarme et al. J Bacteriol. 177:3573-3578 (1995); Willke and Vorlop, Appl Microbiol. Biotechnol 56:289-295 (2001)). A cis-aconitate decarboxylase (CAD) (EC 4.1.16) has been purified and characterized from Aspergillus terreus (Dwiarti et al., J Biosci. Bioeng. 94(1): 29-33 (2002)). Recently, the gene has been cloned and functionally characterized (Kanamasa et al., Appl. Microbiol Biotechnol 80:223-229 (2008)) and (WO/2009/014437). Several close homologs of CAD are listed below (EP 2017344A1; WO 2009/014437 A1). The gene and protein sequence of CAD were reported previously (EP 2017344 A1; WO 2009/014437 A1), along with several close homologs listed in the table below.
Aspergillus terreus
Aspergillus terreus
Aspergillus terreus
Aspergillus oryzae
Aspergillus niger
Gibberella zeae
Aspergillus niger
Pichia stipitis
Mycobacterium smegmatis
Mycobacterium avium
Mycobacterium avium
Salinispora arenicola
An additional class of decarboxylases has been characterized that catalyze the conversion of cinnamate (phenylacrylate) and substituted cinnamate derivatives to the corresponding styrene derivatives. These enzymes are common in a variety of organisms and specific genes encoding these enzymes that have been cloned and expressed in E. coli are: pad/from Saccharomyces cerevisae (Clausen et al., Gene 142:107-112 (1994)), pdc from Lactobacillus plantarum (Barthelmebs et al., 67:1063-1069 (2001); Qi et al., Metab Eng 9:268-276 (2007); Rodriguez et al., J. Agric. Food Chem. 56:3068-3072 (2008)), pofK (pad) from Klebsiella oxytoca (Uchiyama et al., Biosci. Biotechnol. Biochem. 72:116-123 (2008); Hashidoko et al., Biosci. Biotech. Biochem. 58:217-218 (1994)), Pedicoccus pentosaceus (Barthelmebs et al., 67:1063-1069 (2001)), and padC from Bacillus subtilis and Bacillus pumilus (Shingler et al., 174:711-724 (1992)). A ferulic acid decarboxylase from Pseudomonas fluorescens also has been purified and characterized (Huang et al., J. Bacteriol. 176:5912-5918 (1994)). Importantly, this class of enzymes have been shown to be stable and do not require either exogenous or internally bound co-factors, thus making these enzymes ideally suitable for biotransformations (Sariaslani, Annu. Rev. Microbiol. 61:51-69 (2007)).
Saccharomyces cerevisae
Lactobacillus plantarum
Klebsiella oxytoca
Bacillus subtilis
Pedicoccus pentosaceus
Bacillus pumilus
4-Oxalocronate decarboxylase catalyzes the decarboxylation of 4-oxalocrotonate to 2-oxopentanoate. This enzyme has been isolated from numerous organisms and characterized. The decarboxylase typically functions in a complex with vinylpyruvate hydratase. Genes encoding this enzyme include dmpH and dmpE in Pseudomonas sp. (strain 600) (Shingler et al., 174:711-724 (1992)), xylII and xylIII from Pseudomonas putida (Kato et al., Arch. Microbiol 168:457-463 (1997); Stanley et al., Biochemistry 39:3514 (2000); Lian et al., J. Am. Chem. Soc. 116:10403-10411 (1994)) and Reut B5691 and Reut B5692 from Ralstonia eutropha JMP 134 (Hughes et al., J Bacteriol, 158:79-83 (1984)). The genes encoding the enzyme from Pseudomonas sp. (strain 600) have been cloned and expressed in E. coli (Shingler et al., J. Bacteriol. 174:711-724 (1992)). The 4-oxalocrotonate decarboxylase encoded by xyll in Pseudomonas putida functions in a complex with vinylpyruvate hydratase. A recombinant form of this enzyme devoid of the hydratase activity and retaining wild type decarboxylase activity has been characterized (Stanley et al., Biochem. 39:718-26 (2000)). A similar enzyme is found in Ralstonia pickettii (formerly Pseudomonas pickettii) (Kukor et al., J Bacteriol. 173:4587-94 (1991)).
Pseudomonas sp. CF600
Pseudomonas sp. CF600
Pseudomonas putida
Pseudomonas putida
Ralstonia eutropha JMP134
Ralstonia eutropha JMP134
Pseudomonas putida
Ralstonia pickettii
Pseudomonas fluorescens
The decarboxylation of 2-keto-acids such as 2-oxoadipate (step D of
Zymomonas mobilis
Saccharomyces cerevisiae
Acetobacter pasteurians
Kluyveromyces lactis
Like PDC, benzoylformate decarboxylase (EC 4.1.1.7) has a broad substrate range and has been the target of enzyme engineering studies. The enzyme from Pseudomonas putida has been extensively studied and crystal structures of this enzyme are available (Polovnikova et al., 42:1820-1830 (2003); Hasson et al., 37:9918-9930 (1998)). Site-directed mutagenesis of two residues in the active site of the Pseudomonas putida enzyme altered the affinity (Km) of naturally and non-naturally occurring substrates (Siegert et al., Protein Eng Des Sel 18:345-357 (2005)). The properties of this enzyme have been further modified by directed engineering (Lingen et al., Chembiochem. 4:721-726 (2003); Lingen et al., Protein Eng 15:585-593 (2002)). The enzyme from Pseudomonas aeruginosa, encoded by md1C, has also been characterized experimentally (Barrowman et al., 34:57-60 (1986)). Additional gene candidates from Pseudomonas stutzeri, Pseudomonas fluorescens and other organisms can be inferred by sequence homology or identified using a growth selection system developed in Pseudomonas putida (Henning et al., Appl. Environ. Microbiol. 72:7510-7517 (2006)).
Pseudomonas putida
Pseudomonas aeruginosa
Pseudomonas stutzeri
Pseudomonas fluorescens
A third enzyme capable of decarboxylating 2-oxoacids is alpha-ketoglutarate decarboxylase (KGD). The substrate range of this class of enzymes has not been studied to date. The KDC from Mycobacterium tuberculosis (Tian et al., 102:10670-10675 (2005)) has been cloned and functionally expressed. KDC enzyme activity has been detected in several species of rhizobia including Bradyrhizobium japonicum and Mesorhizobium loti (Green et al., 182:2838-2844 (2000)). Although the KDC-encoding gene(s) have not been isolated in these organisms, the genome sequences are available and several genes in each genome are annotated as putative KDCs. A KDC from Euglena gracilis has also been characterized but the gene associated with this activity has not been identified to date (Shigeoka et al., Arch. Biochem. Biophys. 288:22-28 (1991)). The first twenty amino acids starting from the N-terminus were sequenced MTYKAPVKDVKFLLDKVFKV (SEQ ID NO.) (Shigeoka and Nakano, Arch. Biochem. Biophys. 288:22-28 (1991)). The gene could be identified by testing candidate genes containing this N-terminal sequence for KDC activity.
Mycobacterium tuberculosis
Bradyrhizobium japonicum
Mesorhizobium loti
A fourth candidate enzyme for catalyzing this reaction is branched chain alpha-ketoacid decarboxylase (BCKA). This class of enzyme has been shown to act on a variety of compounds varying in chain length from 3 to 6 carbons (Oku et al., J Biol Chem. 263:18386-18396 (1988); Smit et al., Appl Environ Microbiol 71:303-311 (2005)). The enzyme in Lactococcus lactis has been characterized on a variety of branched and linear substrates including 2-oxobutanoate, 2-oxohexanoate, 2-oxopentanoate, 3-methyl-2-oxobutanoate, 4-methyl-2-oxobutanoate and isocaproate (Smit et al., Appl Environ Microbiol 71:303-311 (2005)). The enzyme has been structurally characterized (Berg et al., Science. 318:1782-1786 (2007)). Sequence alignments between the Lactococcus lactis enzyme and the pyruvate decarboxylase of Zymomonas mobilus indicate that the catalytic and substrate recognition residues are nearly identical (Siegert et al., Protein Eng Des Sel 18:345-357 (2005)), so this enzyme would be a promising candidate for directed engineering. Decarboxylation of alpha-ketoglutarate by a BCKA was detected in Bacillus subtilis; however, this activity was low (5%) relative to activity on other branched-chain substrates (Oku and Kaneda, J Biol Chem. 263:18386-18396 (1988)) and the gene encoding this enzyme has not been identified to date. Additional BCKA gene candidates can be identified by homology to the Lactococcus lactis protein sequence. Many of the high-scoring BLASTp hits to this enzyme are annotated as indolepyruvate decarboxylases (EC 4.1.1.74). Indolepyruvate decarboxylase (IPDA) is an enzyme that catalyzes the decarboxylation of indolepyruvate to indoleacetaldehyde in plants and plant bacteria. Recombinant branched chain alpha-keto acid decarboxylase enzymes derived from the E1 subunits of the mitochondrial branched-chain keto acid dehydrogenase complex from Homo sapiens and Bos taurus have been cloned and functionally expressed in E. coli (Davie et al., J. Biol. Chem. 267:16601-16606 (1992); Wynn et al., J. Biol. Chem. 267:12400-12403 (1992); Wynn et al., J. Biol. Chem. 267:1881-1887 (1992)). In these studies, the authors found that co-expression of chaperonins GroEL and GroES enhanced the specific activity of the decarboxylase by 500-fold (Wynn et al., J. Biol. Chem. 267:12400-12403 (1992)). These enzymes are composed of two alpha and two beta subunits.
Lactococcus lactis
Homo sapiens
Homo sapiens
Bos taurus
Bos taurus
A decarboxylase enzyme suitable for decarboxylating 3-ketoacids is acetoacetate decarboxylase (EC 4.1.1.4). The enzyme from Clostridium acetobutylicum, encoded by adc, has a broad substrate specificity and has been shown to decarboxylate numerous alternate substrates including 2-ketocyclohexane carboxylate, 3-oxopentanoate, 2-oxo-3-phenylpropionic acid, 2-methyl-3-oxobutyrate and benzoyl-acetate (Rozzel et al., J. Am. Chem. Soc. 106:4937-4941 (1984); Benner and Rozzell, J. Am. Chem. Soc. 103:993-994 (1981); Autor et al., J Biol. Chem. 245:5214-5222 (1970)). An acetoacetate decarboxylase has also been characterized in Clostridium beijerinckii (Ravagnani et al., Mol. Microbiol 37:1172-1185 (2000)). The acetoacetate decarboxylase from Bacillus polymyxa, characterized in cell-free extracts, also has a broad substrate specificity for 3-keto acids and can decarboxylate 3-oxopentanoate (Matiasek et al., Curr.Microbiol 42:276-281 (2001)). The gene encoding this enzyme has not been identified to date and the genome sequence of B. polymyxa is not yet available. Another adc is found in Clostridium saccharoperbutylacetonicum (Kosaka, et al., Biosci. Biotechnol Biochem. 71:58-68 (2007)). Additional gene candidates in other organisms, including Clostridium botulinum and Bacillus amyloliquefaciens FZB42, can be identified by sequence homology.
Clostridium acetobutylicum
Clostridium
saccharoperbutylacetonicum
Clostridium beijerinckii
Clostridium botulinum
Bacillus amyloliquefaciens
Numerous characterized enzymes decarboxylate amino acids and similar compounds, including aspartate decarboxylase, lysine decarboxylase and ornithine decarboxylase. Aspartate decarboxylase (EC 4.1.1.11) decarboxylates aspartate to form beta-alanine. This enzyme participates in pantothenate biosynthesis and is encoded by gene panD in Escherichia coli (Dusch et al., Appl. Environ. Microbiol 65:1530-1539 (1999); Ramjee et al., Biochem.J323 (Pt 3):661-669 (1997); Merkel et al., FEMS Microbiol Lett. 143:247-252 (1996); Schmitzberger et al., EMBO J 22:6193-6204 (2003)). The enzymes from Mycobacterium tuberculosis (Chopra et al., Protein Expr. Purif. 25:533-540 (2002)) and Corynebacterium glutanicum (Dusch et al., Appl. Environ. Microbiol 65:1530-1539 (1999)) have been expressed and characterized in E. coli.
Escherichia coli K12
Corynebacterium glutanicum
Mycobacterium tuberculosis
Lysine decarboxylase (EC 4.1.1.18) catalyzes the decarboxylation of lysine to cadaverine. Two isozymes of this enzyme are encoded in the E. coli genome by genes cadA and ldcC. CadA is involved in acid resistance and is subject to positive regulation by the cadC gene product (Lemonnier et al., Microbiology 144 (Pt 3):751-760 (1998)). CadC accepts hydroxylysine and S-aminoethylcysteine as alternate substrates, and 2-aminopimelate and 6-aminocaproate act as competitive inhibitors to this enzyme (Sabo et al., Biochemistry 13:662-670 (1974)). The constitutively expressed ldc gene product is less active than CadA (Lemonnier and Lane, Microbiology 144 (Pt 3):751-760 (1998)). A lysine decarboxylase analogous to CadA was recently identified in Vibrio parahaemolyticus (Tanaka et al., J Appl Microbiol 104:1283-1293 (2008)). The lysine decarboxylase from Selenomonas ruminantium, encoded by ldc, bears sequence similarity to eukaryotic ornithine decarboxylases, and accepts both L-lysine and L-ornithine as substrates (Takatsuka et al., Biosci. Biotechnol Biochem. 63:1843-1846 (1999)). Active site residues were identified and engineered to alter the substrate specificity of the enzyme (Takatsuka et al., J Bacteriol. 182:6732-6741 (2000)). Several ornithine decarboxylase enzymes (EC 4.1.1.17) also exhibit activity on lysine and other similar compounds. Such enzymes are found in Nicotiana glutinosa (Lee et al., Biochem. J 360:657-665 (2001)), Lactobacillus sp. 30a (Guirard et al., J Biol. Chem. 255:5960-5964 (1980)) and Vibrio vulnificus (Lee et al., J Biol. Chem. 282:27115-27125 (2007)). The enzymes from Lactobacillus sp. 30a (Momany et al., J Mol. Biol. 252:643-655 (1995)) and V. vulnificus have been crystallized. The V. vulnificus enzyme efficiently catalyzes lysine decarboxylation and the residues involved in substrate specificity have been elucidated (Lee et al., J Biol. Chem. 282:27115-27125 (2007)). A similar enzyme has been characterized in Trichomonas vaginalis but the gene encoding this enzyme is not known (Yarlett et al., Biochem. J 293 (Pt 2):487-493 (1993)).
Escherichia coli
Escherichia coli
Selenomonas ruminantium
Vibrio parahaemolyticus
Nicotiana glutinosa
Lactobacillus sp. 30a
Vibrio vulnificus
Glutaryl-CoA dehydrogenase (GCD, EC 1.3.99.7 and EC 4.1.1.70) is a bifunctional enzyme that catalyzes the oxidative decarboxylation of glutaryl-CoA to crotonyl-CoA (
Azoarcus sp. CIB
Azoarcus sp. CIB
Pseudomonas putida KT2440
Pseudomonas putida KT2440
Pseudomonasfluorescens Pf-5
Pseudomonas fluorescens Pf-5
Paracoccus denitrificans
Paracoccus denitrificans
Homo sapiens
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Alternatively, the carboxylation of crotonyl-CoA to glutaconyl-CoA and subsequent reduction to glutaryl-CoA can be catalyzed by separate enzymes: glutaconyl-CoA decarboxylase and glutaconyl-CoA reductase. Glutaconyl-CoA decarboxylase enzymes, characterized in glutamate-fermenting anaerobic bacteria, are sodium-ion translocating decarboxylases that utilize biotin as a cofactor and are composed of four subunits (alpha, beta, gamma, and delta) (Boiangiu et al., J Mol. Microbiol Biotechnol 10:105-119 (2005); Buckel, Biochim. Biophys. Acta 1505:15-27 (2001)). Such enzymes have been characterized in Fusobacterium nucleatum (Beatrix et al., Arch. Microbiol 154:362-369 (1990)) and Acidaminococcus fermentans (Braune et al., Mol. Microbiol 31:473-487 (1999)). Analogs to the F. nucleatum glutaconyl-CoA decarboxylase alpha, beta and delta subunits are found in S. aciditrophicus. A gene annotated as an enoyl-CoA dehydrogenase, syn_00480, another GCD, is located in a predicted operon between a biotin-carboxyl carrier (syn_00479) and a glutaconyl-CoA decarboxylase alpha subunit (syn_00481). The protein sequences for exemplary gene products can be found using the following GenBank accession numbers shown below. Enoyl-CoA reductase enzymes are described above (see EC 1.3.1).
Acidaminococcus fermentans
Acidaminococcus fermentans
Acidaminococcus fermentans
Acidaminococcus fermentans
Fusobacterium nucleatum
Fusobacterium nucleatum
Fusobacterium nucleatum
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Syntrophus aciditrophicus
Syntrophus aciditrophicus
An olefin-forming decarboxylase enzyme catalyzes the conversion of 5-hydroxyvalerate to 3-buten-1-ol (step W of
Jeotgalicoccus sp. ATCC8456
Macrococcus caseolyticus
Staphylococcus pseudintermedius
Bacillus pseudofirmus
Sporosarcina newyorkensis
Solibacillus silvestris
Bacillus coahuilensis
The conversion of penta-2,4-dienal to butadiene is catalyzed by a decarbonylase (Step B of
Arabidopsis thaliana
Medicago truncatula
Vitis vinifera
Oryza sativa
Alternately, an oxidative decarbonylase can convert an aldehyde into an alkane. Oxidative decarbonylases are cytochrome P450 enzymes that utilize NADPH and O2 as cofactors and release CO2, water and NADP+. This activity was demonstrated in the CYP4G2v1 and CYP4G1 gene products of Musca domestica and Drosophila melanogaster (US Patent Application 2010/0136595). Additional enzyme candidates with oxidative decarbonylase activity can be identified in other organisms, for example Mamestra brassicae, Helicoverpa zea and Acyrthosiphon pisum, by sequence homology.
Musca domestica
Drosophila melanogaster
Antheraea yamamai
Helicoverpa zea
Acyrthosiphon pisum
The condensation of pyruvate and acetaldehyde to 4-hydroxy-2-oxovalerate (Step A of
Escherichia coli
Pseudomonas putida
Pseudomonas putida
Pseudomonas sp. CF600
Pseudomonas sp. CF600
Burkholderia xenovorans
Burkholderia xenovorans
The removal of water to form a double bond is catalyzed by dehydratase enzymes in the 4.2.1 family of enzymes. Hydratase enzymes are sometimes reversible and also catalyze dehydration. Dehydratase enzymes are sometimes reversible and also catalyze hydration. The removal of water from a given substrate is required by steps G, N and V of
For example, many dehydratase enzymes catalyze the alpha, beta-elimination of water which involves activation of the alpha-hydrogen by an electron-withdrawing carbonyl, carboxylate, or CoA-thiol ester group and removal of the hydroxyl group from the beta-position (Buckel et al, J Bacteriol, 117:1248-60 (1974); Martins et al, PNAS 101:15645-9 (2004)). Exemplary enzymes include 2-(hydroxymethyl)glutarate dehydratase (EC 4.2.1.-), fumarase (EC 4.2.1.2), 3-dehydroquinate dehydratase (EC 4.2.1.10), cyclohexanone hydratase (EC 4.2.1.-) and 2-keto-4-pentenoate dehydratase (EC 4.2.1.80), citramalate hydrolyase and dimethylmaleate hydratase.
2-(Hydroxymethyl)glutarate dehydratase is a [4Fe-4S]-containing enzyme that dehydrates 2-(hydroxymethyl)glutarate to 2-methylene-glutarate, studied for its role in nicontinate catabolism in Eubacterium barkeri (formerly Clostridium barkeri) (Alhapel et al., Proc Natl Acad Sci 103:12341-6 (2006)). Similar enzymes with high sequence homology are found in Bacteroides capillosus, Anaerotruncus colihominis, and Natranaerobius thermophilius. These enzymes are homologous to the alpha and beta subunits of [4Fe-4S]-containing bacterial serine dehydratases (e.g., E. coli enzymes encoded by tdcG, sdhB, and sdaA). An enzyme with similar functionality in E. barkeri is dimethylmaleate hydratase, a reversible Fe2+-dependent and oxygen-sensitive enzyme in the aconitase family that hydrates dimethylmaeate to form (2R,3S)-2,3-dimethylmalate. This enzyme is encoded by dmdAB (Alhapel et al., Proc Natl Acad Sci USA 103:12341-6 (2006); Kollmann-Koch et al., Hoppe Seylers. Z. Physiol Chem. 365:847-857 (1984)).
Eubacterium
barkeri
Bacteroides
capillosus
Anaerotruncus
colihominis
Natranaerobius
thermophilus
Eubacterium
barkeri
Eubacterium
barkeri
Fumarate hydratase (EC 4.2.1.2) enzymes naturally catalyze the reversible hydration of fumarate to malate. Although the ability of fumarate hydratase to react with 3-oxobutanol as a substrate has not been described in the literature, a wealth of structural information is available for this enzyme and other researchers have successfully engineered the enzyme to alter activity, inhibition and localization (Weaver, 61:1395-1401 (2005)). E. coli has three fumarases: FumA, FumB, and FumC that are regulated by growth conditions. FumB is oxygen sensitive and only active under anaerobic conditions. FumA is active under microanaerobic conditions, and FumC is the only active enzyme in aerobic growth (Tseng et al., J Bacteriol, 183:461-467 (2001); Woods et al., 954:14-26 (1988); Guest et al., J Gen Microbiol 131:2971-2984 (1985)). Additional enzyme candidates are found in Campylobacter jejuni (Smith et al., Int. J Biochem.Cell Biol 31:961-975 (1999)), Thermus thermophilus (Mizobata et al., Arch. Biochem. Biophys. 355:49-55 (1998)) and Rattus norvegicus (Kobayashi et al., J Biochem, 89:1923-1931 (1981)). Similar enzymes with high sequence homology include fum1 from Arabidopsis thaliana and fumC from Corynebacterium glutamicum. The MmcBC fumarase from Pelotomaculum thermopropionicum is another class of fumarase with two subunits (Shimoyama et al., FEMS Microbiol Lett, 270:207-213 (2007)).
Escherichia coli
Escherichia coli
Escherichia coli
Campylobacter jejuni
Thermus thermophilus
Rattus norvegicus
Arabidopsis thaliana
Corynebacterium glutamicum
Pelotomaculum
thermopropionicum
Pelotomaculum
thermopropionicum
Dehydration of 4-hydroxy-2-oxovalerate to 2-oxopentenoate is catalyzed by 4-hydroxy-2-oxovalerate hydratase (EC 4.2.1.80). This enzyme participates in aromatic degradation pathways and is typically co-transcribed with a gene encoding an enzyme with 4-hydroxy-2-oxovalerate aldolase activity. Exemplary gene products are encoded by mhpD of E. coli (Ferrandez et al., J Bacteriol. 179:2573-2581 (1997); Pollard et al., Eur J Biochem. 251:98-106 (1998)), todG and cmtF of Pseudomonas putida (Lau et al., Gene 146:7-13 (1994); Eaton, J Bacteriol. 178:1351-1362 (1996)), cnbE of Comamonas sp. CNB-1 (Ma et al., Appl Environ Microbiol 73:4477-4483 (2007)) and mhpD of Burkholderia xenovorans (Wang et al., FEBS J 272:966-974 (2005)). A closely related enzyme, 2-oxohepta-4-ene-1,7-dioate hydratase, participates in 4-hydroxyphenylacetic acid degradation, where it converts 2-oxo-hept-4-ene-1,7-dioate (OHED) to 2-oxo-4-hydroxy-hepta-1,7-dioate using magnesium as a cofactor (Burks et al., J. Am. Chem. Soc. 120: (1998)). OHED hydratase enzyme candidates have been identified and characterized in E. coli C (Roper et al., Gene 156:47-51 (1995); Izumi et al., J Mol. Biol. 370:899-911 (2007)) and E. coli W (Prieto et al., J Bacteriol. 178:111-120 (1996)). Sequence comparison reveals homologs in a wide range of bacteria, plants and animals. Enzymes with highly similar sequences are contained in Klebsiella pneumonia (91% identity, eval=2e-138) and Salmonella enterica (91% identity, eval=4e-138), among others.
Escherichia coli
Pseudomonas putida
Pseudomonas putida
Comamonas sp. CNB-1
Burkholderia xenovorans
Escherichia coli C
Escherichia coli W
Klebsiella pneumoniae
Salmonella enterica
Another enzyme candidate is citramalate hydrolyase (EC 4.2.1.34), an enzyme that naturally dehydrates 2-methylmalate to mesaconate. This enzyme has been studied in Methanocaldococcus jannaschii in the context of the pyruvate pathway to 2-oxobutanoate, where it has been shown to have a broad substrate range (Drevland et al., J Bacteriol. 189:4391-4400 (2007)). This enzyme activity was also detected in Clostridium tetanomorphum, Morganella morganii, Citrobacter amalonaticus where it is thought to participate in glutamate degradation (Kato et al., Arch. Microbiol 168:457-463 (1997)). The M. jannaschii protein sequence does not bear significant homology to genes in these organisms.
Methanocaldococcus jannaschii
Dimethylmaleate hydratase (EC 4.2.1.85) is a reversible Fe2+-dependent and oxygen-sensitive enzyme in the aconitase family that hydrates dimethylmaeate to form (2R,3S)-2,3-dimethylmalate. This enzyme is encoded by dmdAB in Eubacterium barkeri (Alhapel et al., supra; Kollmann-Koch et al., Hoppe Seylers. Z. Physiol Chem. 365:847-857 (1984)).
Eubacterium barkeri
Eubacterium barkeri
Oleate hydratases represent additional suitable candidates as suggested in WO2011076691. Examples include the following proteins.
Elizabethkingia meningoseptica
Streptococcus
pyogenes ATCC 10782
Psychroflexus
torquis ATCC 700755
Rhodopseudomonas palustris
Enoyl-CoA hydratases (EC 4.2.1.17) catalyze the dehydration of a range of 3-hydroxyacyl-CoA substrates (Roberts et al., Arch. Microbiol 117:99-108 (1978); Agnihotri et al., Bioorg. Med. Chem. 11:9-20 (2003); Conrad et al., J Bacteriol. 118:103-111 (1974)). The enoyl-CoA hydratase of Pseudomonas putida, encoded by ech, catalyzes the conversion of 3-hydroxybutyryl-CoA to crotonyl-CoA (Roberts et al., Arch. Microbiol 117:99-108 (1978)). This transformation is also catalyzed by the crt gene product of Clostridium acetobutylicum, the crtl gene product of C. kluyveri, and other clostridial organisms Atsumi et al., Metab Eng 10:305-311 (2008); Boynton et al., J Bacteriol. 178:3015-3024 (1996); Hillmer et al., FEBS Lett. 21:351-354 (1972)). Additional enoyl-CoA hydratase candidates are phaA and phaB, of P. putida, and paaA and paaB from P. fluorescens (Olivera et al., Proc.Natl.Acad.Sci US.A 95:6419-6424 (1998)). The gene product of pimF in Rhodopseudomonas palustris is predicted to encode an enoyl-CoA hydratase that participates in pimeloyl-CoA degradation (Harrison et al., Microbiology 151:727-736 (2005)). Lastly, a number of Escherichia coli genes have been shown to demonstrate enoyl-CoA hydratase functionality including maoC (Park et al., J Bacteriol. 185:5391-5397 (2003)), paaF (Ismail et al., Eur. J Biochem. 270:3047-3054 (2003); Park et al., Appl. Biochem. Biotechnol 113-116:335-346 (2004); Park et al., Biotechnol Bioeng 86:681-686 (2004)) and paaG (Ismail et al., Eur. J Biochem. 270:3047-3054 (2003); Park and Lee, Appl. Biochem. Biotechnol 113-116:335-346 (2004); Park and Yup, Biotechnol Bioeng 86:681-686 (2004)).
Pseudomonas putida
Clostridium acetobutylicum
Clostridium kluyveri
Pseudomonas putida
Pseudomonas putida
Pseudomonas fluorescens
Pseudomonas fluorescens
Escherichia coli
Escherichia coli
Escherichia coli
Alternatively, the E. coli gene products of fadA and fadB encode a multienzyme complex involved in fatty acid oxidation that exhibits enoyl-CoA hydratase activity (Yang et al., Biochemistry 30:6788-6795 (1991); Yang, J Bacteriol. 173:7405-7406 (1991); Nakahigashi et al., Nucleic Acids Res. 18:4937 (1990)). Knocking out a negative regulator encoded by fadR can be utilized to activate the fadB gene product (Sato et al., J Biosci.Bioeng 103:38-44 (2007)). The fadI and fadJ genes encode similar functions and are naturally expressed under anaerobic conditions (Campbell et al., Mol. Microbiol 47:793-805 (2003)).
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
In step J of
Escherichia coli
Haemophilus influenzae
Pseudomonas fluorescens
Bacillus subtilis
Serratia marcescens
Clostridium tetanomorphum
Citrobacter amalonaticus
Clostridium tetani
Escherichia coli
Several characterized enzymes shift the double bond of enoyl-CoA substrates from the 2- to the 3-position. Such a transformation is required in step D of
Clostridium aminobutyricum
Clostridium kluyveri
Porphyromonas gingivalis
Metallosphaera sedula
Escherichia coli
Escherichia coli
Cucumis sativus
The conversion of acyl-CoA substrates to their acid products can be catalyzed by a CoA acid-thiol ligase or CoA synthetase in the 6.2.1 family of enzymes, several of which are reversible. Several reactions shown in
For example, ADP-forming acetyl-CoA synthetase (ACD, EC 6.2.1.13) is an enzyme that couples the conversion of acyl-CoA esters to their corresponding acids with the concomitant synthesis of ATP. ACD I from Archaeoglobus fulgidus, encoded by AF1211, was shown to operate on a variety of linear and branched-chain substrates including isobutyrate, isopentanoate, and fumarate (Musfeldt et al., J Bacteriol. 184:636-644 (2002)). A second reversible ACD in Archaeoglobus fulgidus, encoded by AF1983, was also shown to have a broad substrate range with high activity on cyclic compounds phenylacetate and indoleacetate (Musfeldt and Schonheit, J Bacteriol. 184:636-644 (2002)). The enzyme from Haloarcula marismortui (annotated as a succinyl-CoA synthetase) accepts propionate, butyrate, and branched-chain acids (isovalerate and isobutyrate) as substrates, and was shown to operate in the forward and reverse directions (Brasen et al., Arch Microbiol 182:277-287 (2004)). The ACD encoded by PAE3250 from hyperthermophilic crenarchaeon Pyrobaculum aerophilum showed the broadest substrate range of all characterized ACDs, reacting with acetyl-CoA, isobutyryl-CoA (preferred substrate) and phenylacetyl-CoA (Brasen et al, supra). Directed evolution or engineering can be used to modify this enzyme to operate at the physiological temperature of the host organism. The enzymes from A. fulgidus, H. marismortui and P. aerophilum have all been cloned, functionally expressed, and characterized in E. coli (Brasen and Schonheit, supra; Musfeldt and Schonheit, J Bacteriol. 184:636-644 (2002)). An additional candidate is succinyl-CoA synthetase, encoded by sucCD of E. coli and LSC1 and LSC2 genes of Saccharomyces cerevisiae. These enzymes catalyze the formation of succinyl-CoA from succinate with the concomitant consumption of one ATP in a reaction which is reversible in vivo (Buck et al., Biochemistry 24:6245-6252 (1985)). The acyl CoA ligase from Pseudomonas putida has been demonstrated to work on several aliphatic substrates including acetic, propionic, butyric, valeric, hexanoic, heptanoic, and octanoic acids and on aromatic compounds such as phenylacetic and phenoxyacetic acids (Fernandez-Valverde et al., Appl. Environ. Microbiol. 59:1149-1154 (1993)). A related enzyme, malonyl CoA synthetase (6.3.4.9) from Rhizobium leguminosarum could convert several diacids, namely, ethyl-, propyl-, allyl-, isopropyl-, dimethyl-, cyclopropyl-, cyclopropylmethylene-, cyclobutyl-, and benzyl-malonate into their corresponding monothioesters (Pohl et al., J. Am. Chem. Soc. 123:5822-5823 (2001)).
Archaeoglobus fulgidus
Archaeoglobus fulgidus
Haloarcula marismortui
Pyrobaculum aerophilum str.
Escherichia coli
Escherichia coli
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Pseudomonas putida
Rhizobium leyuminosarum
Another candidate enzyme for these steps is 6-carboxyhexanoate-CoA ligase, also known as pimeloyl-CoA ligase (EC 6.2.1.14), which naturally activates pimelate to pimeloyl-CoA during biotin biosynthesis in gram-positive bacteria. The enzyme from Pseudomonas mendocina, cloned into E. coli, was shown to accept the alternate substrates hexanedioate and nonanedioate (Binieda et al., Biochem. J 340 (Pt 3):793-801 (1999)). Other candidates are found in Bacillus subtilis (Bower et al., J Bacteriol. 178:4122-4130 (1996)) and Lysinibacillus sphaericus (formerly Bacillus sphaericus) (Ploux et al., Biochem. J 287 (Pt 3):685-690 (1992)).
Bacillus subtilis
Pseudomonas mendocina
Bacillus sphaericus
Additional CoA-ligases include the rat dicarboxylate-CoA ligase for which the sequence is yet uncharacterized (Vamecq et al., Biochem. J 230:683-693 (1985)), either of the two characterized phenylacetate-CoA ligases from P. chrysogenum (Lamas-Maceiras et al., Biochem.J395:147-155 (2006); Wang et al., 360:453-458 (2007)), the phenylacetate-CoA ligase from Pseudomonas putida (Martinez-Blanco et al., J Biol Chem 265:7084-7090 (1990)) and the 6-carboxyhexanoate-CoA ligase from Bacillus subtilis (Bower et al. J Bacteriol 178(14):4122-4130 (1996)). Acetoacetyl-CoA synthetases from Mus musculus (Hasegawa et al., Biochim Biophys Acta 1779:414-419 (2008)) and Homo sapiens (Ohgami et al., Biochem. Pharmacol. 65:989-994 (2003)) naturally catalyze the ATP-dependent conversion of acetoacetate into acetoacetyl-CoA.
Penicillium chrysoyenum
Penicillium chrysoyenum
Pseudomonas putida
Bacillus subtilis
Mus musculus
Homo sapiens
Like enzymes in other classes, certain enzymes in the EC class 6.2.1 have been determined to have broad substrate specificity. The acyl CoA ligase from Pseudomonas putida has been demonstrated to work on several aliphatic substrates including acetic, propionic, butyric, valeric, hexanoic, heptanoic, and octanoic acids and on aromatic compounds such as phenylacetic and phenoxyacetic acids (Fernandez-Valverde et al., Applied and Environmental Microbiology 59:1149-1154 (1993)). A related enzyme, malonyl CoA synthetase (6.3.4.9) from Rhizobium trifolii could convert several diacids, namely, ethyl-, propyl-, allyl-, isopropyl-, dimethyl-, cyclopropyl-, cyclopropylmethylene-, cyclobutyl-, and benzyl-malonate into their corresponding monothioesters (Pohl et al., J. Am. Chem. Soc. 123:5822-5823 (2001)).
In step Q of
Clostridium sp. SS2/1
Anaerostipes caccae DSM 14662
Pseudoramibacter alactolyticus
Peptoniphilus harei
Fusobacterium gonidiaformans
Fusobacterium nucleatum
Pseudoramibacter alactolyticus
Carboxydothermus
hydrogenoformans
Eubacterium yurii
Alcohols can be converted to olefins by reaction with a suitable dehydration catalyst under appropriate conditions. Typical dehydration catalysts that convert alcohols such as butanols and pentanols into olefins include various acid treated and untreated alumina (e.g., γ-alumina) and silica catalysts and clays including zeolites (e.g., β-type zeolites, ZSM-5 or Y-type zeolites, fluoride-treated β-zeolite catalysts, fluoride-treated clay catalysts, etc.), sulfonic acid resins (e.g., sulfonated styrenic resins such as Amberlyst® 15), strong acids such as phosphoric acid and sulfuric acid, Lewis acids such boron trifluoride and aluminum trichloride, and many different types of metal salts including metal oxides (e.g., zirconium oxide or titanium dioxide) and metal chlorides (e.g., Latshaw B E, Dehydration of Isobutanol to Isobutylene in a Slurry Reactor, Department of Energy Topical Report, February 1994).
Dehydration reactions can be carried out in both gas and liquid phases with both heterogeneous and homogeneous catalyst systems in many different reactor configurations. Typically, the catalysts used are stable to the water that is generated by the reaction. The water is usually removed from the reaction zone with the product. The resulting alkene(s) either exit the reactor in the gas or liquid phase (e.g., depending upon the reactor conditions) and are captured by a downstream purification process or are further converted in the reactor to other compounds (such as butadiene or isoprene) as described herein. The water generated by the dehydration reaction exits the reactor with unreacted alcohol and alkene product(s) and is separated by distillation or phase separation. Because water is generated in large quantities in the dehydration step, the dehydration catalysts used are generally tolerant to water and a process for removing the water from substrate and product may be part of any process that contains a dehydration step. For this reason, it is possible to use wet (i.e., up to about 95% or 98% water by weight) alcohol as a substrate for a dehydration reaction and remove this water with the water generated by the dehydration reaction (e.g., using a zeolite catalyst as described U.S. Pat. Nos. 4,698,452 and 4,873,392). Additionally, neutral alumina and zeolites will dehydrate alcohols to alkenes but generally at higher temperatures and pressures than the acidic versions of these catalysts.
Dehydration of 1,3-butaediol to 3-buten-1-ol and butadiene is known in the art. For example, 3-buten-1-ol is synthesized from 1,3-butanediol by heating the diol in the presence of a trivalent metal sulfate to a temperature in the range of 70-100 degrees Celcius (U.S. Pat. No. 4,400,562). The dehydration of 1,3-butanediol to butadiene entails, for example, heating 1,3-butanediol in the presence of superheated steam and a phosphate-phosphoric acid catalyst (Sato, et al, Catalysis Communications, 5 (8), 2004, p. 397-400). Dehydration of 3-buten-1-ol to butadiene is also well known in the art (Gustay. Egloff and George. Hulla, Chem. Rev., 1945, 36 (1), pp 63-141).
Enzymes of the reductive TCA cycle useful in the non-naturally occurring microbial organisms of the present invention include one or more of ATP-citrate lyase and three CO2-fixing enzymes: isocitrate dehydrogenase, alpha-ketoglutarate:ferredoxin oxidoreductase, pyruvate:ferredoxin oxidoreductase. The presence of ATP-citrate lyase or citrate lyase and alpha-ketoglutarate:ferredoxin oxidoreductase indicates the presence of an active reductive TCA cycle in an organism. Enzymes for each step of the reductive TCA cycle are shown below.
ATP-citrate lyase (ACL, EC 2.3.3.8), also called ATP citrate synthase, catalyzes the ATP-dependent cleavage of citrate to oxaloacetate and acetyl-CoA. ACL is an enzyme of the RTCA cycle that has been studied in green sulfur bacteria Chlorobium limicola and Chlorobium tepidum. The alpha(4)beta(4) heteromeric enzyme from Chlorobium limicola was cloned and characterized in E. coli (Kanao et al., Eur. J. Biochem. 269:3409-3416 (2002). The C. limicola enzyme, encoded by aclAB, is irreversible and activity of the enzyme is regulated by the ratio of ADP/ATP. A recombinant ACL from Chlorobium tepidum was also expressed in E. coli and the holoenzyme was reconstituted in vitro, in a study elucidating the role of the alpha and beta subunits in the catalytic mechanism (Kim and Tabita, J. Bacteriol. 188:6544-6552 (2006). ACL enzymes have also been identified in Balnearium lithotrophicum, Sulfurihydrogenibium subterraneum and other members of the bacterial phylum Aquificae (Hugler et al., Environ. Microbiol. 9:81-92 (2007)). This acitivy has been reported in some fungi as well. Exemplary organisms include Sordaria macrospora (Nowrousian et al., Curr. Genet. 37:189-93 (2000), Aspergillus nidulans, Yarrowia lipolytica (Hynes and Murray, Eukaryotic Cell, July: 1039-1048, (2010) and Aspergillus niger (Meyer et al. J. Ind. Microbiol. Biotechnol. 36:1275-1280 (2009). Other candidates can be found based on sequence homology. Information related to these enzymes is tabulated below:
Chlorobium limicola
Chlorobium limicola
Chlorobium tepidum
Chlorobium tepidum
Balnearium lithotrophicum
Balnearium lithotrophicum
Sulfurihydrogenibium
subterraneum
Sulfurihydrogenibium
subterraneum
Sulfurimonas denitrificans
Sulfurimonas denitrificans
Yarrowia lipolytica
Yarrowia lipolytica
Schizosaccharomyces pombe
Schizosaccharomyces pombe
Sordaria macrospora
Sordaria macrospora
Aspergillus nidulans
Aspergillus nidulans
In some organisms the conversion of citrate to oxaloacetate and acetyl-CoA proceeds through a citryl-CoA intermediate and is catalyzed by two separate enzymes, citryl-CoA synthetase (EC 6.2.1.18) and citryl-CoA lyase (EC 4.1.3.34) (Aoshima, M., Appl. Microbiol. Biotechnol. 75:249-255 (2007). Citryl-CoA synthetase catalyzes the activation of citrate to citryl-CoA. The Hydrogenobacter thermophilus enzyme is composed of large and small subunits encoded by ccsA and ccsB, respectively (Aoshima et al., Mol. Micrbiol. 52:751-761 (2004)). The citryl-CoA synthetase of Aquifex aeolicus is composed of alpha and beta subunits encoded by sucCl and sucDl (Hugler et al., Environ. Microbiol. 9:81-92 (2007)). Citryl-CoA lyase splits citryl-CoA into oxaloacetate and acetyl-CoA. This enzyme is a homotrimer encoded by ccl in Hydrogenobacter thermophilus (Aoshima et al., Mol. Microbiol. 52:763-770 (2004)) and aq 150 in Aquifex aeolicus (Hugler et al., supra (2007)). The genes for this mechanism of converting citrate to oxaloacetate and citryl-CoA have also been reported recently in Chlorobium tepidum (Eisen et al., PNAS 99(14): 9509-14 (2002).
Hydrogenobacter thermophilus
Hydrogenobacter thermophilus
Aquifex aeolicus
Aquifex aeolicus
Hydrogenobacter thermophilus
Aquifex aeolicus
Chlorobium tepidum
Chlorobium tepidum
Chlorobium tepidum
Oxaloacetate is converted into malate by malate dehydrogenase (EC 1.1.1.37), an enzyme which functions in both the forward and reverse direction. S. cerevisiae possesses three copies of malate dehydrogenase, MDH1 (McAlister-Henn and Thompson, J. Bacteriol. 169:5157-5166 (1987), MDH2 (Minard and McAlister-Henn, Mol. Cell. Biol. 11:370-380 (1991); Gibson and McAlister-Henn, J. Biol. Chem. 278:25628-25636 (2003)), and MDH3 (Steffan and McAlister-Henn, J. Biol. Chem. 267:24708-24715 (1992)), which localize to the mitochondrion, cytosol, and peroxisome, respectively. E. coli is known to have an active malate dehydrogenase encoded by mdh.
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Escherichia coli
Fumarate hydratase (EC 4.2.1.2) catalyzes the reversible hydration of fumarate to malate. The three fumarases of E. coli, encoded by fumA, fumB and fumC, are regulated under different conditions of oxygen availability. FumB is oxygen sensitive and is active under anaerobic conditions. FumA is active under microanaerobic conditions, and FumC is active under aerobic growth conditions (Tseng et al., J. Bacteriol. 183:461-467 (2001); Woods et al., Biochim. Biophys. Acta 954:14-26 (1988); Guest et al., J. Gen. Microbiol. 131:2971-2984 (1985)). S. cerevisiae contains one copy of a fumarase-encoding gene, FUM1, whose product localizes to both the cytosol and mitochondrion (Sass et al., J. Biol. Chem. 278:45109-45116 (2003)). Additional fumarase enzymes are found in Campylobacter jejuni (Smith et al., Int. J. Biochem. Cell. Biol. 31:961-975 (1999)), Thermus thermophilus (Mizobata et al., Arch. Biochem. Biophys. 355:49-55 (1998)) and Rattus norvegicus (Kobayashi et al., J. Biochem. 89:1923-1931 (1981)). Similar enzymes with high sequence homology include fum1 from Arabidopsis thaliana and fumC from Corynebacterium glutamicum. The MmcBC fumarase from Pelotomaculum thermopropionicum is another class of fumarase with two subunits (Shimoyama et al., FEMS Microbiol. Lett. 270:207-213 (2007)).
Escherichia coli
Escherichia coli
Escherichia coli
Saccharomyces cerevisiae
Corynebacterium glutamicum
Campylobacter jejuni
Thermus thermophilus
Rattus norvegicus
Pelotomaculum
thermopropionicum
Pelotomaculum
thermopropionicum
Fumarate reductase catalyzes the reduction of fumarate to succinate. The fumarate reductase of E. coli, composed of four subunits encoded by frdABCD, is membrane-bound and active under anaerobic conditions. The electron donor for this reaction is menaquinone and the two protons produced in this reaction do not contribute to the proton gradient (Iverson et al., Science 284:1961-1966 (1999)). The yeast genome encodes two soluble fumarate reductase isozymes encoded by FRDS1 (Enomoto et al., DNA Res. 3:263-267 (1996)) and FRDS2 (Muratsubaki et al., Arch. Biochem. Biophys. 352:175-181 (1998)), which localize to the cytosol and promitochondrion, respectively, and are used during anaerobic growth on glucose (Arikawa et al., FEMS Microbiol. Lett. 165:111-116 (1998)).
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
The ATP-dependent acylation of succinate to succinyl-CoA is catalyzed by succinyl-CoA synthetase (EC 6.2.1.5). The product of the LSC1 and LSC2 genes of S. cerevisiae and the sucC and sucD genes of E. coli naturally form a succinyl-CoA synthetase complex that catalyzes the formation of succinyl-CoA from succinate with the concomitant consumption of one ATP, a reaction which is reversible in vivo (Buck et al., Biochemistry 24:6245-6252 (1985)). These proteins are identified below:
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Escherichia coli
Escherichia coli
Alpha-ketoglutarate:ferredoxin oxidoreductase (EC 1.2.7.3), also known as 2-oxoglutarate synthase or 2-oxoglutarate:ferredoxin oxidoreductase (OFOR), forms alpha-ketoglutarate from CO2 and succinyl-CoA with concurrent consumption of two reduced ferredoxin equivalents. OFOR and pyruvate:ferredoxin oxidoreductase (PFOR) are members of a diverse family of 2-oxoacid:ferredoxin (flavodoxin) oxidoreductases which utilize thiamine pyrophosphate, CoA and iron-sulfur clusters as cofactors and ferredoxin, flavodoxin and FAD as electron carriers (Adams et al., Archaea. Adv. Protein Chem. 48:101-180 (1996)). Enzymes in this class are reversible and function in the carboxylation direction in organisms that fix carbon by the RTCA cycle such as Hydrogenobacter thermophilus, Desulfobacter hydrogenophilus and Chlorobium species (Shiba et al. 1985; Evans et al., Proc. Natl. Acad. ScI. U.S.A. 55:92934 (1966); Buchanan, 1971). The two-subunit enzyme from H. thermophilus, encoded by korAB, has been cloned and expressed in E. coli (Yun et al., Biochem. Biophys. Res. Commun. 282:589-594 (2001)). A five subunit OFOR from the same organism with strict substrate specificity for succinyl-CoA, encoded by forDABGE, was recently identified and expressed in E. coli (Yun et al. 2002). The kinetics of CO2 fixation of both H. thermophilus OFOR enzymes have been characterized (Yamamoto et al., Extremophiles 14:79-85 (2010)). A CO2-fixing OFOR from Chlorobium thiosulfatophilum has been purified and characterized but the genes encoding this enzyme have not been identified to date. Enzyme candidates in Chlorobium species can be inferred by sequence similarity to the H. thermophilus genes. For example, the Chlorobium limicola genome encodes two similar proteins. Acetogenic bacteria such as Moorella thermoacetica are predicted to encode two OFOR enzymes. The enzyme encoded by Moth_0034 is predicted to function in the CO2-assimilating direction. The genes associated with this enzyme, Moth_0034 have not been experimentally validated to date but can be inferred by sequence similarity to known OFOR enzymes.
OFOR enzymes that function in the decarboxylation direction under physiological conditions can also catalyze the reverse reaction. The OFOR from the thermoacidophilic archaeon Sulfolobus sp. strain 7, encoded by ST2300, has been extensively studied (Zhang et al. 1996. A plasmid-based expression system has been developed for efficiently expressing this protein in E. coli (Fukuda et al., Eur. J. Biochem. 268:5639-5646 (2001)) and residues involved in substrate specificity were determined (Fukuda and Wakagi, Biochim. Biophys. Acta 1597:74-80 (2002)). The OFOR encoded by Ape1472/Ape1473 from Aeropyrum pernix str. K1 was recently cloned into E. coli, characterized, and found to react with 2-oxoglutarate and a broad range of 2-oxoacids (Nishizawa et al., FEBS Lett. 579:2319-2322 (2005)). Another exemplary OFOR is encoded by oorDABC in Helicobacter pylori (Hughes et al. 1998). An enzyme specific to alpha-ketoglutarate has been reported in Thauera aromatica (Dorner and Boll, J, Bacteriol. 184 (14), 3975-83 (2002). A similar enzyme can be found in Rhodospirillum rubrum by sequence homology. A two subunit enzyme has also been identified in Chlorobium tepidum (Eisen et al., PNAS 99(14): 9509-14 (2002)).
Hydrogenobacter thermophilus
Hydrogenobacter thermophilus
Hydrogenobacter thermophilus
Hydrogenobacter thermophilus
Hydrogenobacter thermophilus
Hydrogenobacter thermophilus
Hydrogenobacter thermophilus
Chlorobium limicola
Chlorobium limicola
Chlorobium limicola
Chlorobium limicola
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Sulfolobus sp. strain 7
Aeropyrum pernix
Aeropyrum pernix
Helicobacter pylori
Helicobacter pylori
Helicobacter pylori
Helicobacter pylori
Chlorobium tepidum
Chlorobium tepidum
Thauera aromatica
Thauera aromatica
Rhodospirillum rubrum
Rhodospirillum rubrum
Isocitrate dehydrogenase catalyzes the reversible decarboxylation of isocitrate to 2-oxoglutarate coupled to the reduction of NAD(P)+. IDH enzymes in Saccharomyces cerevisiae and Escherichia coli are encoded by IDP1 and icd, respectively (Haselbeck and McAlister-Henn, J. Biol. Chem. 266:2339-2345 (1991); Nimmo, H. G., Biochem. J. 234:317-2332 (1986)). The reverse reaction in the reductive TCA cycle, the reductive carboxylation of 2-oxoglutarate to isocitrate, is favored by the NADPH-dependent CO2-fixing IDH from Chlorobium limicola and was functionally expressed in E. coli (Kanao et al., Eur. J Biochem. 269:1926-1931 (2002)). A similar enzyme with 95% sequence identity is found in the C. tepidum genome in addititon to some other candidates listed below.
Escherichia coli
Saccharomyces cerevisiae
Chlorobium limicola
Chlorobium tepidum
Geobacter sulfurreducens
Sulfurimonas denitrificans
In H. thermophilus the reductive carboxylation of 2-oxoglutarate to isocitrate is catalyzed by two enzymes: 2-oxoglutarate carboxylase and oxalosuccinate reductase. 2-Oxoglutarate carboxylase (EC 6.4.1.7) catalyzes the ATP-dependent carboxylation of alpha-ketoglutarate to oxalosuccinate (Aoshima and Igarashi, Mol. Microbiol. 62:748-759 (2006)). This enzyme is a large complex composed of two subunits. Biotinylation of the large (A) subunit is required for enzyme function (Aoshima et al., Mol. Microbiol. 51:791-798 (2004)). Oxalosuccinate reductase (EC 1.1.1.-) catalyzes the NAD-dependent conversion of oxalosuccinate to D-threo-isocitrate. The enzyme is a homodimer encoded by icd in H. thermophilus. The kinetic parameters of this enzyme indicate that the enzyme only operates in the reductive carboxylation direction in vivo, in contrast to isocitrate dehydrogenase enzymes in other organisms (Aoshima and Igarashi, J. Bacteriol. 190:2050-2055 (2008)). Based on sequence homology, gene candidates have also been found in Thiobacillus denitrificans and Thermocrinis albus.
Hydrogenobacter
thermophilus
Hydrogenobacter
thermophilus
Hydrogenobacter
thermophilus
Thiobacillus denitrificans
Thiobacillus denitrificans
Thiobacillus denitrificans
Thermocrinis albus
Thermocrinis albus
Thermocrinis albus
Aconitase (EC 4.2.1.3) is an iron-sulfur-containing protein catalyzing the reversible isomerization of citrate and iso-citrate via the intermediate cis-aconitate. Two aconitase enzymes are encoded in the E. coli genome by acnA and acnB. AcnB is the main catabolic enzyme, while AcnA is more stable and appears to be active under conditions of oxidative or acid stress (Cunningham et al., Microbiology 143 (Pt 12):3795-3805 (1997)). Two isozymes of aconitase in Salmonella typhimurium are encoded by acnA and acnB (Horswill and Escalante-Semerena, Biochemistry 40:4703-4713 (2001)). The S. cerevisiae aconitase, encoded by ACO1, is localized to the mitochondria where it participates in the TCA cycle (Gangloff et al., Mol. Cell. Biol. 10:3551-3561 (1990)) and the cytosol where it participates in the glyoxylate shunt (Regev-Rudzki et al., Mol. Biol. Cell. 16:4163-4171 (2005)).
Escherichia coli
Escherichia coli
Salmonella typhimurium
Helicobacter pylori 26695
Ralstonia eutropha
Desulfovibrio fructosovorans JJ
Sulfurimonas denitrificans
Hydrogenobacter thermophilus
Chlorobium tepidum
Chlorobium limicola
Chlorobium limicola
Salmonella typhimurium
Saccharomyces cerevisiae
Pyruvate:ferredoxin oxidoreductase (PFOR) catalyzes the reversible oxidation of pyruvate to form acetyl-CoA. The PFOR from Desulfovibrio africanus has been cloned and expressed in E. coli resulting in an active recombinant enzyme that was stable for several days in the presence of oxygen (Pieulle et al., J. Bacteriol. 179:5684-5692 (1997)). Oxygen stability is relatively uncommon in PFORs and is believed to be conferred by a 60 residue extension in the polypeptide chain of the D. africanus enzyme. Two cysteine residues in this enzyme form a disulfide bond that prtotects it against inactivation in the form of oxygen. This disulfide bond and the stability in the presence of oxygen has been found in other Desulfovibrio species also (Vita et al., Biochemistry, 47: 957-64 (2008)). The M. thermoacetica PFOR is also well characterized (Menon and Ragsdale, Biochemistry 36:8484-8494 (1997)) and was shown to have high activity in the direction of pyruvate synthesis during autotrophic growth (Furdui and Ragsdale, J. Biol. Chem. 275:28494-28499 (2000)). Further, E. coli possesses an uncharacterized open reading frame, ydbK, encoding a protein that is 51% identical to the M. thermoacetica PFOR. Evidence for pyruvate oxidoreductase activity in E. coli has been described (Blaschkowski et al., Eur. J. Biochem. 123:563-569 (1982)). PFORs have also been described in other organisms, including Rhodobacter capsulatas (Yakunin and Hallenbeck, Biochimica et Biophysica Acta 1409 (1998) 39-49 (1998)) and Choloboum tepidum (Eisen et al., PNAS 99(14): 9509-14 (2002)). The five subunit PFOR from H. thermophilus, encoded by porEDABG, was cloned into E. coli and shown to function in both the decarboxylating and CO2-assimilating directions (Ikeda et al. 2006; Yamamoto et al., Extremophiles 14:79-85 (2010)). Homologs also exist in C. carboxidivorans P7. Several additional PFOR enzymes are described in the following review (Ragsdale, S. W., Chem. Rev. 103:2333-2346 (2003)). Finally, flavodoxin reductases (e.g., fqrB from Helicobacter pylori or Campylobacter jejuni) (St Maurice et al., J. Bacteriol. 189:4764-4773 (2007)) or Rnf-type proteins (Seedorf et al., Proc. Natl. Acad. Sci. U.S.A. 105:2128-2133 (2008); and Herrmann, J. Bacteriol 190:784-791 (2008)) provide a means to generate NADH or NADPH from the reduced ferredoxin generated by PFOR. These proteins are identified below.
Desulfovibrio fructosovorans JJ
Desulfovibrio africanus
Desulfovibrio vulgaris str.
DesulfoVibrio desulfuricans
Desulfovibrio desulfuricans
Moorella thermoacetica
Escherichia coli
Chlorobium tepidum
Campylobacter jejuni
Rhodobacter capsulatus
Hydrogenobacter
thermophilus
Hydrogenobacter
thermophilus
Hydrogenobacter
thermophilus
Hydrogenobacter
thermophilus
Hydrogenobacter
thermophilus
Campylobacter jejuni
Helicobacter pylori
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
The conversion of pyruvate into acetyl-CoA can be catalyzed by several other enzymes or their combinations thereof. For example, pyruvate dehydrogenase can transform pyruvate into acetyl-CoA with the concomitant reduction of a molecule of NAD into NADH. It is a multi-enzyme complex that catalyzes a series of partial reactions which results in acylating oxidative decarboxylation of pyruvate. The enzyme comprises of three subunits: the pyruvate decarboxylase (E1), dihydrolipoamide acyltransferase (E2) and dihydrolipoamide dehydrogenase (E3). This enzyme is naturally present in several organisms, including E. coli and S. cerevisiae. In the E. coli enzyme, specific residues in the E1 component are responsible for substrate specificity (Bisswanger, H., J. Biol. Chem. 256:815-82 (1981); Bremer, J., Eur. J. Biochem. 8:535-540 (1969); Gong et al., J. Biol. Chem. 275:13645-13653 (2000)). Enzyme engineering efforts have improved the E. coli PDH enzyme activity under anaerobic conditions (Kim et al., J. Bacteriol. 190:3851-3858 (2008); Kim et al., Appl. Environ. Microbiol. 73:1766-1771 (2007); Zhou et al., Biotechnol. Lett. 30:335-342 (2008)). In contrast to the E. coli PDH, the B. subtilis complex is active and required for growth under anaerobic conditions (Nakano et al., J. Bacteriol. 179:6749-6755 (1997)). The Klebsiella pneumoniae PDH, characterized during growth on glycerol, is also active under anaerobic conditions (5). Crystal structures of the enzyme complex from bovine kidney (18) and the E2 catalytic domain from Azotobacter vinelandii are available (4). Yet another enzyme that can catalyze this conversion is pyruvate formate lyase. This enzyme catalyzes the conversion of pyruvate and CoA into acetyl-CoA and formate. Pyruvate formate lyase is a common enzyme in prokaryotic organisms that is used to help modulate anaerobic redox balance. Exemplary enzymes can be found in Escherichia coli encoded by pflB (Knappe and Sawers, FEMS. Microbiol Rev. 6:383-398 (1990)), Lactococcus lactis (Melchiorsen et al., Appl Microbiol Biotechnol 58:338-344 (2002)), and Streptococcus mutans (Takahashi-Abbe et al., Oral.Microbiol Immunol. 18:293-297 (2003)). E. coli possesses an additional pyruvate formate lyase, encoded by tdcE, that catalyzes the conversion of pyruvate or 2-oxobutanoate to acetyl-CoA or propionyl-CoA, respectively (Hesslinger et al., Mol. Microbiol 27:477-492 (1998)). Both pflB and tdcE from E. coli require the presence of pyruvate formate lyase activating enzyme, encoded by pflA. Further, a short protein encoded by yfiD in E. coli can associate with and restore activity to oxygen-cleaved pyruvate formate lyase (Vey et al., Proc.Natl. Acad. Sci. U.S.A. 105:16137-16141 (2008). Note that pflA and pflB from E. coli were expressed in S. cerevisiae as a means to increase cytosolic acetyl-CoA for butanol production as described in WO/2008/080124]. Additional pyruvate formate lyase and activating enzyme candidates, encoded by pfl and act, respectively, are found in Clostridium pasteurianum (Weidner et al., J Bacteriol. 178:2440-2444 (1996)).
Further, different enzymes can be used in combination to convert pyruvate into acetyl-CoA. For example, in S. cerevisiae, acetyl-CoA is obtained in the cytosol by first decarboxylating pyruvate to form acetaldehyde; the latter is oxidized to acetate by acetaldehyde dehydrogenase and subsequently activated to form acetyl-CoA by acetyl-CoA synthetase. Acetyl-CoA synthetase is a native enzyme in several other organisms including E. coli (Kumari et al., J. Bacteriol. 177:2878-2886 (1995)), Salmonella enterica (Starai et al., Microbiology 151:3793-3801 (2005); Starai et al., J. Biol. Chem. 280:26200-26205 (2005)), and Moorella thermoacetica (described already). Alternatively, acetate can be activated to form acetyl-CoA by acetate kinase and phosphotransacetylase. Acetate kinase first converts acetate into acetyl-phosphate with the accompanying use of an ATP molecule. Acetyl-phosphate and CoA are next converted into acetyl-CoA with the release of one phosphate by phosphotransacetylase. Both acetate kinase and phosphotransacetlyase are well-studied enzymes in several Clostridia and Methanosarcina thermophila.
Yet another way of converting pyruvate to acetyl-CoA is via pyruvate oxidase. Pyruvate oxidase converts pyruvate into acetate, using ubiquione as the electron acceptor. In E. coli, this activity is encoded by poxB. PoxB has similarity to pyruvate decarboxylase of S. cerevisiae and Zymomonas mobilis. The enzyme has a thiamin pyrophosphate cofactor (Koland and Gennis, Biochemistry 21:4438-4442 (1982)); O'Brien et al., Biochemistry 16:3105-3109 (1977); O'Brien and Gennis, J. Biol. Chem. 255:3302-3307 (1980)) and a flavin adenine dinucleotide (FAD) cofactor. Acetate can then be converted into acetyl-CoA by either acetyl-CoA synthetase or by acetate kinase and phosphotransacetylase, as described earlier. Some of these enzymes can also catalyze the reverse reaction from acetyl-CoA to pyruvate.
For enzymes that use reducing equivalents in the form of NADH or NADPH, these reduced carriers can be generated by transferring electrons from reduced ferredoxin. Two enzymes catalyze the reversible transfer of electrons from reduced ferredoxins to NAD(P)+, ferredoxin:NAD+ oxidoreductase (EC 1.18.1.3) and ferredoxin:NADP+ oxidoreductase (FNR, EC 1.18.1.2). Ferredoxin:NADP+ oxidoreductase (FNR, EC 1.18.1.2) has a noncovalently bound FAD cofactor that facilitates the reversible transfer of electrons from NADPH to low-potential acceptors such as ferredoxins or flavodoxins (Blaschkowski et al., Eur. J. Biochem. 123:563-569 (1982); Fujii et al., 1977). The Helicobacter pylori FNR, encoded by HP1164 (fqrB), is coupled to the activity of pyruvate:ferredoxin oxidoreductase (PFOR) resulting in the pyruvate-dependent production of NADPH (St et al. 2007). An analogous enzyme is found in Campylobacter jejuni (St et al. 2007). A ferredoxin:NADP+ oxidoreductase enzyme is encoded in the E. coli genome by fpr (Bianchi et al. 1993). Ferredoxin:NAD+ oxidoreductase utilizes reduced ferredoxin to generate NADH from NAD+. In several organisms, including E. coli, this enzyme is a component of multifunctional dioxygenase enzyme complexes. The ferredoxin:NAD+ oxidoreductase of E. coli, encoded by hcaD, is a component of the 3-phenylproppionate dioxygenase system involved in involved in aromatic acid utilization (Diaz et al. 1998). NADH:ferredoxin reductase activity was detected in cell extracts of Hydrogenobacter thermophilus strain TK-6, although a gene with this activity has not yet been indicated (Yoon et al. 2006). Finally, the energy-conserving membrane-associated Rnf-type proteins (Seedorf et al., Proc. Natl. Acad. Sci. U.S.A. 105:2128-2133 (2008); Herrmann et al., J. Bacteriol. 190:784-791 (2008)) provide a means to generate NADH or NADPH from reduced ferredoxin. Additional ferredoxin:NAD(P)+ oxidoreductases have been annotated in Clostridium carboxydivorans P7.
Helicobacter pylori
Rhodopseudomonas palustris
Hydrogenobacter
thermophilus
Bacillus subtilis
Campylobacter jejuni
Escherichia coli
Escherichia coli
Zea mays
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
Clostridium kluyveri
Clostridiu
carboxidivoran sP7
Clostridium
carboxidivorans P7
Clostridium
carboxidivorans P7
Clostridium
carboxidivorans P7
Clostridium
carboxidivorans P7
Clostridium
carboxidivorans P7
Ferredoxins are small acidic proteins containing one or more iron-sulfur clusters that function as intracellular electron carriers with a low reduction potential. Reduced ferredoxins donate electrons to Fe-dependent enzymes such as ferredoxin-NADP+ oxidoreductase, pyruvate:ferredoxin oxidoreductase (PFOR) and 2-oxoglutarate:ferredoxin oxidoreductase (OFOR). The H. thermophilus gene fdx1 encodes a [4Fe-4S]-type ferredoxin that is required for the reversible carboxylation of 2-oxoglutarate and pyruvate by OFOR and PFOR, respectively (Yamamoto et al., Extremophiles 14:79-85 (2010)). The ferredoxin associated with the Sulfolobus solfataricus 2-oxoacid:ferredoxin reductase is a monomeric dicluster [3Fe-4S][4Fe-4S] type ferredoxin (Park et al. 2006). While the gene associated with this protein has not been fully sequenced, the N-terminal domain shares 93% homology with the zfx ferredoxin from S. acidocaldarius. The E. coli genome encodes a soluble ferredoxin of unknown physiological function, fdx. Some evidence indicates that this protein can function in iron-sulfur cluster assembly (Takahashi and Nakamura, 1999). Additional ferredoxin proteins have been characterized in Helicobacter pylori (Mukhopadhyay et al. 2003) and Campylobacter jejuni (van Vliet et al. 2001). A 2Fe-2S ferredoxin from Clostridium pasteurianum has been cloned and expressed in E. coli (Fujinaga and Meyer, Biochemical and Biophysical Research Communications, 192(3): (1993)). Acetogenic bacteria such as Moorella thermoacetica, Clostridium carboxidivorans P7 and Rhodospirillum rubrum are predicted to encode several ferredoxins, listed in the table below.
Hydrogenobacter thermophilus
Clostridium pasteurianum
Sulfolobus acidocalarius
Escherichia coli
Helicobacter pylori
Campylobacter jejuni
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Clostridium carboxidivorans
Clostridium carboxidivorans
Clostridium carboxidivorans
Clostridium carboxidivorans
Clostridium carboxidivorans
Clostridium carboxidivorans
Carboxydothermus
hydrogenoformans
Rhodobacter capsulatus
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Allochromatium vinosum DSM
Azotobacter vinelandii DJ
Clostridium kluyveri DSM 555
Rhodopseudomonas palustris
Thauera aromatica
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Bacillus subtilis
Pseudomonas aeruginosa PA01
Escherichia coli K-12
Succinyl-CoA transferase catalyzes the conversion of succinyl-CoA to succinate while transferring the CoA moiety to a CoA acceptor molecule. Many transferases have broad specificity and can utilize CoA acceptors as diverse as acetate, succinate, propionate, butyrate, 2-methylacetoacetate, 3-ketohexanoate, 3-ketopentanoate, valerate, crotonate, 3-mercaptopropionate, propionate, vinylacetate, and butyrate, among others.
The conversion of succinate to succinyl-CoA can be carried by a transferase which does not require the direct consumption of an ATP or GTP. This type of reaction is common in a number of organisms. The conversion of succinate to succinyl-CoA can also be catalyzed by succinyl-CoA:Acetyl-CoA transferase. The gene product of cat1 of Clostridium kluyveri has been shown to exhibit succinyl-CoA: acetyl-CoA transferase activity (Sohling and Gottschalk, J. Bacteriol. 178:871-880 (1996)). In addition, the activity is present in Trichomonas vaginalis (van Grinsven et al. 2008) and Trypanosoma brucei (Riviere et al. 2004). The succinyl-CoA:acetate CoA-transferase from Acetobacter aceti, encoded by aarC, replaces succinyl-CoA synthetase in a variant TCA cycle (Mullins et al. 2008). Similar succinyl-CoA transferase activities are also present in Trichomonas vaginalis (van Grinsven et al. 2008), Trypanosoma brucei (Riviere et al. 2004) and Clostridium kluyveri (Sohling and Gottschalk, 1996c). The beta-ketoadipate:succinyl-CoA transferase encoded by pcaI and pcaJ in Pseudomonas putida is yet another candidate (Kaschabek et al. 2002). The aforementioned proteins are identified below.
Clostridium kluyveri
Trichomonas
vaginalis G3
Trypanosoma brucei
Pseudomonas putida
Pseudomonas putida
Acetobacter aceti
An additional exemplary transferase that converts succinate to succinyl-CoA while converting a 3-ketoacyl-CoA to a 3-ketoacid is succinyl-CoA:3:ketoacid-CoA transferase (EC 2.8.3.5). Exemplary succinyl-CoA:3:ketoacid-CoA transferases are present in Helicobacter pylori (Corthesy-Theulaz et al. 1997), Bacillus subtilis, and Homo sapiens (Fukao et al. 2000; Tanaka et al. 2002). The aforementioned proteins are identified below.
Helicobacter pylori
Helicobacter pylori
Bacillus subtilis
Bacillus subtilis
Homo sapiens
Homo sapiens
Converting succinate to succinyl-CoA by succinyl-CoA:3:ketoacid-CoA transferase requires the simultaneous conversion of a 3-ketoacyl-CoA such as acetoacetyl-CoA to a 3-ketoacid such as acetoacetate. Conversion of a 3-ketoacid back to a 3-ketoacyl-CoA can be catalyzed by an acetoacetyl-CoA:acetate:CoA transferase. Acetoacetyl-CoA:acetate:CoA transferase converts acetoacetyl-CoA and acetate to acetoacetate and acetyl-CoA, or vice versa. Exemplary enzymes include the gene products of atoAD from E. coli (Hanai et al., Appl Environ Microbiol 73:7814-7818 (2007), ctfAB from C. acetobutylicum (Jojima et al., Appl Microbiol Biotechnol 77:1219-1224 (2008), and ctfAB from Clostridium saccharoperbutylacetonicum (Kosaka et al., Biosci. Biotechnol Biochem. 71:58-68 (2007)) are shown below.
Escherichia coli
Escherichia coli
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium
saccharoperbutylacetonicum
Clostridium
saccharoperbutylacetonicum
Yet another possible CoA acceptor is benzylsuccinate. Succinyl-CoA:(R)-Benzylsuccinate CoA-Transferase functions as part of an anaerobic degradation pathway for toluene in organisms such as Thauera aromatica (Leutwein and Heider, J. Bact. 183(14) 4288-4295 (2001)). Homologs can be found in Azoarcus sp. T, Aromatoleum aromaticum EbN1, and Geobacter metallireducens GS-15. The aforementioned proteins are identified below.
Thauera aromatic
Thauera aromatic
Azoarcus sp. T
Azoarcus sp. T
Aromatoleum aromaticum
Aromatoleum aromaticum
Geobacter metallireducens
Geobacter metallireducens
Additionally, ygfH encodes a propionyl CoA: succinate CoA transferase in E. coli (Haller et al., Biochemistry, 39(16) 4622-4629). Close homologs can be found in, for example, Citrobacter youngae ATCC 29220, Salmonella enterica subsp. arizonae serovar, and Yersinia intermedia ATCC 29909. The aforementioned proteins are identified below.
Escherichia coli
Citrobacter youngae
Salmonella enterica
serovar
Yersinia intermedia
Citrate lyase (EC 4.1.3.6) catalyzes a series of reactions resulting in the cleavage of citrate to acetate and oxaloacetate. The enzyme is active under anaerobic conditions and is composed of three subunits: an acyl-carrier protein (ACP, gamma), an ACP transferase (alpha), and a acyl lyase (beta). Enzyme activation uses covalent binding and acetylation of an unusual prosthetic group, 2′-(5″-phosphoribosyl)-3-′-dephospho-CoA, which is similar in structure to acetyl-CoA. Acylation is catalyzed by CitC, a citrate lyase synthetase. Two additional proteins, CitG and CitX, are used to convert the apo enzyme into the active holo enzyme (Schneider et al., Biochemistry 39:9438-9450 (2000)). Wild type E. coli does not have citrate lyase activity; however, mutants deficient in molybdenum cofactor synthesis have an active citrate lyase (Clark, FEMS Microbiol. Lett. 55:245-249 (1990)). The E. coli enzyme is encoded by citEFD and the citrate lyase synthetase is encoded by citC (Nilekani and SivaRaman, Biochemistry 22:4657-4663 (1983)). The Leuconostoc mesenteroides citrate lyase has been cloned, characterized and expressed in E. coli (Bekal et al., J. Bacteriol. 180:647-654 (1998)). Citrate lyase enzymes have also been identified in enterobacteria that utilize citrate as a carbon and energy source, including Salmonella typhimurium and Klebsiella pneumoniae (Bott, Arch. Microbiol. 167: 78-88 (1997); Bott and Dimroth, Mol. Microbiol. 14:347-356 (1994)). The aforementioned proteins are tabulated below.
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Leuconostoc mesenteroides
Leuconostoc mesenteroides
Leuconostoc mesenteroides
Leuconostoc mesenteroides
Leuconostoc mesenteroides
Leuconostoc mesenteroides
Salmonella typhimurium
Salmonella typhimurium
Salmonella typhimurium
Salmonella typhimurium
Salmonella typhimurium
Salmonella typhimurium
Klebsiella pneumoniae
Klebsiella pneumoniae
Klebsiella pneumoniae
Klebsiella pneumoniae
Klebsiella pneumoniae
Klebsiella pneumoniae
Acetate kinase (EC 2.7.2.1) catalyzes the reversible ATP-dependent phosphorylation of acetate to acetylphosphate. Exemplary acetate kinase enzymes have been characterized in many organisms including E. coli, Clostridium acetobutylicum and Methanosarcina thermophila (Ingram-Smith et al., J. Bacteriol. 187:2386-2394 (2005); Fox and Roseman, J. Biol. Chem. 261:13487-13497 (1986); Winzer et al., Microbioloy 143 (Pt 10):3279-3286 (1997)). Acetate kinase activity has also been demonstrated in the gene product of E. coli purT (Marolewski et al., Biochemistry 33:2531-2537 (1994). Some butyrate kinase enzymes (EC 2.7.2.7), for example buk1 and buk2 from Clostridium acetobutylicum, also accept acetate as a substrate (Hartmanis, M. G., J. Biol. Chem. 262:617-621 (1987)).
Escherichia coli
Clostridium acetobutylicum
Methanosarcina thermophila
Escherichia coli
Clostridium acetobutylicum
Clostridium acetobutylicum
The formation of acetyl-CoA from acetylphosphate is catalyzed by phosphotransacetylase (EC 2.3.1.8). The pta gene from E. coli encodes an enzyme that reversibly converts acetyl-CoA into acetyl-phosphate (Suzuki, T., Biochim. Biophys. Acta 191:559-569 (969)). Additional acetyltransferase enzymes have been characterized in Bacillus subtilis (Rado and Hoch, Biochim. Biophys. Acta 321:114-125 (1973), Clostridium kluyveri (Stadtman, E., Methods Enzymol. 1:5896-599 (1955), and Thermotoga maritima (Bock et al., J. Bacteriol. 181:1861-1867 (1999)). This reaction is also catalyzed by some phosphotranbutyrylase enzymes (EC 2.3.1.19) including the ptb gene products from Clostridium acetobutylicum (Wiesenborn et al., App. Environ. Microbiol. 55:317-322 (1989); Walter et al., Gene 134:107-111 (1993)). Additional ptb genes are found in butyrate-producing bacterium L2-50 (Louis et al., J. Bacteriol. 186:2099-2106 (2004) and Bacillus megaterium (Vazquez et al., Curr. Microbiol. 42:345-349 (2001).
Escherichia coli
Bacillus subtilis
Clostridium kluyveri
Thermotoga maritima
Clostridium acetobutylicum
Bacillus megaterium
The acylation of acetate to acetyl-CoA is catalyzed by enzymes with acetyl-CoA synthetase activity. Two enzymes that catalyze this reaction are AMP-forming acetyl-CoA synthetase (EC 6.2.1.1) and ADP-forming acetyl-CoA synthetase (EC 6.2.1.13). AMP-forming acetyl-CoA synthetase (ACS) is the predominant enzyme for activation of acetate to acetyl-CoA. Exemplary ACS enzymes are found in E. coli (Brown et al., J. Gen. Microbiol. 102:327-336 (1977)), Ralstonia eutropha (Priefert and Steinbuchel, J. Bacteriol. 174:6590-6599 (1992)), Methanothermobacter thermautotrophicus (Ingram-Smith and Smith, Archaea 2:95-107 (2007)), Salmonella enterica (Gulick et al., Biochemistry 42:2866-2873 (2003)) and Saccharomyces cerevisiae (Jogl and Tong, Biochemistry 43:1425-1431 (2004)). ADP-forming acetyl-CoA synthetases are reversible enzymes with a generally broad substrate range (Musfeldt and Schonheit, J. Bacteriol. 184:636-644 (2002)). Two isozymes of ADP-forming acetyl-CoA synthetases are encoded in the Archaeoglobus fulgidus genome by are encoded by AF1211 and AF1983 (Musfeldt and Schonheit, supra (2002)). The enzyme from Haloarcula marismortui (annotated as a succinyl-CoA synthetase) also accepts acetate as a substrate and reversibility of the enzyme was demonstrated (Brasen and Schonheit, Arch. Microbiol. 182:277-287 (2004)). The ACD encoded by PAE3250 from hyperthermophilic crenarchaeon Pyrobaculum aerophilum showed the broadest substrate range of all characterized ACDs, reacting with acetate, isobutyryl-CoA (preferred substrate) and phenylacetyl-CoA (Brasen and Schonheit, supra (2004)). Directed evolution or engineering can be used to modify this enzyme to operate at the physiological temperature of the host organism. The enzymes from A. fulgidus, H. marismortui and P. aerophilum have all been cloned, functionally expressed, and characterized in E. coli (Brasen and Schonheit, supra (2004); Musfeldt and Schonheit, supra (2002)). Additional candidates include the succinyl-CoA synthetase encoded by sucCD in E. coli (Buck et al., Biochemistry 24:6245-6252 (1985)) and the acyl-CoA ligase from Pseudomonas putida (Fernandez-Valverde et al., Appl. Environ. Microbiol. 59:1149-1154 (1993)). The aforementioned proteins are tabulated below.
Escherichia coli
Ralstonia eutropha
Methanothermobacter
thermautotrophicus
Salmonella enterica
Saccharomyces cerevisiae
Archaeoglobus fulgidus
Archaeoglobus fulgidus
Haloarcula marismortui
Pyrobaculum aerophilum str.
Escherichia coli
Escherichia coli
Pseudomonas putida
The product yields per C-mol of substrate of microbial cells synthesizing reduced fermentation products such as 2,4-pentadienoate, butadiene, 1,3-butanediol or 3-buten-1-ol, are limited by insufficient reducing equivalents in the carbohydrate feedstock. Reducing equivalents, or electrons, can be extracted from synthesis gas components such as CO and H2 using carbon monoxide dehydrogenase (CODH) and hydrogenase enzymes, respectively. The reducing equivalents are then passed to acceptors such as oxidized ferredoxins, oxidized quinones, oxidized cytochromes, NAD(P)+, water, or hydrogen peroxide to form reduced ferredoxin, reduced quinones, reduced cytochromes, NAD(P)H, H2, or water, respectively. Reduced ferredoxin and NAD(P)H are particularly useful as they can serve as redox carriers for various Wood-Ljungdahl pathway and reductive TCA cycle enzymes.
Here, we show specific examples of how additional redox availability from CO and/or H2 can improve the yields of reduced products such as 2,4-pentadienoate, butadiene, 1,3-butanediol or 3-buten-1-ol.
In some embodiments of the invention, a combined feedstock strategy where syngas is combined with a sugar-based feedstock or other carbon substrate can greatly improve the theoretical yields. In this co-feeding appoach, syngas components H2 and CO can be utilized by the hydrogenase and CO dehydrogenase to generate reducing equivalents, that can be used to power chemical production pathways in which the carbons from sugar or other carbon substrates will be maximally conserved and the theoretical yields improved. Such improvements provide environmental and economic benefits and greatly enhance sustainable chemical production.
Herein below the enzymes and the corresponding genes used for extracting redox from synags components are described. CODH is a reversible enzyme that interconverts CO and CO2 at the expense or gain of electrons. The natural physiological role of the CODH in ACS/CODH complexes is to convert CO2 to CO for incorporation into acetyl-CoA by acetyl-CoA synthase. Nevertheless, such CODH enzymes are suitable for the extraction of reducing equivalents from CO due to the reversible nature of such enzymes. Expressing such CODH enzymes in the absence of ACS allows them to operate in the direction opposite to their natural physiological role (i.e., CO oxidation).
In M. thermoacetica, C. hydrogenoformans, C. carboxidivorans P7, and several other organisms, additional CODH encoding genes are located outside of the ACS/CODH operons. These enzymes provide a means for extracting electrons (or reducing equivalents) from the conversion of carbon monoxide to carbon dioxide. The M. thermoacetica gene (Genbank Accession Number: YP_430813) is expressed by itself in an operon and is believed to transfer electrons from CO to an external mediator like ferredoxin in a “Ping-pong” reaction. The reduced mediator then couples to other reduced nicolinamide adenine dinucleotide phosphate (NAD(P)H) carriers or ferredoxin-dependent cellular processes (Ragsdale, Annals of the New York Academy of Sciences 1125: 129-136 (2008)). The genes encoding the C. hydrogenoformans CODH-II and CooF, a neighboring protein, were cloned and sequenced (Gonzalez and Robb, FEMS Microbiol Lett. 191:243-247 (2000)). The resulting complex was membrane-bound, although cytoplasmic fractions of CODH-II were shown to catalyze the formation of NADPH suggesting an anabolic role (Svetlitchnyi et al., J Bacteriol. 183:5134-5144 (2001)). The crystal structure of the CODH-II is also available (Dobbek et al., Science 293:1281-1285 (2001)). Similar ACS-free CODH enzymes can be found in a diverse array of organisms including Geobacter metallireducens GS-15, Chlorobium phaeobacteroides DSM 266, Clostridium cellulolyticum H10, Desulfovibrio desulfuricans subsp. desulfuricans str. ATCC 27774, Pelobacter carbinolicus DSM 2380, and Campylobacter curvus 525.92.
Moorella thermoacetica
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Clostridium carboxidivorans
Clostridium carboxidivorans
Clostridium carboxidivorans
Clostridium carboxidivorans
Geobacter metallireducens GS-
Chlorobium
phaeobacteroides DSM 266
Chlorobium
phaeobacteroides DSM 266
Clostridium cellulolyticum H10
Desulfovibrio desulfuricans
Desulfovibrio desulfuricans
Pelobacter carbinolicus DSM
Pelobacter carbinolicus DSM
Pelobacter carbinolicus DSM
Campylobacter curvus 525.92
In some cases, hydrogenase encoding genes are located adjacent to a CODH. In Rhodospirillum rubrum, the encoded CODH/hydrogenase proteins form a membrane-bound enzyme complex that has been indicated to be a site where energy, in the form of a proton gradient, is generated from the conversion of CO and H2O to CO2 and H2 (Fox et al., J Bacteriol. 178:6200-6208 (1996)). The CODH-J. of C. hydrogenoformans and its adjacent genes have been proposed to catalyze a similar functional role based on their similarity to the R. rubrum CODH/hydrogenase gene cluster (Wu et al., PLoS Genet. 1:e65 (2005)). The C. hydrogenoformans CODH-I was also shown to exhibit intense CO oxidation and CO2 reduction activities when linked to an electrode (Parkin et al., J Am. Chem. Soc. 129:10328-10329 (2007)). The protein sequences of exemplary CODH and hydrogenase genes can be identified by the following GenBank accession numbers.
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Carboxydothermus
hydrogenoformans
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Rhodospirillum rubrum
Native to E. coli and other enteric bacteria are multiple genes encoding up to four hydrogenases (Sawers, G., Antonie Van Leeuwenhoek 66:57-88 (1994); Sawers et al., J Bacteriol. 164:1324-1331 (1985); Sawers and Boxer, Eur. J Biochem. 156:265-275 (1986); Sawers et al., J Bacteriol. 168:398-404 (1986)). Given the multiplicity of enzyme activities, E. coli or another host organism can provide sufficient hydrogenase activity to split incoming molecular hydrogen and reduce the corresponding acceptor. E. coli possesses two uptake hydrogenases, Hyd-1 and Hyd-2, encoded by the hyaABCDEF and hybOABCDEFG gene clusters, respectively (Lukey et al., How E. coli is equipped to oxidize hydrogen under different redox conditions, J Biol Chem published online Nov. 16, 2009). Hyd-1 is oxygen-tolerant, irreversible, and is coupled to quinone reduction via the hyaC cytochrome. Hyd-2 is sensitive to O2, reversible, and transfers electrons to the periplasmic ferredoxin hybA which, in turn, reduces a quinone via the hybB integral membrane protein. Reduced quinones can serve as the source of electrons for fumarate reductase in the reductive branch of the TCA cycle. Reduced ferredoxins can be used by enzymes such as NAD(P)H:ferredoxin oxidoreductases to generate NADPH or NADH. They can alternatively be used as the electron donor for reactions such as pyruvate ferredoxin oxidoreductase, AKG ferredoxin oxidoreductase, and 5,10-methylene-H4folate reductase.
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
The hydrogen-lyase systems of E. coli include hydrogenase 3, a membrane-bound enzyme complex using ferredoxin as an acceptor, and hydrogenase 4 that also uses a ferredoxin acceptor. Hydrogenase 3 and 4 are encoded by the hyc and hyf gene clusters, respectively. Hydrogenase 3 has been shown to be a reversible enzyme (Maeda et al., Appl Microbiol Biotechnol 76(5):1035-42 (2007)). Hydrogenase activity in E. coli is also dependent upon the expression of the hyp genes whose corresponding proteins are involved in the assembly of the hydrogenase complexes (Jacobi et al., Arch. Microbiol 158:444-451 (1992); Rangarajan et al., J. Bacteriol. 190:1447-1458 (2008)).
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
Escherichia coli
The M. thermoacetica hydrogenases are suitable for a host that lacks sufficient endogenous hydrogenase activity. M. thermoacetica can grow with CO2 as the exclusive carbon source indicating that reducing equivalents are extracted from H2 to enable acetyl-CoA synthesis via the Wood-Ljungdahl pathway (Drake, H. L., J. Bacteriol. 150:702-709 (1982); Drake and Daniel, Res. Microbiol. 155:869-883 (2004); Kellum and Drake, J. Bacteriol. 160:466-469 (1984)) (see
Proteins in M. thermoacetica whose genes are homologous to the E. coli hyp genes are shown below.
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Proteins in M. thermoacetica that are homologous to the E. coli Hydrogenase 3 and/or 4 proteins are listed in the following table.
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
In addition, several gene clusters encoding hydrogenase functionality are present in M. thermoacetica and their corresponding protein sequences are provided below.
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Moorella thermoacetica
Ralstonia eutropha H16 uses hydrogen as an energy source with oxygen as a terminal electron acceptor. Its membrane-bound uptake [NiFe]-hydrogenase is an “O2-tolerant” hydrogenase (Cracknell, et al. Proc Nat Acad Sci, 106(49) 20681-20686 (2009)) that is periplasmically-oriented and connected to the respiratory chain via a b-type cytochrome (Schink and Schlegel, Biochim. Biophys. Acta, 567, 315-324 (1979); Bernhard et al., Eur. J. Biochem. 248, 179-186 (1997)). R. eutropha also contains an O2-tolerant soluble hydrogenase encoded by the Hox operon which is cytoplasmic and directly reduces NAD+ at the expense of hydrogen (Schneider and Schlegel, Biochim. Biophys. Acta 452, 66-80 (1976); Burgdorf, J. Bact. 187(9) 3122-3132(2005)). Soluble hydrogenase enzymes are additionally present in several other organisms including Geobacter sulfurreducens (Coppi, Microbiology 151, 1239-1254 (2005)), Synechocystis str. PCC 6803 (Germer, J. Biol. Chem., 284(52), 36462-36472 (2009)), and Thiocapsa roseopersicina (Rakhely, Appl. Environ. Microbiol. 70(2) 722-728 (2004)). The Synechocystis enzyme is capable of generating NADPH from hydrogen. Overexpression of both the Hox operon from Synechocystis str. PCC 6803 and the accessory genes encoded by the Hyp operon from Nostoc sp. PCC 7120 led to increased hydrogenase activity compared to expression of the Hox genes alone (Germer, J. Biol. Chem. 284(52), 36462-36472 (2009)).
Ralstonia eutropha H16
Ralstonia eutropha H16
Ralstonia eutropha H16
Ralstonia eutropha H16
Ralstonia eutropha H16
Ralstonia eutropha H16
Geobacter sulfurreducens
Geobacter sulfurreducens
Geobacter sulfurreducens
Geobacter sulfurreducens
Geobacter sulfurreducens
Geobacter sulfurreducens
Synechocystis str. PCC
Synechocystis str. PCC
Synechocystis str. PCC
Synechocystis str. PCC
Synechocystis str. PCC
Synechocystis str. PCC
Synechocystis str. PCC
Synechocystis str. PCC
Nostoc sp. PCC 7120
Nostoc sp. PCC 7120
Nostoc sp. PCC 7120
Nostoc sp. PCC 7120
Nostoc sp. PCC 7120
Nostoc sp. PCC 7120
Nostoc sp. PCC 7120
Thiocapsa roseopersicina
Thiocapsa roseopersicina
Thiocapsa roseopersicina
Thiocapsa roseopersicina
Thiocapsa roseopersicina
Several enzymes and the corresponding genes used for fixing carbon dioxide to either pyruvate or phosphoenolpyruvate to form the TCA cycle intermediates, oxaloacetate or malate are described below.
Carboxylation of phosphoenolpyruvate to oxaloacetate is catalyzed by phosphoenolpyruvate carboxylase. Exemplary PEP carboxylase enzymes are encoded by ppc in E. coli (Kai et al., Arch. Biochem. Biophys. 414:170-179 (2003), ppcA in Methylobacterium extorquens AM1 (Arps et al., J. Bacteriol. 175:3776-3783 (1993), and ppc in Corynebacterium glutamicum (Eikmanns et al., Mol. Gen. Genet. 218:330-339 (1989).
Escherichia coli
Methylobacterium extorquens
Corynebacterium glutamicum
An alternative enzyme for converting phosphoenolpyruvate to oxaloacetate is PEP carboxykinase, which simultaneously forms an ATP while carboxylating PEP. In most organisms PEP carboxykinase serves a gluconeogenic function and converts oxaloacetate to PEP at the expense of one ATP. S. cerevisiae is one such organism whose native PEP carboxykinase, PCK1, serves a gluconeogenic role (Valdes-Hevia et al., FEBS Lett. 258:313-316 (1989). E. coli is another such organism, as the role of PEP carboxykinase in producing oxaloacetate is believed to be minor when compared to PEP carboxylase, which does not form ATP, possibly due to the higher Km for bicarbonate of PEP carboxykinase (Kim et al., Appl. Environ. Microbiol. 70:1238-1241 (2004)). Nevertheless, activity of the native E. coli PEP carboxykinase from PEP towards oxaloacetate has been recently demonstrated in ppc mutants of E. coli K-12 (Kwon et al., J. Microbiol. Biotechnol. 16:1448-1452 (2006)). These strains exhibited no growth defects and had increased succinate production at high NaHCO3 concentrations. Mutant strains of E. coli can adopt Pck as the dominant CO2-fixing enzyme following adaptive evolution (Zhang et al. 2009). In some organisms, particularly rumen bacteria, PEP carboxykinase is quite efficient in producing oxaloacetate from PEP and generating ATP. Examples of PEP carboxykinase genes that have been cloned into E. coli include those from Mannheimia succiniciproducens (Lee et al., Biotechnol. Bioprocess Eng. 7:95-99 (2002)), Anaerobiospirillum succiniciproducens (Laivenieks et al., Appl. Environ. Microbiol. 63:2273-2280 (1997), and Actinobacillus succinogenes (Kim et al. supra). The PEP carboxykinase enzyme encoded by Haemophilus influenza is effective at forming oxaloacetate from PEP.
Saccharomyces cerevisiae
Escherichia coli
Mannheimia succiniciproducens
Anaerobiospirillum
succiniciproducens
Actinobacillus succinogenes
Haemophilus influenza
Pyruvate carboxylase (EC 6.4.1.1) directly converts pyruvate to oxaloacetate at the cost of one ATP. Pyruvate carboxylase enzymes are encoded by PYC1 (Walker et al., Biochem. Biophys. Res. Commun. 176:1210-1217 (1991) and PYC2 (Walker et al., supra) in Saccharomyces cerevisiae, and pyc in Mycobacterium smegmatis (Mukhopadhyay and Purwantini, Biochim. Biophys. Acta 1475:191-206 (2000)).
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Mycobacterium smegmatis
Malic enzyme can be applied to convert CO2 and pyruvate to malate at the expense of one reducing equivalent. Malic enzymes for this purpose can include, without limitation, malic enzyme (NAD-dependent) and malic enzyme (NADP-dependent). For example, one of the E. coli malic enzymes (Takeo, J. Biochem. 66:379-387 (1969)) or a similar enzyme with higher activity can be expressed to enable the conversion of pyruvate and CO2 to malate. By fixing carbon to pyruvate as opposed to PEP, malic enzyme allows the high-energy phosphate bond from PEP to be conserved by pyruvate kinase whereby ATP is generated in the formation of pyruvate or by the phosphotransferase system for glucose transport. Although malic enzyme is typically assumed to operate in the direction of pyruvate formation from malate, overexpression of the NAD-dependent enzyme, encoded by maeA, has been demonstrated to increase succinate production in E. coli while restoring the lethal Apfl-AldhA phenotype under anaerobic conditions by operating in the carbon-fixing direction (Stols and Donnelly, Appl. Environ. Microbiol. 63(7) 2695-2701 (1997)). A similar observation was made upon overexpressing the malic enzyme from Ascaris suum in E. coli (Stols et al., Appl. Biochem. Biotechnol. 63-65(1), 153-158 (1997)). The second E. coli malic enzyme, encoded by maeB, is NADP-dependent and also decarboxylates oxaloacetate and other alpha-keto acids (Iwakura et al., J. Biochem. 85(5):1355-65 (1979)).
Escherichia coli
Escherichia coli
Ascaris suum
The enzymes used for converting oxaloacetate (formed from, for example, PEP carboxylase, PEP carboxykinase, or pyruvate carboxylase) or malate (formed from, for example, malic enzyme or malate dehydrogenase) to succinyl-CoA via the reductive branch of the TCA cycle are malate dehydrogenase, fumarate dehydratase (fumarase), fumarate reductase, and succinyl-CoA transferase. The genes for each of the enzymes are described herein above.
Enzymes, genes and methods for engineering pathways from succinyl-CoA to various products into a microorganism are now known in the art. The additional reducing equivalents obtained from CO and/or H2, as disclosed herein, improve the yields of 2,4-pentadienoate, butadiene, 1,3-butanediol or 3-buten-1-ol when utilizing carbohydrate-based feedstock.
Enzymes, genes and methods for engineering pathways from glycolysis intermediates to various products into a microorganism are known in the art. The additional reducing equivalents obtained from CO and H2, as described herein, improve the yields of all these products on carbohydrates.
This example describes methods used in handling CO and anaerobic cultures.
A. Handling of CO in Small Quantities for Assays and Small Cultures.
CO is an odorless, colorless and tasteless gas that is a poison. Therefore, cultures and assays that utilized CO required special handling. Several assays, including CO oxidation, acetyl-CoA synthesis, CO concentration using myoglobin, and CO tolerance/utilization in small batch cultures, called for small quantities of the CO gas that were dispensed and handled within a fume hood. Biochemical assays called for saturating very small quantities (<2 mL) of the biochemical assay medium or buffer with CO and then performing the assay. All of the CO handling steps were performed in a fume hood with the sash set at the proper height and blower turned on; CO was dispensed from a compressed gas cylinder and the regulator connected to a Schlenk line. The latter ensures that equal concentrations of CO were dispensed to each of several possible cuvettes or vials. The Schlenk line was set up containing an oxygen scrubber on the input side and an oil pressure release bubbler and vent on the other side. Assay cuvettes were both anaerobic and CO-containing. Threfore, the assay cuvettes were tightly sealed with a rubber stopper and reagents were added or removed using gas-tight needles and syringes. Secondly, small (˜50 mL) cultures were grown with saturating CO in tightly stoppered serum bottles. As with the biochemical assays, the CO-saturated microbial cultures were equilibrated in the fume hood using the Schlenk line setup. Both the biochemical assays and microbial cultures were in portable, sealed containers and in small volumes making for safe handling outside of the fume hood. The compressed CO tank was adjacent to the fume hood.
Typically, a Schlenk line was used to dispense CO to cuvettes, each vented. Rubber stoppers on the cuvettes were pierced with 19 or 20 gage disposable syringe needles and were vented with the same. An oil bubbler was used with a CO tank and oxygen scrubber. The glass or quartz spectrophotometer cuvettes have a circular hole on top into which a Kontes stopper sleeve, Sz7 774250-0007 was fitted. The CO detector unit was positioned proximal to the fume hood.
B. Handling of CO in Larger Quantities Fed to Large-Scale Cultures.
Fermentation cultures are fed either CO or a mixture of CO and H2 to simulate syngas as a feedstock in fermentative production. Therefore, quantities of cells ranging from 1 liter to several liters can include the addition of CO gas to increase the dissolved concentration of CO in the medium. In these circumstances, fairly large and continuously administered quantities of CO gas are added to the cultures. At different points, the cultures are harvested or samples removed. Alternatively, cells are harvested with an integrated continuous flow centrifuge that is part of the fermenter.
The fermentative processes are carried out under anaerobic conditions. In some cases, it is uneconomical to pump oxygen or air into fermenters to ensure adequate oxygen saturation to provide a respiratory environment. In addition, the reducing power generated during anaerobic fermentation may be needed in product formation rather than respiration. Furthermore, many of the enzymes for various pathways are oxygen-sensitive to varying degrees. Classic acetogens such as M. thermoacetica are obligate anaerobes and the enzymes in the Wood-Ljungdahl pathway are highly sensitive to irreversible inactivation by molecular oxygen. While there are oxygen-tolerant acetogens, the repertoire of enzymes in the Wood-Ljungdahl pathway might be incompatible in the presence of oxygen because most are metallo-enzymes, key components are ferredoxins, and regulation can divert metabolism away from the Wood-Ljungdahl pathway to maximize energy acquisition. At the same time, cells in culture act as oxygen scavengers that moderate the need for extreme measures in the presence of large cell growth.
C. Anaerobic Chamber and Conditions.
Exemplary anaerobic chambers are available commercially (see, for example, Vacuum Atmospheres Company, Hawthorne Calif.; MBraun, Newburyport Mass.). Conditions included an O2 concentration of 1 ppm or less and 1 atm pure Na. In one example, 3 oxygen scrubbers/catalyst regenerators were used, and the chamber included an O2 electrode (such as Teledyne; City of Industry Calif.). Nearly all items and reagents were cycled four times in the airlock of the chamber prior to opening the inner chamber door. Reagents with a volume >5 mL were sparged with pure N2 prior to introduction into the chamber. Gloves are changed twice/yr and the catalyst containers were regenerated periodically when the chamber displays increasingly sluggish response to changes in oxygen levels. The chamber's pressure was controlled through one-way valves activated by solenoids. This feature allowed setting the chamber pressure at a level higher than the surroundings to allow transfer of very small tubes through the purge valve.
The anaerobic chambers achieved levels of O2 that were consistently very low and were needed for highly oxygen sensitive anaerobic conditions. However, growth and handling of cells does not usually require such precautions. In an alternative anaerobic chamber configuration, platinum or palladium can be used as a catalyst that requires some hydrogen gas in the mix. Instead of using solenoid valves, pressure release can be controlled by a bubbler. Instead of using instrument-based O2 monitoring, test strips can be used instead.
D. Anaerobic Microbiology.
Small cultures were handled as described above for CO handling. In particular, serum or media bottles are fitted with thick rubber stoppers and aluminum crimps are employed to seal the bottle. Medium, such as Terrific Broth, is made in a conventional manner and dispensed to an appropriately sized serum bottle. The bottles are sparged with nitrogen for ˜30 min of moderate bubbling. This removes most of the oxygen from the medium and, after this step, each bottle is capped with a rubber stopper (such as Bellco 20 mm septum stoppers; Bellco, Vineland, N.J.) and crimp-sealed (Bellco 20 mm). Then the bottles of medium are autoclaved using a slow (liquid) exhaust cycle. At least sometimes a needle can be poked through the stopper to provide exhaust during autoclaving; the needle needs to be removed immediately upon removal from the autoclave. The sterile medium has the remaining medium components, for example buffer or antibiotics, added via syringe and needle. Prior to addition of reducing agents, the bottles are equilibrated for 30-60 minutes with nitrogen (or CO depending upon use). A reducing agent such as a 100×150 mM sodium sulfide, 200 mM cysteine-HCl is added. This is made by weighing the sodium sulfide into a dry beaker and the cysteine into a serum bottle, bringing both into the anaerobic chamber, dissolving the sodium sulfide into anaerobic water, then adding this to the cysteine in the serum bottle. The bottle is stoppered immediately as the sodium sulfide solution generates hydrogen sulfide gas upon contact with the cysteine. When injecting into the culture, a syringe filter is used to sterilize the solution. Other components are added through syringe needles, such as B12 (10 μM cyanocobalamin), nickel chloride (NiCl2, 20 microM final concentration from a 40 mM stock made in anaerobic water in the chamber and sterilized by autoclaving or by using a syringe filter upon injection into the culture), and ferrous ammonium sulfate (final concentration needed is 100 μM—made as 100-1000× stock solution in anaerobic water in the chamber and sterilized by autoclaving or by using a syringe filter upon injection into the culture). To facilitate faster growth under anaerobic conditions, the 1 liter bottles were inoculated with 50 mL of a preculture grown anaerobically. Induction of the pA1-lacO1 promoter in the vectors was performed by addition of isopropyl β-D-1-thiogalactopyranoside (IPTG) to a final concentration of 0.2 mM and was carried out for about 3 hrs.
Large cultures can be grown in larger bottles using continuous gas addition while bubbling. A rubber stopper with a metal bubbler is placed in the bottle after medium addition and sparged with nitrogen for 30 minutes or more prior to setting up the rest of the bottle. Each bottle is put together such that a sterile filter will sterilize the gas bubbled in and the hoses on the bottles are compressible with small C clamps. Medium and cells are stirred with magnetic stir bars. Once all medium components and cells are added, the bottles are incubated in an incubator in room air but with continuous nitrogen sparging into the bottles.
This example describes assay methods for measuring CO oxidation (CO dehydrogenase; CODH).
The 7 gene CODH/ACS operon of Moorella thermoacetica was cloned into E. coli expression vectors. The intact ˜10 kbp DNA fragment was cloned, and it is likely that some of the genes in this region are expressed from their own endogenous promoters and all contain endogenous ribosomal binding sites. These clones were assayed for CO oxidation, using an assay that quantitatively measures CODH activity. Antisera to the M. thermoacetica gene products was used for Western blots to estimate specific activity. M. thermoacetica is Gram positive, and ribosome binding site elements are expected to work well in E. coli. This activity, described below in more detail, was estimated to be ˜ 1/50th of the M. thermoacetica specific activity. It is possible that CODH activity of recombinant E. coli cells could be limited by the fact that M. thermoacetica enzymes have temperature optima around 55° C. Therefore, a mesophilic CODH/ACS pathway could be advantageous such as the close relative of Moorella that is mesophilic and does have an apparently intact CODH/ACS operon and a Wood-Ljungdahl pathway, Desulfitobacterium hafniense. Acetogens as potential host organisms include, but are not limited to, Rhodospirillum rubrum, Moorella thermoacetica and Desulfitobacterium hafniense.
CO oxidation is both the most sensitive and most robust of the CODH/ACS assays. It is likely that an E. coli-based syngas using system will ultimately need to be about as anaerobic as Clostridial (i.e., Moorella) systems, especially for maximal activity. Improvement in CODH should be possible but will ultimately be limited by the solubility of CO gas in water.
Initially, each of the genes was cloned individually into expression vectors. Combined expression units for multiple subunits/1 complex were generated. Expression in E. coli at the protein level was determined. Both combined M. thermoacetica CODH/ACS operons and individual expression clones were made.
CO oxidation assay. This assay is one of the simpler, reliable, and more versatile assays of enzymatic activities within the Wood-Ljungdahl pathway and tests CODH (Seravalli et al., Biochemistry 43:3944-3955 (2004)). A typical activity of M. thermoacetica CODH specific activity is 500 U at 55° C. or −60U at 25° C. This assay employs reduction of methyl viologen in the presence of CO. This is measured at 578 nm in stoppered, anaerobic, glass cuvettes.
In more detail, glass rubber stoppered cuvettes were prepared after first washing the cuvette four times in deionized water and one time with acetone. A small amount of vacuum grease was smeared on the top of the rubber gasket. The cuvette was gassed with CO, dried 10 min with a 22 Ga. needle plus an exhaust needle. A volume of 0.98 mlL of reaction buffer (50 mM Hepes, pH 8.5, 2 mM dithiothreitol (DTT) was added using a 22 Ga. needle, with exhaust needled, and 100% CO. Methyl viologen (CH3 viologen) stock was 1 M in water. Each assay used 20 microliters for 20 mM final concentration. When methyl viologen was added, an 18 Ga needle (partial) was used as a jacket to facilitate use of a Hamilton syringe to withdraw the CH3 viologen. 4-5 aliquots were drawn up and discarded to wash and gas equilibrate the syringe. A small amount of sodium dithionite (0.1 M stock) was added when making up the CH3 viologen stock to slightly reduce the CH3 viologen. The temperature was equilibrated to 55° C. in a heated Olis spectrophotometer (Bogart GA). A blank reaction (CH3 viologen+buffer) was run first to measure the base rate of CH3 viologen reduction. Crude E. coli cell extracts of ACS90 and ACS91 (CODH-ACS operon of M. thermoacetica with and without, respectively, the first cooC). 10 microliters of extract were added at a time, mixed and assayed. Reduced CH3 viologen turns purple. The results of an assay are shown in Table I.
Mta98/Mta99 are E. coli MG1655 strains that express methanol methyltransferase genes from M thermoacetia and, therefore, are negative controls for the ACS90 ACS91 E. coli strains that contain M. thermoacetica CODH operons.
If ˜1% of the cellular protein is CODH, then these figures would be approximately 100× less than the 500 U/mg activity of pure M. thermoacetica CODH. Actual estimates based on Western blots are 0.5% of the cellular protein, so the activity is about 50× less than for M. thermoacetica CODH. Nevertheless, this experiment demonstrates CO oxidation activity in recombinant E. coli with a much smaller amount in the negative controls. The small amount of CO oxidation (CH3 viologen reduction) seen in the negative controls indicates that E. coli may have a limited ability to reduce CH3 viologen.
To estimate the final concentrations of CODH and Mtr proteins, SDS-PAGE followed by Western blot analyses were performed on the same cell extracts used in the CO oxidation, ACS, methyltransferase, and corrinoid Fe—S assays. The antisera used were polyclonal to purified M. thermoacetica CODH-ACS and Mtr proteins and were visualized using an alkaline phosphatase-linked goat-anti-rabbit secondary antibody. The Westerns were performed and results are shown in
The CO oxidation assays were repeated using extracts of Moorella thermoacetica cells for the positive controls. Though CODH activity in E. coli ACS90 and ACS91 was measurable, it was at about 130-150× lower than the M. thermoacetica control. The results of the assay are shown in
These results describe the CO oxidation (CODH) assay and results. Recombinant E. coli cells expressed CO oxidation activity as measured by the methyl viologen reduction assay.
This example describes the tolerance of E. coli for high concentrations of CO.
To test whether or not E. coli can grow anaerobically in the presence of saturating amounts of CO, cultures were set up in 120 ml serum bottles with 50 ml of Terrific Broth medium (plus reducing solution, NiCl2, Fe(II)NH4SO4, cyanocobalamin, IPTG, and chloramphenicol) as described above for anaerobic microbiology in small volumes. One half of these bottles were equilibrated with nitrogen gas for 30 min. and one half was equilibrated with CO gas for 30 min. An empty vector (pZA33) was used as a control, and cultures containing the pZA33 empty vector as well as both ACS90 and ACS91 were tested with both N2 and CO. All were inoculated and grown for 36 hrs with shaking (250 rpm) at 37° C. At the end of the 36 hour period, examination of the flasks showed high amounts of growth in all. The bulk of the observed growth occurred overnight with a long lag.
Given that all cultures appeared to grow well in the presence of CO, the final CO concentrations were confirmed. This was performed using an assay of the spectral shift of myoglobin upon exposure to CO. Myoglobin reduced with sodium dithionite has an absorbance peak at 435 nm; this peak is shifted to 423 nm with CO. Due to the low wavelength and need to record a whole spectrum from 300 nm on upwards, quartz cuvettes must be used. CO concentration is measured against a standard curve and depends upon the Henry's Law constant for CO of maximum water solubility=970 micromolar at 20° C. and 1 atm.
For the myoglobin test of CO concentration, cuvettes were washed 10× with water, 1× with acetone, and then stoppered as with the CODH assay. N2 was blown into the cuvettes for ˜10 min. A volume of 1 ml of anaerobic buffer (HEPES, pH 8.0, 2 mM DTT) was added to the blank (not equilibrated with CO) with a Hamilton syringe. A volume of 10 microliter myoglobin (˜1 mM—can be varied, just need a fairly large amount) and 1 microliter dithionite (20 mM stock) were added. A CO standard curve was made using CO saturated buffer added at 1 microliter increments. Peak height and shift was recorded for each increment. The cultures tested were pZA33/CO, ACS90/CO, and ACS91/CO. Each of these was added in 1 microliter increments to the same cuvette. Midway through the experiment a second cuvette was set up and used. The results are shown in Table II.
The results shown in Table II indicate that the cultures grew whether or not a strain was cultured in the presence of CO or not. These results indicate that E. coli can tolerate exposure to CO under anaerobic conditions and that E. coli cells expressing the CODH-ACS operon can metabolize some of the CO.
These results demonstrate that E. coli cells, whether expressing CODH/ACS or not, were able to grow in the presence of saturating amounts of CO. Furthermore, these grew equally well as the controls in nitrogen in place of CO. This experiment demonstrated that laboratory strains of E. coli are insensitive to CO at the levels achievable in a syngas project performed at normal atmospheric pressure. In addition, preliminary experiments indicated that the recombinant E. coli cells expressing CODH/ACS actually consumed some CO, probably by oxidation to carbon dioxide.
Pathways to 1,3-butanediol, propylene and crotyl alcohol are shown in
Several pathways are shown in
Pathways to propylene are also shown in
Exemplary pathways from shown in
Enzyme activities required for the reactions shown in
Enzyme candidates in many of these EC classes have been described earlier and represent suitable candidates for to the transformations depicted in
Several reactions shown in
The reduction of acetoacetyl-ACP to 3-hydroxyacetyl-ACP is catalyzed by acetoacetyl-ACP reductase or 3-oxoacyl-ACP reductase (EC 1.1.1.100). The E. coli 3-oxoacyl-ACP reductase is encoded by fabG. Key residues responsible for binding the acyl-ACP substrate to the enzyme have been elucidated (Zhang et al, J Biol Chem 278:52935-43 (2003)). Additional enzymes with this activity have been characterized in Bacillus anthracis (Zaccai et al, Prot Struct Funct Gen 70:562-7 (2008)) and Mycobacterium tuberculosis (Gurvitz, Mol Genet Genomics 282:407-16 (2009)). The beta-ketoacyl reductase (KR) domain of eukaryotic fatty acid synthase also catalyzes this activity (Smith, FASEB J, 8:1248-59 (1994)).
Escherichia coli
Bacillus anthracis
Mycobacterium tuberculosis
Mycobacterium tuberculosis
The reduction of an acyl-ACP to its corresponding aldehyde is catalyzed by an acyl-ACP reductase (AAR). Such a transformation is depicted in steps J, M and U of
Synechococcus
elongatus PCC7942
Prochlorococcus
Synechococcus
elongatus PCC 6301
Anabaena
variabilis
Nostoc
Nostoc azollae
Cyanothece
Nodularia
spumigena
Lyngbya
Several transformations in
Enoyl-ACP reductase catalyzes the formation of a saturated acyl-ACP by an NAD(P)H-dependent reduction of the enoyl-ACP double bond. The Fabl protein of E. coli is a well-characterized enoyl-ACP reductase that catalyzes the reduction of enoyl substrates of length 4 to 16 carbons (Rafe et al, JBC 281:39285-93 (2006)). Fabl is inhibited by acyl-ACP by product inhibition (Heath, J Biol Chem 271:1833-6 (1996)). Bacillus subtilis contains two enoyl-ACP reductase isozymes, Fabl and FabL (Heath et al, J Biol Chem 275:40128-33 (2000)). The Streptococcus pneumoniae FabK protein is a triclosan-resistant flavoprotein catalyzing the same activity (Heath and Rock, Nature 406:145-6 (2000)). An additional candidate is the Pseudomonas aeruginosa Fabl protein, which was recently crystallized (Lee et al, Acta Cryst Sect F 67:214-216 (2011)).
Escherichia coli
Bacillus subtilis
Bacillus subtilis
Streptococcus pneumoniae
Pseudomonas aeruginosa
In step A of
Escherichia coli
Escherichia coli
Escherichia coli
Bacillus subtilis
Bacillus subtilis
Alternately, acetyl-CoA can first be activated to acetyl-ACP and subsequently condensed to acetoacetyl-ACP by two enzymes, acetyl-CoA:ACP transacylase (EC 2.3.1.38) and acetoacetyl-ACP synthase (EC 2.3.1.41). Acetyl-CoA:ACP transacylase converts acetyl-CoA and an acyl carrier protein to acetyl-ACP, releasing CoA. Enzyme candidates for acetyl-CoA:ACP transacylase are described in section EC 2.3.1.f below. Acetoacetyl-ACP synthase enzymes catalyze the condensation of acetyl-ACP and malonyl-ACP. This activity is catalyzed by FabF and FabB of E. coli, as well as the multifunctional eukaryotic fatty acid synthase enzyme complexes described in EC 2.3.1.g.
The exchange of an ACP moiety for a CoA is catalyzed by enzymes in EC class 2.3.1. This reaction is shown in steps D, X, AE and AJ. of
The FabH (KASIII) enzyme of E. coli functions as an acyl-CoA:ACP transacylase, in addition to its primary activity of forming acetoacetyl-ACP. Butyryl-ACP is accepted as an alternate substrate of FabH (Prescott et al, Adv. Enzymol. Relat. Areas Mol, 36:269-311 (1972)). Acetyl-CoA:ACP transacylase enzymes from Plasmodium falciparum and Streptomyces avermitillis have been heterologously expressed in E. coli (Lobo et al, Biochem 40:11955-64 (2001)). A synthetic KASIII (FabH) from P. falciparum expressed in a fabH-deficient Lactococcus lactis host was able to complement the native fadH activity (Du et al, AEM 76:3959-66 (2010)). The acetyl-CoA:ACP transacylase enzyme from Spinacia oleracea accepts other acyl-ACP molecules as substrates, including butyryl-ACP (Shimakata et al, Methods Enzym 122:53-9 (1986)). The sequence of this enzyme has not been determined to date. Malonyl-CoA:ACP transacylase enzymes include FabD of E. coli and Brassica napsus (Verwoert et al, J Bacteriol, 174:2851-7 (1992); Simon et al, FEBS Lett 435:204-6 (1998)). FabD of B. napsus was able to complementfabD-deficient E. coli. The multifunctional eukaryotic fatty acid synthase enzyme complexes (described in EC 2.3.1.g) also catalyze this activity.
Escherichia coli
Streptomyces avermitillis
Plasmodium falciparum
Plasmodium falciparum
Lactococcus lactis
Escherichia coli
Brassica nansus
Steps A, B, C and AL of
Saccharomyces cerevisiae
Saccharomyces cerevisiae
Thermomyces lanuyinosus
Thermomyces lanuginosus
Mycobacterium tuberculosis
Homo sapiens
Acyl-ACP thioesterase enzymes convert an acyl-ACP to its corresponding acid.
Such a transformation is required in steps H, L, T and AP of
Arabidopsis thaliana
Arabidopsis thaliana
Cuphea hookeriana
Cuphea palustris
Carthamus tinctorius
Umbellularia
californica
Escherichia coli
Decarbonylase enzyme candidates described in Example VII are also relevant here. Additional enzyme candidates suitable for catalyzing decarbonylation reactions in
Synechococcus elongatus
Several reactions in
Elizabethkingia
meningoseptica
Streptococcus pyogenes
Psychroflexus torquis
Rhodopseudomonas
palustris
3-Hydroxyacyl-ACP dehydratase enzymes are suitable candidates for dehydrating 3-hydroxybutyryl-ACP to crotonyl-ACP (step C of
Escherichia coli
Escherichia coli
Plasmodium falciparum
Saccharomyces cerevisiae
Homo sapiens
In a typical process for converting crotyl alcohol into butadiene, crotyl alcohol is passed, either neat or in a solvent and either in presence or absence of steam, over a solid inorganic, organic or metal-containing dehydration catalyst heated to temperatures in the range 40-400° C. inside of the reaction vessel or tube, leading to elimination of water and release of butadiene as a gas, which is condensed (butadiene bp=−4.4° C.) and collected in a reservoir for further processing, storage, or use. Typical catalysts can include bismuth molybdate, phosphate-phosphoric acid, cerium oxide, kaolin-iron oxide, kaolin-phosphoric acid, silica-alumina, and alumina. Typical process throughputs are in the range of 0.1-20,000 kg/h. Typical solvents are toluene, heptane, octane, ethylbenzene, and xylene.
This example describes enzymatic pathways for converting crotyl alcohol to butadiene. The two pathways are shown in
Crotyl alcohol kinase enzymes catalyze the transfer of a phosphate group to the hydroxyl group of crotyl alcohol. The enzymes described below naturally possess such activity or can be engineered to exhibit this activity. Kinases that catalyze transfer of a phosphate group to an alcohol group are members of the EC 2.7.1 enzyme class. The table below lists several useful kinase enzymes in the EC 2.7.1 enzyme class.
Mevalonate kinase (EC 2.7.1.36) phosphorylates the terminal hydroxyl group of mevalonate. Gene candidates for this step include erg12 from S. cerevisiae, mvk from Methanocaldococcus jannaschi, MVK from Homo sapiens, and mvk from Arabidopsis thaliana col. Additional mevalonate kinase candidates include the feedback-resistant mevalonate kinase from the archeon Methanosarcina mazei (Primak et al, AEM, in press (2011)) and the Mvk protein from Streptococcus pneumoniae (Andreassi et al, Protein Sci, 16:983-9 (2007)). Mvk proteins from S. cerevisiae, S. pneumoniae and M. mazei were heterologously expressed and characterized in E. coli (Primak et al, supra). The S. pneumoniae mevalonate kinase was active on several alternate substrates including cylopropylmevalonate, vinylmevalonate and ethynylmevalonate (Kudoh et al, Bioorg Med Chem 18:1124-34 (2010)), and a subsequent study determined that the ligand binding site is selective for compact, electron-rich C(3)-substituents (Lefurgy et al, J Biol Chem 285:20654-63 (2010)).
Sachharomyces cerevisiae
Methanocaldococcus
jannaschii
Homo sapiens
Arabidopsis thaliana
Methanosarcina mazei
Streptococcus pneumoniae
Glycerol kinase also phosphorylates the terminal hydroxyl group in glycerol to form glycerol-3-phosphate. This reaction occurs in several species, including Escherichia coli, Saccharomyces cerevisiae, and Thermotoga maritima. The E. coli glycerol kinase has been shown to accept alternate substrates such as dihydroxyacetone and glyceraldehyde (Hayashi et al., J Biol. Chem. 242:1030-1035 (1967)). T, maritime has two glycerol kinases (Nelson et al., Nature 399:323-329 (1999)). Glycerol kinases have been shown to have a wide range of substrate specificity. Crans and Whiteside studied glycerol kinases from four different organisms (Escherichia coli, S. cerevisiae, Bacillus stearothermophilus, and Candida mycoderma) (Crans et al., J. Am. Chem. Soc. 107:7008-7018 (2010); Nelson et al., supra, (1999)). They studied 66 different analogs of glycerol and concluded that the enzyme could accept a range of substituents in place of one terminal hydroxyl group and that the hydrogen atom at C2 could be replaced by a methyl group. Interestingly, the kinetic constants of the enzyme from all four organisms were very similar.
Escherichia coli K12
Thermotoga maritime MSB8
Thermotoga maritime MSB8
Saccharomyces cerevisiae
Homoserine kinase is another possible candidate. This enzyme is also present in a number of organisms including E. coli, Streptomyces sp, and S. cerevisiae. Homoserine kinase from E. coli has been shown to have activity on numerous substrates, including, L-2-amino,1,4-butanediol, aspartate semialdehyde, and 2-amino-5-hydroxyvalerate (Huo et al., Biochemistry 35:16180-16185 (1996); Huo et al., Arch. Biochem. Biophys. 330:373-379 (1996)). This enzyme can act on substrates where the carboxyl group at the alpha position has been replaced by an ester or by a hydroxymethyl group. The gene candidates are:
Escherichia
Streptomyces
Saccharomyces
serevisiae
2-Butenyl-4-phosphate kinase enzymes catalyze the transfer of a phosphate group to the phosphate group of 2-butenyl-4-phosphate. The enzymes described below naturally possess such activity or can be engineered to exhibit this activity. Kinases that catalyze transfer of a phosphate group to another phosphate group are members of the EC 2.7.4 enzyme class. The table below lists several useful kinase enzymes in the EC 2.7.4 enzyme class.
Phosphomevalonate kinase enzymes are of particular interest. Phosphomevalonate kinase (EC 2.7.4.2) catalyzes the analogous transformation to 2-butenyl-4-phosphate kinase. This enzyme is encoded by erg8 in Saccharomyces cerevisiae (Tsay et al., Mol. Cell Biol. 11:620-631 (1991)) and mvaK2 in Streptococcus pneumoniae, Staphylococcus aureus and Enterococcus faecalis (Doun et al., Protein Sci. 14:1134-1139 (2005); Wilding et al., J Bacteriol. 182:4319-4327 (2000)). The Streptococcus pneumoniae and Enterococcus faecalis enzymes were cloned and characterized in E. coli (Pilloff et al., J Biol. Chem. 278:4510-4515 (2003); Doun et al., Protein Sci. 14:1134-1139 (2005)). The S. pneumoniae phosphomevalonate kinase was active on several alternate substrates including cylopropylmevalonate phosphate, vinylmevalonate phosphate and ethynylmevalonate phosphate (Kudoh et al, Bioorg Med Chem 18:1124-34 (2010)).
Saccharomyces cerevisiae
Staphylococcus aureus
Streptococcus pneumoniae
Enterococcus faecalis
Farnesyl monophosphate kinase enzymes catalyze the CTP dependent phosphorylation of farnesyl monophosphate to farnesyl diphosphate. Similarly, geranylgeranyl phosphate kinase catalyzes CTP dependent phosphorylation. Enzymes with these activities were identified in the microsomal fraction of cultured Nicotiana tabacum (Thai et al, PNAS 96:13080-5 (1999)). However, the associated genes have not been identified to date.
Butadiene synthase catalyzes the conversion of 2-butenyl-4-diphosphate to 1,3-butadiene. The enzymes described below naturally possess such activity or can be engineered to exhibit this activity. Carbon-oxygen lyases that operate on phosphates are found in the EC 4.2.3 enzyme class. The table below lists several useful enzymes in EC class 4.2.3.
Particularly useful enzymes include isoprene synthase, myrcene synthase and farnesene synthase. Enzyme candidates are described below.
Isoprene synthase naturally catalyzes the conversion of dimethylallyl diphosphate to isoprene, but can also catalyze the synthesis of 1,3-butadiene from 2-butenyl-4-diphosphate. Isoprene synthases can be found in several organisms including Populus alba (Sasaki et al., FEBS Letters, 2005, 579 (11), 2514-2518), Pueraria montana (Lindberg et al., Metabolic Eng, 12(1):70-79 (2010); Sharkey et al., Plant Physiol., 137(2):700-712 (2005)), and Populus tremula x Populus alba, also called Populus canescens (Miller et al., Planta, 2001, 213 (3), 483-487). The crystal structure of the Populus canescens isoprene synthase was determined (Koksal et al, J Mol Biol 402:363-373 (2010)). Additional isoprene synthase enzymes are described in (Chotani et al., WO/2010/031079, Systems Using Cell Culture for Production of Isoprene; Cervin et al., US Patent Application 20100003716, Isoprene Synthase Variants for Improved Microbial Production of Isoprene).
Populus alba
Pueraria montana
Populus tremula × Populus alba
Myrcene synthase enzymes catalyze the dephosphorylation of geranyl diphosphate to beta-myrcene (EC 4.2.3.15). Exemplary myrcene synthases are encoded by MST2 of Solanum lycopersicum (van Schie et al, Plant Mol Biol 64:D473-79 (2007)), TPS-Myr of Picea abies (Martin et al, Plant Physiol 135:1908-27 (2004)) g-myr of Abies grandis (Bohlmann et al, J Biol Chem 272:21784-92 (1997)) and TPS10 of Arabidopsis thaliana (Bohlmann et al, Arch Biochem Biophys 375:261-9 (2000)). These enzymes were heterologously expressed in E. coli.
Solanum lycopersicum
Picea abies
Abies grandis
Arabidopsis thaliana
Farnesyl diphosphate is converted to alpha-farnesene and beta-farnesene by alpha-farnesene synthase and beta-farnesene synthase, respectively. Exemplary alpha-farnesene synthase enzymes include TPS03 and TPS02 of Arabidopsis thaliana (Faldt et al, Planta 216:745-51 (2003); Huang et al, Plant Physiol 153:1293-310 (2010)), afs of Cucumis sativus (Mercke et al, Plant Physiol 135:2012-14 (2004), eafar of Malus x domestica (Green et al, Phytochem 68:176-88 (2007)) and TPS-Far of Picea abies (Martin, supra). An exemplary beta-farnesene synthase enzyme is encoded by TPSJ of Zea mays (Schnee et al, Plant Physiol 130:2049-60 (2002)).
Arabidopsis thaliana
Arabidopsis thaliana
Picea abies
Cucumis sativus
Malus × domestica
Zea mays
Crotyl alcohol diphosphokinase enzymes catalyze the transfer of a diphosphate group to the hydroxyl group of crotyl alcohol. The enzymes described below naturally possess such activity or can be engineered to exhibit this activity. Kinases that catalyze transfer of a diphosphate group are members of the EC 2.7.6 enzyme class. The table below lists several useful kinase enzymes in the EC 2.7.6 enzyme class.
Of particular interest are ribose-phosphate diphosphokinase enzymes which have been identified in Escherichia coli (Hove-Jenson et al., J Biol Chem, 1986, 261(15); 6765-71) and Mycoplasma pneumoniae M129 (McElwain et al, International Journal of Systematic Bacteriology, 1988, 38:417-423) as well as thiamine diphosphokinase enzymes. Exemplary thiamine diphosphokinase enzymes are found in Arabidopsis thaliana (Ajjawi, Plant Mol Biol, 2007, 65(1-2); 151-62).
Escherichia coli
Mycoplasma pneumoniae
Arabidopsis thaliana col
Arabidopsis thaliana col
Throughout this application various publications have been referenced. The disclosures of these publications in their entireties, including GenBank and GI number publications, are hereby incorporated by reference in this application in order to more fully describe the state of the art to which this invention pertains. Although the invention has been described with reference to the examples provided above, it should be understood that various modifications can be made without departing from the spirit of the invention.
This application is a continuation of U.S. patent application Ser. No. 14/935,182, filed Nov. 6, 2015, which is a continuation of U.S. patent application Ser. No. 13/588,971, filed Aug. 17, 2012, now abandoned, which claims the benefit of priority of U.S. Provisional application Ser. No. 61/645,509, filed May 10, 2012, U.S. Provisional application Ser. No. 61/535,264, filed Sep. 15, 2011, U.S. Provisional application Ser. No. 61/530,885, filed Sep. 2, 2011, and U.S. Provisional application Ser. No. 61/525,659, filed Aug. 19, 2011, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61645509 | May 2012 | US | |
| 61535264 | Sep 2011 | US | |
| 61530885 | Sep 2011 | US | |
| 61525659 | Aug 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14935182 | Nov 2015 | US |
| Child | 16741618 | US | |
| Parent | 13588971 | Aug 2012 | US |
| Child | 14935182 | US |
