Patent Application
20230227864
This invention relates to metabolically engineered microorganisms, such as bacterial strains, and bioprocesses utilizing such strains. These strains provide dynamic control of metabolic pathways resulting in the production of products from acetyl-CoA.
The instant application contains a Sequence Listing which has been filed electronically in ASCII format as 49186-48_ST25.txt created Jul. 13, 2021 that is 26,740 bytes in size and is hereby incorporated by reference in its entirety.
Biotechnology based fermentation processes have made rapid advancements in recent years due to technology developments in the fields of fermentation science and synthetic biology, as well as metabolic and enzyme engineering. However improvements in rates, titers and yields are often needed to enable commercially competitive processes. Most metabolic engineering strategies aimed at improving these metrics rely on the overexpression of desired pathway enzymes and deletion and/or downregulation of competing biochemical activities. Over the last several decades, stoichiometric models of metabolism have helped to move the field from manipulating gene expression levels to manipulating networks, which can now be designed to couple growth with product formation, and selection can be used to optimize for both.
A remaining limitation of these approaches are the metabolic boundary conditions required for cellular growth. Dynamic metabolic control and specifically two-stage control offer a potential engineering strategy to overcome these limitations, by switching to a production state where metabolite and enzyme levels can be pushed past the boundaries required for growth. Significant efforts have been made to develop tools for dynamic metabolic control including control systems, metabolic valves and modeling approaches. However to date, previous work has largely focused on dynamically redirecting fluxes by switching “OFF” pathways that stoichiometrically compete with a desired pathway.
We demonstrate increased stationary phase flux attributable to dynamic reduction in metabolites which act as feedback regulators of central metabolism, and not reductions in competing metabolic pathways. Employing two-stage dynamic metabolic control we describe manipulating feedback regulation in central metabolism and improve biosynthesis in genetically modified microorganisms. Specifically, we describe the impact of dynamic control over two central metabolic enzymes: citrate synthase, and glucose-6-phosphate dehydrogenase, on stationary phase fluxes. Reduced citrate synthase levels lead to a reduction in α-ketoglutarate, which is an inhibitor of sugar transport, resulting in increased glucose uptake and glycolytic fluxes.
Other methods, features and/or advantages is, or will become, apparent upon examination of the following Figures and detailed description. It is intended that all such additional methods, features, and advantages be included within this description and be protected by the accompanying claims.
The novel features of the invention are set forth with particularity in the claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are used, and the accompanying drawings of which:
Demonstrated herein is the use of two-stage dynamic metabolic control to manipulate feedback regulation in central metabolism and improve biosynthesis in engineered E. coli. Specifically, we report the impact of dynamic control over two central metabolic enzymes: citrate synthase, and glucose-6-phosphate dehydrogenase, on stationary phase fluxes. Firstly, reduced citrate synthase levels lead to a reduction in α-ketoglutarate, which is an inhibitor of sugar transport, resulting in increased glucose uptake and glycolytic fluxes. Reduced glucose-6-phosphate dehydrogenase activity activates the SoxRS regulon and expression of pyruvate-ferredoxin oxidoreductase, which is in turn responsible for large increases in acetyl-CoA production. These two mechanisms lead to the improved stationary phase production of citramalic acid enabling titers of 126±7 g/L. These results identify pyruvate oxidation via the pyruvate-ferredoxin oxidoreductase as a “central” metabolic pathway in stationary phase and highlight the potential of improving fluxes by manipulating essential central regulatory mechanisms using two-stage dynamic metabolic control
As used in the specification and the claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an “expression vector” includes a single expression vector as well as a plurality of expression vectors, either the same (e.g., the same operon) or different; reference to “microorganism” includes a single microorganism as well as a plurality of microorganisms; and the like.
The term “heterologous DNA,” “heterologous nucleic acid sequence,” and the like as used herein refers to a nucleic acid sequence wherein at least one of the following is true: (a) the sequence of nucleic acids is foreign to (i.e., not naturally found in) a given host microorganism; (b) the sequence may be naturally found in a given host microorganism, but in an unnatural (e.g., greater than expected) amount; or (c) the sequence of nucleic acids comprises two or more subsequences that are not found in the same relationship to each other in nature. For example, regarding instance (c), a heterologous nucleic acid sequence that is recombinantly produced will have two or more sequences from unrelated genes arranged to make a new functional nucleic acid, such as a nonnative promoter driving gene expression.
The term “synthetic metabolic valve,” and the like as used herein refers to either the use of controlled proteolysis, gene silencing or the combination of both proteolysis and gene silencing to alter metabolic fluxes.
The term “heterologous” is intended to include the term “exogenous” as the latter term is generally used in the art. With reference to the host microorganism's genome prior to the introduction of a heterologous nucleic acid sequence, the nucleic acid sequence that codes for the enzyme is heterologous (whether or not the heterologous nucleic acid sequence is introduced into that genome). As used herein, chromosomal and native and endogenous refer to genetic material of the host microorganism.
As used herein, the term “gene disruption,” or grammatical equivalents thereof (and including “to disrupt enzymatic function,” “disruption of enzymatic function,” and the like), is intended to mean a genetic modification to a microorganism that renders the encoded gene product as having a reduced polypeptide activity compared with polypeptide activity in or from a microorganism cell not so modified. The genetic modification can be, for example, deletion of the entire gene, deletion or other modification of a regulatory sequence required for transcription or translation, deletion of a portion of the gene which results in a truncated gene product (e.g., enzyme) or by any of various mutation strategies that reduces activity (including to no detectable activity level) the encoded gene product. A disruption may broadly include a deletion of all or part of the nucleic acid sequence encoding the enzyme, and also includes, but is not limited to other types of genetic modifications, e.g., introduction of stop codons, frame shift mutations, introduction or removal of portions of the gene, and introduction of a degradation signal, those genetic modifications affecting mRNA transcription levels and/or stability, and altering the promoter or repressor upstream of the gene encoding the enzyme.
Bio-production, Micro-fermentation (microfermentation) or Fermentation, as used herein, may be aerobic, microaerobic, or anaerobic.
When the genetic modification of a gene product, i.e., an enzyme, is referred to herein, including the claims, it is understood that the genetic modification is of a nucleic acid sequence, such as or including the gene, that normally encodes the stated gene product, i.e., the enzyme.
As used herein, the term “metabolic flux” and the like refers to changes in metabolism that lead to changes in product and/or byproduct formation, including production rates, production titers and production yields from a given substrate.
Species and other phylogenic identifications are according to the classification known to a person skilled in the art of microbiology.
Enzymes are listed here within, with reference to a UniProt identification number, which would be well known to one skilled in the art. The UniProt database can be accessed at UniProt.org. When the genetic modification of a gene product, i.e., an enzyme, is referred to herein, including the claims, it is understood that the genetic modification is of a nucleic acid sequence, such as or including the gene, that normally encodes the stated gene product, i.e., the enzyme.
Where methods and steps described herein indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain steps may be performed concurrently in a parallel process when possible, as well as performed sequentially.
The meaning of abbreviations is as follows: “C” means Celsius or degrees Celsius, or ° C. as is clear from its usage, DCW means dry cell weight, “s” means second(s), “min” means minute(s), “h,” “hr,” or “hrs” means hour(s), “psi” means pounds per square inch, “nm” means nanometers, “d” means day(s), “μL” or “uL” or “ul” means microliter(s), “mL” means milliliter(s), “L” means liter(s), “mm” means millimeter(s), “nm” means nanometers, “mM” means millimolar, “μM” or “uM” means micromolar, “M” means molar, “mmol” means millimole(s), “μmol” or “uMol” means micromole(s)”, “g” means gram(s), “μg” or “ug” means microgram(s) and “ng” means nanogram(s), “PCR” means polymerase chain reaction, “OD” means optical density, “OD600” means the optical density measured at a photon wavelength of 600 nm, “kDa” means kilodaltons, “g” means the gravitation constant, “bp” means base pair(s), “kbp” means kilobase pair(s), “% w/v” means weight/volume percent, “% v/v” means volume/volume percent, “IPTG” means isopropyl-μ-thiogalactopyranoiside, “aTc” means anhydrotetracycline, “RBS” means ribosome binding site, “rpm” means revolutions per minute, “HPLC” means high performance liquid chromatography, and “GC” means gas chromatography.
Bio-production media, which is used in the present invention with recombinant microorganisms must contain suitable carbon sources or substrates for both growth and production stages. Suitable substrates may include, but are not limited to glucose, or a combination of xylose, glucose, sucrose, xylose, mannose, arabinose, oils, carbon dioxide, carbon monoxide, methane, methanol, formaldehyde or glycerol. It is contemplated that all of the above mentioned carbon substrates and mixtures thereof are suitable in the present invention as a carbon source(s).
Features as described and claimed herein may be provided in a microorganism selected from the listing herein, or another suitable microorganism, that also comprises one or more natural, introduced, or enhanced product bio-production pathways. Thus, in some embodiments the microorganism(s) comprise an endogenous product production pathway (which may, in some such embodiments, be enhanced), whereas in other embodiments the microorganism does not comprise an endogenous product production pathway.
More particularly, based on the various criteria described herein, suitable microbial hosts for the bio-production of a chemical product generally may include, but are not limited to the organisms described in the Common Methods Section.
The host microorganism or the source microorganism for any gene or protein described here may be selected from the following list of microorganisms: Citrobacter, Enterobacter, Clostridium, Klebsiella, Aerobacter, Lactobacillus, Aspergillus, Saccharomyces, Schizosaccharomyces, Zygosaccharomyces, Pichia, Kluyveromyces, Candida, Hansenula, Debaryomyces, Mucor, Torulopsis, Methylobacter, Escherichia, Salmonella, Bacillus, Streptomyces, and Pseudomonas. In some aspects the host microorganism is an E. coli microorganism.
In addition to an appropriate carbon source, such as selected from one of the herein-disclosed types, bio-production media must contain suitable minerals, salts, cofactors, buffers and other components, known to those skilled in the art, suitable for the growth of the cultures and promotion of chemical product bio-production under the present invention.
Another aspect of the invention regards media and culture conditions that comprise genetically modified microorganisms of the invention and optionally supplements.
Typically cells are grown at a temperature in the range of about 25° C. to about 40° C. in an appropriate medium, as well as up to 70° C. for thermophilic microorganisms. Suitable growth media are well characterized and known in the art. Suitable pH ranges for the bio-production are between pH 2.0 to pH 10.0, where pH 6.0 to pH 8.0 is a typical pH range for the initial condition. However, the actual culture conditions for a particular embodiment are not meant to be limited by these pH ranges. Bio-productions may be performed under aerobic, microaerobic or anaerobic conditions with or without agitation.
Fermentation systems utilizing methods and/or compositions according to the invention are also within the scope of the invention. Any of the recombinant microorganisms as described and/or referred to herein may be introduced into an industrial bio-production system where the microorganisms convert a carbon source into a product in a commercially viable operation. The bio-production system includes the introduction of such a recombinant microorganism into a bioreactor vessel, with a carbon source substrate and bio-production media suitable for growing the recombinant microorganism, and maintaining the bio-production system within a suitable temperature range (and dissolved oxygen concentration range if the reaction is aerobic or microaerobic) for a suitable time to obtain a desired conversion of a portion of the substrate molecules to a selected chemical product. Bio-productions may be performed under aerobic, microaerobic, or anaerobic conditions, with or without agitation. Industrial bio-production systems and their operation are well-known to those skilled in the arts of chemical engineering and bioprocess engineering.
The amount of a product produced in a bio-production media generally can be determined using a number of methods known in the art, for example, high performance liquid chromatography (HPLC), gas chromatography (GC), or GC/Mass Spectroscopy (MS).
Embodiments of the present invention may result from introduction of an expression vector into a host microorganism, wherein the expression vector contains a nucleic acid sequence coding for an enzyme that is, or is not, normally found in a host microorganism.
The ability to genetically modify a host cell is essential for the production of any genetically modified (recombinant) microorganism. The mode of gene transfer technology may be by electroporation, conjugation, transduction, or natural transformation. A broad range of host conjugative plasmids and drug resistance markers are available. The cloning vectors are tailored to the host organisms based on the nature of antibiotic resistance markers that can function in that host. Also, as disclosed herein, a genetically modified (recombinant) microorganism may comprise modifications other than via plasmid introduction, including modifications to its genomic DNA.
More generally, nucleic acid constructs can be prepared comprising an isolated polynucleotide encoding a polypeptide having enzyme activity operably linked to one or more (several) control sequences that direct the expression of the coding sequence in a microorganism, such as E. coli, under conditions compatible with the control sequences. The isolated polynucleotide may be manipulated to provide for expression of the polypeptide. Manipulation of the polynucleotide's sequence prior to its insertion into a vector may be desirable or necessary depending on the expression vector. The techniques for modifying polynucleotide sequences utilizing recombinant DNA methods are well established in the art.
The control sequence may be an appropriate promoter sequence, a nucleotide sequence that is recognized by a host cell for expression of a polynucleotide encoding a polypeptide of the present invention. The promoter sequence may contain transcriptional control sequences that mediate the expression of the polypeptide. The promoter may be any nucleotide sequence that shows transcriptional activity in the host cell of choice including mutant, truncated, and hybrid promoters, and may be obtained from genes encoding extracellular or intracellular polypeptides either homologous or heterologous to the host cell. The techniques for modifying and utilizing recombinant DNA promoter sequences are well established in the art.
For various embodiments of the invention the genetic manipulations may include a manipulation directed to change regulation of, and therefore ultimate activity of, an enzyme or enzymatic activity of an enzyme identified in any of the respective pathways. Such genetic modifications may be directed to transcriptional, translational, and post-translational modifications that result in a change of enzyme activity and/or selectivity under selected culture conditions. Genetic manipulation of nucleic acid sequences may increase copy number and/or comprise use of mutants of an enzyme related to product production. Specific methodologies and approaches to achieve such genetic modification are well known to one skilled in the art.
In various embodiments, to function more efficiently, a microorganism may comprise one or more gene deletions. For example, in E. coli, the genes encoding the lactate dehydrogenase (ldhA), phosphate acetyltransferase (pta), pyruvate oxidase (poxB), pyruvate-formate lyase (pflB), methylglyoxal synthase (mgsA), acetate kinase (ackA), alcohol dehydrogenase (adhE), the clpXP protease specificity enhancing factor (sspB), the ATP-dependent Lon protease (lon), the outer membrane protease (ompT), the arcA transcriptional dual regulator (arcA), and the iclR transcriptional regulator (iclR) may be disrupted, including deleted. Such gene disruptions, including deletions, are not meant to be limiting, and may be implemented in various combinations in various embodiments. Gene deletions may be accomplished by numerous strategies well known in the art, as are methods to incorporate foreign DNA into a host chromosome.
In various embodiments, to function more efficiently, a microorganism may comprise one or more synthetic metabolic valves, composed of enzymes targeted for controlled proteolysis, expression silencing or a combination of both controlled proteolysis and expression silencing. For example, one enzyme encoded by one gene or a combination of numerous enzymes encoded by numerous genes in E. coli may be designed as synthetic metabolic valves to alter metabolism and improve product formation. Representative genes in E. coli may include but are not limited to the following: fabI, zwf, gltA, ppc, udhA, lpd, sucD, aceA, pfkA, lon, rpoS, pykA, pykF, tktA or tktB. It is appreciated that it is well known to one skilled in the art how to identify homologues of these genes and or other genes in additional microbial species.
For all nucleic acid and amino acid sequences provided herein, it is appreciated that conservatively modified variants of these sequences are included, and are within the scope of the invention in its various embodiments. Functionally equivalent nucleic acid and amino acid sequences (functional variants), which may include conservatively modified variants as well as more extensively varied sequences, which are well within the skill of the person of ordinary skill in the art, and microorganisms comprising these, also are within the scope of various embodiments of the invention, as are methods and systems comprising such sequences and/or microorganisms.
Accordingly, as described in various sections above, some compositions, methods and systems of the present invention comprise providing a genetically modified microorganism that comprises both a production pathway to make a desired product from a central intermediate in combination with synthetic metabolic valves to redistribute flux.
Aspects of the invention also regard provision of multiple genetic modifications to improve microorganism overall effectiveness in converting a selected carbon source into a selected product. Particular combinations are shown, such as in the Examples, to increase specific productivity, volumetric productivity, titer and yield substantially over more basic combinations of genetic modifications.
In addition to the above-described genetic modifications, in various embodiments genetic modifications, including synthetic metabolic valves also are provided to increase or decrease the pool and availability of a cofactor such as NADPH and/or NADH which may be consumed in the production of a product.
Use of synthetic metabolic valves allows for simpler models of metabolic fluxes and physiological demands during a production phase, turning a growing cell into a stationary phase biocatalyst. These synthetic metabolic valves can be used to turn off essential genes and redirect carbon, electrons and energy flux to product formation in a multi-stage fermentation process. One or more of the following provides the described synthetic valves: 1) transcriptional gene silencing or repression technologies in combination with 2) inducible and selective enzyme degradation and 3) nutrient limitation to induce a stationary or non-dividing cellular state. SMVs are generalizable to any pathway and microbial host. These synthetic metabolic valves allow for novel rapid metabolic engineering strategies useful for the production of renewable chemicals and fuels and any product that can be produced via whole cell catalysis.
In particular, the invention describes the construction of synthetic metabolic valves comprising one or more or a combination of the following: controlled gene silencing and controlled proteolysis. It is appreciated that one well skilled in the art is aware of several methodologies for gene silencing and controlled proteolysis.
In particular, the invention describes the use of controlled gene silencing to provide the control over metabolic fluxes in controlled multi-stage fermentation processes. There are several methodologies known in the art for controlled gene silencing, including but not limited to mRNA silencing or RNA interference, silencing via transcriptional repressors and CRISPR interference. Methodologies and mechanisms for RNA interference are taught by Agrawal et al. “RNA Interference: Biology, Mechanism, and Applications” Microbiology and Molecular Biology Reviews, December 2003; 67(4) p 657-685. DOI: 10.1128/MMBR.67.657-685.2003. Methodologies and mechanisms for CRISRPR interference are taught by Qi et al. “Repurposing CRISPR as an RNA-guided platform for sequence-specific control of gene expression” Cell February 2013; 152(5) p 1173-1183. DOI: 10.1016/j.ce11.2013.02.022. In addition, methodologies and mechanisms for CRISRPR interference using the native E. coli CASCADE system are taught by Luo et al. “Repurposing endogenous type I CRISPR-Cas systems for programmable gene repression” NAR. October 2014; DOI: 10.1093. In additional numerous transcriptional repressor systems are well known in the art and can be used to turn off gene expression.
In particular, the invention describes the use of controlled protein degradation or proteolysis to provide the control over metabolic fluxes in controlled multi-stage fermentation processes. There are several methodologies known in the art for controlled protein degradation, including but not limited to targeted protein cleavage by a specific protease and controlled targeting of proteins for degradation by specific peptide tags. Systems for the use of the E. coli clpXP protease for controlled protein degradation are taught by McGinness et al, “Engineering controllable protein degradation”, Mol Cell. June 2006; 22(5) p 701-707. This methodology relies upon adding a specific C-terminal peptide tag such as a DAS4 (or DAS+4) tag. Proteins with this tag are not degraded by the clpXP protease until the specificity enhancing chaperone sspB is expressed. sspB induces degradation of DAS4 tagged proteins by the clpXP protease. In additional numerous site specific protease systems are well known in the art. Proteins can be engineered to contain a specific target site of a given protease and then cleaved after the controlled expression of the protease. In some embodiments, the cleavage can be expected lead to protein inactivation or degradation. For example Schmidt et al (“ClpS is the recognition component for Escherichia coli substrates of the N-end rule degradation pathway” Molecular Microbiology March 2009. 72(2), 506-517. doi:10.1111), teaches that an N-terminal sequence can be added to a protein of interest in providing clpS dependent clpAP degradation. In addition, this sequence can further be masked by an additional N-terminal sequence, which can be controllable cleaved such as by a ULP hydrolase. This allows for controlled N-rule degradation dependent on hydrolase expression. It is therefore possible to tag proteins for controlled proteolysis either at the N-terminus or C-terminus. The preference of using an N-terminal vs. C-terminal tag will largely depend on whether either tag affects protein function prior to the controlled onset of degradation.
The invention describes the use of controlled protein degradation or proteolysis to provide the control over metabolic fluxes in controlled multi-stage fermentation processes, in E. coli. There are several methodologies known in the art for controlled protein degradation in other microbial hosts, including a wide range of gram-negative as well as gram-positive bacteria, yeast and even archaea. In particular, systems for controlled proteolysis can be transferred from a native microbial host and used in a non-native host. For example Grilly et al, “A synthetic gene network for tuning protein degradation in Saccharomyces cerevisiae” Molecular Systems Biology 3, Article 127. doi:10.1038, teaches the expression and use of the E. coli clpXP protease in the yeast Saccharomyces cerevisiae. Such approaches can be used to transfer the methodology for synthetic metabolic valves to any genetically tractable host.
In particular the invention describes the use of synthetic metabolic valves to control metabolic fluxes in multi-stage fermentation processes. There are numerous methodologies known in the art to induce expression that can be used at the transition between stages in multi-stage fermentations. These include but are not limited to artificial chemical inducers including: tetracycline, anhydrotetracycline, lactose, IPTG (isopropyl-beta-D-1-thiogalactopyranoside), arabinose, raffinose, tryptophan and numerous others. Systems linking the use of these well known inducers to the control of gene expression silencing and/or controlled proteolysis can be integrated into genetically modified microbial systems to control the transition between growth and production phases in multi-stage fermentation processes.
In addition, it may be desirable to control the transition between growth and production in multi-stage fermentations by the depletion of one or more limiting nutrients that are consumed during growth. Limiting nutrients can include but are not limited to: phosphate, nitrogen, sulfur and magnesium. Natural gene expression systems that respond to these nutrient limitations can be used to operably link the control of gene expression silencing and/or controlled proteolysis to the transition between growth and production phases in multi-stage fermentation processes.
Within the scope of the invention are genetically modified microorganism, wherein the microorganism is capable of producing a product at a specific rate selected from the rates of greater than 0.05 g/gDCW-hr, 0.08 g/gDCW-hr, greater than 0.1 g/gDCW-hr, greater than 0.13 g/gDCW-hr, greater than 0.15 g/gDCW-hr, greater than 0.175 g/gDCW-hr, greater than 0.2 g/gDCW-hr, greater than 0.25 g/gDCW-hr, greater than 0.3 g/gDCW-hr, greater than 0.35 g/gDCW-hr, greater than 0.4 g/gDCW-hr, greater than 0.45 g/gDCW-hr, or greater than 0.5 g/gDCW-hr.
In various embodiments, the invention includes a culture system comprising a carbon source in an aqueous medium and a genetically modified microorganism according to any one of claims herein, wherein said genetically modified organism is present in an amount selected from greater than 0.05 gDCW/L, 0.1 gDCW/L, greater than 1 gDCW/L, greater than 5 gDCW/L, greater than 10 gDCW/L, greater than 15 gDCW/L or greater than 20 gDCW/L, such as when the volume of the aqueous medium is selected from greater than 5 mL, greater than 100 mL, greater than 0.5 L, greater than 1 L, greater than 2 L, greater than 10 L, greater than 250 L, greater than 1000 L, greater than 10,000 L, greater than 50,000 L, greater than 100,000 L or greater than 200,000 L, and such as when the volume of the aqueous medium is greater than 250 L and contained within a steel vessel.
In one aspect, a genetically modified microorganism that is usable in a biofermentation process is provided, the microorganism including a production pathway comprising at least one enzyme for producing a product from an acetyl CoA precursor. The microorganism, under conditions of depleting of a limiting nutrient from a growth medium in which the genetically modified microorganism is growing, is induced into a stationary phase or non-dividing cellular state. In this stationary phase, pyruvate-flavodoxin/ferredoxin oxidoreductase enzyme activity is increased within the genetically modified microorganism under aerobic or partially aerobic conditions during the stationary phase or non-dividing cellular state to produce an acetyl CoA pool; and further sugar uptake is enhanced within the genetically modified microorganism, when compared to a non-genetically modified microorganism.
In one aspect, the genetically modified microorganism includes a conditionally triggered synthetic metabolic valve that silences gene expression of the citrate synthase (gltA) and/or glucose-6-phosphate-dehydrogenase (zwf) gene(s); or a conditionally triggered synthetic metabolic valve that enables selective proteolysis of the citrate synthase (gltA) and/or glucose phosphate-dehydrogenase (zwf) enzyme(s) and the synthetic metabolic valve(s) of the microorganism are conditionally triggered during the stationary phase or non-dividing cellular state.
In one aspect, the genetically modified microorganism includes a deletion of endogenous poxB and pflB genes.
In one aspect, the increased pyruvate-flavodoxin/ferredoxin oxidoreductase enzyme activity of the genetically modified microorganism is due to overexpression of a gene encoding pyruvate ferredoxin oxidoreductase during the stationary phase or non-dividing cellular state.
In one aspect, the increased pyruvate-flavodoxin/ferredoxin oxidoreductase enzyme activity of the genetically modified microorganism the pyruvate-flavodoxin/ferredoxin oxidoreductase enzyme is encoded by the ydbK gene and the genetically modified microorganism is an Enterobacter microorganism.
In one aspect, the increased pyruvate-flavodoxin/ferredoxin oxidoreductase enzyme activity of the genetically modified microorganism is due to induction of the oxidative soxRS regulon during the stationary phase or non-dividing cellular state.
In one aspect, the increased pyruvate-flavodoxin/ferredoxin oxidoreductase enzyme activity of the genetically modified microorganism the increased pyruvate ferredoxin oxidoreductase enzyme activity is increased as the result of reduced NADPH levels within the genetically modified microorganism during the stationary phase or non-dividing cellular state.
In one aspect, the activity of at least one sugar transporter of the genetically modified microorganism causes activity of at least one sugar transporter is increased to enhance sugar uptake.
In one aspect, the activity of at least one sugar transporter of the genetically modified microorganism is the result of constitutive expression of a sugar transporter gene results in increased sugar transporter activity within the genetically modified microorganism.
In one aspect, the activity of at least one sugar transporter of the genetically modified microorganism is the result of conditionally overexpressed during the stationary phase or non-dividing cellular state.
In one aspect, the sugar transporter of the genetically modified microorganism is encoded by a pts gene.
In one aspect, the genetically modified microorganism is an Enterobacter microorganism. In one aspect, the microorganism in an E. coli microorganism.
In one aspect, the genetically modified microorganism includes citramalate synthase as an enzyme of the production pathway.
In one aspect, a bioprocess for production of a protein product from the genetically modified microorganism is provided. The bioprocess including in a first stage, growing the genetically modified microorganism in a medium and in a second stage, upon depletion of a limiting nutrient from a growth medium, inducing a stationary phase or non-dividing cellular state. The bioprocess, the genetically modified microorganism in the stationary phase or non-dividing cellular state produces product at a rate of 30 g/L or greater.
In another aspect, the bioprocess includes activity of a pyruvate-flavodoxin/ferredoxin oxidoreductase enzyme is caused by overexpression of a gene encoding an active pyruvate ferredoxin oxidoreductase, induction of the oxidative soxRS regulon, reducing NADPH levels, reducing glucose-6-phosphate dehydrogenase levels with a synthetic metabolic valve directed to gene silencing of the zwf gene or selective proteolysis of the glucose-6-phosphate dehydrogenase enzyme, the valve activated in the stationary phase or non-dividing cellular state, or a combination thereof.
In one aspect, the bioprocess, the activity of at least one sugar transporter is increased.
In one aspect, the bioprocess results in citramalate product and an enzyme of the production pathway comprises citramalate synthase, and the bioprocess produces citramalate at or greater than 100 g/L. In one aspect, the citramalate synthase enzyme is encoded by the cimA3.7 gene.
In one aspect, the genetically modified microorganism of the bioprocess includes a plasmid comprising a citramalate synthase gene is operably linked to a low phosphate inducible promotor.
In one aspect, a bioprocess includes the use of a genetically modified microorganism comprises deletion of endogenous poxB and pflB genes.
While various embodiments of the present invention have been shown and described herein, it is emphasized that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein in its various embodiments. Specifically, and for whatever reason, for any grouping of compounds, nucleic acid sequences, polypeptides including specific proteins including functional enzymes, metabolic pathway enzymes or intermediates, elements, or other compositions, or concentrations stated or otherwise presented herein in a list, table, or other grouping (such as metabolic pathway enzymes shown in a
Also, and more generally, in accordance with disclosures, discussions, examples and embodiments herein, there may be employed conventional molecular biology, cellular biology, microbiology, and recombinant DNA techniques within the skill of the art. Such techniques are explained fully in the literature. See, e.g., Sambrook and Russell, “Molecular Cloning: A Laboratory Manual,” Third Edition 2001 (volumes 1-3), Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.; Animal Cell Culture, R. I. Freshney, ed., 1986. These published resources are incorporated by reference herein.
The following published resources are incorporated by reference herein for description useful in conjunction with the invention described herein, for example, methods of industrial bio-production of chemical product(s) from sugar sources, and also industrial systems that may be used to achieve such conversion (Biochemical Engineering Fundamentals, 2nd Ed. J. E. Bailey and D. F. 011 is, McGraw Hill, New York, 1986, e.g.Chapter 9, pages 533-657 for biological reactor design; Unit Operations of Chemical Engineering, 5th Ed., W. L. McCabe et al., McGraw Hill, New York 1993, e.g., for process and separation technologies analyses; Equilibrium Staged Separations, P. C. Wankat, Prentice Hall, Englewood Cliffs, N.J. USA, 1988, e.g., for separation technologies teachings).
All publications, patents, and patent applications mentioned in this specification are entirely incorporated by reference herein, including PCT/US2015/035306 filed Jun. 11, 2015 and PCT/US2018/019040, filed Feb. 21, 2018.
The examples herein provide some examples, not meant to be limiting. All reagents, unless otherwise indicated, are obtained commercially. Species and other phylogenic identifications are according to the classification known to a person skilled in the art of microbiology, molecular biology and biochemistry.
Common Methods
Media & Reagents
Unless otherwise stated, all materials and reagents were purchased from Sigma (St. Louis, Mo.). Luria Broth Lennox formulation was used for routine strain and plasmid propagation and construction. FGM1, FGM30, and SM10++ seed media was prepared as previously described Menacho-Melgar et al. (doi: 10.1101/820787). SM10++ and SM10 no phosphate media were prepared as described by Moreb et al. (doi: 10.1021/acssynbio.0c00182). FGM3 media used in biolector studies is detailed in Supplemental Materials. Working antibiotic concentrations were as follows: kanamycin: 35 μg/mL, chloramphenicol: 35 μg/mL, zeocin: 100 μg/mL, blasticidin: 100 μg/mL, spectinomycin: 25 μg/mL, tetracycline: 5 μg/mL.
FGM 3 Media/Media Stock Solutions:
10× concentrated Ammonium-Citrate 30 salts (1 L) by mixing 30 g of (NH4)2SO4 and 1.5 g Citric Acid in water with stirring, adjust pH to 7.5 with NaOH. Autoclave and store at room temperature (RT).
10× concentrated Ammonium-Citrate 90 salts (1 L) by mixing 90 g of (NH4)2SO4 and 2.5 g Citric Acid in water with stirring, adjust pH to 7.5 with NaOH. Autoclave and store at RT.
1 M Potassium 3-(N-morpholino) propanesulfonic Acid (MOPS), adjust to pH 7.4 with KOH. Filter sterilize (0.2 μm) and store at RT.
0.5 M potassium phosphate buffer, pH 6.8 by mixing 248.5 mL of 1.0 M K2HPO4 and 251.5 mL of 1.0 M KH2PO4 and adjust to a final volume of 1000 mL with ultrapure water. Filter sterilize (0.2 μm) and store at RT.
2 M MgSO4 and 10 mM CaSO4 solutions. Filter sterilize (0.2 μm) and store at RT.
50 g/L solution of thiamine-HCl. Filter sterilize (0.2 μm) and store at 4° C.
500 g/L solution of glucose, dissolving by stirring with heat. Cool, filter sterilize (0.2 μm), and store at RT.
500× Trace Metal Stock: Prepare a solution of micronutrients in 1000 mL of water containing 10 mL of concentrated H2SO4. 0.6 g CoSO4·7H2O, 5.0 g CuSO4·5H2O, 0.6 g ZnSO4·7H2O, 0.2 g Na2MoO4·2H2O, 0.1 g H3BO3, and 0.3 g MnSO4·H2O. Filter sterilize (0.2 μm) and store at RT in the dark.
Prepare a fresh solution of 40 mM ferric sulfate heptahydrate in water, filter sterilize (0.2 μm) before preparing media each time.
Media Components: Prepare the final working medium by aseptically mixing stock solutions based on the following tables in the order written to minimize precipitation, then filter sterilize (with a 0.2 μm filter).
Modified Strains
Biomed.
Biotechnol.
Strains & Plasmids
Plasmid and strain information are found in Tables 2-4. Sequences of oligonucleotides and synthetic linear DNA (Gblocks™) were obtained from Integrated DNA Technologies (IDT, Coralville, Iowa). Deletions were constructed with tet-sacB based selection and counterselection. C-terminal DAS+4 tag (with or without superfolder GFP tags) were added to chromosomal genes by direct integration and selected through integration of antibiotic resistance cassettes 3′ of the gene. All strains were confirmed by PCR, agarose gel electrophoresis and confirmed by sequencing (Eton Biosciences, or Genewiz) using paired oligonucleotides, either flanking the entire region. The recombineering plasmid pSIM5 and the tet-sacB selection/counterselection marker cassette were kind gifts from Donald Court (NCI, redrecombineering.ncifcrf.gov/court-lab.html). Strain BW25113 was obtained from the Yale Genetic Stock Center (CGSC: cgsc.biology.yale.edu). Strain DLF_R002 was constructed as previously reported by Menacho-Melgar et al. (doi: 10.1101/820787). Strain DLFZ_0025 was constructed from DLF_R002 by first deleting the native sspB gene (using tet-sacB based selection and counterselection). Subsequently, the cas3 gene was deleted and replaced with a low phosphate inducible sspB (using the ugpB gene promoter) allele as well as a constitutive promoter to drive expression of the Cascade operon (again using tet-sacB based selection and counterselection). C-terminal DAS+4 tag modifications (with or without superfolder GFP tags) were added to the chromosome of DLF_Z0025 and its derivatives by direct integration and selected through integration of antibiotic resistance cassettes 3′ of the gene.
Plasmids, pCDF-ev (Addgene #89596), pHCKan-yibDp-GFPuv (Addgene #127078) and pHCKan-yibDp-cimA3.7 (Addgene #134595) were constructed as previously reported (doi: 10.1101/820787). Plasmids pCDF-mCherry1 (Addgene #87144) and pCDF-mCherry1 (Addgene #87145) were constructed from pCDF-ev by PCR and Gibson assembly with synthetic DNA encoding an mCherry open reading frame with out without a C-terminal DAS+4 degron tag along with a strong synthetic constitutive proD promoter previously reported by Davis et al.
Gene silencing guides and guide arrays were expressed from a series of pCASCADE plasmids. The pCASCADE-control plasmid was prepared by swapping the pTet promoter in perRNA.Tet (a kind gift from C. Beisel) with an insulated low phosphate induced ugpB promoter. In order to design CASCADE guide array, CASCADE PAM sites near the −35 or −10 box of the promoter of interest were identified, 30 bp at the 3′ end of PAM site was selected as the guide sequence and cloned into pCASCADE plasmid using Q5 site-directed mutagenesis (NEB, MA) following manufacturer's protocol, with the modification that 5% v/v DMSO was added to the Q5 PCR reaction. PCR cycles were as follows: amplification involved an initial denaturation step at 98° C. for 30 second followed by cycling at 98° C. for 10 second, 72° C. for 30 second, and 72° C. for 1.5 min (the extension rate was 30 second/kb) for 25 cycles, then a final extension for 2 min at 72° C. 2 μL of PCR mixture was used for 10 μL, KLD reaction (NEB, MA), which proceeded under room temperature for 1 hour, after which, 1 μL KLD mixture was used for electroporation. The pCASCADE guide array plasmid (pCASCADE-G2Z) was prepared by sequentially amplifying complementary halves of each smaller guide plasmid by PCR, followed by subsequent DNA assembly as illustrated in Tables. Primers used for pCASCADE assembly and gRNA sequences are provided in Supplemental Table 5 below. Additionally, all strains containing gRNA plasmids were routinely confirmed to assess gRNA stability via PCR as described below.
TCGAGTTCCCCGCGCCAGCGGGGATAAACCGTATTGACCAA
GGGGATAAACCG (SEQ ID NO: 27)
TCGAGTTCCCCGCGCCAGCGGGGATAAACCGAGTGGTTGCT
GGGATAAACCG (SEQ ID NO: 30)
TCGAGTTCCCCGCGCCAGCGGGGATAAACCGCTCGTAAAA
GGGGATAAACCG (SEQ ID NO: 33)
TCGAGTTCCCCGCGCCAGCGGGGATAAACCGTATTGACCAAT
TCATTCGGGACAGTTATTAGTTCGAGTTCCCCGCGCCAGCG
GGGATAAACCGCTCGTAAAAGCAGTACAGTGCACCGTAAG
BioLector Studies
Single colonies of each strain were inoculated into 5 mL LB with appropriate antibiotics and cultured at 37° C., 220 rpm for 9 hours or until OD600 reached >2. 500 μL of the culture was inoculated into 10 mL SM10 medium with appropriate antibiotics, and cultured in a square shake flask (CAT #: 25-212, Genesee Scientific, Inc. San Diego, Calif.) at 37° C., 220 rpm for 16 hours. Cells were pelleted by centrifugation and the culture density was normalized to OD600=5 using FGM3 media. Growth and fluorescence measurements were obtained in a Biolector (m2p labs, Baesweiler, Germany) using a high mass transfer FlowerPlate (CAT #: MTP-48-B, m2p-labs, Germany). 40 μL of the OD normalized culture was inoculated into 760 μL of FGM3 medium with appropriate antibiotics. Biolector settings were as follows: RFP gain=100, GFP gain=20, Biomass gain=20, shaking speed=1300 rpm, temperature=37° C., humidity=85%. Every strain was analyzed in triplicate.
ELISAs
Quantification of proteins via C-terminal GFP tags was performed using a GFP quantification kit from AbCam (Cambridge, UK, product #ab171581) according to manufacturer's instructions. Briefly, samples were obtained from microfermentations as described above. Cells were harvested 24 hour post phosphate depletion, washed in water and lysed with the provided extraction buffer.
Guide RNA Stability Testing
The stability of guide RNA arrays was confirmed by colony PCR using the following 2 primers: gRNA-for: 5′-GGGAGACCACAACGG-3′ (SEQ ID NO: 25), gRNA-rev: 5′-CGCAGTCGAACGACCG-3′ (SEQ ID NO: 26), using 2× EconoTaq Master mix (Lucigen) in 10 μL, PCR reactions consisting of 5 μL of 2×EconoTaq Master mix (Lucigen), 1 uL of each primer (10 μM), 3 μL dH2O. A 98° C., 2 minute initial denaturation was followed by 35 cycles of 94° C., 30 seconds, 60° C. 30 seconds, and 72° C., 30 seconds and a final 72° C., 5 min final extension. PCR reactions were then run on agarose gels and band size compared to control PCR reactions using purified plasmid DNA as a template. Guide protospacer loss occurred when guide array size was smaller than expected, indicating the loss of one or more protospacers.
Fermentations
Minimal media microfermentations were performed as previously reported (doi: 10.1021/acssynbio.0c00182). For microfermentations where paraquat induction was used, paraquat was added for 1 hour prior to phosphate depletion and subsequently removed during the cell wash step used to deplete phosphate in the media. 1 L fermentations in instrumented bioreactors were also performed as previously reported, with slight modifications to the glucose feeding profiles, which were a function of strain and process. Generally, feeding was increased to enable excess residual glucose to ensure production rates were not feed limited. Glucose feeding was as follows. For 10 gCDW/L fermentations, starting batch glucose concentration was 25 g/L. A constant concentrated sterile filtered glucose feed (500 g/L) was added to the tanks at 1.5 g/h when cells entered mid-exponential growth. For 25 gCDW/L fermentations, starting batch glucose concentration was 25 g/L. Concentrated sterile filtered glucose feed (500 g/L) was added to the tanks at an initial rate of 9 g/h when cells entered mid-exponential growth. This rate was then increased exponentially, doubling every 1.083 hours (65 min) until 40 g total glucose had been added, after which the feed was maintained at 1.75 g/hr.
Production of Isotopically Labelled Metabolites.
C13 pyruvate (CLM-1082-PK) and C13 D-glucose (U-13C6, 99%) were purchased from Cambridge Isotope Laboratories, Inc. (Tewksbury, Mass.). Isotopically labelled citramalate was produced in two stage minimal media shake flask studies, mimicking microfermentations, using strain DLF_Z0044 expressing cimA3.7. Briefly, 20 mL cultures of SM10++ media were inoculated with the strain which was grown overnight at 37 Celsius, shaking at 150 rpm in baffled 250 mL Erlenmyer shake flasks. After 16 hrs of growth cells were harvested by centrifugation washed and resuspended in 20 mL of SM10 minimal media (lacking phosphate) where glucose was replaced with C13 labelled glucose. Cultures were grown for 25 hrs at 37 Celsius, shaking at 150 rpm, after which cells were removed by centrifugation, and the spent media filter sterilized prior to use as an internal standard.
Analytical Methods
Cell dry weights: The OD/cell dry weight correlation coefficient (1 OD (600 nm)=0.35 gCDW/L, as determined by Menacho-Melgar et al. was used in this work.
Glucose and Organic Acid Quantification: Two methods were used for glucose and organic acid quantification. First, a UPLC-RI method was developed for the simultaneous quantification of glucose, citramalate, acetic acid, pyruvate, citraconate, citrate and other organic acids including lactate, succinate, fumarate, malate, and mevalonate. Chromatographic separation was performed using a Rezex Fast Acid Analysis HPLC Column (100×7.8 mm, 9 μm particle size; CAT #: #1250100, Bio-Rad Laboratories, Inc., Hercules, Calif.) at 55° C. 5 mM sulfuric acid was used as the isocratic eluent, with a flow rate of XmL/min. Sample injection volume was 10 μL. Second, quantification was performed using a Bio-Rad Fast Acid Analysis HPLC Column (100×7.8 mm, 9 μm particle size; CAT #: #1250100, Bio-Rad Laboratories, Inc., Hercules, Calif.) at 65° C. 10 mM sulfuric acid was used as the eluent, with an isocratic flow rate of 0.3 mL/min. In both methods, sample injection volume was 10 μL and chromatography and detection were accomplished using a Waters Acquity H-Class UPLC integrated with a Waters 2414 Refractive Index (RI) detector (Waters Corp., Milford, Mass. USA). Samples were diluted as needed to be within the accurate linear range. Dilution was performed using ultrapure water.
Organic acid Quantification via RapidFire-qTOE-MS: Micro-fermentation samples (as well as a confirmatory subset of samples from bioreactors) were centrifuged to remove cells. Broth was diluted 100 fold in water to a final volume of 20 μL. To this either a final concentration of 10 mg/L of C13 pyruvate was added or 2 uL of broth containing C13 labelled citramalate was added. The final sample was injected onto a HILIC (type H1 or the equivalent H6) RapidFire™ cartridge (Agilent Technologies, Santa Clara, Calif.). Injections were loaded on the cartridge with 95% hexane, 5% isopropanol for 3000 ms after a 600 ms aspiration, at a flow rate of 1.0 mL/min. After loading, the cartridge was washed with isopropanol for 2000 ms, at a flow rate of 1.0 mL/min. Elution was carried out for 8000 ms with 50% water/50% methanol with 0.2% acetic acid and 0.5 uM (NH4)3PO4, at a flow rate of 1.0 mL/min. Column equilibration was performed for 4000 ms. The qTOF was tuned in the mass range of 50-250 m/z in fragile ion, negative ESI mode. Settings during detection were as follows: drying gas: 250 C at a flow rate of 13 L/minute, sheath gas: 400 C at a flow rate of 12 L/minute, nebulizer pressure: 35 psi, Fragmenter voltage: 100 V, skimmer voltage: 65 V, nozzle voltage: 2000 V, capillary voltage: 3500V. The acquisition rate was 1 spectra/second.
pCASCADE Guide Array based Gene Silencing
The design and construction of CASCADE guides and guide arrays is illustrated below in
TCGAGTTCCCCGCGCCAGCGGGGATAAACCGTATTGACCAA
GGGGATAAACCG (SEQ ID NO: 27)
TCGAGTTCCCCGCGCCAGCGGGGATAAACCGAGTGGTTGCT
GGGATAAACCG (SEQ ID NO: 30)
TCGAGTTCCCCGCGCCAGCGGGGATAAACCGCTCGTAAAA
GGGGATAAACCG (SEQ ID NO: 33)
TCGAGTTCCCCGCGCCAGCGGGGATAAACCGTATTGACCAAT
TCATTCGGGACAGTTATTAGTTCGAGTTCCCCGCGCCAGCG
GGGATAAACCGCTCGTAAAAGCAGTACAGTGCACCGTAAG
1
1
1
Plasmids expressing fluorescent proteins and silencing guides were transformed into the corresponding hosts strain listed in Table 2. Strains were evaluated in triplicate in an m2p-labs Biolector™, which simultaneously measures fluorescence including GFPuv and mCherry levels, as well as biomass levels. Results are given in
OD600 readings were corrected using the formula below, where OD600 refers to an offline measurement, OD600* refers to Biolector biomass reading, t0 indicates the start point, and tf indicates the final point.
As illustrated in
We first developed control systems capable of the dynamic reduction of protein levels in two-stage processes, as illustrated in
In order to dynamically reduce levels of GltA and Zwf (
The impact of “G” and “Z” valve combinations on metabolic fluxes were measured in minimal media micro-fermentations, performed without any heterologous production pathway. As the strains used had deletions in the major pathways leading to acetate production (poxB, and pta-ackA), pyruvate synthesis was initially evaluated as a measure of metabolic fluxes through glycolysis (
Thus increased sugar uptake with the “G” valves was likely due to a direct regulatory effect of metabolites produced by the TCA cycle, namely α-ketoglutarate (αKG). αKG, a precursor to glutamic acid, has several key regulatory roles, including the regulation of sugar transport by direct inhibition of Enzyme I of the PTS dependent glucose transporter (
To assess the impact of dynamic control over acetyl-CoA fluxes we leveraged citramalate synthase which produces one mole of citramalate from one mole of pyruvate and one mole of acetyl-CoA. Citramalate is a precursor to the industrial chemicals itaconic acid and methyl methacrylate, as well as an intermediate in branched chain amino acid biosynthesis. To produce citramalate, we used a low phosphate inducible plasmid expressing a previously reported feedback resistant mutant citramalate synthase (cimA3.7). This plasmid was introduced into the set of “G” and “Z” valve strains which were then assessed for citramalate production in two stage micro-fermentations (
In the case of pyruvate, the “Z” valve had no significant impact on production (
As illustrated in
Lastly, we evaluated citramalate production strains in instrumented bioreactors. The control strain made reasonable citramalate titers (˜40 g/L), whereas the introduction of SMVs improved production. The combined “GZ” valve strain had the highest citramalate production, reaching titers of ˜100 g/L. This process was then intensified, by increasing biomass levels from ˜10 gCDW/L to ˜25 gCDW/L, leading to titers of 126+/−7 g/L. This process is illustrated in
Previous studies utilizing dynamic control have primarily been informed by a stoichiometric framework, wherein pathways are switched “ON” and “OFF” to reduce fluxes that stoichiometrically compete for a desired product, or in other words pathway redirection. For example Venayak and colleagues have highlighted the importance of GltA/CS as a central valve candidate for dynamic metabolic control, based in part on stoichiometric modelling. However these studies and models have missed the importance of the regulatory role of downstream metabolites, such as αKG. This work demonstrates that increasing flux by dysregulation of feedback control can have a large impact on production, independent of stoichiometry or the minimization of competing pathways. In particular, it was unexpected that reducing Zwf activity increases acetyl-CoA fluxes.
This is the first report of the interaction between minimal Zwf levels, SoxRS activation and Pfo activity in stationary phase. Additionally, the magnitude of the metabolic flux through Pfo is unexpected. Although Pfo, an iron sulfur cluster containing enzyme, has been successfully expressed in both aerobic and anaerobic conditions, it is quickly inactivated by molecular oxygen in vitro, and as a result, conventional wisdom would suggest it is unlikely to support these types of fluxes. These data suggest that the Pfo pathway can operate as a central metabolic pathway under certain conditions, and that high levels of activity can be maintained even aerobically in vivo. Improved understanding may lead to alternative strategies (independent of decreasing Zwf levels) for optimizing flux through this pathway, such as pathway overexpression and/or enzyme engineering.
Referring now to
Referring now to
Referring now to
More generally, this invention highlights the potential of manipulating known and unknown feedback regulatory mechanisms to improve in vivo enzyme activities and metabolic fluxes. This approach can open numerous novel engineering strategies, and leads to significant improvements in production rates, titers and yields. Furthermore these results confirm the metabolic potential of stationary phase cultures. Dynamic metabolic control in two-stage cultures is uniquely suited to implement these strategies. Simply overexpressing key enzymes does not bypass native regulation and the complete removal of central metabolic enzymes and/or metabolites will often lead to growth defects and strains which need to evolve compensatory metabolic changes to meet the demands of growth. In contrast changes to levels of central regulatory metabolites in stationary phase enable rewiring of the regulatory network and metabolic fluxes without this constraint.
As stated above, while the present application has been illustrated by the description of embodiments, and while the embodiments have been described in considerable detail, it is not the intention to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art, having the benefit of this application. Therefore, the application, in its broader aspects, is not limited to the specific details and illustrative examples shown. Departures may be made from such details and examples without departing from the spirit or scope of the general inventive concept
This application claims priority to U.S. Provisional Patent Application No. 63/056,031 filed Jul. 24, 2020 which is incorporated by reference herein in its entirety.
This invention was made with government support under NSF EAGER: #1445726, DARPA #HR0011-14-C-0075, ONR YIP #N00014-16-1-2558, DOE EERE grant #EE0007563. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US21/43023 | 7/23/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63056031 | Jul 2020 | US |
