Patent Grant
9957529
This application claims the priority of Korean Patent Application No. 10-2012-0131850 filed on Nov. 20, 2012 in the Korean Patent and Trademark Office. Further, this application is the National Phase application of International Application No. PCT/KR2013/001954 filed on Mar. 11, 2013, which is incorporated herein by reference in its entirety.
The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Aug. 20, 2015, is named 5230-0469_SL.txt and is 16,251 bytes in size.
The present invention relates to a recombinant microorganism with improved butanol production ability and a method for producing butanol using the same.
Butanol is an intermediate compound with a wide range of applications such as cosmetics, perfumes, hormones, sanitary agents, industrial coating agents, additives for paints, fibers, plastic monomers, medicinal products, vitamins, antibiotics, pesticides, and the like, and thus considered to be very useful (Durre, Biotechnol J., 2:1525-1534, 2007).
As a prior method for producing butanol, a method for producing butanol, acetone and ethanol by fermenting sugars using Clostridium strains (Weizmann, U.S. Pat. No. 1,315,585) was utilized until the 1980's. After that, an oxo process of synthesizing butanol from propylene obtained from petroleum has been widely utilized. However, such a petroleum-based method for producing butanol has drawbacks in that the production process is complex due to employment of high pressures and high temperatures, and that a large amount of hazardous waste and carbon dioxide are discharged from the method (Tsuchida et al., Ind. Eng. Chem. Res., 45:8634, 2006). In this regard, recently there has been a growing need for an environmentally friendly method for producing butanol through fermentation of renewable sources using microorganisms.
However, in order to produce butanol at an industrial level using microorganisms, butanol selectivity, yield and productivity (namely, produced amount of butanol per hour) should be good. However, wild type or recombinant microorganisms used in the production of biobutanol have to meet such conditions.
Specifically, wild type Clostridium acetobutylicum ATCC 824 is known to produce acetone, ethanol and butanol in a weight ratio of about 3:1:6 through fermentation, wherein a small amount of acetic acid and butyric acid are also produced. The yield of the wild type strain is about 25%, and the final concentration is about 10 g/L. Microorganisms having an acetyl-CoA biosynthetic pathway and a butyryl-CoA biosynthetic pathway, such as Clostridium acetobutylicum, are generally known to synthesize acetone, butanol and ethanol by a pathway depicted in
For example, test results in which adhE1 (alcohol/aldehyde dehydrogenase) and ctfAB genes are simultaneously overexpressed in a Clostridium acetobutylicum M5 strain that has lost magaplasmid having butanol production related genes (adc, ctfAB, adhE1 (alcohol/aldehyde dehydrogenase) and adhE2 (alcohol/aldehyde dehydrogenase)) were reported. According to the report, butanol selectivity was found to be enhanced to 0.78 in a weight ratio, but there were some limitations in that productivity and yield were greatly decreased due to the inhibited strain growth and increased acetic acid production (Lee, et al., Biotechnol. J., 4:1432-1440, 2009; Lee, et al., WO 2009/082148).
In the case that a pta gene converting acetyl-CoA to acetate was deleted, and in the case that a pta gene and a buk gene converting butyryl-CoA to butyrate were deleted and then an aad gene (alcohol/aldehyde dehydrogenase) was overexpressed, it was reported that butanol concentration, selectivity and yield were increased. However, both cases still had limitations in view of productivity and stability of strains (LEE et al., WO 2011/037415). Further, in the case that the ctfB gene encoding CoA transferase (CoAT) was additionally deleted from the pta and buk deleted mutant, the productivity was still found to be low (LEE et al., WO 2011/037415).
Besides, there has been an example that reports the production of 18.6 g/l of butanol as the result of fermentation by a randomly mutated mutant Clostridium beijerinckii BA101 strain and using maltodextrin as a carbon source (Ezeji et al., Appl. Microbiol. Biotechnol., 63:653, 2004). However, use of the recombinant strains showed low productivity of the final product, butanol, which makes industrial applicability impossible.
Further, there has been an example that reports decrease in acetone concentration and increase in butanol selectivity by deleting the ctfAB gene encoding CoA transferase or the adc (acetoacetic acid decarboxylase) gene. However, this example has problems in that the final concentration of butanol is less than 10 g/L and the strain is not stable (Jiang et al., Metab. Eng., 11(4-5):284-291, 2009).
Furthermore, in the case of overexpressing adc (acetoacetic acid decarboxylase) and ctfAB (CoA transferase) genes in wild type Clostridium acetobutylicum, acetone, ethanol and butanol productivity are reported to be increased to 95%, 90%, and 37%, respectively, as compared to those of the wild type Clostridium acetobutylicum. However, the example has problems in that butanol selectivity and yield are low (Mermelstein et al., Biotechnol. Bioeng., 42:1053, 1993).
In the course of the present inventors' earnest research to find a microorganism having excellent butanol selectivity, yield and productivity, a recombinant microorganism with inhibited phosphotransacetylase and butyrate kinase activity, increased CoA transferase and aldehyde/alcohol dehydrogenase activity, and increased thiolase or hbd-crt-bcd operon activity among the microorganisms having an acetyl-CoA biosynthetic pathway and a butyryl-CoA biosynthetic pathway has been found to exhibit high butanol selectivity and yield with low ethanol selectivity, thereby allowing continuous production of biobutanol on an industrial scale. Based on this finding, the present invention has been accomplished.
It is an object of the present invention to provide a recombinant microorganism having high butanol selectivity and yield with low ethanol selectivity, allowing the continuous production of biobutanol on an industrial scale.
In accordance with one aspect of the present invention, there is provided a recombinant microorganism with improved butanol production ability which has an acetyl-CoA biosynthetic pathway and a butyryl-CoA biosynthetic pathway, wherein a pathway converting acetyl-CoA into acetate is inhibited and a pathway converting acetyl-CoA to butyryl-CoA is promoted.
In accordance with another aspect of the present invention, there is provided a method for producing butanol including: culturing the recombinant microorganism according to the present invention; and recovering butanol from the culture solution.
The recombinant microorganism according to the present invention exhibits high ABE (acetone, butanol and ethanol) yield, butanol productivity, and butanol selectivity with low ethanol selectivity. Therefore, the recombinant microorganism according to the present invention is capable of continuously producing biobutanol on industrial scale.
The present invention relates to a recombinant microorganism with improved butanol production ability, which has an acetyl-CoA biosynthetic pathway and a butyryl-CoA biosynthetic pathway, wherein a pathway converting acetyl-CoA into acetate is inhibited and a pathway converting acetyl-CoA into butyryl-CoA is promoted.
Further, the present invention relates to a method for producing butanol including: culturing the recombinant microorganism according to the present invention; and recovering butanol from the culture solution.
Hereinafter, the present invention will be described in detail.
The recombinant microorganism according to the present invention is a recombinant microorganism with improved butanol production ability which has an acetyl-CoA biosynthetic pathway and a butyryl-CoA biosynthetic pathway, wherein a pathway converting acetyl-CoA to acetate is inhibited and a pathway converting acetyl-CoA into butyryl-CoA is promoted.
The recombinant microorganism can promote or inhibit other pathways. For example, the recombinant microorganism can promote one or more pathways selected from a pathway converting acetyl-CoA into acetoacetyl-CoA, a pathway converting acetoacetyl-CoA into butyryl-CoA, a pathway converting acetate into acetyl-CoA, a pathway converting butyrate into butyryl-CoA, and a pathway converting butyryl-CoA into butanol. Further, the recombinant microorganism can inhibit a pathway converting butyryl-CoA to butyrate.
Preferably, as shown in
In one embodiment, the recombinant microorganism is a recombinant microorganism having an acetyl-CoA biosynthetic pathway and a butyryl-CoA biosynthetic pathway, wherein phosphotransacetylase and butyrate kinase activities are inhibited, CoA transferase and aldehyde/alcohol dehydrogenase activities are increased, and thiolase or hbd-crt-bcd operon activity is increased.
Acetyl-CoA Biosynthetic Pathway
Herein, the acetyl-CoA biosynthetic pathway refers to a pathway in which acetyl-CoA is synthesized from a specific metabolic product in a microorganism. The acetyl-CoA biosynthetic pathway may be a pathway in which acetyl-CoA is synthesized from pyruvate or a pathway in which acetyl-CoA is synthesized from acetate, and the like. The pathway in which acetyl-CoA is synthesized from acetate may be regulated by CoA transferase.
Butyryl-CoA Biosynthetic Pathway
Herein, the butyryl-CoA biosynthetic pathway refers to a pathway in which butyryl-CoA is synthesized from a specific metabolic product in a microorganism. The butyryl-CoA biosynthetic pathway may be a pathway in which butyryl-CoA is synthesized from acetyl-CoA, a pathway in which butyryl-CoA is synthesized from acetoacetyl-CoA, or a pathway in which butyryl-CoA is synthesized from butyrate, and the like. The pathway in which butyryl-CoA is synthesized from butyrate may be regulated by CoA transferase.
Microorganism Having Acetyl-CoA Biosynthetic Pathway and Butyryl-CoA Biosynthetic Pathway
Microorganisms having the acetyl-CoA biosynthetic pathway and the butyryl-CoA biosynthetic pathway are not particularly limited so long as microorganisms have those biosynthetic pathways. Further, the microorganism according to the present invention may be a wild type microorganism having the acetyl-CoA biosynthetic pathway and the butyryl-CoA biosynthetic pathway or a recombinant microorganism having the acetyl-CoA biosynthetic pathway and the butyryl-CoA biosynthetic pathway through genetic recombination. Preferably, the microorganism according to the present invention is Clostridium without being limited thereto.
Inhibition of Pathway Converting Acetyl-CoA to Acetate
The biosynthesized acetyl-CoA may be converted to acetate via acetyl phosphate. The pathway may be inhibited by regulating the step of converting acetyl-CoA into acetyl-phosphate or the step of converting acetyl-phosphate into acetate. Those steps may be inhibited by known methods such as expression regulation of enzymes regulating each step or inhibition of enzyme activity.
For example, phosphotransacetylase regulates conversion of acetyl-CoA to acetyl-phosphate. The pathway converting acetyl-CoA into acetate may be inhibited by inhibiting phosphotransacetylase. The inhibition of phosphotransacetylase may be performed by inhibiting expression and enzyme activity of phosphotransacetylase, and the like. For example, those skilled in the art can inhibit phosphotransacetylase by selecting an appropriate method such as deleting a pta gene encoding phosphotransacetylase, causing mutations in the pta gene (mutations such as inhibition of normal gene expression of genes through changing, substituting or deleting a part of the base sequence or introducing a part of the base sequence), regulating gene expression in the course of transcription or translation procedures, and the like.
Further, acetate kinase (ack) regulates conversion of acetyl phosphate into acetate. The pathway converting acetyl-CoA into acetate may be inhibited by inhibiting acetate kinase. The inhibition of acetate kinase may be performed by inhibiting expression and enzyme activity of acetate kinase, and the like. For example, those skilled in the art can inhibit acetate kinase by selecting an appropriate method such as deleting an ack gene encoding acetate kinase, causing mutations in the ack gene (mutations such as inhibition of normal gene expression of genes through changing, substituting or deleting a part of the base sequence or introducing a part of the base sequence), regulating gene expression in the course of transcription or translation procedures, and the like.
Inhibition of Pathway Converting Butyryl-CoA into Butyrate
The biosynthesized butyryl-CoA may be converted into butyrate via butyryl phosphate. The pathway may be inhibited by regulating the step of converting butyryl-CoA into butyryl-phosphate or the step of converting butyryl-phosphate into butyrate. Those steps may be inhibited by known methods such as expression regulation of enzymes regulating each step or inhibition of enzyme activity.
For example, butyrate kinase regulates conversion of butyryl phosphate to butyrate. The pathway converting butyryl-CoA to butyrate may be inhibited by inhibiting butyrate kinase. The inhibition of butyrate kinase may be performed by inhibiting expression and enzyme activity of butyrate kinase, and the like. For example, those skilled in the art can inhibit butyrate kinase by selecting an appropriate method such as deleting a buk gene encoding butyrate kinase, causing mutations in the buk gene (mutations such as inhibition of normal gene expression of genes through changing, substituting or deleting a part of the base sequence or introducing a part of the base sequence), regulating gene expression in the course of transcription or translation procedures, and the like.
Further, phosphotransbutylase regulates conversion of butyryl-CoA to butyryl-phosphate. The pathway converting acetyl-CoA to acetate may be inhibited by inhibiting phosphotransbutylase. The inhibition of phosphotransbutylase may be performed by inhibiting expression and enzyme activity of phosphotransbutylase, and the like. For example, those skilled in the art can inhibit acetate kinase by selecting an appropriate method such as deleting a ptb gene encoding the phosphotransbutylase, causing mutations in the ptb gene (mutations such as inhibition of normal gene expression of genes by changing, substituting or deleting a part of the base sequence or introducing a part of the base sequence), regulating gene expression in the course of transcription or translation, and the like.
Acceleration of Pathway Converting Butyrate to Butyryl-CoA
CoA transferase regulates conversion of butyrate to butyryl-CoA. The pathway converting butyrate to butyryl-CoA may be accelerated by increasing the activity of CoA transferase. Increase in the activity of CoA transferase may be performed by increasing expression and enzyme activity of CoA transferase, and the like. For example, those skilled in the art can increase CoA transferase activity by selecting an appropriate method such as introduction, amplification, rearrangement of cftA or ctfB (hereinafter referred to as “ctfAB”) gene encoding CoA transferase, or regulation of gene expression in the course of transcription or translation, and the like.
Acceleration of Pathway Converting Acetate to Acetyl-CoA
CoA transferase regulates conversion of acetate to acetyl-CoA. The pathway converting acetate to acetyl-CoA may be accelerated by increasing the activity of CoA transferase. Increase in the activity of CoA transferase may be performed by increasing expression and enzyme activity of CoA transferase and the like. For example, those skilled in the art can increase CoA transferase activity by selecting an appropriate method such as introduction, amplification, rearrangement of ctfAB gene encoding CoA transferase, or regulation of gene expression in the course of transcription or translation, and the like.
CoA transferase also regulates the pathway converting acetoacetyl-CoA to acetoacetate. Therefore, in the case that activity of CoA transferase is increased, the pathway converting acetoacetyl-CoA to acetone via acetoacetate may also be affected. However, the recombinant microorganism according to the present invention shows that other pathways such as a pathway converting acetyl-CoA to butyryl-CoA and the like, and enzymes related to such pathways are appropriately regulated regardless of increase of CoA transferase activity. As a result, acetone production ability is not increased to the extent that performance as a butanol producing strain is significantly inhibited.
Acceleration of Pathway Converting Butyryl-CoA to Butanol
The synthesized butyryl-CoA may be converted to butanol via butanal. The pathway may be accelerated by promoting the step of converting butyryl-CoA to butanal or the step of converting butanal to butanol. Each step may be accelerated by utilizing a known method such as increasing enzyme activity.
For example, aldehyde/alcohol dehydrogenase regulates conversion of butyryl-CoA to butanal and conversion of butanal to butanol. The pathway converting butyryl-CoA to butanol may be accelerated by increasing aldehyde/alcohol dehydrogenase activity. Increase of aldehyde/alcohol dehydrogenase activity may be performed by increasing expression and enzyme activity of aldehyde/alcohol dehydrogenase, and the like. For example, those skilled in the art can increase aldehyde/alcohol dehydrogenase activity by selecting an appropriate method such as introduction, amplification, rearrangement of adhE gene encoding aldehyde/alcohol dehydrogenase, or regulation of gene expression in the course of transcription or translation, and the like.
Aldehyde/alcohol dehydrogenase also regulates the pathway converting acetyl-CoA to ethanol. Therefore, in the case that aldehyde/alcohol dehydrogenase activity is increased, the pathway converting acetyl-CoA to ethanol via acetoaldehyde may also be affected. However, the recombinant microorganism according to the present invention shows that other pathways such as a pathway converting acetyl-CoA to butyryl-CoA and the like, and enzymes related to such pathways are appropriately regulated, regardless of increase of aldehyde/alcohol dehydrogenase activity. As a result, ethanol production ability and ethanol selectivity are decreased.
Acceleration of Pathway Converting Acetyl-CoA to Butyryl-CoA
The synthesized acetyl-CoA may be converted to butyryl-CoA via acetoacetyl-CoA. The pathway may be accelerated by promoting the step of converting acetyl-CoA to acetoacetyl-CoA or the step of converting acetoacetyl-CoA to butyryl-CoA. Each step may be performed by increasing expression and activity of enzymes that regulates each step.
Acceleration of Pathway Converting Acetyl-CoA to Acetoacetyl-CoA
Thiolase regulates conversion of acetyl-CoA to acetoacetyl-CoA. The pathway converting acetyl-CoA to acetoacetyl-CoA may be accelerated by increasing thiolase activity. The increase in thiolase activity may be performed by increasing expression and enzyme activity of thiolase, and the like. For example, those skilled in the art can increase thiolase activity by selecting an appropriate method such as introduction, amplification, rearrangement of atoB gene encoding thiolase, or regulation of gene expression in the course of transcription or translation, and the like.
Acceleration of Pathway Converting Acetoacetyl-CoA to Butyryl-CoA
hbd-crt-bcd operon regulates conversion of acetoacetyl-CoA to butyryl-CoA. The pathway converting acetoacetyl-CoA to butyryl-CoA may be accelerated by increasing activity of hbd-crt-bcd operon. The increase in activity of hbd-crt-bcd operon may be performed by increasing gene expression and enzyme activity of hbd-crt-bcd operon, and the like. For example, those skilled in the art can increase hbd-crt-bcd operon activity by selecting an appropriate method such as introduction, amplification, rearrangement of hbd-crt-bcd operon gene, or regulation of gene expression in the course of transcription or translation, and the like.
Improvement of Butanol Production Ability
Improvement of butanol production ability refers to enhancement in view of butanol selectivity (proportion of butanol among produced ABE), butanol productivity (amount of butanol produced per hour) and ABE production yield (the amount of produced ABE with respect to the amount of carbon source consumed in the production) (hereinafter referred to as “yield”). Preferably, improvement of butanol production ability means that butanol selectivity becomes 70% or more, butanol productivity becomes 1.0 g/L/h or more, or yield becomes 28% or more, on a batch culture basis.
Decrease in Ethanol Production Ability
In order to produce biobutanol persistently and continuously on industrial scale, ethanol concentration in a culture solution should be less than a certain level. High ethanol concentration may give rise to toxicity to microorganisms, which makes persistent cultivation difficult and thereby reduces efficiency of the cultivation process. The recombinant microorganism according to the present invention exhibits improved butanol production ability but reduced ethanol production ability.
Decrease in ethanol production ability refers to reduction of ethanol proportion in the produced ABE, namely decrease in ethanol selectivity. Preferably, decrease in ethanol production ability means that ethanol selectivity is 15% or less on a batch culture or fed-batch culture basis. The decrease in ethanol production ability means that ethanol selectivity is 20% or less on a continuous culture basis.
Method for Producing Butanol
The method for producing butanol according to the present invention includes culturing the recombinant microorganism according to the present invention; and recovering butanol from the culture solution.
The culturing step may be any culture method generally used in the process for producing alcohols using microorganisms, without being particularly limited thereto. For example, the culture method according to the present invention may be liquid cultivation or solid cultivation, or batch culture, continuous culture or fed-batch culture, without being particularly limited thereto. Those skilled in the art could easily select an appropriate culture method and perform the present invention.
The method for recovering butanol is any method generally employed in recovery of bioalcohols, and is not particularly limited. For example, the step of recovering butanol according to the present invention may be performed by separation membranes, distillation, or the like. Further, the steps of culturing microorganisms and recovering butanol may be performed simultaneously or sequentially. For example, butanol may be recovered while continuously culturing microorganisms.
The above and other aspects, features, and advantages of the present invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings. However, it should be understood that the present invention is not limited to the following embodiments and may be embodied in different ways, and that the embodiments are provided for complete disclosure and thorough understanding of the invention by those skilled in the art. The scope of the invention should be defined only by the accompanying claims and equivalents thereof.
Materials and Methods
A gene deleted strain Clostridium acetobutylicum PJC4BK Δbuk::MLSr* is the strain reported in the Journal of Microbiology (E M Green et al., 142, pp 2079) in 1996; Clostridium acetobutylicum ATCC824 Δpta and Clostridium acetobutylicum ATCC824 Δpta Δbuk are constructed in accordance with the method disclosed in WO2011/037415.
On evaluating biobutanol production ability of the recombinant C. acetobutylicum strain, alcohol selectivity (proportion of a specific alcohol in the produced mixed solvent (ABE: acetone, butanol, ethanol)), butanol productivity and yield are calculated as below:
(Butanol productivity in batch culture and fed-batch culture method is based on exponential phase. In continuous culture, butanol productivity is based on cumulative amount of ABE produced in total phase.)
Construction of pGS1-atoB
First of all, E. coli W3110 was streaked on solid LB medium, followed by aerobic culturing for 24 hours. A colony selected from the streaked solid medium was cultured in 3 ml of a liquid culture medium for 18 hours, followed by centrifuging the culture solution to obtain cells. The cells were washed with 10 ml Tris buffer, followed by purification using a Wizard Genomic DNA Purification Kit (manufactured by Promega Corp., USA) to isolate chromosome of the strain.
atoB gene (SEQ ID NO: 1) was amplified using primers atoB-UP-PstI (SEQ ID NO: 2) and atoB-DN-XhoI (SEQ ID NO: 3) and using the isolated chromosome as a template (Table 1). 100 μl of PCR mixture includes 250 μM dNTP, 20 pmol of each primer, 1.5 mM MgCl2, 10 μl of 10× buffer, 100 ng of DNA template, and 1 unit of pfu polymerase. In PCR, the reaction was repeated for 25 cycles consisting of initial denaturing at 95° C. for 5 minutes, followed by denaturing at 95° C. for 1 minute, annealing at 50° C. for 1 minute and then polymerizing at 72° C. for 1 minute.
The amplified gene was purified on 1% agarose gel, and then digested with PstI and XhoI restriction enzymes to cleave a DNA fragment. pGS1-MCS vector (
Construction of pGS1-HCB
First of all, Clostridium acetobutylicum ATCC 824 was streaked on solid RCM medium, followed by anaerobic culturing for 48 hours. A colony selected from the streaked solid medium was cultured in 3 ml of a liquid RCM culture medium for 18 hours, followed by centrifuging the culture solution to obtain cells. The cells were washed with 10 ml Tris buffer, followed by purification using a Wizard Genomic DNA Purification Kit (manufactured by Promega Corp., USA) to isolate chromosome of the strain.
hbd-crt-bcd operon (SEQ ID NO: 4,
100 μl of PCR mixture includes 250 μM dNTP, 20 pmol of each primer, 1.5 mM MgCl2, 10 μl of 10× buffer, 100 ng of DNA template, and 5 units of pfu polymerase. In PCR, the reaction was repeated for 30 cycles consisting of initial denaturing at 95° C. for 5 minutes, followed by denaturing at 95° C. for 1 minute, annealing at 50° C. for 1 minute and then polymerizing at 72° C. for 4 minutes.
The amplified gene was purified on 1% agarose gel, and digested with PstI and XhoI restriction enzymes to cleave the DNA fragment, which was then ligated to a pGS1-MCS vector to construct pGS1-HCB (
Construction of pGS1-E1AB
Clostridium acetobutylicum ATCC 824 was streaked on solid RCM medium, followed by anaerobic culturing for 24 hours. A colony selected from the streaked solid medium was cultured in 3 ml of a liquid culture medium for 18 hours, followed by centrifuging the culture solution to obtain cells. The cells were washed with 10 ml Tris buffer, followed by purification using a Wizard Genomic DNA purification Kit (manufactured by Promega Corp., USA) to isolate chromosome of the strain.
adhE1 gene (SEQ ID NO: 7) was amplified using primers AdhE1-UP-PstI (SEQ ID NO: 8) and AdhE1-DN-XhoI (SEQ ID NO: 9) and using the isolated chromosome as a template (Table 3). 100 μl of PCR mixture includes 250 μM dNTP, 20 pmol of each primer, 1.5 mM MgCl2, 10 μl of 10× buffer, 100 ng of DNA template, and 1 unit of pfu polymerase. In PCR, the reaction was repeated for 30 cycles consisting of initial denaturing at 95° C. for 5 minutes, followed by denaturing at 95° C. for 1 minute, annealing at 50° C. for 1 minute and then polymerizing at 72° C. for 2 minute. The amplified gene was purified on 1% agarose gel, and then digested with PstI and XhoI restriction enzymes to cleave the DNA fragment. pGS1-MCS vector was digested with the same restriction enzymes, and the DNA fragment was ligated to construct pGS1-AdhE1 (
pGS1-E1AB was constructed using previously constructed recombinant plasmids. First of all, ctfAB gene (SEQ ID NO: 10) was amplified using primers CtfAB-UP-XhoI (SEQ ID NO: 11) and E1AB-DN-SalI (SEQ ID NO: 12) and using the isolated chromosome of Clostridium acetobutylicum ATCC 824 as a template (Table 4).
The amplified gene was purified on a 1% agarose gel, and digested with XhoI and SalI restriction enzymes to cleave the DNA fragment. A pGS1-AdhE1 vector was digested with the same restriction enzymes, and the DNA fragment was ligated to construct pGS1-E1AB (
Construction of pGS1-E1 AB-atoB
pGS1-E1AB-atoB was constructed using previously constructed recombinant plasmids pGS1-atoB and pGS1-E1AB.
First, atoB gene (SEQ ID NO: 1) and promoter and terminator regions of the plasmid were amplified using primers pTh1-UP-SalI (SEQ ID NO: 13) and pGS-R4 (SEQ ID NO: 14) and using the constructed pGS1-atoB as a template (Table 5). 100 μl of PCR mixture includes 250 μM dNTP, 20 pmol of each primer, 1.5 mM MgCl2, 10 μl of 10× buffer, 100 ng of DNA template, and 1 unit of pfu polymerase. In PCR, the reaction repeated 25 cycles consisting of initial denaturing at 95° C. for 5 minutes, followed by denaturing at 95° C. for 1 minute, annealing at 50° C. for 1 minute and then polymerizing at 72° C. for 4 minute.
The amplified gene was purified on a 1% agarose gel, and then digested with SalI and XmaI restriction enzymes to cleave a DNA fragment. pGS1-E1AB vector was digested with the same restriction enzymes, and the DNA fragment was ligated to construct pGS1-E1AB-atoB (
Construction of pGS1-E1AB-HCB
pGS1-E1AB-HCB was constructed using the previously constructed recombinant plasmids pGS1-HCB and pGS1-E1AB.
A gene encoding hbd-crt-bcd operon (SEQ ID NO: 4) and promoter and terminator regions were amplified using primers pTh1-UP-SalI (SEQ ID NO: 13) and pGS-R4 (SEQ ID NO: 14) and using pGS1-HCB constructed in the above as a template. 100 μl of PCR mixture includes 250 μM dNTP, 20 pmol of each primer, 1.5 mM MgCl2, 10 μl of 10× buffer, 100 ng of DNA template, and 5 units of pfu polymerase. In PCR, the reaction was repeated for 30 cycles consisting of initial denaturing at 95° C. for 5 minutes, followed by denaturing at 95° C. for 1 minute, annealing at 50° C. for 1 minute and then polymerizing at 72° C. for 1 minute.
The amplified gene was purified on a 1% agarose gel, and then digested with SalI and XmaI restriction enzymes to cleave a DNA fragment. pGS1-E1AB vector was digested with the same restriction enzymes, the DNA fragment was ligated to construct pGS1-E1AB-HCB (
The recombinant plasmids manufactured in the Experimental Example 1 were introduced into the gene deleted strains listed in Table 6 to construct recombinant microorganisms.
Clostridium acetobutylicum PJC4BK Δbuk::MLSr
Clostridium acetobutylicum ATCC824 Δpta
Clostridium acetobutylicum ATCC824 Δpta Δbuk
Each gene deleted Clostridium strain was cultured in 60 ml of liquid CGM (Clostridium Growth Media) (0.75 g/L K2HPO4, 0.75 g/L KH2PO4, 0.7 g/L, MgSO4.7H2O, 0.017 g/L MnSO4.5H2O, 0.01 g/L, FeSO4.7H2O, 2 g/L (NH4)2SO4, 1 g/L NaCl, 2 g/L asparagine, 0.004 g/L p-aminobenzoic acid, 5 g/L, yeast extract, 4.08 g/L CH3COONa.3H2O, and 80 g/L glucose) under anaerobic conditions until OD600 became 0.5. The culture solution was stood on ice for 10 minutes, followed by centrifuging the culture solution at 7000 g at 4° C. for 10 minutes. The cell pellets were washed with an electroporation buffer solution three times, and suspended in 2 ml of the same buffer solution to manufacture cells for transformation. To 500 μl of the prepared cells for transformation, 0.5˜2.0 μg of plasmids were added to perform electroporation (4 mm cuvette, 2.5 kV, ∞Ω, 25 uF) by Gene Pulser II manufactured by Bio-Rad Corporation. Subsequently, the cells were cultured anaerobically in a medium with antibiotics to obtain transformed strains (Table 7).
The plasmids used for transformation were all methylated in E. coli TOP10 strain transformed with a pAN1 vector prior to electroporation such that the plasmids could not be affected by restriction system of Clostridium strains.
Clostridium acetobutylicum PJC4BK
Clostridium acetobutylicum PJC4BK
Clostridium acetobutylicum PJC4BK
Clostridium acetobutylicum PJC4BK
Clostridium acetobutylicum PJC4BK
Clostridium acetobutylicum PJC4BK
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Clostridium acetobutylicum ATCC824
Throughout batch culture, butanol production ability depending on the recombinant microorganisms was tested. The recombinant Clostridium strains (#1 to #18) constructed in Experimental Example 2 were streaked on a solid CGM medium, followed by anaerobic culture at 37° C. overnight. Each of the cultured colony was inoculated to a 50 ml disposable tube (manufactured by Falcon, USA) containing 40 ml of CCM, followed by standing at 37° C., and then cultured anaerobically until OD600 became 1. The cultured microorganisms were inoculated again to a liquid CGM medium containing 400 ml of 6% glucose, followed by standing at 37° C., and then culturing anaerobically until OD600 became 1. The resulting microorganisms were inoculated to a fermenter including 1.6 L of liquid CGM medium to which 8% glucose was added, thereby initiating cultivation. pH was maintained at pH 5.0 using ammonium hydroxide (NH4OH) during the anaerobic culture, wherein the anaerobic conditions were maintained by purging nitrogen at a speed of 20 ml/min. The concentration of the produced butanol and mixed solvent was analyzed every three hours after the cultivation. The analysis of butanol and mixed solvent was performed using a gas chromatography (Agilent, USA). The analysis conditions are summarized in Table 8. The culture solution was centrifuged to give a supernatant, which was then subjected to HPLC and sugar analyzer to determine the concentration of sugars and organic acids. In HPLC, water containing 0.01N sulfuric acid was used as a mobile phase, and flow rate was 0.6 ml/min. As columns, Aminex87H and Aminex87P (Bio-Rad, USA) were employed. The sugars and organic acids were analyzed using an RI (Reflective Index) detector. As a control group, wild type C. acetobutylicum ATCC 824 was used (C1).
Comparing #1˜#3 strains, it was confirmed that ethanol selectivity was greatly reduced from 17% to 7% when HCB operon and atoB gene were overexpressed in buk gene-deleted PJC4BK strain. Since ethanol causes toxicity to microorganisms, it is very important to keep the concentration of ethanol low when butanol is produced through continuous fermentation. However, in the case of #2 and #3 strains, although ethanol selectivity is decreased, there are problems that butanol productivity and yield are still low.
On the other hand, comparing strain #1 with strain #4, it was confirmed that butanol productivity was enhanced when adhE1 and ctfAB were overexpressed simultaneously in PJC4BK strain. Accordingly, the present inventors aimed to increase butanol productivity and keep ethanol selectivity low by overexpressing atoB gene or HCB operon in #4 strain. As a result, comparing strains #2 and #3 with strains #5 and #6, respectively, it was confirmed that butanol productivity was increased by 41% and 17%, respectively. However, in the case of #5 and #6 strains, it was confirmed that ethanol selectivity was slightly increased from 7% to 16% and 13%, respectively.
On the contrary, pta gene-deleted strains (#7˜#12) exhibited generally low yield and specifically low ethanol selectivity. From the result, it was determined that the deletion of pta gene decreased ethanol selectivity. In this regard, the present inventors estimated that a further deletion of pta in strains #5 and #6 would reduce ethanol selectivity while keeping butanol productivity high. Based on such estimation, the performances of strains #17 and #18 were measured. In the case of strain #17, it was confirmed that ethanol selectivity was decreased by half, and butanol productivity, selectivity and ABE yield were improved by 7%, 21% and 15%, respectively, as compared to strain #5. On the other hand, in the case of strain #18, it was confirmed that ethanol selectivity was decreased by 7%, butanol selectivity was also decreased by about 4%, and butanol productivity and yield were increased by 11%, 10%, respectively, as compared to strain #6.
In summary, it could be confirmed that butanol productivity and yield tended to increase, when adhE and ctfAB were simultaneously overexpressed in a strain in which pta and buk related to organic acid production were deleted. In addition, it could be confirmed that, when atoB or HCB operon were further overexpressed, ethanol selectivity was decreased while butanol selectivity was increased (Table 9).
C. acetobutylicum ATCC824
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
#6, #16˜#18 recombinant strains which were determined to have excellent butanol selectivity, butanol productivity and yield, and low ethanol selectivity in Experimental Example 3 were subjected to fed-batch cultivation in a culture medium containing an adsorbent capable of selectively adsorbing butanol.
First, recombinant Clostridium strains #6, #16, #17 and #18 constructed in Experimental Example 2 were streaked on solid CGM, followed by culturing anaerobically at 37° C. overnight. Each of the cultured colony was inoculated to a 50 ml disposable tube (manufactured by Falcon, USA) containing 40 ml of CCM, followed by standing at 37° C., and culturing the colony anaerobically until OD600 became 1. The cultured microorganism was again inoculated to liquid CGM containing 400 ml of 6% glucose, followed by standing at 37° C., and culturing the colony anaerobically until OD600 became 1. The obtained microorganism was inoculated to a fermenter containing 1.6 L of liquid CGM containing 8% glucose and 200 g of an adsorbent capable of selectively adsorbing butanol, and then cultured. pH was maintained at pH 5.0 using ammonium hydroxide (NH4OH) during anaerobic cultivation, wherein the anaerobic conditions were maintained by purging nitrogen at a speed of 20 ml/min. The concentration of the produced butanol and mixed solvent was analyzed every three hours after the cultivation. In order to maintain the glucose concentration in the culture solution at 10 g/L or more, 700 g/L glucose solution was used as a feeding solution.
In order to produce butanol through continuous cultivation with high yield, high productivity and high selectivity, it is very important to keep the concentration of ethanol low such that ethanol does not cause toxicity to strains during the culture period. As can be seen from results of fed-batch cultivation, it was confirmed that strains #17 and #18 maintained very low ethanol selectivity while maintaining high performance as butanol producing strains. Accordingly, these strains were expected to be suitable for long-term continuous culture (Table 10).
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Clostridium acetobutylicum
Based on the results from Experimental Example 4, recombinant strains #16, #17 and #18 were tested for the performance of butanol producing strains through continuous cultivation. First, an incubator for continuous culture process was manufactured in accordance with Korean patent application no. 10-2012-0038770. At upper and lower ends of a 3 L column, a filter having a size of about 150 μm was provided in order to prevent an adsorbent from elution, followed by providing a stirrer and charging 200 g of an adsorbent. Two columns were prepared. These incubators were linked by a silicon tube, followed by providing pumps, thereby allowing a culture solution to be circulated between the columns. As the inlet and outlet for the columns, 4-way valves were provided such that, in the course of culturing, the columns could be subjected to desorption in real time by flowing a solvent for elution when the adsorbent in the columns was saturated with butanol and mixed solvent. In the case that the first column was subjected to desorption, the culture solution was circulated to the second column such that the culture solution flew continuously. The culture solution was circulated in a direction from upper to lower of the column, but the direction is not particularly limited. #16 strain (control group), #17 and #18 strains having butanol and mixed solvent productivity were cultured in the incubator manufactured above. First, 800 ml of microorganism which was anaerobically cultured in liquid CGM overnight was inoculated to an incubator comprising 3.2 L liquid CGM to initiate culture. In the present Experimental Example, the microorganism was cultured by general batch fermentation. After initiation of the culture, the culture solution was circulated by passing through columns with a flow rate of 50 ml/min through a pump when the butanol concentration became about 7 g/L˜8 g/L. As the culture solution passed through the columns, the adsorbent was suspended in the culture solution to form a slurry phase, which prevented the culture solution from flocking, thereby passing through the columns. The butanol concentration was maintained at 8 g/L or less just before and after the culture solution passed through the columns.
As a result, it could be confirmed that yield, selectivity and productivity were all excellent, particularly remarkable enhancement was found in view of process stability (culture period) when hcb operon or atoB encoding thiolase were overexpressed. However, in the case of recombinant strain #16 in which HCB operon or thiolase was not overexpressed, as the culture period got longer, ethanol was accumulated in high concentration, which greatly deteriorated performance of the strain, particularly in view of butanol and mixed solvent productivity. Accordingly, it was impossible to culture the microorganism for more than 88 hours.
Comparing the produced cumulative amount of butanol and total mixed solvent for the three strains #16, #17 and #18, it was confirmed that strain #16 in which HCB operon or thiolase was not overexpressed showed high ethanol selectivity of 27%, and thus, due to toxicity to the strain, solvent productivity and butanol selectivity were remarkably decreased. On the contrary, in the case of strains #17 and #18 in which hcb operon or atoB were overexpressed respectively, it was confirmed that butanol and solvents were stably produced while maintaining solvent productivity for more than 100 hours of cultivation (Table 11). This means that the process stability was improved during continuous culture, thereby greatly enhancing utility and operation cost.
The present invention relates to a recombinant microorganism with improved butanol production ability which has an acetyl-CoA biosynthetic pathway and a butyryl-CoA biosynthetic pathway, wherein a pathway converting acetyl-CoA to acetate is inhibited and a pathway converting acetyl-CoA to butyryl-CoA is promoted. In addition, the present invention relates to a method for producing butanol using the recombinant microorganism.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2012-0131850 | Nov 2012 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2013/001954 | 3/11/2013 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2014/081084 | 5/30/2014 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 1315585 | Weizmann | Sep 1919 | A |
| 8039239 | Reeves | Oct 2011 | B2 |
| 9096872 | Lee | Aug 2015 | B2 |
| 20090155869 | Buelter et al. | Jun 2009 | A1 |
| 20130017588 | Lee | Jan 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 1020110033086 | Mar 2011 | KR |
| 1020110033087 | Mar 2011 | KR |
| 1020110033089 | Mar 2011 | KR |
| 2009082148 | Jul 2009 | WO |
| 2011037415 | Mar 2011 | WO |
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| 20150376655 A1 | Dec 2015 | US |
