# Patent

## Title
Microorganism producing 4-hydroxybutyrate and a method for producing 4-hydroxybutyrate in anaerobic condition using the same

## Abstract

A genetically modified microorganism comprising a polynucleotide encoding α-ketoglutarate synthase or a mutant thereof, and a polynucleotide encoding pyruvate carboxylase or a mutant thereof; wherein the genetically modified microorganism has decreased malate quinone oxidoreductase activity and/or decreased phosphoenolpyruvate carboxykinase activity compared to an unmodified microorganism of the same type, and wherein the genetically modified microorganism produces 4-hydroxybutyrate.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Patent Application No. 10-2013-0100568, filed on Aug. 23, 2013, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference.
INCORPORATION BY REFERENCE OF ELECTRONICALLY SUBMITTED MATERIALS
Incorporated by reference in its entirety herein is a computer-readable nucleotide/amino acid sequence listing submitted concurrently herewith and identified as follows: One 149,196 Byte ASCII (Text) file named “718145 ST25-Revised.TXT” created on Nov. 3, 2014.
BACKGROUND
1. Field
The present disclosure relates to a genetically modified microorganism that produces 4-hydroxybutyrate and a method of producing 4-hydroxybutyrate using the genetically modified microorganism.
2. Description of the Related Art
Biodegradable polymers have been suggested as an alternative to the synthetic polymers which account for a great part of severe environmental pollution. Accordingly, various biodegradable polymers have been developed. One such biodegradable polymer is poly-β-hydroxybutyrate, which is a biodegradable polymer accumulated in a nutritionally imbalanced state by various microorganisms and has excellent properties such as biodegradability, moisture resistance, piezoelectricity, and biocompatibility. 4-hydroxybutyrate (4HB), which is one of the various types of poly-β-hydroxybutyrate, is a representative polyhydroxyalkanoate (PHA). 4HB is a substance produced as a white powder in a small quantity from wine, beef, and fruit. Many studies are conducted with regard to 4HB as a biodegradable plastic material as 4HB shows a wide range of physical properties from crystalline plastic to highly elastic rubber as 4HB is similar to polyester. 4HB for medical use is generally produced by fermentation. Although a method of producing 1,4-butandiol (1,4-BDO) from 4HB is known, it has not been commercialized yet.
4HB has been used as a starting material in producing other C4-chemicals such as 1,4-BDO and γ-butyrolactone (GBL) by methods using a microorganism. 4HB may easily be converted to various other C4-chemicals such as 1,4-BDO, GBL, and tetrahydrofuran (THF). These various chemicals are used in the chemical industries as polymer, solvent, and fine chemical intermediates.
Most C4-chemicals that are currently synthesized are derived from 1,4-butandiol or maleic anhydride, but the chemical production process needs to be improved or replaced by a newly developed process as production costs are increasing due to rising oil prices. A biological process for producing C4-chemicals is suggested as an alternative to the chemical process, but the yield of 4HB production using conventional microorganisms is low. Thus, there is a need for a mutant microorganism capable of producing 4HB, and a biological method of producing 4HB using the mutant microorganism.
SUMMARY
Provided is a genetically modified (i.e. engineered) microorganism that produces 4-hydroxybutyrate (4HB), and a method of increasing 4HB production by using the prepared strain. The genetically modified microorganism comprises a polynucleotide encoding α-ketoglutarate synthase or a mutant thereof, and a polynucleotide encoding pyruvate carboxylase or a mutant thereof; and has decreased malate quinone oxidoreductase activity and/or decreased phosphoenolpyruvate carboxykinase activity compared to an unmodified microorganism of the same type.



BRIEF DESCRIPTION OF THE DRAWINGS
These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a flow chart displaying genes for alteration, deletion, and introduction in metabolic pathways and glycolysis pathways for 4HB production in a microorganism;
FIG. 2 is a map of the expression vector pGSK+ used in preparing a genetically modified microorganism;
FIG. 3 is a map of the expression vector pGST1 used in preparing a genetically modified microorganism;
FIG. 4 is a map of the expression vector MD0376 used in preparing a genetically modified microorganism; and
FIG. 5 is a graph comparing 4HB production concentration between the basic Corynebacteria strain and a genetically engineered strain.



DETAILED DESCRIPTION
Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Provided is a genetically modified microorganism (i.e., a strain) that produces 4-hydroxybutyrate (4HB).
An embodiment of invention provides a genetically modified microorganism that produces 4HB, wherein the activity of malate quinone oxidoreductase and/or the activity of phosphoenolpyruvate carboxykinase is eliminated or decreased compared to an unmodified microorganism of the same type, and wherein the genetically modified microorganism comprises a polynucleotide encoding α-ketoglutarate synthase or a mutant thereof, and/or a polynucleotide encoding pyruvate carboxylase or a mutant thereof.
The term “unmodified microorganism of the same type” means a reference microorganism that is compared to a genetically modified microorganism comprising a subject modification. The reference microorganism refers to a wild-type microorganism or a parental microorganism. The parental microorganism refers to a microorganism that has not undergone the subject modification that the genetically modified microorganism has undergone and is genetically identical to the genetically modified microorganism except for the modification, and thus serves as a reference microorganism for the modification.
In addition, the genetically modified microorganism may be a microorganism wherein the activity of succinate semialdehyde dehydrogenase is eliminated or decreased.
In addition, the genetically modified microorganism may further include a polynucleotide encoding pyruvate dehydrogenase or a mutant thereof.
In addition, the genetically modified microorganism may further include a polynucleotide encoding formate dehydrogenase or a mutant thereof.
The strain may be a strain selected from the group consisting of lumen bacteria, Corynebacterium genus, Brevibacterium genus, and Escherichia coli. The strain may be Corynebacterium glutamicum. In particular, Corynebacterium glutamicum may be cultured in a wide range of culture conditions and at a high growth rate. In addition, Corynebacterium glutamicum is non-pathogenic and harmless to environment, as they do not produce a spore. In particular, Corynebacterium glutamicum is highly available in industries as it may be cultured to a concentration four times higher than that of Escherichia coli. 
The strain capable of producing 4HB may be a strain wherein the activity of lactate dehydrogenase is eliminated or decreased compared to an unmodified microorganism of the same type. The strain capable of producing 4HB may include succinyl-CoA:coenzyme A transferase or a mutant thereof, coenzyme-dependent succinate semialdehyde dehydrogenase or a mutant thereof, and 4-hydroxybutyrate dehydrogenase or a mutant thereof.
Lactate dehydrogenase is an enzyme that catalyzes the conversion of pyruvate to lactate. The lactate dehydrogenase may include lactate dehydrogenase (Ldh), lactate dehydrogenase A (LdhA), lactate dehydrogenase B (LdhB), and lactate dehydrogenase C (LdhC). The activity of the lactate dehydrogenase may be eliminated or decreased in a genetically modified microorganism. The lactate dehydrogenase may an enzyme classified as EC.1.1.1.27. The lactate dehydrogenase may be referred to as LdhA. The genetically modified microorganism may be a microorganism wherein a gene encoding lactate dehydrogenase is inactivated or attenuated. The mutant of lactate dehydrogenase may be an enzyme having catalytic activity the same as that of lactate dehydrogenase and sequence identity of 80% or higher with amino acid sequence of a wild type lactate dehydrogenase. The mutant may be an enzyme having catalytic activity the same as that of lactate dehydrogenase and sequence identity of 85% or higher, 90% or higher, 95% or higher, or 99% or higher with amino acid sequence of a wild type lactate dehydrogenase.
The succinyl-CoA:coenzyme A transferase may be referred to as Cat1. The enzyme catalyzes the conversion of succinate to succinyl-CoA. The succinyl-CoA:coenzyme A transferase may be an enzyme classified as EC.2.8.3. The enzyme may be derived from Corynebacterium glutamicum or Clostridium kluyveri. The succinyl-CoA:coenzyme A transferase may have an amino acid sequence of SEQ ID NO: 1. A polynucleotide encoding the succinyl-CoA:coenzyme A transferase may have a nucleic acid of SEQ ID NO: 2. The mutant of the succinyl-CoA:coenzyme A transferase may be an enzyme having catalytic activity the same as that of the succinyl-CoA:coenzyme A transferase and sequence identity of 80% or higher with amino acid sequence of a wild type the succinyl-CoA:coenzyme A transferase. The mutant may be an enzyme having catalytic activity the same as that of the succinyl-CoA:coenzyme A transferase and sequence identity of 85% or higher, 90% or higher, 95% or higher, or 99% or higher with amino acid sequence of a wild type the succinyl-CoA:coenzyme A transferase.
The CoA-dependent succinate semialdehyde dehydrogenase may be referred to as SucD. The enzyme catalyzes the conversion of succinyl-CoA to succinyl semialdehyde. A polynucleotide encoding the CoA-dependent succinate semialdehyde dehydrogenase (SEQ ID NO: 3) may be derived from a Corynebacterium glutamicum or Porphyromonas gingivalis. The polynucleotide encoding the CoA-dependent succinate semialdehyde dehydrogenase may have a nucleic acid of SEQ ID NO: 4. The mutant of CoA-dependent succinate semialdehyde dehydrogenase may be an enzyme having catalytic activity the same as that of CoA-dependent succinate semialdehyde dehydrogenase and sequence identity of 80% or higher with amino acid sequence of a wild type succinate semialdehyde dehydrogenase. The mutant may be an enzyme having catalytic activity the same as that of CoA-dependent succinate semialdehyde dehydrogenase and sequence identity of 85% or higher, 90% or higher, 95% or higher, or 99% or higher with amino acid sequence of a CoA-dependent succinate semialdehyde dehydrogenase.
The 4-hydroxybutyrate dehydrogenase may be referred to as 4Hbd. The enzyme catalyzes the conversion of succinyl semialdehyde to 4HB. The enzyme may be derived from a Corynebacterium glutamicum or Porphyromonas gingivalis. The 4-hydroxybutyrate dehydrogenase may have an amino acid sequence of SEQ ID NO: 5. A polynucleotide encoding the 4-hydroxybutyrate dehydrogenase may have a nucleic acid of SEQ ID NO: 6. The mutant of 4-hydroxybutyrate dehydrogenase may be an enzyme having catalytic activity the same as that of 4-hydroxybutyrate dehydrogenase and sequence identity of 80% or higher with amino acid sequence of a wild type 4-hydroxybutyrate dehydrogenase. The mutant may be an enzyme having catalytic activity the same as that of 4-hydroxybutyrate dehydrogenase and sequence identity of 85% or higher, 90% or higher, 95% or higher, or 99% or higher with amino acid sequence of a wild type 4-hydroxybutyrate dehydrogenase.
A gene may be additionally introduced into or eliminated from a strain capable of producing 4HB. For example, activity of malate quinone oxidoreductase may be eliminated or decreased in the strain compared to an unmodified microorganism of the same type. Malate quinone oxidoreductase may be referred to as Mqo. The enzyme catalyzes the conversion of converting malate to oxaloacetate. The malate quinone oxidoreductase may have an amino acid sequence of SEQ ID NO: 17. Gene addition, substitution, or deletion may be performed in a polynucleotide encoding malate quinone oxidoreductase in order to decrease activity of malate quinone oxidoreductase. The polynucleotide encoding malate quinone oxidoreductase may be partly or totally deleted by homologous recombination. The polynucleotide encoding malate quinone oxidoreductase may have a nucleic acid sequence of SEQ ID NO: 18.
Activity of phosphoenolpyruvate carboxykinase may be eliminated or decreased in the strain compared to an unmodified microorganism of the same type. Phosphoenolpyruvate carboxykinase may be referred to as PckG. The enzyme catalyzes the conversion of converting oxaloacetate to phosphoenolpyruvate. The phosphoenolpyruvate carboxykinase may have an amino acid sequence of SEQ ID NO: 19. Gene addition, substitution, or deletion may be performed in a polynucleotide encoding phosphoenolpyruvate carboxykinase in order to decrease activity of phosphoenolpyruvate carboxykinase. The polynucleotide encoding phosphoenolpyruvate carboxykinase may be partly or totally deleted by homologous recombination. The polynucleotide encoding phosphoenolpyruvate carboxykinase may have a nucleic acid sequence of SEQ ID NO: 20.
The microorganism may include a polynucleotide encoding α-ketoglutarate synthase or a mutant thereof. α-ketoglutarate synthase may be referred to as SucA. The enzyme catalyzes the conversion of ketoglutarate to succinyl semialdehyde. The enzyme may be derived from Corynebacterium glutamicum or Mycobacterium bovis. The α-ketoglutarate synthase may have an amino acid sequence of SEQ ID NO: 7. A polynucleotide encoding the α-ketoglutarate synthase may have a nucleic acid of SEQ ID NO: 8. The mutant of α-ketoglutarate synthase is an enzyme having catalytic activity the same as that of α-ketoglutarate synthase and sequence identity of 80% or higher with amino acid sequence of a wild type α-ketoglutarate synthase. The mutant may be an enzyme having catalytic activity the same as that of α-ketoglutarate synthase and sequence identity of 85% or higher, 90% or higher, 95% or higher, or 99% or higher with amino acid sequence of a wild type α-ketoglutarate synthase.
The microorganism may include a polynucleotide encoding pyruvate carboxylase or a mutant thereof. Pyruvate carboxylase may be referred to as Pyc. The enzyme catalyzes the conversion of pyruvate to oxaloacetate. The enzyme may be derived from Corynebacterium glutamicum or Escherichia coli. The pyruvate carboxylase may have an amino acid sequence of SEQ ID NO: 9. The mutant of pyruvate carboxylase is an enzyme having catalytic activity the same as that of pyruvate carboxylase and sequence identity of 80% or higher with amino acid sequence of a wild type pyruvate carboxylase. The mutant may be an enzyme having catalytic activity the same as that of pyruvate carboxylase and sequence identity of 85% or higher, 90% or higher, 95% or higher, or 99% or higher with amino acid sequence of a wild type pyruvate carboxylase. The mutant of pyruvate carboxylase may be formed by substituting the 458th amino acid of a wild type pyruvate carboxylase. The 458th amino acid of a wild type pyruvate carboxylase may be proline. The 458th amino acid of a wild type pyruvate carboxylase may be substituted with serine (SEQ ID NO: 10). The polynucleotide encoding pyruvate carboxylase may have a nucleic acid sequence of SEQ ID NO: 11.
Activity of succinate semialdehyde dehydrogenase may be eliminated or decreased in the strain. Succinate semialdehyde dehydrogenase may be referred to as SSADH. The enzyme catalyzes the conversion of succinyl semialdehyde to succinate. The succinate semialdehyde dehydrogenase may have an amino acid sequence of SEQ ID NO:21. Gene addition, substitution, or deletion may be performed in NCgl0049, NCgl0463, or NCgl2619 gene in order to decrease activity of succinate semialdehyde dehydrogenase. The NCgl0049 polynucleotide may be partly or totally deleted by homologous recombination. The NCgl0049 polynucleotide may have a nucleic acid sequence of SEQ ID NO: 22. The NCgl0463 polynucleotide may have a nucleic acid sequence of SEQ ID NO: 23. The NCgl2619 polynucleotide may have a nucleic acid sequence of SEQ ID NO: 24.
The microorganism may include a polynucleotide encoding pyruvate dehydrogenase. The pyruvate dehydrogenase may be referred to as “pyruvate dehydrogenase complex” and also Pdh. The pyruvate dehydrogenase catalyzes the conversion of to acetyl CoA. The pyruvate dehydrogenase complex includes pyruvate dehydrogenase (E1), dihydrolipoyl transacetylase (E2), and dihydrolipoyl dehydrogenase (E3). In the pyruvate dehydrogenase, E1 is also referred to as AceE, E2 is referred to as AceF, and E3 is referred to as lpd or lpdA, depending on microorganisms.
A polynucleotide encoding the pyruvate dehydrogenase includes lpd, aceE, and aceF genes. The genes may be derived from Corynebacterium glutamicum or Escherichia coli. The lpd gene may be a polynucleotide having a nucleic acid sequence of SEQ ID NO: 12. The aceE gene may be a polynucleotide having a nucleic acid sequence of SEQ ID NO: 13. The aceF gene may be a polynucleotide having a nucleic acid sequence of SEQ ID NO: 14.
The microorganism may include a polynucleotide encoding formate dehydrogenase or a mutant thereof. Formate dehydrogenase may be referred to as Fdh. The enzyme catalyzes the conversion of formate to bicarbonate. The enzyme may be derived from Corynebacterium glutamicum or Mycobacterium vaccae. The formate dehydrogenase may have an amino acid sequence of SEQ ID NO: 15. The polynucleotide encoding formate dehydrogenase may have a nucleic acid sequence of SEQ ID NO: 16.
The polynucleotide encoding an enzyme may be introduced to a strain as it is inserted into a vector. The polynucleotide may be operably linked with a regulatory sequence. A regulatory sequence, which is a sequence regulating expression of the polynucleotide, may include a promoter, a terminator, or an enhancer.
The term “vector” refers to a DNA product including a DNA sequence operably linked with an appropriate regulation sequence capable of expressing DNA in an appropriate host cell. The vector may be a plasmid vector, a bacteriophage vector, or a cosmid vector. To operate as an expression vector, a vector may include a replication origin, a promoter, a multi-cloning site (MCS), a selection marker or a combination thereof. A replication origin gives a function to a plasmid to replicate itself independently of hose cell chromosome. A promoter operates in transcription process of an inserted foreign gene. An MCS enables a foreign gene to be inserted through various restriction enzyme sites. A selection marker verifies whether a vector has been properly introduced to a host cell. A selection includes an antibiotic-resistant gene generally used in the art. For example, a selection marker may include a gene resistant to ampicillin, gentamycin, carbenicillin, chloramphenicol, streptomycin, kanamycin, geneticin, neomycin or tetracycline. Considering the cost, ampicillin or gentamycin-resistant gene may be used.
When a vector of an embodiments uses a prokaryotic cell as host cell, a strong promoter, for example, lamda-PL promoter, trp promoter, lac promoter or T7 promoter, is included in the vector. If a vector uses a eukaryotic cell as host cell, the vector may include a promoter derived from genome of a mammal (metallothionin promoter, e.g.) or a promoter derived from a mammal virus (adenovirus late promoter, vaccinia virus 7.5K promoter, SV40 promoter, cytomegalovirus promoter or tk promoter of HSV promoter, e.g.). The promoter may be a lamda-PL promoter, trp promoter, lac promoter or T7 promoter. In this manner, a promoter is operably linked with a sequence encoding a gene.
The promoter is operably linked with a sequence encoding a gene. The term “operably linked” herein means a functional bond between a nucleic acid expression regulatory sequence (e.g. promoter, signal sequence or array at transcription regulation factor binding site, a terminator, or an enhancer) and another nucleic acid sequence. Through the functional bond, the regulatory sequence may control transcription and/or translation of a nucleotide encoding the gene.
The term “transformation” herein refers to introducing a gene to a host cell so that the gene may be expressed in the microorganism by methods known in the art (e.g., heat shock and electroporation). A transformed gene, only if the gene may be expressed in the host cell, may be any gene whether the gene is inserted into a chromosome of the host cell or the gene exists outside a chromosome. The gene, which is a polynucleotide capable of encoding a polypeptide, may be DNA or RNA. The introduction of the gene may be any type of introduction, only if the gene may be introduced into and expressed in the host cell. For example, the gene may be introduced into a host cell by an introduction in the form of an expression cassette, which is a polynucleotide structure including all factors related to the expression of the gene by itself. The expression cassette usually includes a promoter, a transcription termination signal, a ribosome binding site, and a translation termination signals operably linked with the gene. The expression cassette may be an expression vector capable of self-replication. In addition, the gene may be introduced as itself or in the form of a polynucleotide structure to a host cell and then be operably linked with a sequence related to an expression in the host cell.
Attenuation of activity of the enzyme maybe performed by substituting an endogenous gene with a gene which is altered so that enzyme activity may be weakened or deleted, by substituting a promoter of the gene with a promoter weaker than an endogenous promoter, or by deleting the gene from a chromosome. A gene encoding an enzyme may be deleted from genome of a microorganism by homologous recombination.
Another aspect relates to a method of producing C4-chemicals by culturing the genetically modified microorganism in a cell culture medium, whereby the microorganism produces a C4-chemical; and recovering the C4-chemical from the culture solution. The C4-chemicals may include succinic acid, succinate, fumaric acid, malic acid, or a C4 chemical derived therefrom. For example, production of C4-chemicals included in TCA cycle or substances derived therefrom may be increased by culturing the microorganism of an aspect. In addition, the substances derived from succinate may be 4-HB, 1,4-BDO, γ-butyrolactone (GBL) or C4 chemicals derived therefrom but are not limited thereto.
The culturing may be performed under an appropriate culture medium composition and culture conditions known in this art. The culture medium composition and culture conditions may be conveniently adjusted according to the selected microorganism. The culturing method may include batch culturing, continuous culturing, fed-batch culturing or a combination thereof. The fed-batch culturing may use a culture medium having glucose 50 g/L, corn steep liquor 10 g/L, (NH4)2SO4 45 g/L, UREA 4.5 g/L, KH2PO4 0.5 g/L, MgSO4/7H2O 0.5 g/L, FeSO4/7H2O (10 g/L) stock 1 mL, MnSO4/4H2O (10 g/L) stock 1 mL, beta-alanin (5 g/L) stock 1 mL, nicotinic acid (5 g/L) stock 1 mL, thiamine-HCl (5 g/L) stock 1 mL, and D-biotin (0.3 g/L) stock 1 mL. The culture condition may comprise a combination of aerobic and anaerobic conditions. For example, the genetically modified microorganism may be cultured under aerobic condition for 20 hr and subsequently, under anaerobic condition for 80 hr.
The culture medium may include various carbon sources, nitrogen sources, and trace elements. The carbon source may include a carbohydrate such as glucose, sucrose, lactose, fructose, maltose, starch, and cellulose, a lipid such as soybean oil, sunflower oil, castor oil, and coconut oil, a fatty acid such as palmitic acid, stearic acid, and linoleic acid, an organic acid such as acetic acid or a combination thereof. The culturing may be performed by using glucose as a carbon source. The nitrogen source may include an organic nitrogen source such as peptone, yeast extract, meat extract, malt extract, corn steep liquid, and soybean, an inorganic nitrogen source such as urea, ammonium sulfate, ammonium chloride, ammonium phosphate, ammonium carbonate, and ammonium nitrate or a combination thereof. The culture medium may include as a phosphorous source, for example, potassium dihydrogen phosphate, dipotassium phosphate, a sodium-containing salt corresponding to potassium dihydrogen phosphate, and dipotassium phosphate, and a metal salt such as magnesium sulfate and iron sulfate. The culture medium or an individual component may be added to the culture in a batch mode or a continuous mode.
In addition, pH of the culture may be adjusted during the culturing by adding a compound such as ammonium hydroxide, potassium hydroxide, ammonia, phosphoric acid or sulfuric acid to the culture in an appropriate mode. In addition, bubble formation may be repressed by using an endoplasmic reticulum such as fatty acid polyglycol ester.
The microorganism may be cultured under anaerobic conditions. The term “anaerobic conditions” herein refers to a state wherein oxygen content is lower than that of normal atmospheric state. Anaerobic conditions may be formed, for example, by supplying carbon dioxide or nitrogen at a flow rate range from about 0.1 vvm (Volume per Volume per Minute) to about 0.4 vvm, from about 0.2 vvm to about 0.3 vvm or at a flow rate of 0.25 vvm. In addition, anaerobic conditions may be formed by setting an aeration rate in the range from about 0 vvm and to 0.4 vvm, from about 0.1 vvm to about 0.3 vvm or from 0.15 vvm to about 0.25 vvm.
The method of producing C4-chemicals includes recovering of the produced C4-chemicals from the culture. The produced C4-chemicals may be succinic acid, succinate, fumaric acid, malic acid or a C4-chemical derived therefrom. According to one embodiment, the produced C4-chemicals may be 4-HB, 1,4-BDO, GBL or a C4-chemical derived therefrom. For example, the recovery of 4-HB may be performed by using known separation and purification methods. The recovery may be performed by centrifugation, ion exchange chromatography, filtration, precipitation or a combination thereof. Recovery of C4-chemicals, for example, recovery of succinic acid, 4HB, or GBL may be performed by a method known in this art including filtration of culture solution.
In addition, the method of producing C4-chemicals may be used to produce other various organic compounds by converting the C4-chemicals to other organic chemicals. A substrate structurally related to 4-HB may be synthesized by chemically converting the 4-HB yielded in the method described above. According to one embodiment, gamma butyrolactone (GBL) may be yielded by reacting 4-HB at about 100° C. to 200° C. in the presence of a strong acid and then distilling the reactant. The yielded GBL may be converted to N-methyl pyrrolidone (NMP) by amination using an aminating agent, for example, methylamine. In addition, the yielded GBL may be selectively converted to tetrahydrofuran (THF), 1,4-BDO or butanol by hydrogenation using a metal-containing catalyst, for example, Ru or Pd.
The poly-4-hydroxybutyrate may be yielded by biologically converting the produced 4-HB. The biological conversion may be achieved by polyhydroxyalkanoate synthase, 4-HB-CoA:coenzyme A transferase or a combination thereof.
As described above, according to the one or more of the above embodiments, yield of 4HB production was improved by performing additional genetic engineering in a genetically modified microorganism that produces 4HB. In particular, activity of enzymes involved in various metabolic pathways was altered, and a genetically modified microorganism capable of producing 4HB at the optimal yield was developed by a combination of various genetic mutations. As the genetically modified microorganism having increased 4HB productivity may produce 4HB at a high yield by anaerobic fermentation, the strain may be very useful in industries.
A genetically modified microorganism capable of producing 4HB at a high efficiency in anaerobic conditions may be effectively used in 4HB production. As 4HB is a compound highly useful in industries, 4HB productivity increase in the strain may increase utility of 4HB by reducing unit price of 4HB production. Therefore, the transformed microorganism may be very useful in industries.
It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.
Example 1
Preparation of Transformed Strain
1.1 Preparation of CGL (Δldh) Strain
(1) Preparation of Replacement Vector
To prevent excessive lactate accumulation in natural Corynebacterium during anaerobic fermentation, a gene (SEQ ID NO: 42) expressing L-lactate dehydrogenase (NCgl2810) in the strain was eliminated. An open reading frame (ORF) region of 230 bp in the gene was eliminated by gene substitution. Sequence of the eliminated region is shown in SEQ ID NO: 29.
An upstream region corresponding to first 200 bp of ldhA gene was amplified by PCR using genome DNA of CGL ATCC 13032 as a template and using ldhA_up_5′ (SEQ ID NO:25) and ldhA_up_3′ (SEQ ID NO: 26) primer sets. A downstream region corresponding to last 200 bp of ldhA gene was amplified by PCR using primer sets ldhA_down_5′ (SEQ ID NO:27) and ldhA_down_3′ (SEQ ID NO:28). The PCR amplification was performed by repeating, 30 times, a cycle including a denaturation step at 95° C. for 30 seconds, an annealing step at 55° C. for 30 seconds, and an extension step at 72° C. for 30 seconds. All the PCR amplifications hereinafter were performed under the same conditions. Afterward, flanking regions upstream and downstream from ldhA gene was overlapped with an extended region of an oligonucleotide and linked with each other by using 16 bp In-Fusion® HD Cloning Kit (cat no. 639691 manufactured by Clontech). The linked regions upstream and downstream from the ldhA product were ligated with pK19mobsacB (obtained from ATCC 87098) at BamHI and SalI restriction enzyme sites. As a result, pK19mobsacB-Δldh was obtained.
(2) Preparation of CGL (Δldh) Strain
The obtained plasmid, pK19mobsacB-ΔldhA, was used to delete a corresponding gene in CGL by homologous recombination according to Schafer et al. (1994). The pK19mobsacB-Δldh vector was introduced to CGL ATCC13032 bp electroporation. The strain wherein the vector was introduced was cultured at 30° C. by streaking the strain on lactobacillus selection (LBHIS) culture medium including kanamycin 25 μg/ml. The LBHIS culture medium includes brain-heart infusion broth 18.5 g/L, 0.5 M sorbitol, 5 g/L bacto-tryptone, 2.5 g/L bacto-yeast extract, 5 g/L NaCl, and 18 g/L bacto-agar. Hereinafter, composition of LBHIS medium is the same. The colony was streaked on LB-sucrose culture medium and cultured at 30° C. Then, only the colonies wherein double crossing-over occurred were selected. Gene deletion was verified by PCR using primer sets (SEQ ID NO: 25 and SEQ ID NO: 28). The obtained strain was named as CGL(Δldh).










TABLE 1







SEQ




ID




NO
Sequence









25
5′-GCAGGCATGCAAGCTTCTAGTCTGGGGAGCGAAACC-3′



 



26
5′-GAGCTCAGTCAGTCATGGACGCCACGAGGAAGATG-3′



 



27
5′-TGACTGACTGAGCTCCTGGACAAAGACCCAGAGCT-3′



 



28
5′-GGCCAGTGCCAAGCTTTTGCGGGCACCAACGTAATG-3′










1.2 Preparation of Strain Capable of Producing 4HB

The CGL(Δldh) strain prepared in Example 1.1 was genetically engineered further so that the strain may become capable of producing 4HB. In order to attenuate NCgl0049 gene, a polynucleotide encoding succinyl-CoA:coenzyme A transferase, CoA-dependent succinate semialdehyde dehydrogenase, and 4-hydroxybutyrate dehydrogenase (SEQ ID NO:45) was introduced by substituting the gene at the NCgl0049 gene position. The gene was introduced to a Corynebacterium using pK19mobsacB vector (ATCC87098). In other words, sequences of the regions upstream and downstream of the NCgl0049 gene and sequence of the cat1, sucD, and 4hbd gene regions (SEQ ID NO:45) were synthesized and ligated with pK19mobsacB at XbaI and NheI restriction enzyme sites.
The obtained plasmid was used to substitute the NCgl0049 gene with the synthesized cat1, sucD, and 4hbd genes by homologous recombination according to Schafer et al. (1994). Deletion of NCgl0049 and introduction of cat1, sucD, and 4hbd genes were verified by PCR using primer sets (SEQ ID NO: 43 and SEQ ID NO: 44). The obtained strain was named as C011.








TABLE 2





SEQ



ID



NO
Sequence







43
5′-ATT CGG TGA GGA ATC CGG CGG TG-3′


 


44
5′-CTA TGA GAC AGT CGT CCT GTA CCC AT-3′









1.3 Preparation of Gene-Deleted Strain for Efficient Production of 4HB

1.3.1 Deletion of Malate Quinone Oxidoreductase Gene

(1) Preparation of Replacement Vector

An upstream region corresponding to first 200 bp of malate quinone oxidoreductase gene was amplified by PCR using genome DNA of CGL ATCC 13032 as a template and using primer sets (SEQ ID NO: 30 and SEQ ID NO: 31). A downstream region corresponding to last 200 bp of malate quinone oxidoreductase gene was amplified by PCR using primer sets (SEQ ID NO: 32 and SEQ ID NO: 33). Afterward, flanking regions upstream and downstream from malate quinone oxidoreductase gene was overlapped with an extended region of an oligonucleotide and linked with each other by using 16 bp In-Fusion® HD Cloning Kit (cat no. 639691 manufactured by Clontech). The linked regions upstream and downstream from the malate quinone oxidoreductase product were ligated with pK19mobsacB at BamHI and SalI restriction enzyme sites. As a result, pK19mobsacB-Δmqo was obtained.
(2) Preparation of CGL (ΔLdh ΔMqo) Strain
In the C011 strain prepared in Example 1.2), expression of malate quinone oxidoreductase having an amino acid sequence of SEQ ID NO: 17 was additionally repressed. For this, a polynucleotide having a nucleic acid sequence of SEQ ID NO: 18 was deleted by homologous recombination. The obtained plasmid, pK19mobsacB-Δmqo, was used to delete a corresponding gene in CGL C011 by homologous recombination according to Schafer et al. (1994). Gene deletion was verified by PCR using primer sets (SEQ ID NO: 28 and SEQ ID NO: 31).
1.3.2. Deletion of Phosphoenolpyruvate Carboxykinase
(1) Preparation of Replacement Vector
An upstream region corresponding to first 200 bp of phosphoenolpyruvate carboxykinase gene was amplified by PCR using genome DNA of CGL ATCC 13032 as a template and using primer sets (SEQ ID NO: 34 and SEQ ID NO: 35). A downstream region corresponding to last 200 bp of phosphoenolpyruvate carboxykinase gene was amplified by PCR using primer sets (SEQ ID NO: 36 and SEQ ID NO: 37). Afterward, flanking regions upstream and downstream from phosphoenolpyruvate carboxykinase gene was overlapped with an extended region of an oligonucleotide and linked with each other by using 16 bp In-Fusion® HD Cloning Kit (cat no. 639691 manufactured by Clontech). The linked regions upstream and downstream from the phosphoenolpyruvate carboxykinase product were ligated with pK19mobsacB at BamHI and SalI restriction enzyme sites. As a result, pK19mobsacB-pckG was obtained.
(2) Preparation of CGL (Δldh ΔpckG) Strain
Expression of phosphoenolpyruvate carboxykinase having an amino acid sequence of SEQ ID NO: 19 was additionally repressed. For this, a polynucleotide having a nucleic acid sequence of SEQ ID NO: 20 was deleted by homologous recombination. The obtained plasmid, the vector prepared above, pK19mobsacB (ATCC 87098), was used to delete a corresponding gene. Specifically, pckG gene was deleted by homologous recombination according to Schafer et al. (1994) by introducing the plasmid prepared above, pK19mobsacB-ΔpckG, into C011 (Δmqo) strain. Gene deletion was verified by PCR using primer sets (SEQ ID NO: 34 and SEQ ID NO: 37). The obtained strain was named as C011 (ΔmqoΔpckG).








TABLE 3





SEQ



ID



NO
Sequence







30
5′-CTGCAGGTCGACTCTAGAGAAGAAGTAGTCCGTCATGCCGTGAACC-3′


 


31
5′-TAGAAGATTATTTTTGACTGACGCGTGGGGCG-3′


 


32
5′-GTCAAAAATAATCTTCTAACTGCTTTCTTTAAAGCACCCG-3′


 


33
5′-CTCGGTACCCGGGGATCCTCTTAAAGCCTGAGATAGCGAGTTCCA-3′


 


34
5′-GCTCTAGAGTCATGTATTTAGGTAGGGC-3′


 


35
5′-ATCTGAAAGCATGCATTTGCAACGACACCAAGT-3′


 


36
5′-GTTGCAAATGCATGCTTTCAGATACAGAACTAG-3′


 


37
5′-GCTCTAGACAGTCGTTGAACTCAGGT-3′









1.4. Preparation of Gene-Introduced Strain for Efficient Production of 4HB

1.4.1. Introduction of Pyruvate Carboxylase Gene

In an amino acid sequence of pyruvate carboxylase of the strain prepared in Examples 1.2 or 1.3, proline-458 was additionally substituted with serine. Specifically, the substitution was performed by using primers SEQ ID NO: 38 to 41.
An upstream region corresponding to first 200 bp from the proline amino acid position of pyruvate carboxylase was amplified by PCR using primer sets (SEQ ID NO: 38 and SEQ ID NO: 39). A downstream region from the proline amino acid position of pyruvate carboxylase was amplified by PCR using primer sets (SEQ ID NO: 40 and SEQ ID NO: 41). Afterward, the upstream and downstream regions substituting proline with serine in pyruvate carboxylase were overlapped with an extended region of an oligonucleotide and linked with each other by using 16 bp In-Fusion® HD Cloning Kit (cat no. 639691 manufactured by Clontech). The linked regions upstream and downstream from the phosphoenolpyruvate carboxykinase product were ligated with pK19mobsacB at BamHI and SalI restriction enzyme sites.
The obtained plasmid pK19mobsacB-mutated pycP4583 was introduced to the C011 (ΔmqoΔpckG) strain by homologous recombination according to Schafer et al. (1994). Gene introduction was verified by PCR using primer sets (SEQ ID NO: 38 and SEQ ID NO:41). The obtained strain was named as C011 (ΔmqoΔpckG pycP458S).










TABLE 4







SEQ




ID




NO
Sequence









38
5′-GCTCTAGATTGAGCACACCGTGACT-3′



 



39
5′-CCGGATTCATTGCCGATCACTC-3′



 



40
5′-GCTCTAGACTGTCCCACGGATCCTCAAA-3′



 



41
5′-CTGAAGGAGGTGCGAGTGA-3′










1.4.2. Introduction of α-Ketoglutarate Synthase Gene

In order to introduce α-ketoglutarate synthase gene sucA, pK19 mobsacB-sucA was prepared by introducing a synthesized polynucleotide (SEQ ID NO:46) encoding α-ketoglutarate synthase to pK19mobsacB (ATCC 87098) vector cleaved by XbaI and NheI. The obtained plasmid pK19mobsacB-sucA was introduced to the C011 (ΔmqoΔpckG pycP458S) strain by homologous recombination according to Schafer et al. (1994). Gene introduction was verified by PCR using primer sets (SEQ ID NO: 54 and SEQ ID NO: 55). The obtained strain was named as C098.
1.4.3. Introduction of Pyruvate Dehydrogenase
(1) Preparation of pGST1 Vector
Four PCR products were obtained by using Phusion High-Fidelity DNA Polymerase (New England Biolabs, cat.# M0530). PCR was performed by using CGL promoter screening vector pET2 (GenBank accession number: AJ885178.1) as a template and using primer sequences MD-616 (SEQ ID NO: 56) and MD-618 (SEQ ID NO: 57), and using primer sequences MD-615 (SEQ ID NO: 58) and MD-617 (SEQ ID NO: 59). PCR was performed by using mammalian fluorescence protein expression vector pEGFP-C1 (Clonetech) as a template and using primer sequences MD-619 (SEQ ID NO: 60) and MD-620 (SEQ ID NO: 61). PCR was performed by using E. coli cloning vector pBluescriptII SK+ as a template and using primer sequences LacZa-NR (SEQ ID NO: 62) and MD-404 (SEQ ID NO: 63). Each of the PCR products of 3010 bp, 854 bp, 809 bp, and 385 bp was cloned to a circular plasmid by In-Fusion EcoDry PCR Cloning Kit (Clonetech, cat.#639690) method.
The cloned vector was transformed to One Shot TOP10 Chemically Competent Cell (Invitrogen, cat.# C4040-06), which was then cultured in LB culture medium including kanamycin 25 mg/L. Growing colonies were selected, and vectors were recovered from selected colonies. Then, the vector sequences were verified through full sequence analysis. The vector was named as pGSK+. To prepare a CGL shuttle vector including a transcription terminator and a 3′ untranslated region (UTR), a 3′UTR of CGL gltA (NCgl0795) and a rho-independent terminator of rrnB of E. coli rrnB were inserted to the pGSK+ vector. A 108 bp PCR fragment of gltA 3′UTR was obtained by performing PCR using CGL (ATCC13032) genome DNA as a template with the primer sequences MD-627 (SEQ ID NO: 64) and MD-628 (SEQ ID NO: 65).
In addition, an rrnB transcription terminator 292 bp PCR product was obtained by performing PCR using E. coli (MG1655) genome DNA as a template with the primer sequences MD-629 (SEQ ID NO: 66) and MD-630 (SEQ ID NO: 67). The two amplified fragments were inserted to SacI digested pGSK+ by using In-Fusion EcoDry PCR Cloning Kit (Clonetech, cat.#639690). The cloned vector was transformed to One Shot TOP10 Chemically Competent Cell (Invitrogen, cat.# C4040-06), which was then cultured in LB culture medium including kanamycin 25 mg/L. Growing colonies were selected, and vectors were recovered from selected colonies. Then, the vector sequences were verified through full sequence analysis. The vector was named as pGST1.
A CGL shuttle vector wherein each gene of E. coli Pdh complex is over-expressed under NCgl1929 promoter was prepared. 206 bp, 1454 bp, 2694 bp, and 1935 bp DNA fragments were obtained by performing PCR using CGL NCgl1929 promoter, Ec.lpd open reading frame (SEQ ID NO: 53) encoding E. coli dehydrolipoamide dehydrogenase (SEQ ID NO: 52) next to natural ribosome binding site, Ec.aceE open reading frame (SEQ ID NO: 49) encoding E. coli pyruvate dehydrogenase (SEQ ID NO: 48) next to natural ribosome binding site, and Ec.aceF open reading frame (SEQ ID NO: 51) encoding E. coli dihydrolipoamide acetyltransferase (SEQ ID NO:50) next to natural ribosome binding site, with primers J0180 (SEQ ID NO: 68) and MD-1081 (SEQ ID NO: 69), MD-1082 (SEQ ID NO: 70) and MD-1083 (SEQ ID NO: 71), MD-1084 (SEQ ID NO: 72) and MD-1085 (SEQ ID NO: 73), and MD-1086 (SEQ ID NO: 74) and MD-1087 (SEQ ID NO: 55), respectively.
The DNA fragments were ligated with KpnI/XbaI digested pGST1 vector using In-Fusion EcoDry PCR Cloning Kit (Clonetech, cat.#639690). The cloned vector was transformed to One Shot TOP10 Chemically Competent Cell (Invitrogen, cat.# C4040-06), which was then cultured in LB culture medium including kanamycin 25 mg/L. Vectors were recovered from the colonies. Then, the vector preparation was verified through full sequence analysis. The vector was named as MD0376. C158 strain was obtained by transforming the MD0376 vector in the form of a vector to C098 strain.
1.4.4 Introduction of Formate Dehydrogenase Gene
In order to introduce formate dehydrogenase gene, pK19 mobsacB-fdh was prepared by introducing a synthesized polynucleotide (SEQ ID NO: 47) encoding synthesized formate dehydrogenase to pK19mobsacB (ATCC 87098) vector cleaved by BamHI and EcoRI. The obtained plasmid pK19mobsacB-fdh was introduced to the C098 strain by homologous recombination according to Schafer et al. (1994). Gene introduction was verified by PCR using primer sets (SEQ ID NO: 76 and SEQ ID NO: 77). The obtained strain was named as C209.







TABLE 5







Genetically engineered CGL








Name of strain
Genotype





CGL(Δldh)
ATCC13032 Δldh


C011
ATCC13032 Δldh, ΔNcgl0049, cat1, sucD, 4hbD


C098
ATCC13032 Δldh ΔNcgl0049, cat1, sucD, 4hbD,



Δmqo, ΔpckG, pycP458S, sucA


C158
ATCC13032 Δldh, ΔNcgl0049, cat1, sucD, 4hbD,



Δmqo, ΔpckG, pycP458S, sucA, MD0376


C209
ATCC13032 Δldh, ΔNcgl0049, cat1, sucD, 4hbD,



Δmqo, ΔpckG, pycP458S, sucA, fdh









Example 2
Production of Various C4 Chemicals Using Transformed Strains
Each of the various CGL strains prepared in Example 1 was fermented in a fermenter at 30° C. Glucose was used as a carbon source. Fermentation was performed in anaerobic conditions for producing various C4 chemicals. Specifically, fed-batch fermentation was performed. The culture medium included glucose 50 g/L, corn steep liquor 10 g/L, (NH4)2SO4 45 g/L, urea 4.5 g/L, KH2PO4 0.5 g/L, MgSO4/7H2O
0.5 g/L, FeSO4/7H2O (10 g/L) stock 1 mL, MnSO4/4H2O (10 g/L) stock 1 mL, beta-ALANIN (5 g/L) stock 1 mL, nicotinic acid (5 g/L) stock 1 mL, thiamine-HCl (5 g/L) stock 1 mL, and D-Biotin (0.3 g/L) stock 1 mL. Fermentation was performed by supplying oxygen until OD600 80, and then by blocking oxygen supply for 100 hours.
4HB production of the strains was verified in the conditions. The basic C011 strain was verified to produce 4HB of 4.0 g/L. The additionally transformed strain C098, which was fermented in the conditions the same as those of the C011 strain, produced 28.4 g/L 4HB, which was 7.1 times the 4HB production of the C011 strain (Refer to Table 6 and FIG. 3). In addition, the C158 strain produced 40.5 g/L 4HB, which was 10.1 times and 1.4 times the 4HB production of the C011 strain and the C098 strain, respectively (Refer to Table 6 and FIG. 3). In addition, the C158 strain produced 45.7 g/L 4HB, which was 11.4 times and 1.6 times the 4HB production of the C011 strain and the C098 strain, respectively (Refer to Table 6 and FIG. 3). Under the same condition, the concentrations of succinic acid and GBL produced by the C029 strain were also measured. The C029 strain produced 12.7 g/L succinic acid and 0.3 g/L GBL, while the Δldh strain did not produce succinic acid or GBL.










TABLE 6







Strain
4HB Production (g/L)



















Δldh
0



C011
4



C098
28.4



C158
40.5



C209
45.7










All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

## Claims

1. A genetically modified microorganism comprising
a polynucleotide encoding exogenous α-ketoglutarate synthase, and
a polynucleotide encoding endogenous pyruvate carboxylase or a mutant thereof;
wherein the genetically modified microorganism has decreased malate quinone oxidoreductase activity, decreased phosphoenolpyruvate carboxykinase activity, or a combination thereof, compared to an unmodified microorganism of the same type,
wherein the genetically modified microorganism produces 4-hydroxybutyrate, and
wherein the genetically modified microorganism is a strain selected from the group consisting of lumen bacteria, Corynebacterium genus, Brevibacterium genus, and Escherichia coli.

2. The genetically modified microorganism of claim 1, wherein the microorganism comprises a polynucleotide encoding succinyl-CoA:coenzyme A transferase or a mutant thereof, a polynucleotide encoding coenzyme A-dependent succinate semialdehyde dehydrogenase or a mutant thereof, and a polynucleotide encoding 4-hydroxybutyrate dehydrogenase or a mutant thereof.

3. The genetically modified microorganism of claim 1, wherein the microorganism has decreased succinate semialdehyde dehydrogenase activity compared to an unmodified microorganism of the same type.

4. The genetically modified microorganism of claim 1, wherein one or more of NCg10049, NCg10463, and NCg12619 genes in the microorganism has an addition, substitution, or deletion mutation that eliminates succinate semialdehyde dehydrogenase activity, wherein the NCg10049 gene comprises the nucleic acid sequence of SEQ ID NO: 22, the NCg10463 gene comprises the nucleic acid sequence of SEQ ID NO: 23, and the NCg12619 gene comprises the nucleic acid sequence of SEQ ID NO: 24.

5. The genetically modified microorganism of claim 1, wherein the microorganism additionally comprises a polynucleotide encoding pyruvate dehydrogenase or a mutant thereof.

6. The genetically modified microorganism of claim 1, wherein the microorganism additionally comprises a gene encoding dihydrolipoyl dehydrogenase (E3), a gene encoding pyruvate dehydrogenase (E1), and a gene encoding dihydrolipoyl transacetylase (E2).

7. The genetically modified microorganism of claim 6, wherein the gene encoding dihydrolipoyl dehydrogenase (E3) comprises the nucleic acid sequence of SEQ ID NO: 12, the gene encoding pyruvate dehydrogenase (E1) comprises the nucleic acid sequence of SEQ ID NO: 13, and the gene dihydrolipoyl transacetylase (E2) comprises the nucleic acid sequence of SEQ ID NO: 14.

8. The genetically modified microorganism of claim 1, wherein the microorganism additionally comprises a polynucleotide encoding formate dehydrogenase or a mutant thereof.

9. The genetically modified microorganism of claim 1, wherein the microorganism is a strain of the Corynebacterium genus.

10. The genetically modified microorganism of claim 9, wherein the strain of Corynebacterium genus is Corynebacterium glutamicum.

11. The genetically modified microorganism of claim 1, wherein the pyruvate carboxylase comprises the amino acid sequence of SEQ ID NO: 9.

12. The genetically modified microorganism of claim 1, wherein the mutant pyruvate carboxylase comprises the amino acid sequence of SEQ ID NO: 10.

13. The genetically modified microorganism of claim 1, wherein the α-ketoglutarate synthase comprises the amino acid sequence of SEQ ID NO: 7.

14. The genetically modified microorganism of claim 2, wherein the succinyl-CoA:coenzyme A transferase comprises the amino acid sequence of SEQ ID NO: 1, the CoA-dependent succinate semialdehyde dehydrogenase comprises the amino acid sequence of SEQ ID NO: 3, and the 4-hydroxybutyrate dehydrogenase comprises the amino acid sequence of SEQ ID NO: 5.

15. The genetically modified microorganism of claim 8, wherein the formate dehydrogenase comprises the amino acid sequence of SEQ ID NO: 15.

16. A method of producing a C4-chemical comprising:
culturing the genetically modified microorganism of claim 1 in a cell culture medium, whereby the microorganism produces a C4-chemical; and
recovering the C4-chemical from the cell culture medium.

17. The method of claim 16, wherein the C4-chemical is 4-hydroxybutyrate.

18. The method of claim 16, wherein the genetically modified microorganism additionally comprises a polynucleotide encoding pyruvate dehydrogenase or a mutant thereof and a polynucleotide encoding formate dehydrogenase or a mutant thereof.

19. The method of claim 18, wherein the C4-chemical is selected from the group consisting of succinic acid, 4-hydroxybutyrate, and gamma butyrolactone.