US20100248311A1 - Increasing methionine yield - Google Patents

Increasing methionine yield Download PDF

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US20100248311A1
US20100248311A1 US12/681,177 US68117708A US2010248311A1 US 20100248311 A1 US20100248311 A1 US 20100248311A1 US 68117708 A US68117708 A US 68117708A US 2010248311 A1 US2010248311 A1 US 2010248311A1
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microorganism
methionine
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Rainer Figge
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Metabolic Explorer SA
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    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C12N9/14—Hydrolases (3)
    • C12N9/78—Hydrolases (3) acting on carbon to nitrogen bonds other than peptide bonds (3.5)
    • C12N9/80—Hydrolases (3) acting on carbon to nitrogen bonds other than peptide bonds (3.5) acting on amide bonds in linear amides (3.5.1)
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P13/00—Preparation of nitrogen-containing organic compounds
    • C12P13/04—Alpha- or beta- amino acids
    • C12P13/12—Methionine; Cysteine; Cystine
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Y—ENZYMES
    • C12Y305/00—Hydrolases acting on carbon-nitrogen bonds, other than peptide bonds (3.5)
    • C12Y305/01—Hydrolases acting on carbon-nitrogen bonds, other than peptide bonds (3.5) in linear amides (3.5.1)
    • C12Y305/0101—Formyltetrahydrofolate deformylase (3.5.1.10)
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

  • the present invention relates to a process for the production of methionine or its derivatives by culturing a microorganism in an appropriate culture medium comprising a source of carbon and a source of sulfur.
  • the microorganism and/or the culture medium were modified in a way that the methionine/carbon source yield is increased.
  • the isolation of methionine or its derivates from the fermentation medium is also claimed.
  • Sulphur-containing compounds such as cysteine, homocysteine, methionine or S-adenosylmethionine are critical to cellular metabolism and are produced industrially to be used as food or feed additives and pharmaceuticals.
  • methionine an essential amino acid, which cannot be synthesized by animals, plays an important role in many body functions. Aside from its role in protein biosynthesis, methionine is involved in transmethylation and in the bioavailability of selenium and zinc. Methionine is also directly used as a treatment for disorders like allergy and rheumatic fever. Nevertheless most of the methionine which is produced is added to animal feed.
  • Microorganisms have developed highly complex regulatory mechanisms that fine-tune the biosynthesis of cell components thus permitting maximum growth rates. Consequently only the required amounts of metabolites, such as amino acids, are synthesized and can usually not be detected in the culture supernatant of wild-type strains. Bacteria control amino acid biosynthesis mainly by feedback inhibition of enzymes, and repression or activation of gene transcription. Effectors for these regulatory pathways are in most cases the end products of the relevant pathways. Consequently, strategies for overproducing amino acids in microorganisms require the deregulation of these control mechanisms.
  • Methionine is derived from the amino acid aspartate, but its synthesis requires the convergence of two additional pathways, cysteine biosynthesis and C1 metabolism.
  • Aspartate is synthesized from oxaloacetate.
  • E. coli a stable oxaloacetate pool is required for the proper functioning of the citric acid cycle. Therefore the transformation of oxaloacetate into aspartate requires reactions that compensate for oxaloacetate withdraw al from this pool.
  • Several pathways, called anaplerotic reactions, fulfill these functions in E. coli (Sauer & Eikmanns (2005) FEMS Microbiol Reviews 29 p765-94).
  • PEP carboxylase catalyzes the carboxylation of PEP yielding oxaloacetate. Carboxylation efficiency depends among other on the intracellular PEP concentration.
  • PEP is a central metabolite that undergoes a multitude of reactions.
  • glycolytic transformation of PEP to pyruvate is not essential for E. coli , since the import of glucose via the PTS system transforms one of two PFP molecules generated from glucose into pyruvate.
  • the enzyme pyruvate kinase which in E. coli is encoded by two isoenzymes encoded by the genes pykA and pykF, catalyzes the transformation of PEP to pyruvate.
  • Aspartate is converted into homoserine by a sequence of three reactions.
  • Homoserine can subsequently enter the threonine/isoleucine or methionine biosynthetic pathway.
  • E. coli entry into the methionine pathway requires the acylation of homoserine to succinyl-homoserine.
  • This activation step allows subsequent condensation with cysteine, leading to the thioether-containing cystathionine, which is hydrolyzed to give homocysteine.
  • the final methyl transfer leading to methionine is carried out by either a B 12 -dependent or a B 12 -independent methyltransferase.
  • Methionine biosynthesis in E. coli is regulated by repression and activation of methionine biosynthetic genes via the MetJ and MetR proteins, respectively (reviewed in Figge R M (2006), ed Wendisch V F, Microbiol Monogr (5) Amino acid biosynthesis p164-185).
  • MetJ together with its corepressor S-adenosylmethionine is known to regulate the genes metA, metB, metC, metE and metF.
  • GlyA encoding enzymes involved in methionine production, such as glyA, metE, metH and metF are activated by MetR in presence of its co-activator homocysteine, whereas metA is only activated by MetR in the absence of homocysteine. All these enzymes are involved in the production and the transfer of C1 units from serine to methionine.
  • GlyA encoding serine hydroxymethyl transferase catalyzes the conversion of serine to glycine and the concomitant transfer of a C1 unit on the coenzyme tetrahydrofolate (THF). Glycine can then be transformed into CO 2 , NH 3 while another C1 unit is transferred onto THF. This reaction is catalyzed by the glycine cleavage complex encoded by the genes gcvTHP and lpd.
  • C1 units produced by the two reactions in form of methylene-THE can subsequently either be reduced to methyl-THF or further oxidized to formyl-THE.
  • Methionine biosynthesis requires the reduction to methyl-THF.
  • the oxidation reaction competes with methionine biosynthesis for C1 units.
  • Formyl-THE or formate is required for the biosynthesis of purines and histidine.
  • formyl-THF can be transformed into THF and free formate in a reaction catalyzed by formyl-THF deformylase encoded by the purU gene (Nagy et al. (1995) J. Bacteriol 177 (5) p. 1292-98).
  • the reduction of methylene-THF to methyl-THF is catalyzed by the MetF protein.
  • Transfer of the methyl group onto homocysteine is either catalyzed by MetH via vitamin B12 or directly by MetE.
  • the MetH enzyme is known to have a catalytic rate that is hundred times higher than the MetE enzyme.
  • MetE can compose up to 5% of the total cellular protein.
  • the presence of active MetH reduces MetE activity probably by reducing the amount of homocysteine that normally activates the transcription of metE via MetR. Therefore the production of methionine via MetH saves important resources for the cell, since MetE is not expressed in large quantities.
  • the accumulation of homocysteine is toxic for E.
  • E. coli reduced sulfur is integrated into cysteine and then transferred onto the methionine precursor O-succinyl-homoserine, a process called transulfuration (reviewed in Neidhardt, F. C. (Ed. in Chief), R. Curtiss III, J. L. Ingraham, E. C. C. Lin, K. B. Low, B. Magasanik, W. S. Reznikoff, M. Riley, M. Schaechter, and H. E. Umbarger (eds). 1996. Escherichia coli and Salmonella : Cellular and Molecular Biology. American Society for Microbiology). Cysteine is produced from O-acetylserine and H 2 S by sulfhydrylation.
  • the process is negatively feed-back regulated by the product, cysteine, acting on serine transacetylase, encoded by cysE.
  • N-acetyl-serine which is spontaneously produced from O-acetyl-serine, together with the transcription factor CysB activates genes encoding enzymes involved in the transport of sulfur compounds, their reduction to H 2 S and their integration in the organo-sulfur compound cysteine, which, as methionine, is an essential amino acid.
  • 60/650,124 describes how ⁇ -elimination can be reduced by optimizing the enzyme MetB.
  • Optimizing cysteine biosynthesis can also reduce ⁇ -elimination and thus the production of the byproduct isoleucine and constitutes an embodiment of this invention.
  • the invention relates to a method for the production of methionine, its derivatives, or precursors in a fermentative process comprising the following steps:
  • microorganism or the method has been modified to present an enhanced methionine/carbon source yield by at least one of the following modifications and combinations thereof:
  • genes and proteins are identified using the denominations of the corresponding genes in E. coli .
  • use of these denominations has a more general meaning according to the invention and covers all the corresponding genes and proteins in other organisms, more particularly microorganisms.
  • Genes and proteins from other organisms may also be specified, particularly for Corynebacterium glutamicum as additional information. The purpose of this additional information is not to limit the general definition for a gene or a protein.
  • methionine/carbon source yield is increased by decreasing the deformylation of formyl-THF, which is accomplished by attenuating the expression of the purU gene (YP — 001137322 in C. glutamicum ).
  • the PurU enzyme catalyzes the formyl-THF deformylase reaction.
  • the attenuation of the deformylase activity increases the production of methyl-THF that is required for methylation of homocysteine.
  • Loss of C1 metabolites by deformylation leads to an increased production of homocysteine that cannot be transformed into methionine.
  • Homocysteine can then be a substrate for the enzyme cystathionine gamma synthase (MetB) that can catalyze the reaction between O-succinylhomoserine and homocysteine resulting in the production of homolanthionine.
  • MethodB cystathionine gamma synthase
  • the methionine/carbon source yield is increased by decreasing the consumption of phosphoenol pyruvate (PEP), which is accomplished by the attenuation of at least one or both of the pyruvate kinase encoding genes pykA and pykF.
  • PEP phosphoenol pyruvate
  • Increased availability of PEP can increase the production of oxaloacetate an important precursor of aspartate, which in turn is a precursor of methionine.
  • C. glutamicum harbors only one pyruvate kinase gene which corresponds to YP — 226326.
  • methionine/carbon source yield is increased by limiting the growth of the microorganism or starving the microorganism for an inorganic substrate. This might be achieved by limiting the amount of available phosphate and/or potassium in the culture medium.
  • concentration of phosphate in the culture medium permits growth to an OD 600 of less than 200, preferentially of 150, more preferentially of 100.
  • An OD 600 of 100 corresponds to 30 to 35 g/l biomass for E. coli , for yeast to 40-50 g/l.
  • the conversion factor will be known by the expert in the field.
  • the amount of phosphate required to produce one g biomass is between 10 and 20 mg, preferentially about 18 mg.
  • the amount of potassium required to produce one g biomass is between 10 and 20 mg, preferentially about 18 mg.
  • the amount of phosphate required to produce one g biomass is between 14 and 21 mg, preferentially about 17 mg.
  • the amount of potassium required to produce one g biomass is between 23 and 33 g, preferentially about 28 mg.
  • the conversion factor will be known by the expert in the field.
  • the microorganism is grown in rich or minimal medium, preferentially in minimal medium. Suitable minimal media are described below.
  • the reduction of the formyl-THF deformylation by attenuating the expression of the purU gene can be associated with a reduction of the consumption of PEP by attenuating the expression of the genes pykA, pykF or both and with a limitation or starvation of phosphate and/or potassium in the culture medium.
  • the reduction of the formyl-THF deformylation by attenuating the expression of the purU gene can be associated with a reduction of the consumption of PEP by attenuating the expression of the genes pykA, pykF or both.
  • the reduction of the formyl-THF deformylation by attenuating the expression of the purU gene can be associated with a limitation or starvation of phosphate and/or potassium in the culture medium.
  • the reduction of the consumption of PEP by attenuating the expression of the genes pykA, pykF or both can be associated with a limitation or starvation of phosphate and/or potassium in the culture medium.
  • culture ‘fermentation” or “fermentative process’ are used interchangeably to denote the growth of bacteria on an appropriate growth medium containing a simple carbon source.
  • Total methionine carbon source yield is defined as the amount of methionine+NAM (for NAM mass of equivalent amount of methionine) (g) %/per glucose (g) consumed during the fermentation run.
  • methionine originates from methionine transforming and or degrading pathways.
  • these products are S-adenosyl-methionine (SAM) thio-methyl-ribose and N-acetylmethionine (NAM).
  • SAM S-adenosyl-methionine
  • NAM N-acetylmethionine
  • NAM is an easily recoverable methionine derivative that may be isolated and transformed into methionine by deacylation.
  • the phrase “recovering methionine from the culture medium” designates the action of recovering methionine, SAM and NAM and all other derivatives that may be useful.
  • Precursors of methionine are defined as metabolites that are part of the methionine specific metabolic pathway or can be derived of these metabolites.
  • precursors are O-succinyl-homoserine (OSH), gamma-cystathionine, homocysteine and homolanthionine.
  • OSH O-succinyl-homoserine
  • gamma-cystathionine gamma-cystathionine
  • homocysteine homolanthionine
  • the methionine specific pathway starts with the transformation of homoserine to succinylhomoserine by the enzyme homoserine succinyl transferase (MetA).
  • microorganism designates a bacterium, yeast or a fungus.
  • the microorganism is selected among Enterobacteriaceae, Bacillaceae, Streptomycetaceae and Corynebacteriaceae. More preferentially the microorganism is a species of Escherichia, Klebsiella, Pantoea, Salmonella or Corvnebacterium . Even more preferentially the microorganism is either the species Escherichia coli or Corynebacterium glutamicum.
  • modified microorganism denotes a microorganism that has been genetically modified with the goal to increase the methionine/carbon source yield.
  • the man skilled in the art knows how to modulate the expression of specific genes. Usual modifications include transforming microorganisms with genetic elements, including gene replacements, modification of promoters, and introduction of vectors for the expression of heterologous genes.
  • methionine/carbon source yield defines the quantity of methionine obtained during the fermentation divided by the quantity of the carbon source that has been consumed. It can be expressed in percent g methionine/g carbon source or mol methionine/mol carbon source.
  • the term “enhanced” in this context describes a measurable increase compared to the microorganism without the specified modifications and/or the culture medium without the modifications. In preferred embodiments, the increase is of at least 2% g/g, preferably of at least 4% g/g, more preferably of at least 7% g/g.
  • the total methionine/carbon source yield is preferentially at least 7% g/g, preferentially at least 12% g/g, preferentially at least 15% g/g, most preferentially at least 19% g/g.
  • the quantity of the carbon source that has been consumed is calculated by determining the glucose concentration in the growth medium by HPLC with refractometric detection or according to the method of Brix for fed-batch solutions.
  • the consumed glucose corresponds to the amount of residual glucose at the beginning of the experiment from which the amount of the residual glucose at the end of the experiment is subtracted.
  • the amount of consumed glucose corresponds to the sum of glucose in the batch culture, the added glucose in the inoculum and the amount of glucose injected during the fed batch phase from which the amount of residual glucose at the end of the experiment is subtracted.
  • methionine obtained includes L-methionine and the easily recoverable methionine derivative NAM.
  • the quantity of methionine obtained in the medium is measured by HPLC after OPA/Fmoc derivatization with fluorometric detection using L-methionine (Fluka, Ref 64319) as a standard.
  • the amount of NAM is determined using refractometric HPLC using NAM (Sigma, Ref 01310) as a standard.
  • carbon source denotes any source of carbon that can be used by those skilled in the art to support the normal growth of a micro-organism, which can be hexoses (such as glucose, galactose or lactose), pentoses, monosaccharides, disaccharides, oligosaccharides (such as sucrose, cellobiose or maltose), molasses, starch or its derivatives, hemicelluloses, glycerol and combinations thereof.
  • An especially preferred simple carbon source is glucose.
  • Another preferred simple carbon source is sucrose.
  • the term ‘attenuation of the expression of a gene’ according to the invention denotes the partial or complete suppression of the expression of a gene, which is then said to be ‘attenuated’.
  • This suppression of expression can be either an inhibition of the expression of the gene, a deletion of all or part of the promoter region necessary for the gene expression, a deletion in the coding region of the gene, or the exchange of the wildtype promoter by a weaker natural or synthetic promoter.
  • the attenuation of a gene is essentially the complete deletion of that gene, which can be replaced by a selection marker gene that facilitates the identification, isolation and purification of the strains according to the invention.
  • a gene is inactivated preferentially by the technique of homologous recombination (Datsenko, K. A. & Wanner, B. L. (2000) “One-step inactivation of chromosomal genes in Escherichia coli K-12 using PCR products”. Proc. Natl. Acad. Sci. USA 97: 6640-6645).
  • enhanced or “overexpressed” in this context describe the increase in the intracellular activity of an enzymatic activity which is encoded by the corresponding DNA, for example by increasing the number of copies of the gene, using a stronger promoter or using an allele with increased activity and possibly combining these measures.
  • Chromosomally there may be one or several copies on the genome that can be introduced by methods of recombination know n to the expert in the field.
  • Extrachromosomally genes may be carried by different types of plasmids that differ with respect to their origin of replication and thus their copy number in the cell. They may be present as 1-5 copies, about 20 or up to 500 copies, corresponding to low copy number plasmids with tight replication (pSC101, RK2), low copy number plasmids (pACYC, pRSF1010) or high copy number plasmids (pSK bluescript II)
  • the gene may be expressed using promoters with different strength, which may be inducible. These promoters may be homologous or heterologous. The man skilled in the art knows which promoters are the most convenient, for example promoters Ptrc, Ptac. Plac or the lambda promoter cI are widely used.
  • Expression of the enzymes may be boosted or reduced by elements stabilizing or destabilizing the corresponding messenger RNA (Carrier and Keasling (1998) Biotechnol. Prog. 15, 58-64) or the proteins (e.g. GST tags, Amersham Biosciences)
  • the present invention also relates to microorganisms that contain one or several alleles of the gene to be enhanced according to the invention.
  • genes and proteins are identified using the denominations of the corresponding genes in E. coli .
  • use of these denominations has a more general meaning according to the invention and covers all the corresponding genes and proteins in other organisms, more particularly microorganisms.
  • PFAM protein families database of alignments and hidden Markov models; http://www.sanger.ac.uk/Software/Pfam/) represents a large collection of protein sequence alignments. Each PFAM makes it possible to visualize multiple alignments, see protein domains, evaluate distribution among organisms, gain access to other databases, and visualize known protein structures.
  • COGs clusters of orthologous groups of proteins; http://www.ncbi.nlm.nih.gov/COG/ are obtained by comparing protein sequences from 66 fully sequenced genomes representing 30 major phylogenic lines. Each COG is defined from at least three lines, which permits the identification of former conserved domains.
  • the means of identifying homologous sequences and their percentage homologies are well known to those skilled in the art, and include in particular the BLAST programs, which can be used from the website http://www.ncbi.nlm.nih.gov/BLAST/ with the default parameters indicated on that website.
  • the sequences obtained can then be exploited (e.g., aligned) using, for example, the programs CLUSTALW (http://www.ebi.ac.uk/clustalw/) or MULTALIN (http://prodes.toulouse.inra.fr/multalin/cgi-bin/multalin.pl), with the default parameters indicated on those websites.
  • Subjecting an organism to a limitation of an inorganic substrate defines a condition under which growth of the microorganisms is governed by the quantity of a non-organic chemical supplied that still permits weak growth. Examples for these substrates are phosphate, potassium, magnesium or a combination of these.
  • Starving a microorganism for an inorganic substrate defines the condition under which growth of the microorganism stops completely due to the absence of the inorganic substrate.
  • examples for these substrates are phosphate, potassium, magnesium or a combination of these.
  • methionine/glucose and/or methionine/sucrose yield is at least 10% g/g, preferentially at least 15% g/g, more preferentially 19% g/g.
  • the expression of at least one gene involved in sulfur assimilation, the production of serine, its transformation to glycine or the cleavage of glycine is increased. It is advantageous to increase the sulfur assimilation of the microorganism since methionine is an amino acid containing sulfur (C5H11NO2S). Moreover it is advantageous to increase the production of the amino acids serine and glycine and cleavage (i.e. the catabolism) of glycine.
  • Glycine cleavage and transformation of serine to glycine are the two major reactions that produce methylene-THF that can be reduced to methyl-THF, which in turn is required for the methylation of homocysteine to methionine.
  • Serine production is catalyzed by the enzymes 3-phosphoglycerate dehydrogenase, phosphoserine phosphatase and phosphoserine aminotransferase
  • Glycine cleavage is catalyzed by the glycine cleavage complex.
  • accession number C. glutamicum jekeium indicated gene E. coli in parentheses
  • function cysA 1788761 Cgl0216 sulfate permease cysU, 1788764 Cgl0213 component of sulfate ABC cysT transporter cysW 1788762 membrane bound sulphate transport protein cysH 1789121 Cgl2816 adenylylsulfate reductase cysI 1789122 Cgl2817 sulfite reductase, alpha subunit cysJ 1789123 YP_22705 sulfite reductase, beta subunit cysK 1788754 Cgl2562 cysteine synthase cysM 2367138 Cgl2136 O-acetyl serine sulfhydrylase cysP 1788765 Periplasmic sulfate binding protein cysE 17900
  • the expression of the operons cysPUWAM, encoding the sulfate/thiosulfate importer and thiosulfate specific cysteine synthase, and/or the operon cysJIH encoding sulfite reductase and PAPS reductase are increased.
  • the expression of Corynebacterium cysA, cysT, cyI and cysJ are preferably increased in their expression.
  • the expression of the operon gcvTHP, and/or gene lpd encoding the glycine cleavage complex is/are increased.
  • the glycine cleavage complex may be introduced and overexpressed in Corynebacterium glutamicum by introducing the genes gcvTHP from Corynebacterium jekeium possibly as synthetic gene.
  • At least one gene involved in the in the production of glycine such as serA, serB, serC or glyA, is overexpressed.
  • enzymes involved in the metabolic pathway of methionine biosynthesis may be overexpressed or their activity increased, to boost methionine production.
  • at least one of the following genes encoding for such enzymes may be overexpressed:
  • metY Cgl0653
  • C. glutamicum The overexpression of metY (Cgl0653) in C. glutamicum can be envisioned with or without overexpressing the genes aecD/metB. (Cgl2309/Cgl2446).
  • metF and metH have been suggested in WO 2007/077041 and WO02007/012078, which are incorporated by reference into this application.
  • the inventors have demonstrated that even further overexpression of metF using elements that stabilize the messenger RNA of metF further increased methionine production. These stabilizing elements are usually loop structures that reduce the attack by RNA degrading nucleases (Carrier and Keasling (1998) Biotechnol. Prog. 15, 58-64).
  • Production of methionine may be further increased by using an altered metB allele that uses preferentially or exclusively H 2 S and thus produces homocysteine from O-succinyl-homoserine as has been described in the patent application WO 2004/076659 that is incorporated herein by reference.
  • the production of the byproduct isoleucine is reduced.
  • Isoleucine is an amino acid that can be separated from methionine only with great difficulty increasing drastically the cost for the production of pure methionine.
  • the production of isoleucine consumes carbon that could be used for the production of methionine. Therefore it is desirable that the production of isoleucine is kept as low as possible.
  • Isoleucine is produced either via the threonine biosynthesis pathway or via a reaction of ⁇ -elimination of O-succinylhomoserine, in the absence of cysteine. Means to reduce ⁇ -elimination activity have been described in the patent applications WO 2006/082254 and WO 2007/077041 that are incorporated by references into this application.
  • Isoleucine production is below the detection level (HPLC) in a non-modified microorganism such as E. coli .
  • the produced amount can reach 2% g isoleucine/g glucose.
  • the quantity of isoleucine recovered in the medium may be greater than 40 mM.
  • the inventors have shown that the overexpression of at least one of the following genes involved in serine biosynthesis also reduces the production of isoleucine.
  • homolanthionine is an amino acid that is produced form activated homoserine and homocysteine (Kromer et al (2006) J Bacteriol 188, 609-18; and patent application WO 2007/051725 by BASF).
  • Homolanthionine is an amino acid that can be separated from methionine only with great difficulty increasing drastically the cost for the production of pure methionine.
  • homolanthionine comprises two aspartate derived homoserine molecules and a reduced sulfur molecule, all of which could increase methionine/carbon source yield, if transformed into methionine.
  • Means that favor the transformation of homocysteine to methionine specifically are the attenuation of the formyl-THF deformylase activity encoded by the purU gene, the overexpression of methylene-THF reductase activity encoded by the metF gene, the attenuation of the expression of the pykA and/or pykF gene, the overexpression of serA, serB or serC or the overexpression of the lpd gene.
  • the sulfur source used for the fermentative production of L-methionine, its precursors or compounds derived thereof, may be any of the following: sulfate, thiosulfate, hydrogen sulfide, dithionate, dithionite, sulfite or a combination thereof.
  • the sulfur source is sulfate and/or thiosulfate.
  • the inventors recommend glucose or sucrose.
  • the invention also concerns the process for the production of L-methionine, its precursors or compounds derived thereof, comprising the fermentation of the methionine producing microorganism described above, the concentration of methionine, its precursors or derivatives and the isolation of the desired product(s) of the fermentation broth.
  • the bacteria are fermented at a temperature between 20° C. and 55° C., preferentially between 25° C. and 40° C., and more specifically about 30° C. for C. glutamicum and about 37° C. for E. coli.
  • the fermentation is generally conducted in fermentors with an inorganic culture medium of known defined composition adapted to the bacteria used, containing at least one simple carbon source, and if necessary a co-substrate necessary for the production of the metabolite.
  • the inorganic culture medium for E. coli can be of identical or similar composition to an M9 medium (Anderson. 1946 . Proc. Natl. Acad. Sci. USA 32:120-128), an M63 medium (Miller. 1992: A Short Course in Bacterial Genetics: A Laboratory Manual and Handbook for Escherichia coli and Related Bacteria. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.) or a medium such as defined by Schaefer et al. (1999 , Anal. Biochem. 270: 88-96).
  • the inorganic culture medium for C. glutamicum can be of identical or similar composition to BMCG medium (Liebl et al., 1989 , Appl. Microbiol. Biotechnol. 32: 205-210) or to a medium such as described by Riedel et al. (2001, J. Mol. Microbiol. Biotechnol. 3: 573-583).
  • the media can be supplemented to compensate for auxotrophies introduced by mutations.
  • L-methionine After fermentation L-methionine, its precursors or compounds derived thereof, is/are recovered and purified if necessary.
  • the methods for the recovery and purification of the produced compound such as methionine and N-acetyl-methionine in the culture media are well known to those skilled in the art.
  • preferentially at least 90%, more preferentially 95%, even more preferentially at least 99% of the biomass may be retained during the purification of the fermentation product.
  • the methionine derivative N-acetyl-methionine is transformed into methionine by deacylation, before methionine is recovered.
  • the invention also relates to a microorganism that is optimized for the fermentative production of methionine, i.e. having an improved methionine/carbon source yield compared to a non-modified microorganism, and that comprises the genetic modifications described above.
  • FIG. 1 A first figure.
  • Methionine biosynthesis in E. coli Abbreviation: P phosphate, GA3P glyceraldehyde-3-phosphate, PGA phosphoglycerate, PEP phosphoenolpyruvate, Pyr pyruvate, Asp aspartate. Asp-P aspartylphosphate, Asp-SA aspartatesemialdehyde, homoser homoserine. OSH O-succinylhomoserine. ⁇ -cys ⁇ -cystathionine, homocys homocysteine, homolan homolanthionine. THF tetrahydrofolate, Ser serine, Cyst Cysteine, Gly glycine, PPP pentose phosphate shunt.
  • FIG. 2
  • strain1 has the genotype ⁇ metJ metA*11 Ptrc-metH Ptrc-metF (pME101-thrA*1-cysE-PgapA-metA*11). All subsequent constructions described below are based on these constructs.
  • Ptrc-cysPUWAM F (SEQ ID NO 1) GCGCGAGTGAGTTCTTTTTCAGTAAGTTAACGGCCATTGCGCACCCTTAT AAATTTAATGACTTTC TTCCACAC ATTATA CGAGCCGGATGATTAAT TGT CAA CAGCT TGTAGGCTGGAGCTGCTTCG
  • Ptrc-cysPUWAM R (SEQ ID NO 2) CCAAATCACCAAACGGTATATAAAACCGTTACTCCTTTCACGTCCGTTAT AAATATGATGGCTATTA TCACACTGGCTCACCTTCGGGTGGGCCTTTCTG C CATATGAATATCCTCCTTAG
  • the oligonucleotides Ptrc-cysPUWAM F and Ptrc-cysPUWAM R were used to amplify the chloramphenicol resistance cassette from the plasmid pKD3.
  • the obtained PCR product was then introduced into the strain MG1655 (pKD46) by electroporation. In this strain the Red recombinase enzyme was expressed and permitted homologous recombination. Chloramphenicol resistant transformants were then selected and the insertion of the resistance cassette was verified by PCR analysis with the oligonucleotides Ptrc-cysPUWAMRv and Ptrc-cysPUWAMFv shown below. The strain retained was
  • Ptrc-cysPUWAMRv (SEQ ID NO 3): GCAGGATTTGTACGTCGGT CACC (homologous to the sequence from 2541260 to 2541282).
  • Ptrc-cysPUWAMFv (SEQ ID NO 4): cgtcttgaactaagttc accaggc (homologous to the sequence from 2541812 to 2541789).
  • PtrcF-cysJIH R (SEQ ID NO 5) CCAGTAAGCAAAGCTGTTTCTGCGCCCTGTCAGCGCCCATAAAACAGAAG AGA TTCCACAC ATTATA CGAGCCGGATGATTAAT TGTCAA CAGC TTGTAG GCTGGAGCTGCTTCG
  • PtrcF-cysJIH F (SEQ ID NO 6) GGTTATTAGTTATCGCTATCCCGTCTTTAATCCACACCGTTTGCCCCGTT AACCTTACCT TCACACTGGCTCACCTTCGGGTGGGCCTTTCTGC CATATG AATATCCTCCTTAG
  • the oligonucleotides PtrcF-cysJIH F and PtrcF-cysJIH R were used to amplify the kanamycin resistance cassette from the plasmid pKD4.
  • the obtained PCR product was then introduced into the strain MG1655 (pKD46) by electroporation. In this strain the Red recombinase enzyme was expressed and permitted the homologous recombination. Kanamycin resistant transformants were then selected and the insertion of the resistance cassette was verified by a PCR analysis with the oligonucleotides Ptrc-cysJIHFv and Ptrc-cysJIHRv shown below. The strain retained was designated MG1655 Ptrc-cysJIH:Km.
  • Ptrc-cysJIHFv (SEQ ID NO 7): GCAGTTCGACAAGTTCTTTCA CC (homologous to the sequence from 2889042 to 2889064).
  • Ptrc-cysJIHRv (SEQ ID NO 8): CCAGAACACAACACCCTAACA TAGCG (homologous to the sequence from 2890663 to 2890638). Construction of MG1655 Ptrc09-gcvTHP
  • Ptrc-gcvTHP F (SEQ ID NO 9) CCACCATGCGAGCGCCGCAAAGCGTGTGTTGTTCGTACAAAGGAGTCTGT TGTGC CAT AATATA TATTCCACAC ATTATA CGAGCCGGATG ATTAATTGTC AACAGCTCTGTAGGCTGGAGCTGCTTCG
  • Ptrc-gcvTHP R (SEQ ID NO 10) CTGTCGCGATTTTTGCATTTTTTAACCATAAGCTAATGTGATGATCAATT TTACCTTA CATATGAATATCCTCCTTAG
  • the oligonucleotides Ptrc-gcvTHP F and Ptrc-gcvTHP R were used to amplify the kanamycin resistance cassette from the plasmid pKD4.
  • the obtained PCR product was then introduced by electroporation into the strain MG1655 (pKD46). In this strain the Red recombinase enzyme was expressed and permitted the homologous recombination. Kanamycin resistant transformants were then selected and the insertion of the resistance cassette was verified by a PCR analysis with the oligonucleotides Ptrc-gcvTHP F2 and Ptrc-gcvTHP R2 shown below. The strain retained was designated MG1655 Ptrc-gcvTHP:Km.
  • Ptrc-gcvTHP F2 (SEQ ID NO 11): CTATCACACCGCCAGAGGC ATTC (homologous to the sequence from 3048399 to 3048421).
  • Ptrc-gcvTHP R2 (SEQ ID NO 12): CCCATCACACTTTCATCTC CCG (homologous to the sequence from 3049106 to 3049085). Construction of MG 1655 ⁇ pykA
  • DpykA F (SEQ ID NO 13) cgcggcgggtgccaacgttgtacgtatgaacttttctcacggctcgcctg aagatcacaaatgcgcgcggataaagttcg TGTAGGCTGGAGCTG CTTCG
  • DpykA R (SEQ ID NO 14) CGCCGCATCCGGCAACGTACTTACTCTACCGTTAAAATACGCGTGGTA TTAGTAGAACCCACGGTACTCATCACGTCGCCC CATATGAATATCCTCC TTAG
  • the oligonucleotides DpykA F and DpykA R were used to amplify the chloramphenicol resistance cassette from the plasmid pKD3.
  • the obtained PCR product was then introduced by electroporation into the strain MG1655 (pKD46). In this strain the Red recombinase enzyme was expressed and permitted the homologous recombination. Chloramphenicol resistant transformants were then selected and the insertion of the resistance cassette was verified by a PCR analysis with the oligonucleotides pykA F and pykA R shown below.
  • the strain retained was designated MG1655 ⁇ pykA::Cm.
  • PykA F (SEQ ID NO 15): ggcaattaccctcgacgtaccgg (homologous to the sequence from 1935338 to 1935360).
  • PykA R (SEQ ID NO 16): ccgcctctaacagatcatccatcgg (homologous to the sequence from 1935401 to 1937425). Construction of MG1655 ⁇ pykF
  • DpykF F (SEQ ID NO 17) cccatccttctcaacttaaagactaagactgtcatgaaaaagaccaaa attgtttgcaccatcggaccgaaaaccgaa TGTAGGCTGGAGCTGCTTCG
  • DpykF R (SEQ ID NO 18) ggacgtgaacagatgcggtgttagtagtgccgctcggtaccagtgcacca gaaaccataactacaacgtcacctttgtg CATATGAATATCCTCCTTAG
  • the oligonucleotides DpykF F and DpykF R were used to amplify the kanamycin resistance cassette from the plasmid pKD4.
  • the obtained PCR product was then introduced by electroporation into the strain MG1655 (pKD46). In this strain the Red recombinase enzyme was expressed and permitted the homologous recombination. Kanamycin resistant transformants were then selected and the insertion of the resistance cassette was verified by a PCR analysis with the oligonucleotides pykF F and pykF R shown below.
  • the strain retained was designated MG1655 DpykF::Km.
  • PykF F (SEQ ID NO 19): gcgtaaccttttccctggaacg (homologous to the sequence from 1753371 to 1753392).
  • PykF R (SEQ ID NO 20): gcgttgctggagcaacctgccagc (homologous to the sequence from 1755518 to 1755495). Construction of MG1655 ⁇ purU
  • DpurU F (SEQ ID NO 21) ggtaaaaaatttaaaaagtgctgcggccaataatggttgacggtacggtt tagcaaacactctcaacaaggtttttccagc TGTAGGCTGGAGCTGCTT CG
  • DpurU R (SEQ ID NO 22) ggttgcgtaattttcatccgtaacggattaaaggtaaccagttattttttg ctggcgattaaagaataatcgttcgattacc CATATGAATATCCTCCTT AG
  • the oligonucleotides DpurU F and DpurU R were used to amplify the kanamycin resistance cassette from the plasmid pKD4.
  • the obtained PCR product was then introduced by electroporation into the strain MG1655 (pKD46). In this strain the Red recombinase enzyme was expressed and permitted the homologous recombination. Kanamycin resistant transformants were then selected and the insertion of the resistance cassette was verified by a PCR analysis with the oligonucleotides purU F and purU R shown below. The strain retained was designated MG1655 DpurU::Km.
  • PurU F (SEQ ID NO 23): ggaatgcaatcgtagccacatcgc (homologous to the sequence from 1288447 to 1288424).
  • PurU R (SEQ ID NO 24): gcggattcgttgggaagttcaggg (homologous to the sequence from 1286129 to 1286452). Construction pCC1BAC-serA-serC
  • the gene dosage of the two genes was increased in the methionine producing cell by expressing the enzymes from the copy control vector pCC1BAC (Epicentre) using their proper promoters.
  • the serC gene was amplified from the E. coli genome using the oligonucleotides -serC F (XbaI) and serC R (HindIII).
  • the PCR product was restricted using enzymes XbaI and HindIII and cloned into the vector pUC18 (Stratagene) restricted by the same restriction enzymes.
  • the resulting vector was named pUC18-serC, serC F(XbaI) (SEQ ID NO 25):
  • serC R (HindIII) (SEQ ID NO 26): ccc AAGCTT AACTCTCTACAACAGAAATAAAAAC
  • serA F (XbaI) (SEQ ID NO 27): ctag TCTAGA ttagtacagcagacgggcgcg
  • serA R (SmaI-HindIII) (SEQ ID NO 28): tcc CCCGGGaagctt CCGTCAGGGCGTGGTGACCG
  • the vector pUC18-serA-serC was restricted with the enzyme HindIII and cloned into HindIII cloning ready pCC1BAC (Epicentre).
  • the gene dosage of the three genes was increased in the methionine producing cell by expressing the enzymes from the copy control vector pCC1BAC (Epicentre) using their proper promoters.
  • the serB gene was amplified from the E. coli genome using the oligonucleotides serB (SphI) and serB (SmaI).
  • the PCR product was restricted using enzymes SphI and SmaI and cloned into the vector pUC18-serA-serC restricted by the same restriction enzymes.
  • the resulting vector was named pUC18-serB-serA-serC.
  • serB (SphI) (SEQ ID NO 29): atgc GCATGC CCACCCTTTGAAAATTTGAGAC
  • serB (SmaI) (SEQ ID NO 30): gcatgtcgacat CCCGGG GCAGAAAGGCCCACCCGAAGGTGAGCCAGTGT G ATTACTTCTGATTCAGGCTGCC
  • the vector pUC18-serB-serA-serC was restricted with the enzyme HindIII and cloned into HindIII cloning ready pCC1BAC (Epicentre).
  • the gene dosage of the three genes was increased in the methionine producing cell by expressing the enzymes from the copy control vector pCC1BAC (Epicentre) using their proper promoters.
  • the glyA gene was amplified from the E. coli genome using the oligonucleotides PglyA F (HindIII) and glyA R (EcoRI-HindIII).
  • the PCR product was restricted using enzyme HindIII, blunted with the Klenow fragment and cloned into the vector pUC18-serB-serA-serC restricted by the restriction enzyme SmaI.
  • the resulting vector was named pUC18-serB-glyA-serA-serC.
  • PglyA F (HindIII) (SEQ ID NO 31): TCATCGGATCCATC AAGCTT GA AAGAATGTGATGAAGTG
  • glyA R (EcoRI-HindIII) (SEQ ID NO 32): ATCTAGT AAGCTT AGT GAATTC GTTACGACAGATTTGATGGCGCG
  • the vector pUC18-serB-glyA-serA-serC was restricted with the enzyme HindIII and cloned into HindIII cloning ready pCC1BAC (Epicentre).
  • the lpd gene was amplified from the E. coli genome using the oligonucleotides lpd F (HindIII) and lpd R (EcoRI).
  • the PCR product was restricted using enzymes EcoRI and HindIII and cloned into the vector pJB137 restricted by the same restriction enzymes.
  • the resulting vector was named pJB137-lpd.
  • lpd R (EcoRI) (SEQ ID NO 34): gcatgatc GAATTC TGCAGACGTAAAAAAAGCGGCGTGG
  • strains were derived from strain ⁇ metJ metA*11 Ptrc-metH Ptrc-metF by P1 phage transduction and removal of resistance cassettes when required.
  • Chloramphenicol resistant transformants were selected and the presence of the promoter construct MG1655 PtrcF-cysPUWAM::Cm was verified by PCR analysis with the oligonucleotides described above for the verification of the strain MG1165 PtrcF-cysPUWAM::Cm.
  • the strain retained was designated ⁇ metJ metA*11 Ptrc-metH Ptrc-metF PtrcF-cysPUWAM::Cm.
  • the PtrcF-cysJIH allele was introduced using the P1 transduction procedure as described above.
  • the resulting strain was named ⁇ metJ metA*11 Ptrc-metH Ptrc-metF PtrcF-cysPUWAM::Cm PtrcF-cysJIH::Km.
  • the plasmid pCP20 carrying FLP recombinase acting at the FRT sites of the resistance cassettes was introduced into the recombinant strain by electroporation. After a series of cultures at 42° C., the loss of the two cassettes was verified by PCR analysis. The strain retained vas designated ⁇ metJ metA*11 Ptrc-metH Ptrc-metF PtrcF-cysPUWAM PtrcF-cysJIH. Then the deletions of the pykA and pykF alleles could be introduced via P1 transduction. Similarly the deletion of the purU gene and the glycine cleavage complex overexpression construct Ptrc09-gcvTHP were introduced after the elimination of the corresponding cassettes.
  • Ptrc36-ARNmst-metF (SEQ ID NO 35) (GGCTCTGATTCAGGGCATCCCGCTGGCTGGCGTGAAAAAAGCTCAT AAT ATA CCTCCT cgtcaacaatatctcactcgagataactccacc TATTCCAC AC ATTATA CGAGCCGG
  • SEQ ID NO 35 GGCTCTGATTCAGGGCATCCCGCTGGCTGGCGTGAAAAAAGCTCAT AAT ATA CCTCCT cgtcaacaatatctcactcgagataactccacc TATTCCAC AC ATTATA CGAGCCGG
  • Ptrc-metF F (SEQ ID NO 36) ccttcatctttacatctggacgtctaaacggatagatgtgcacaacacaa catataactacaagcgattgatgaggtaaggt tcacactggctcaccttc gggtgggcctttctgc CATATGAATATCCTCCTTAG with:
  • the oligonucleotides Ptrc-metF F and Ptrc36-ARNmst-metF were used to amplify the kanamycin resistance cassette from the plasmid pKD4.
  • the PCR product obtained was then introduced by electroporation into the strain ⁇ metJ metA*11 Ptrc-metH Ptrc-metF PtrcF-cysPUWAM PtrcF-cysJIH ⁇ pykF ⁇ pykA Ptrc09-gcvTHP ⁇ purU (pKD46), in which the Red recombinase enzyme expressed permits the homologous recombination.
  • the kanamycin resistant transformants were selected and the insertion of the resistance cassette was verified by a PCR analysis with the oligonucleotides Ptrc-metFv F and Ptrc-metFv R defined below.
  • Ptrc-metFv F GCCCGGTACTCATGTTTTCGG GTTTATGG (homologous to the sequence from 4129866 to 4129894).
  • Ptrc-metFv R SEQ ID NO 38: CCGTTATTCCAGTAGTCGCGT GCAATGG (homologous to the sequence from 4130524 to 4130497).
  • the resulting strain was called ⁇ metJ metA*11 Ptrc-metH Ptrc-metF PtrcF-cysPUWAM PtrcF-cysJIH ⁇ pykF ⁇ pykA Ptrc09-gcvTHP ⁇ purU Ptrc36-ARNmst17-metF:Km.
  • Production strains were initially evaluated in small Erlenmeyer flasks.
  • a 5.5 mL preculture was grown in a mixed medium (10% LB medium (Sigma 25%) with 2.5 g ⁇ L ⁇ 1 glucose and 90% minimal medium PC1) and was used to inoculate a 50 mL culture to an OD 600 of 0.2 in medium PC1.
  • Kanamycin and spectinomycin were added if necessary at a concentration of 50 mg ⁇ L ⁇ 1 , chloramphenicol at 30 mg ⁇ L ⁇ 1 .
  • PC1 Compound Concentration ZnSO 4 •7H 2 O 0.0040 g ⁇ L ⁇ 1 CuCl 2 •2H 2 O 0.0020 g ⁇ L ⁇ 1 MnSO 4 •H 2 O 0.0200 g ⁇ L ⁇ 1 CoCl 2 •6H 2 O 0.0080 g ⁇ L ⁇ 1 H 3 BO 3 0.0010 g ⁇ L ⁇ 1 Na 2 MoO 4 •2H 2 O 0.0004 g ⁇ L ⁇ 1 MgSO 4 •7H 2 O 1 g ⁇ L ⁇ 1 Citric acid 6 g ⁇ L ⁇ 1 CaCl 2 •2H 2 O 0.04 g ⁇ L ⁇ 1 K 2 HPO 4 •3H 2 O 10.5 g ⁇ L ⁇ 1 Na 2 HPO 4 2 g ⁇ L ⁇ 1 (NH 4 ) 2 HPO 4 8 g ⁇ L ⁇ 1 NH 4 Cl 0.13 g ⁇ L ⁇ 1 NaOH 4M Adjusted to pH 6.8
  • the methionine/glucose yield (Y met ) is increased upon overexpression of cvsJIH and cysPUWAM.
  • the deletion of the pyruvate kinase encoding alleles pykA and pykF can further increase methionine/glucose yield.
  • the deletion of the formyl-THF deformylase encoded by the purU gene further boosts methionine/glucose yield.
  • Additional further expression of the metF gene by the construct Ptrc36-ARNmst17-metF still gives higher methionine/glucose yield.
  • the overexpression of serA serC and serB even further increase methionine/glucose yield and the additional expression of giyA still increases the methionine/glucose yield.
  • E. coli strains were cultured in minimal medium as described above and harvested at mid log phase. Cells were suspended in cold potassium phosphate buffer and sonicated on ice (Branson sonifier, 70 W). In two cases (shown in grey cases in table 3), proteins were extracted by using a precellys extraction system (Bertin technologies, France): Cells were suspended in cold potassium phosphate buffer, mixed with 0.1 mm glass beads and extracted with one run of 30 s. After centrifugation, proteins contained in the supernatants were quantified (Bradford, 1976).
  • CysM Sulfocysteine synthase activity
  • a lactate dehydrogenase (LDH) coupled assay was performed. 10 ⁇ L of protein extract were added to a solution buffered with Tris-HCl (0.5 M, pH 7.5) containing 10 mM DTT, 100 mM MgCl 2 , 100 mM KCl, 10 mM PEP, 50 mM AMP, 10 mM fructose 1,6 bis phosphate, 10 mM NADH and 10 units of LDH. The reaction was followed at 340 nm at 30° C. for 30 min in a thermostated spectrophotometer.
  • Tris-HCl 0.5 M, pH 7.5
  • the activity of GcvTHP was estimated by measuring CO 2 production occurring during the glycine decarboxylation reaction.
  • the reaction was performed in a sided arm Warburg flask containing 0.5 M potassium phosphate buffer at pH 7, 2 mM, pyridoxal phosphate, 200 mM lipoamide and 1-14C-glycine 1M at 50 ⁇ Ci/mL. 400 ⁇ L of hyamine were placed in the center well of the flask and the whole reaction system was pre-incubated 5 min at 37° C.
  • the enzymatic reaction was started by adding 2 mg of protein and run at 37° C.
  • MTHFR Methylene tetrahydrofolate reductase activity
  • Lipoamide dehydrogenase activity of Lpd was determined based on the reduction of lipoamide with NADH as the electron donor. EDTA 10 mM, NADH 1 mM and NAD + 25 mM and 1 ⁇ g of protein extract were added to a Tris-HCl (0.5 M, pH 8.0) buffered solution. The reaction was started by adding 200 mM of lipoamide and the NADH disappearance was followed at 340 nm at 30° C. for 30 min in a thermostated spectrophotometer.
  • Phosphoglycerate dehydrogenase activity of SerA was monitored by following the disappearance of NADH.
  • 30 ⁇ L of protein extract were placed in Tris-HCl (10 mM, pH 8.8) solution containing 360 ⁇ M 3-P-hydroxypyruvate.
  • 200 ⁇ M NADH were added to start the reaction and the disappearance of NADH was followed at 340 nm at 30° C. for 30 min in a thermostated spectrophotometer.
  • the phosphoserine phosphatase activity carried by the SerB protein was determined by measuring the serine produced by GC-MS.
  • the reaction mixture contained TEA-HCl (10 mM, pH 7.5), 1 mM MgCl2, 1 mM O-phospho-L-serine and 15 ⁇ g of protein.
  • the reaction was incubated at 37° C. and stopped at 10 and 30 minutes by addition of acetone and further processed for GC-MS quantification.
  • Phosphophoserine-amino-transferase activity of SerC was measured by coupling the assay with glutamate dehydrogenase.
  • the reaction mixture was buffered by Tris-HCl (50 mM, pH 8.2) and contained 32 mM ammonium acetate, 2 mM glutamate, 2 uts Glutamate Dehydrogenase, 200 ⁇ M NADH.
  • the reaction was started by adding 30 ⁇ L of protein extract and the disappearance of NADH was followed at 340 nm at 30° C. for 30 min in a thermostated spectrophotometer.
  • Serine hydroxymethyl transferase activity was measured by monitoring the glycine produced by GC-MS. 30 ⁇ g of protein were added to a solution containing potassium phosphate (50 mM, pH 7.3), 400 ⁇ M of tetrahydropteroyl glutamate, 10 mM L-serine and 500 M DTT. The reaction was run 10 minutes at 37° C. and stopped after 10 minutes by addition of acetone and further processed for GC-MS quantification.
  • Glycine decarboxylase activity of GcvTHP is in ⁇ U/mg of protein.. Activities marked in grey cases were obtained from cultures extracted on a Precellys system. LOQ: limit of quantification; ND: not determined
  • the constructs PtrcF-cysPUWAM, PtrcF-cysJIH Ptrc09-gcvTHP and Ptrc39-ARNmst17-metF, pJB137-lpd, pCC1BAC-serB-serA-serC and pCC1BAC-serB-glyA-serA-serC all increase the activity of the corresponding enzyme when compared to the strain not modified for the corresponding allele. Deletion of pykA and pykF leads to a complete loss of pyruvate kinase activity.
  • the preculture medium B1 contained only 50 mM phosphate to avoid introducing additional phosphate into the batch medium with the inoculum.
  • phosphate was added to 28.7 mM added to the mineral medium B2.
  • the fed batch media (F1 and F2) were phosphate free.
  • a third preculture step was carried out in bio-reactors (Sixfors) filled with 200 mL of minimal medium (B1) inoculated to a biomass concentration of 0.05 g ⁇ L ⁇ 1 with 1.5 mL concentrated preculture (5 g ⁇ L ⁇ 1 ).
  • the preculture temperature was maintained constant at 37° C. and the pH was automatically maintained at a value of 6.8 using a 10% NH 4 OH solution.
  • the dissolved oxygen concentration was continuously adjusted to a value of 30% of the partial air pressure saturation with air supply and/or agitation.
  • the fed batch was started with an initial flow rate of 0.7 mL ⁇ h ⁇ 1 , increased exponentially for 24 hours with a growth rate of 0.18 h ⁇ 1 in order to obtain a final cellular concentration of about 24 g ⁇ L ⁇ 1 .
  • the culture temperature was maintained constant at 37° C. and pH was maintained to the working value (6.8) by automatic addition of NH 4 OH solutions (NH 4 OH 10% for 10 hours and 24% until the culture end).
  • the initial agitation rate was set at 200 rpm during the batch phase and was increased to up to 1000 rpm during the fed-batch phase.
  • the initial airflow rate was set at 40 NL ⁇ h ⁇ 1 during the batch phase and was increased to 100 NL ⁇ h ⁇ 1 at the beginning of the fed-batch phase.
  • the dissolved oxygen concentration was maintained at values between 20 and 40%, preferentially 30% saturation by increasing the agitation.
  • Genotype Y met+NAM Y iso Y homolanthionine strain1 PtrcF-cysPUWAM PtrcF-cysJIH ⁇ pykF ⁇ pykA 14.4 ⁇ 1 1.3 ⁇ 0.5 2.8 ⁇ 0.03 Ptrc09-gcvTHP strain1 PtrcF-cysPUWAM PtrcF-cysJIH ⁇ pykF ⁇ pykA 15.6 ⁇ 1.2 1.7 ⁇ 0.4 0.93 ⁇ 0.13 Ptrc09-gcvTHP ⁇ purU strain1 PtrcF-cysPUWAM PtrcF-cysJIH ⁇ pykF ⁇ pykF ⁇ py
  • Extracellular methionine concentration was quantified by HPLC after OPA/FMOC derivatization.
  • the NAM concentration and residual glucose concentration was analyzed using HPLC with refractometric detection.
  • the methionine yield was expressed as followed:
  • Y met methionine ⁇ ⁇ ( g ) consummed ⁇ ⁇ glucose ⁇ ⁇ ( g ) * 100
  • Methionine 0 and Methionine f respectively the initial and final methionine concentrations
  • Glucose 0 and Glucose f respectively the initial and final glucose concentrations
  • V 0 and V f the initial and final volumes.
  • the fermentor volume was calculated by adding to the initial volume the amount of solutions added to regulate the pH and to feed the culture and by subtracting the volume used for sampling and lost by evaporation.
  • the fed batch volume was followed continuously by weighing the feeding stock.
  • the amount of injected glucose was then calculated on the basis of the injected weight, the density of the solution and the glucose concentration determined by the method of Brix ([Glucose]).
  • the methionine yield was expressed as followed:
  • Methionine 0 and Methionine t respectively the initial and final methionine concentrations and V 0 and V t the initial and the instant t volumes.
  • the consumed glucose was calculated as follows:

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