WO2007119880A1

WO2007119880A1 - A method for producing an l-amino acid using a bacterium of the enterobacteriaceae family which has been modified to abolish curli formation

Info

Publication number: WO2007119880A1
Application number: PCT/JP2007/058570
Authority: WO
Inventors: Konstantin Vyacheslavovich Rybak; Aleksandra Yurievna Skorokhodova; Elvira Borisovna Voroshilova; Mikhail Markovich Gusyatiner
Original assignee: Ajinomoto Co., Inc.
Priority date: 2006-04-13
Filing date: 2007-04-13
Publication date: 2007-10-25
Also published as: WO2007119880A9

Abstract

The present invention provides a method for producing an L-amino acid using a bacterium of the Enterobacteriaceae family, particularly a bacterium belonging to the genus Escherichia or Pantoea, which has been modified to abolish curli formation, particularly, by attenuation of expression of the csgBAC and/or csgDEFG operons.

Description

DESCRIPTION

A METHOD FOR PRODUCING AN L-AMINO ACID USING A BACTERIUM OF THE ENTEROBACTERIACEAE FAMILY WHICH HAS BEEN MODIFIED TO ABOLISH CURLI FORMATION

Technical Field

The present invention relates to the microbiological industry, and specifically to a method for producing an L-amino acid using a bacterium of the Enterobacteriaceae family which has been modified to abolish curli formation.

Background Art

CsgBAC (curli subunit proteins, fibronectin-binding curli organelles, cell surface- associated polymers) encoded by the csgBAC operon plays a key role as a colonization factor in host-microbe interactions, as well as in adhesion to other bacteria, eukaryotic cells, and extracellular matrix proteins. Finally, the CsgBAC plays a role in surface colonization during the fermentation process (Olsen A., et al., Mol.Microbiol., 7(4)., 523-36(1993)).

It has been shown that the csgA gene encodes the major subunit of the curli organelle, and that transcription of the csgA gene, curli expression, and fibronectin binding are environmentally controlled by positively responding to low temperature, low osmolarity, and stationary-phase growth conditions (Olsen A., et al., Mol.Microbiol., 7(4)., 523-36(1993)).

It has also been shown that two divergently transcribed operons, csgDEFG and csgBAC, which are separated by a 513-bp intergenic region, are required for the biogenesis of curli fibers. The csgBAC operon encodes the CsgA subunit protein and CsgB protein. These two subunits have sequence homology to each other. A non-polar csgB mutant does not effect the production of CsgA, but the CsgA subunit is not assembled into insoluble fibre polymers. A third open reading frame, csgC, positioned downstream of csgA may affect some functional properties of curli since an insertion into this putative gene abolishes the autoagglutinating ability, which is typical of curliated cells without affecting the production of the fibre. Insertions in csgE, csgF, and csgG abolish curli formation but allow CsgA expression, suggesting that one or more of these gene products are involved in secretion/assembly of the CsgA subunit protein (Hammar M., et al., Mol.Microbiol., 18(4), 661-670 (1995)).

The intercellular formation of curli is thought to be a self-assembly process. Curli polymers form as a result of a conformational change of the soluble CsgA, initiated by an interaction with the nucleating CsgB protein. CsgA is actively secreted to the extracellular milieu and CsgB is surface located. As a putative nucleator at the base of the fiber, CsgB may be a very minor protein if only one molecule is required for each curli fiber (Hammar M, et al, Proc Natl Acad Sci USA, 93(13), 6562-6566(1996)).

CsgG is a lipoprotein located in the outer membrane. It is required for stability of the curli structural proteins CsgA and CsgB during curli assembly, and changes in the level of CsgG protein cause corresponding changes in the level of CsgA and CsgB proteins (Loferer H., et al., Mol.Microbiol.,26(l), 11-23 (1997)).

The production of curli in Escherichia coli is a highly regulated phenomenon. Curli expression is activated in hns mutants of curli-deficient strains. Production of csgA transcripts occurs in the very late stationary phase, and the stationary-phase-specific sigma factor, RpoS is also required for the expression of the csgBA operon. In curli-proficient RpoS⁺ Escherichia coli, transcriptional silencing mediated directly or indirectly by H-NS can be relieved once the concentration of RpoS has reached a certain level (Olsen A., et al., MoLMicrobioL, 7(4)., 523-36(1993)).

Transposon insertions in the csgD gene, which encodes a transcriptional regulator of the LuxR family as identified by the sequence similarity of the DNA binding helix-turn- helix motif, completely abolished transcription of the csgBAC and csgDEFG operons. The csgDEFG promoter is active in an rpoS hns background. Absence of H-NS has been shown to make at least the csgD promoter independent of rpoS, suggesting efficient repression of rpoD-dependent transcription by hns. These data mean that pcsgBAC dependence on RpoS sigma factor is indirect via CsgD. The csgD gene is followed by the three genes csgE, csgF, and csgG. Insertions in each of these three genes abolish curli formation without affecting the production of the CsgA subunit protein. (Hammar M., et al., MoLMicrobioL, 18(4), 661-670 (1995)).

Therefore, other regulators must also influence the transcription from the csgD and csgBAC promoters. It has been reported that ompR is required for transcriptional activation of both the csgBAC and the csgDEFG promoters in Escherichia coli. The sequence for OmpR binding is relative to the transcriptional start site of the csgD promoter. So, OmpR transcriptional regulation takes place mainly at the csgD promoter. CsgD may then act upon the csgBAC promoter to initiate transcription there (Romling U., et ah, J Bacteriol, 180(3), 722-31(1998)). The presence of the ompR allele with a single point mutation, resulting in the replacement of a leucine by an arginine residue at position 43 in the regulatory protein, significantly increases the production of curli and the expression of the csgA gene encoding curli synthesis. It is therefore possible that the replacement of a leucine by another arginine at the next position could enhance the affinity of OmpR for the RNA polymerase (Vidal O. et al, J Bacteriol., 180(9), 2442-9 (1998)). The csgBAC and csgDEFG belong to stress-combative genes. Activation of transcription of these genes is mediated by the response regulator CpxR. It senses a variety of envelope stresses, including misfolded proteins and degrading factors. It is a member of the two-component regulatory system CpxA/CpxR. Overproduction of CpxA/CpxR causes a drug resistance phenotype and affects transcription of genes involved in drug efflux (Hiracawa et al., J Bacterid., 185(6), 1851-1856(2003)).

But currently, there have been no reports of attenuating expression of the csgBAC or/and csgDEFG operons for the purpose of producing L-amino acids.

Summary of the Invention

Objects of the present invention include enhancing the productivity of L-amino acid producing strains and providing a method for producing an L-amino acid using these strains.

The above objects were achieved by finding thatattenuating expression of the csgBAC or csgDEFG operons can enhance the production of L-amino acids, such as L- threonine, L-lysine, L-cysteine, L-leucine, L-histidine, L-glutamic acid, L-phenylalanine, L-tryptophan, L-proline, and L-arginine.

The present invention provides a bacterium of the Enterobacteriaceae family having an increased ability to produce amino acids, such as L-threonine, L-lysine, L- cysteine, L-methionine, L-leucine, L-isoleucine, L-valine, L-histidine, glycine, L-serine, L- alanine, L-asperagine, L-aspartic acid, L-glutamine, L-glutamic acid, L-proline, L-arginine, L-phenylalanine, L-tyrosine, and L-tryptophan.

It is an object of the present invention to provide an L-amino acid-producing bacterium of the Enterobacteriaceae family, wherein the bacterium has been modified to abolish curli formation.

It is a further object of the present invention to provide the bacterium as described above, the expression of the csgBAC and/or csgDEFG operons is attenuated.

It is a further object of the present invention to provide the bacterium as described above, wherein the expression of the csgBAC and/or csgDEFG operon is attenuated by inactivation of the csgBAC and/or csgDEFG operon.

It is a further object of the present invention to provide the bacterium as described above, wherein the bacterium belongs to the genus Escherichia.

It is a further object of the present invention to provide the bacterium as described above, wherein the bacterium belongs to the genus Pantoea.

It is a further object of the present invention to provide the bacterium as described above, wherein said L-amino acid is selected from the group consisting of an aromatic L- amino acid and a non-aromatic L-amino acid. It is a further object of the present invention to provide the bacterium as described above, wherein said aromatic L-amino acid is selected from the group consisting of L- phenylalanine, L-tyrosifie, and L-tryptophan.

It is a further object of the present invention to provide the bacterium as described above, wherein said non-aromatic L-amino acid is selected from the group consisting of L- threonine, L-lysine, L-cysteine, L-methionine, L-leucine, L-isoleucine, L-valine, L- histidine, glycine, L-serine, L-alanine, L-asparagine, L-aspartic acid, L-glutamine, L- glutamic acid, L-proline, and L-arginine.

It is a further object of the present invention to provide a method for producing an L-amino acid comprising:

- cultivating the bacterium as described above in a medium, and

- collecting said L-amino acid from the medium.

It is a further object of the present invention to provide the method as described above, wherein said L-amino acid is selected from the group consisting of an aromatic L- amino acid and a non-aromatic L-amino acid.

It is a further object of the present invention to provide the method as described above, wherein said aromatic L-amino acid is selected from the group consisting of L- phenylalanine, L-tyrosine, and L-tryptophan.

It is a further object of the present invention to provide the method as described above, wherein said non-aromatic L-amino acid is selected from the group consisting of L- threonine, L-lysine, L-cysteine, L-methionine, L-leucine, L-isoleucine, L-valine, L- histidine, glycine, L-serine, L-alanine, L-asparagine, L-aspartic acid, L-glutamine, L- glutamic acid, L-proline, and L-arginine.

The present invention is described in detail below.

Detailed Description of the Preferred Embodiments 1. Bacterium of the present invention

The bacterium of the present invention is an L-amino acid-producing bacterium of the Enterobacteήaceae family, wherein the bacterium has been modified to attenuate expression of the csgBAC and/or csgDEFG operons.

In the present invention, "L-amino acid-producing bacterium" means a bacterium which has an ability to produce and excrete an L-amino acid into a medium, when the bacterium is cultured in the medium.

The phrase "L-amino acid-producing bacterium" as used herein also means a bacterium which is able to produce and cause accumulation of an L-amino acid in a culture medium in an amount larger than a wild-type or parental strain of the bacterium, for example, E. coli, such as E. coϊi K- 12, and preferably means that the bacterium is able to cause accumulation in a medium of not less than 0.5 g/L, more preferably not less than 1.0 g/L of the target L-amino acid. The term "L-amino acid" includes L-alanine, L-arginine, L- asparagine, L-aspartic acid, L-cysteine, L-glutamic acid, L-glutamine, glycine, L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-proline, L-serine, L- threonine, L-tryptophan, L-tyrosine, and L-valine.

The term "aromatic L-amino acid" includes L-phenylalanine, L-tyrosine, and L- tryptophan. The term "non-aromatic L-amino acid" includes L-threonine, L-lysine, L- cysteine, L-methionine, L-leucine, L-isoleucine, L-valine, L-histidine, glycine, L-serine, L- alanine, L-asparagine, L-aspartic acid, L-glutamine, L-glutamic acid, L-proline, and L- arginine. L-threonine, L-lysine, L-cysteine, L-leucine, L-histidine, L-glutamic acid, L- phenylalanine, L-tryptophan, L-proline, and L-arginine are particularly preferred.

The Enterobacteriaceae family includes bacteria belonging to the genera Escherichia, Enterobacter, Erwinia, Klebsiella, Pantoea, Photorhabdus, Providencia, Salmonella, Serratia, Shigella, Morganella Yersinia, etc.. Specifically, those classified into the Enterobacteriaceae according to the taxonomy used in the NCBI (National Center for Biotechnology Information) database

(http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=91347) can be used. A bacterium belonging to the genus Escherichia or Pantoea is preferred.

The phrase "a bacterium belonging to the genus Escherichia" means that the bacterium is classified in the genus Escherichia according to the classification known to a person skilled in the art of microbiology. Examples of a bacterium belonging to the genus Escherichia as used in the present invention include, but are not limited to, Escherichia coli (E. coli).

The bacterium belonging to the genus Escherichia that can be used in the present invention is not particularly limited, however for example, bacteria described by Neidhardt, F.C. et al. (Escherichia coli and Salmonella typhimurium, American Society for Microbiology, Washington D. C, 1208, Table 1) are encompassed by the present invention.

The phrase "a bacterium belonging to the genus Pantoea" means that the bacterium is classified as the genus Pantoea according to the classification known to a person skilled in the art of microbiology. Some species of Enterobacter agglomerans have been recently re-classified into Pantoea agglomerans, Pantoea ananatis, Pantoea stewartii or the like, based on the nucleotide sequence analysis of 16S rRNA, etc. (Int. J. Syst. Bacteriol., 43, 162-173 (1993)).

To abolish curli formation, a bacterium can be modified to attenuate expression of any gene coding for a protein involved in curli formation, particularly, genes of the csgBAC and csgDEFG operons. Curli formation can also be abolished by attenuation of expression of the entire csgBAC or csgDEFG operon, or both. The phrase "bacterium has been modified to attenuate expression of any gene coding for a protein involved in curli formation" means that the bacterium has been modified in such a way that the modified bacterium contains a reduced amount of CsgB, CsgA, CsgC, CsgD, CsgE, CsgF, and/or csgG proteins, as compared with an unmodified bacterium, or is unable to synthesize one, several, or even all of these proteins.

The phrase "inactivation of the csgBAC and csgDEFG operons" means that the modified genes encode completely non-functional proteins. It is also possible that the modified DNA region is unable to naturally express the genes due to the deletion of a part of the gene, the shifting of the reading frame of the gene, the introduction of missense/nonsense mutation(s), or the modification of an adjacent region of the gene, including sequences controlling gene expression, such as a promoter, enhancer, attenuator, ribosome-binding site, etc.

The level of gene expression can be estimated by measuring the amount of mRNA transcribed from the gene using various known methods including Northern blotting, quantitative RT-PCR, and the like. The amount of the protein coded by the gene can be measured by known methods including SDS-PAGE followed by immunoblotting assay (Western blotting analysis) and the like.

The csgBAC operon consists of the following three genes in order.

First, the csgA gene (synonyms -blO42, EGl 1489) encodes the major subunit (synonyms - B 1042, CsgA, curlin, coiled surface structures, cryptic). The csgA gene (nucleotide positions 1,103,670 tol, 104,125; GenBank accession no. NC_000913.2; gi:49175990; SEQ ID NO: 1) is located between the csgB and csgC genes on the chromosome of E. coli K-12. The nucleotide sequence of the csgA gene and the amino acid sequence of CsgA encoded by the csgA gene are shown in SΕQ ID NO: 1 and SΕQ ID NO: 2, respectively.

Second, the csgB gene (synonyms - G6547, blO41, EGl 2621) encodes the minor curlin subunit (synonyms - B 1041, CsgB, nucleator for assembly of adhesive surface organelles). The csgB gene (nucleotide positions 1,103,174 tol, 103,629; GenBank accession no. NC_000913.2; gi:49175990; SΕQ ID NO: 1) is located between the csgD and csgA genes on the chromosome of E. coli K-12. The nucleotide sequence of the csgB gene and the amino acid sequence of CsgB encoded by the csgB gene are shown in SΕQ ID NO: 3 and SΕQ ID NO: 4, respectively.

Third, the csgC gene (synonyms -G6548, ycdE, blO43, EG13414) encodes the putative curli production protein (synonyms - B 1043, CsgC). The csgC gene (nucleotide positions 1,104,184 tol, 104,516; GenBank accession no. NC_000913.2; gi:49175990; SΕQ ID NO: 1) is located between the csgA and ymdA genes on the chromosome of E. coli K- 12. The nucleotide sequence of the csgC gene and the amino acid sequence of CsgC encoded by the csgC gene are shown in SEQ ID NO: 5 and SEQ ID NO: 6, respectively.

The csgDEFG operon consists of the following four genes in order.

First, the csgD gene (synonyms - bl040, G6546, EGl 3410) encodes the CsgD transcriptional activator (synonyms — B 1040, CsgD, PP 2-component transcriptional regulator for 2nd curli operon). The csgD gene (nucleotides complementary to nucleotides 1,101,769 to 1,102,419 ; GenBank accession no. NC_000913.2; gi:49175990; SEQ ID NO: 1) is located between the csgE and csgB genes on the chromosome of E. coli K- 12. The nucleotide sequence of the csgD gene and the amino acid sequence of CsgD encoded by the csgD gene are shown in SEQ ID NO: 7 and SEQ ID NO: 8, respectively.

Second, the csgE gene (synonyms - blO39, G6545, EG13411 ) encodes CsgE curli production assembly/transport component (synonyms - B 1039, CsgE). The csgE gene (nucleotides complementary to nucleotides 1,101,375 to 1,101,764; GenBank accession no. NC_000913.2; gi:49175990; SEQ ID NO: 1) is located between the csgFand csgD genes on the chromosome of E. coli K- 12. The nucleotide sequence of the csgE gene and the amino acid sequence of CsgE encoded by the csgE gene are shown in SEQ ID NO: 9 and SEQ ID NO: 10, respectively.

Third, the csgF gene (synonyms - blO38, G6544, EGl 3412) encodes the CsgF curli production assembly/transport component (synonyms - B 1038, CsgF). The csgF gene (nucleotides complementary to nucleotides 1,100,934 to 1,101,350; GenBank accession no. NC_000913.2; gi:49175990; SEQ ID NO: 1) is located between the csgG and csgE genes on the chromosome of E. coli K- 12. The nucleotide sequence of the csgF gene and the amino acid sequence of CsgF encoded by the csgF gene are shown in SΕQ ID NO: 11 and SΕQ ID NO: 12, respectively.

Fourth, the csgG gene (synonyms - b!037, G6543, EG13413) encodes CsgG curli production component (synonyms - B 1037, CsgG). The csgG gene (nucleotides complementary to nucleotides 1,100,074 to 1,100,907; GenBank accession no. NC_000913.2; gi:49175990; SΕQ ID NO: 1) is located between the ycdZ and csgF genes on the chromosome of E. coli K-12. The nucleotide sequence of the csgG gene and the amino acid sequence of CsgG encoded by the csgG gene are shown in SΕQ ID NO: 13 and SΕQ ID NO: 14, respectively.

Since there may be some differences in DNA sequences between the genera or strains of the Enterobαcteriαceαe family, the csgBAC and csgDEFG operons are not limited to the genes shown in SΕQ ID Nos: 1, 3, 5, 7, 9, 11, andl3 but may include genes homologous to SΕQ ID Nos: 1, 3, 5, 7, 9, 11, and 13, and are located separately on the chromosome or organized in the operon, each of which encodes a variant protein of the CsgB, CsgA,.CsgC, CsgD, CsgΕ, CsgF, or CsgF protein. The phrase "variant protein" as used in the present invention means a protein which has changes in the sequence, whether they are deletions, insertions, additions, or substitutions of amino acids, but still maintains the activity of the product as the CsgB, CsgA,.CsgC, CsgD, CsgE, CsgF, or CsgF protein. The number of changes in the variant protein depends on the position or the type of amino acid residues in the three dimensional structure of the protein. It may be 1 to 30, preferably 1 to 15, and more preferably 1 to 5 in SEQ ID NOS: 2, 4, 6, 8, 10, 12 and 14. These changes in the variants are conservative mutations that preserve the function of the protein. In other words, these changes can occur in regions of the protein which are not critical for the function of the protein. A conservative mutation is a mutation wherein substitution takes place mutually among Phe, Trp, Tyr, if the substitution site is an aromatic amino acid; among Leu, He, VaI, if the substitution site is a hydrophobic amino acid; between GIn, Asn, if it is a polar amino acid; among Lys, Arg, His, if it is a basic amino acid; between Asp, GIu, if it is an acidic amino acid; and between Ser, Thr, if it is an amino acid having a hydroxyl group. Typical conservative mutations are conservative substitutions. Specific examples of substitutions that are considered to be conservative include: substitution of Ala with Ser or Thr; substitution of Arg with GIn, His, or Lys; substitution of Asn with GIu, GIn, Lys, His, or Asp; substitution of Asp with Asn, GIu, or GIn; substitution of Cys with Ser or Ala; substitution of GIn with Asn, GIu, Lys, His, Asp, or Arg; substitution of GIu with GIy, Asn, GIn, Lys, or Asp; substitution of GIy with Pro; substitution of His with Asn, Lys, GIn, Arg, or Tyr; substitution of He with Leu, Met, VaI, or Phe; substitution of Leu with lie, Met, VaI, or Phe; substitution of Lys with Asn, GIu, GIn, His, or Arg; substitution of Met with He, Leu, VaI, or Phe; substitution of Phe with Trp, Tyr, Met, He, or Leu; substitution of Ser with Thr or Ala; substitution of Thr with Ser or Ala; substitution of Trp with Phe or Tyr; substitution of Tyr with His, Phe, or Trp; and substitution of VaI with Met, He, or Leu. Substitutions, deletions, insertions, additions, or inversions and the like of the amino acids described above include naturally occurred mutations (mutant or variant) depending on differences in species, or individual differences of microorganisms that retain the genes of the csgBAC and csgDEFG operons. Such genes can be obtained by modifying the nucleotide sequences shown in SEQ ID NO: 1, 3, 5, 7, 9, 11, or 13 using, for example, site-directed mutagenesis, so that the site-specific amino acid residue in the protein encoded includes substitutions, deletions, insertions, or additions.

Moreover, the protein variants encoded by the csgBAC and csgDEFG operons may have a homology of not less than 80%, preferably not less than 90%, and most preferably not less than 95%, with respect to the entire amino acid sequences shown in SEQ ID Nos: 2, 4, 6, 8, 10, 12, and 14 as long as the ability of the CsgBAC proteins to form curli and the CsgDEFG proteins to promote, assemble, and protect curli formation are maintained. Homology between two amino acid sequences can be determined using the well- known methods, for example, the computer program BLAST 2.0, which calculates three parameters: score, identity and similarity.

Moreover, genes of the csgBAC and csgDEFG operons may be variants which hybridize under stringent conditions with the nucleotide sequences shown in SEQ ID Nos: 1, 3, 5, 7, 9, 11, and 13 or probes which can be prepared from the nucleotide sequences, provided that it encodes a functional CsgBAC and CsgDEFG prior to inactivation. "Stringent conditions" include those under which a specific hybrid, for example, a hybrid having homology of not less than 60%, more preferably not less than 70%, further preferably not less than 80%, and still more preferably not less than 90%, and most preferably not less than 95% is formed and a non-specific hybrid, for example, a hybrid having homology lower than the above is not formed. For example, stringent conditions are exemplified by washing one time, preferably two or three times, at a salt concentration of 1 X SSC, 0.1% SDS, preferably 0.1 X SSC, 0.1% SDS, at 6O⁰C. Duration of washing depends on the type of membrane used for blotting and, as a rule, should be what is recommended by the manufacturer. For example, the recommended duration of washing for the Hybond™ N+ nylon membrane (Amersham) under stringent conditions is 15 minutes. Preferably, washing may be performed 2 to 3 times. The length of the probe may be suitably selected, depending on the hybridization conditions, and usually varies from lOO bp to l kbp.

Expression of each of the genes of the csgBAC and csgDEFG operons can be attenuated by introducing a mutation into the gene on the chromosome so that the intracellular activity of protein encoded by the gene is decreased as compared with an unmodified strain. Such a mutation on the gene can be replacement of one base or more to cause amino acid substitution in the protein encoded by the gene (missense mutation), introduction of a stop codon (nonsense mutation), deletion of one or two bases to cause a frame shift, insertion of a drug-resistance gene, or deletion of a part of the gene or the entire gene (Qiu, Z. and Goodman, M.F., J. Biol. Chem., 272, 8611-8617 (1997); Kwon, D. H. et al, J. Antimicrob. Chemother., 46, 793-796 (2000)). Expression of the genes can also be attenuated by modifying an expression regulating sequence such as the promoter, the Shine-Dalgarno (SD) sequence, etc. (WO95/34672, Carrier, T.A. and Keasling, J.D., Biotechnol Prog 15, 58-64 (1999)).

For example, the following methods may be employed to introduce a mutation by gene recombination. A mutant gene encoding a mutant protein having a decreased activity is prepared, and a bacterium is transformed with a DNA fragment containing the mutant gene. Then, the native gene on the chromosome is replaced with the mutant gene by homologous recombination, and the resulting strain is selected. Such gene replacement by homologous recombination can be conducted by employing a linear DNA, which is known as "Red-driven integration" (Datsenko, K.A. and Wanner, B.L., Proc. Natl. Acad. Sci. USA, 97, 12, p 6640-6645 (2000), WO2005/010175), or by methods employing a plasmid containing a temperature-sensitive replication control region (Proc. Natl. Acad. Sci., USA, 97, 12, p 6640-6645 (2000), U.S. Patent Nos. 6,303,383 and 5,616,480). Furthermore, the introduction of a site-specific mutation by gene replacement using homologous recombination as set forth above can also be performed by using a plasmid lacking the ability to replicate in the host. When a marker gene such as antibiotic resistant gene is used to prepare the mutant gene or to detect recombination between the mutant gene and the native gene on the chromosome, the marker gene can be eliminated from the chromosome by, for example, a method described in Examples section.

Expression of the gene can also be attenuated by insertion of a transposon or an IS factor into the coding region of the gene (U.S. Patent No. 5,175,107), or by conventional methods, such as mutagenesis with UV irradiation or nitrosoguanidine (N-methyl-N'-nitro- N-nitrosoguanidine) treatment.

Inactivation of the gene can be performed by conventional methods, such as mutagenesis treatment using UV irradiation or nitrosoguanidine (N-methyl-N'-nitro-N- nitrosoguanidine) treatment, site-directed mutagenesis, gene disruption using homologous recombination, or/and insertion-deletion mutagenesis (Yu, D. et al., Proc. Natl. Acad. Sci. USA, 2000, 97:12: 5978-83 and Datsenko, K.A. and Wanner, B.L., Proc. Natl. Acad. Sci. USA, 2000, 97:12: 6640-45) also called "Red-driven integration".

The ability of a variant gene to form curli organelles can be detected by complementation of mutations csgA^', csgB^', csgC, csgD^', csgK, csgF, csgG^' genes, each particulary or in various combinations, including csgBAO or csgDEFG^' mutations, or both simultaneously. Thus, the reduction or absence of curli formation in the bacterium according to the present invention can be determined when compared to the parent unmodified bacterium, and recognized by their inability both to bind soluble fibronectin and to spontaneously autoaggregate and sediment in static cultures. Such mutants lack curli fibers which are typically visible with electron microscopy and form white colonies on media containing the dye Congo red (CFA medium) at 26 ⁰C (Hammar M., et al., MoLMicrobiol., 18(4), 661-670 (1995)).

Methods for preparation of plasmid DNA, digestion and ligation of DNA, transformation, selection of an oligonucleotide as a primer, and the like may be ordinary methods well-known to one skilled in the art. These methods are described, for instance, in Sambrook, J., Fritsch, E.F., and Maniatis, T., "Molecular Cloning: A Laboratory Manual, Second Edition", Cold Spring Harbor Laboratory Press (1989). L- amino acid producing bacteria

As a bacterium of the present invention which is modified to attenuate expression of the csgBAC or/and csgDEFG operon, bacteria which are able to produce either aromatic or non-aromatic L-amino acids may be used.

The bacterium of the present invention can be obtained by attenuating expression of the csgBAC or/and csgDEFG operon in a bacterium which inherently has the ability to produce L-amino acids. Alternatively, the bacterium of present invention can be obtained by imparting the ability to produce an L-amino acid to a bacterium already having attenuated expreesion of the csgBAC or/and csgDEFG operon.

L-threonine-producing bacteria

Examples of parent strains for deriving the L-threonine-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli TDH-6/pVIC40 (VKPM B-3996) (U.S. Patent No. 5, 175, 107, U.S. Patent No. 5,705,371), E. coli 472T23/pYN7 (ATCC 98081) (U.S. Patent No.5,631,157), E. coli NRRL-21593 (U.S. Patent No. 5,939,307), E. coli FERM BP-3756 (U.S. Patent No. 5,474,918), E. coli FERM BP-3519 and FERM BP-3520 (U.S. Patent No. 5,376,538), E. coli MG442 (Gusyatiner et al., Genetika (in Russian), 14, 947-956 (1978)), E. coli VL643 and VL2055 (EP 1149911 A), and the like.

The strain TDH-6 is deficient in the thrC gene, as well as being sucrose- assimilative, and the UvA gene has a leaky mutation. This strain also has a mutation in the rhtA gene, which imparts resistance to high concentrations of threonine or homoserine. The strain B-3996 contains the plasmid pVIC40 which was obtained by inserting a thrA *BC operon which includes a mutant thrA gene into a RSFlOlO-derived vector. This mutant thrA gene encodes aspartokinase homoserine dehydrogenase I which has substantially desensitized feedback inhibition by threonine. The strain B-3996 was deposited on November 19, 1987 in the All-Union Scientific Center of Antibiotics (Russia, 117105 Moscow, Nagatinskaya Street, 3 -A) under the accession number RIA 1867. The strain was also deposited in the Russian National Collection of Industrial Microorganisms (VKPM) (Russia, 117545 Moscow 1, Dorozhny proezd, 1) on April 7, 1987 under the accession number VKPM B-3996.

E. coli VKPM B-5318 (EP 0593792B) may also be used as a parent strain for deriving L-threonine-producing bacteria of the present invention. The strain B-5318 is prototrophic with regard to isoleucine, and a temperature-sensitive lambda-phage Cl repressor and P_R promoter replaces the regulatory region of the threonine operon in plasmid pVIC40. The strain VKPM B-5318 was deposited in the Russian National Collection of Industrial Microorganisms (VKPM) on May 3, 1990 under accession number ofVKPM B-5318.

Preferably, the bacterium of the present invention is additionally modified to enhance expression of one or more of the following genes: the mutant thrA gene which codes for aspartokinase homoserine dehydrogenase I resistant to feed back inhibition by threonine; the thrB gene which codes for homoserine kinase; the thrC gene which codes for threonine synthase; the rhtA gene which codes for a putative transmembrane protein; the asd gene which codes for aspartate-β-semialdehyde dehydrogenase; and the aspC gene which codes for aspartate aminotransferase (aspartate transaminase);

The thrA gene which encodes aspartokinase homoserine dehydrogenase I of Escherichia coli has been elucidated (nucleotide positions 337 to 2799, GenBank accession NC_000913.2, gi: 49175990). The thrA gene is located between the thrL and thrB genes on the chromosome of E. coli K- 12. The thrB gene which encodes homoserine kinase of Escherichia coli has been elucidated (nucleotide positions 2801 to 3733, GenBank accession NC_000913.2, gi: 49175990). The thrB gene is located between the thrA and thrC genes on the chromosome of E. coli K- 12. The thrC gene which encodes threonine synthase of Escherichia coli has been elucidated (nucleotide positions 3734 to 5020, GenBank accession NC_000913.2, gi: 49175990). The thrC gene is located between the thrB gene and the yaaX open reading frame on the chromosome of E. coli K- 12. All three genes functions as a single threonine operon. To enhance expression of the threonine operon, the attenuator region which affects the transcription is desirably removed from the operon (WO2005/049808, WO2003/097839).

A mutant thrA gene which codes for aspartokinase homoserine dehydrogenase I resistant to feed back inhibition by threonine, as well as, the thrB and thrC genes can be obtained as one operon from the well-known plasmid pVIC40 which is present in the threonine producing E. coli strain VKPM B-3996. Plasmid pVIC40 is described in detail in U.S. Patent No. 5,705,371.

The rhtA gene exists at 18 min on the E. coli chromosome close to the glnHPQ operon, which encodes components of the glutamine transport system. The rhtA gene is identical to ORFl (ybiF gene, nucleotide positions 764 to 1651, GenBank accession number AAA218541, gi:440181) and is located between the pexB and ompX genes. The unit expressing a protein encoded by the ORPl has been designated the rhtA gene (rht: resistance to homoserine and threonine). Also, it was revealed that the rhtA23 mutation is an A-for-G substitution at position -1 with respect to the ATG start codon (ABSTRACTS of the 17th International Congress of Biochemistry and Molecular Biology in conjugation with Annual Meeting of the American Society for Biochemistry and Molecular Biology, San Francisco, California August 24-29, 1997, abstract No. 457, EP 1013765 A).

The asd gene of E. coli has already been elucidated (nucleotide positions 3572511 to 3571408, GenBank accession NC_000913.1, gi:16131307), and can be obtained by PCR (polymerase chain reaction; refer to White, TJ. et al., Trends Genet., 5, 185 (1989)) utilizing primers prepared based on the nucleotide sequence of the gene. The asd genes of other microorganisms can be obtained in a similar manner.

Also, the aspC gene of E. coli has already been elucidated (nucleotide positions 983742 to 984932, GenBank accession NC_000913.1, gi:16128895), and can be obtained by PCR. The aspC genes of other microorganisms can be obtained in a similar manner.

L-lysine-producing bacteria

Examples of L-lysine-producing bacteria belonging to the genus Escherichia include mutants having resistance to an L-lysine analogue. The L-lysine analogue inhibits growth of bacteria belonging to the genus Escherichia, but this inhibition is fully or partially desensitized when L-lysine coexists in a medium. Examples of the L-lysine analogue include, but are not limited to, oxalysine, lysine hydroxamate, S-(2-aminoethyl)- L-cysteine (AEC), γ-methyllysine, α-chlorocaprolactam and so forth. Mutants having resistance to these lysine analogues can be obtained by subjecting bacteria belonging to the genus Escherichia to a conventional artificial mutagenesis treatment. Specific examples of bacterial strains useful for producing L-lysine include Escherichia coli AJl 1442 (FERM BP-1543, NRRL B-12185; see U.S. Patent No. 4,346,170) and Escherichia coli VL611. In these microorganisms, feedback inhibition of aspartokinase by L-lysine is desensitized.

The strain WC 196 may be used as an L-lysine producing bacterium of Escherichia coli. This bacterial strain was bred by conferring AEC resistance to the strain W3110, which was derived from Escherichia coli K-12. The resulting strain was designated Escherichia coli AJl 3069 strain and was deposited at the National Institute of Bioscience and Human-Technology, Agency of Industrial Science and Technology (currently National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Tsukuba Central 6, 1-1, Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, 305-8566, Japan) on December 6, 1994 and received an accession number of FERM P- 14690. Then, it was converted to an international deposit under the provisions of the Budapest Treaty on September 29, 1995, and received an accession number of FERM BP-5252 (U.S. Patent No. 5,827,698).

Examples of parent strains for deriving L-lysine-producing bacteria of the present invention also include strains in which expression of one or more genes encoding an L- lysine biosynthetic enzyme are enhanced. Examples of such genes include, but are not limited to, genes encoding dihydrodipicolinate synthase (dapA), aspartokinase (lysC), dihydrodipicolinate reductase (dapB), diaminopimelate decarboxylase (fysA), diaminopimelate dehydrogenase (ddh) (U.S. Patent No. 6,040,160), phosphoenolpyrvate carboxylase (ppc), aspartate semialdehyde dehydrogenease (asd), and aspartase (aspA) (EP 1253195 A). In addition, the parent strains may have an increased level of expression of the gene involved in energy efficiency (cyo) (EP 1170376 A), the gene encoding nicotinamide nucleotide transhydrogenase (pntAB) (U.S. Patent No. 5,830,716), the ybjE gene (WO2005/073390), or combinations thereof.

Examples of parent strains for deriving L-Iy sine-producing bacteria of the present invention also include strains having decreased or eliminated activity of an enzyme that catalyzes a reaction for generating a compound other than L-lysine by branching off from the biosynthetic pathway of L-lysine. Examples of the enzymes that catalyze a reaction for generating a compound other than L-lysine by branching off from the biosynthetic pathway of L-lysine include homo serine dehydrogenase, lysine decarboxylase (U.S. Patent No. 5,827,698), and the malic enzyme (WO2005/010175).

L-cvsteine-producing bacteria

Examples of parent strains for deriving L-cysteine-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli JM 15 which is transformed with different cysE alleles coding for feedback- resistant serine acetyltransferases (U.S. Patent No. 6,218,168, Russian patent application 2003121601); E. coli W3110 having over-expressed genes which encode proteins suitable for secreting substances toxic for cells (U.S. Patent No. 5,972,663); E. coli strains having lowered cysteine desulfohydrase activity (JPl 1155571A2); E. coli W3110 with increased activity of a positive transcriptional regulator for cysteine regulon encoded by the cysB gene (WO0127307A1), and the like.

L-leucine-producing bacteria

Examples of parent strains for deriving L-leucine-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli strains resistant to leucine (for example, the strain 57 (VKPM B-7386, U.S. Patent No. 6,124,121)) or leucine analogs including β-2-thienylalanine, 3 -hydroxy leucine, 4-azaleucine, 5,5,5-trifluoroleucine (JP 62-34397 B and JP 8-70879 A); E. coli strains obtained by the gene engineering method described in WO96/06926; E. coli H-9068 (JP 8- 70879 A)₅ and the like. The bacterium of the present invention may be improved by enhancing the expression of one or more genes involved in L-leucine biosynthesis. Examples include genes of the leuABCD operon, which are preferably represented by a mutant leuA gene coding for isopropylmalate synthase freed from feedback inhibition by L-leucine (US Patent No.6,403,342). In addition, the bacterium of the present invention may be improved by enhancing the expression of one or more genes coding for proteins which excrete L- amino acid from the bacterial cell. Examples of such genes include the b2682 and b2683 genes (ygaZH genes) (EP 1239041 A2).

L-histidine-producing bacteria

Examples of parent strains for deriving L-histidine-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli strain 24 (VKPM B-5945, RU2003677); E. coli strain 80 (VKPM B-7270, RU2119536); E. coli NRPvL B-12116 - B12121 (U.S. Patent No. 4,388,405); E. coli H- 9342 (FERM BP-6675) and H-9343 (FERM BP-6676) (U.S. Patent No. 6,344,347); E. coli H-9341 (FERM BP-6674) (EP1085087); E. coli AI80/pFM201 (U,S. Patent No. 6,258,554) and the like.

Examples of parent strains for deriving L-histidine-producing bacteria of the present invention also include strains in which expression of one or more genes encoding an L-histidine biosynthetic enzyme are enhanced. Examples of such genes include genes encoding ATP phosphoribosyltransferase (hisG), phosphoribosyl AMP cyclohydrolase (hisϊ), phosphoribosyl-ATP pyrophosphohydrolase (hisIE), phosphoribosylformimino-5- aminoimidazole carboxamide ribotide isomerase (hisA), amidotransferase (MsH), histidinol phosphate aminotransferase (hisQ, histidinol phosphatase (hisB), histidinol dehydrogenase QiisD), and so forth.

It is known that the L-histidine biosynthetic enzymes encoded by hisG and hisBHAFIare inhibited by L-histidine, and therefore an L-histidine-producing ability can also be efficiently enhanced by introducing a mutation conferring resistance to the feedback inhibition into ATP phosphoribosyltransferase (Russian Patent Nos. 2003677 and 2119536).

Specific examples of strains having an L-histidine-producing ability include E. coli FERM P-5038 and 5048 which have been introduced with a vector carrying a DNA encoding an L-histidine-biosynthetic enzyme (JP 56-005099 A), E. coli strains introduced with rhtA gene for an amino acid-export (EPl 016710A), E. coli 80 strain imparted with sulfaguanidine, DL- l,2,4-triazole-3 -alanine, and streptomycin-resistance (VKPM B-7270, Russian Patent No. 2119536), and so forth. L-glutamic acid-producing bacteria

Examples of parent strains for deriving L-glutamic acid-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli VL334thrC+ (EP 1172433). E. coli VL334 (VKPM B-1641) is an L- isoleucine and L-threonine auxotrophic strain having mutations in thrC and HvA genes (U.S. Patent No. 4,278,765). A wild-type allele of the thrC gene was transferred by the method of general transduction using a bacteriophage Pl grown on the wild-type E. coli strain Kl 2 (VKPM B-7) cells. As a result, an L-isoleucine auxotrophic strain VL334thrC+ (VKPM B-8961), which is able to produce L-glutamic acid, was obtained.

Examples of parent strains for deriving the L-glutamic acid-producing bacteria of the present invention include, but are not limited to, strains in which expression of one or more genes encoding an L-glutamic acid biosynthetic enzyme are enhanced. Examples of such genes include genes encoding glutamate dehydrogenase (gdh), glutamine synthetase (glnA), glutamate synthetase (gϊtAB), isocitrate dehydrogenase (icdA), aconitate hydratase (acnA, acnB), citrate synthase (gltA), phosphoenolpyruvate carboxylase (ppc), pyruvate dehydrogenase (aceEF, ipdA), pyruvate kinase (pykA, pykF), phosphoenolpyruvate synthase (ppsA), enolase (eno), phosphoglyceromutase (pgmA, pgml), phosphoglycerate kinase (pgk), glyceraldehyde-3-phophate dehydrogenase {gap A), triose phosphate isomerase (tpiA), fructose bisphosphate aldolase (Jbp), phosphofructokinase (pflcA, pflcB), and glucose phosphate isomerase (pgi).

Examples of strains modified so that expression of the citrate synthetase gene, the phosphoenolpyruvate carboxylase gene, and/or the glutamate dehydrogenase gene is/are enhanced include those disclosed in EP1078989A, EP955368A, and EP952221 A.

Examples of parent strains for deriving the L-glutamic acid-producing bacteria of the present invention also include strains having decreased or eliminated activity of an enzyme that catalyzes synthesis of a compound other than L-glutamic acidby branching off from an L-glutamic acid biosynthesis pathway. Examples of such enzymes include isocitrate lyase (aceA), α-ketoglutarate dehydrogenase (sucA), phosphotransacetylase (ptά), acetate kinase (ack), acetohydroxy acid synthase (HvG), acetolactate synthase (HvI), formate acetyltransferase (pfl), lactate dehydrogenase (Idh), and glutamate decarboxylase (gadAB). Bacteria belonging to the genus Escherichia deficient in the α-ketoglutarate dehydrogenase activity or having a reduced α-ketoglutarate dehydrogenase activity and methods for obtaining them are described in U.S. Patent Nos. 5,378,616 and 5,573,945. Specifically, these strains include the following:

E. cø/z W311 OsucA::Kmr

E. coli AJ12624 (FERM BP-3853)

E. coli AJl 2628 (FERM BP-3854) E. coli AJ12949 (FERM BP-4881)

E. coli W3110sucA::Kmr is a strain obtained by disrupting the α-ketoglutarate dehydrogenase gene (hereinafter referred to as "sucA gene") of E. coli W3110. This strain is completely deficient in α-ketoglutarate dehydrogenase.

Other examples of L-glutamic acid-producing bacterium include those which belong to the genus Escherichia and have resistance to an aspartic acid antimetabolite. These strains can also be deficient in the α-ketoglutarate dehydrogenase activity and include, for example, E. coli AJ13199 (FERM BP-5807) (U.S. Patent No. 5.908,768), FFRM P-12379, which additionally has a low L-glutamic acid decomposing ability (U.S. Patent No. 5,393,671); AJ13138 (FERM BP-5565) (U.S. Patent No. 6,110,714), and the like.

Examples of L-glutamic acid-producing bacteria, include mutant strains belonging to the genus Pantoea which are deficient in α-ketoglutarate dehydrogenase activity or have decreased α-ketoglutarate dehydrogenase activity, and can be obtained as described above. Such strains include Pantoea ananatis AJ13356. (U.S. Patent No. 6,331,419). Pantoea ananatis AJ13356 was deposited at the National Institute of Bioscience and Human- Technology, Agency of Industrial Science and Technology, Ministry of International Trade and Industry (currently, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Central 6, 1-1, Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, 305-8566, Japan) on February 19, 1998 under an accession number of FERM P- 16645. It was then converted to an international deposit under the provisions of Budapest Treaty on January 11, 1999 and received an accession number of FERM BP- 6615. Pantoea ananatis AJ13356 is deficient in α-ketoglutarate dehydrogenase activity as a result of disruption of the αKGDH-El subunit gene (sucA). The above strain was identified as Enterobacter agglomerans when it was isolated and deposited as the Enter obacter agglomerans AJl 3356. However, it was recently re-classified as Pantoea ananatis on the basis of nucleotide sequencing of 16S rRNA and so forth. Although AJ13356 was deposited at the aforementioned depository as Enterobacter agglomerans, for the purposes of this specification, they are described as Pantoea ananatis.

L-phenylalanine-producing bacteria

Examples of parent strains for deriving L-phenylalanine-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli AJ12739 (tyrA::TnlO, tyrR) (VKPM B-8197); E. coli HW1089 (ATCC 55371) harboring the mutant pheAiA gene (U.S. Patent No. 5,354,672); E. coli MWEC101-b (KR8903681); E. coli NRRL B-12141, NRRL B-12145, NRRL B-12146 and NRRL B-12147 (U.S. Patent No. 4,407,952). Also, as a parent strain, E. coli K-12 [W3110 (tyrA)/pPHAB (FERM BP-3566), E. coli K-12 [W3110 (tyrA)/pPHAD] (FERM BP- 12659), E. coli K-12 [W3110 (tyrA)/pPHATerm] (FERM BP-12662) and E. coli K-12 [W3110 (tyrA)/pBR-aroG4, pACMAB] named as AJ 12604 (FERM BP-3579) may be used (EP 488424 Bl). Furthermore, L-phenylalanine producing bacteria belonging to the genus Escherichia with an enhanced activity of the protein encoded by iheyedA gene or thεyddG gene may also be used (U.S. patent applications 2003/0148473 Al and 2003/0157667 Al).

L-trvptophan-producing bacteria

Examples of parent strains for deriving the L-tryptophan-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli JP4735/pMU3028 (DSM10122) and JP6015/pMU91 (DSM10123) which is deficient in the tryptophanyl-tRNA synthetase encoded by mutant trpS gene (U.S. Patent No. 5,756,345); E. coli SV164 (pGH5) having a serA allele encoding phosphoglycerate dehydrogenase free from feedback inhibition by serine and a trpE allele encoding anthranilate synthase free from feedback inhibition by tryptophan (U.S. Patent No. 6,180,373); E coli AGX17 (pGX44) (NRRL B-12263) and AGX6(pGX50)aroP (NRRL B-12264) which is deficient in the enzyme tryptophanase (U.S. Patent No. 4,371,614); E. coli AGX17/pGX50,pACKG4-pps in which a phosphoenolpyruvate-producing ability is enhanced (WO9708333, U.S. Patent No. 6,319,696), and the like may be used. L- tryptophan-producing bacteria belonging to the genus Escherichia with an enhanced activity of the protein encoded by the yedA gene or the yddG gene may also be used (U.S. patent applications 2003/0148473 Al and 2003/0157667 Al).

Examples of parent strains for deriving the L-tryptophan-producing bacteria of the present invention also include strains in which one or more activities of the enzymes selected from anthranilate synthase, phosphoglycerate dehydrogenase, and tryptophan synthase are enhanced. The anthranilate synthase and phosphoglycerate dehydrogenase are both subject to feedback inhibition by L-tryptophan and L-serine, so that a mutation desensitizing the feedback inhibition may be introduced into these enzymes. Specific examples of strains having such a mutation include a E. coli SVl 64 which harbors desensitized anthranilate synthase and a transformant strain obtained by introducing into the E. coli SVl 64 the plasmid pGH5 (WO 94/08031), which contains a mutant serA gene encoding feedback-desensitized phosphoglycerate dehydrogenase.

Examples of parent strains for deriving the L-tryptophan-producing bacteria of the present invention also include strains into which the tryptophan operon which contains a gene encoding desensitized anthranilate synthase has been introduced (JP 57-71397 A, JP 62-244382 A, U.S. Patent No. 4,371,614). Moreover, L-tryptophan-producing ability may be imparted by enhancing expression of a gene which encodes tryptophan synthase, among tryptophan operons (trpBA). The tryptophan synthase consists of α and β subunits which are encoded by the trpA and trpB genes, respectively. In addition, L-tryptophan-producing ability may be improved by enhancing expression of the isocitrate lyase-malate synthase operon (WO2005/103275).

L-proline-producing bacteria

Examples of parent strains for deriving L-proline-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli 702ilvA (VKPM B-8012) which is deficient in the UvA gene and is able to produce L-proline (EP 1172433). The bacterium of the present invention may be improved by enhancing the expression of one or more genes involved in L-proline biosynthesis. Examples of such genes for L-proline producing bacteria which are preferred include the proB gene coding for glutamate kinase of which feedback inhibition by L-proline is desensitized (DE Patent 3127361). In addition, the bacterium of the present invention may be improved by enhancing the expression of one or more genes coding for proteins excreting L-amino acid from bacterial cell. Such genes are exemplified by b2682 and b2683 genes (ygaZH genes) (EP1239041 A2).

Examples of bacteria belonging to the genus Escherichia, which have an activity to produce L-proline include the following E. coli strains: NRRL B- 12403 and NRRL B- 12404 (GB Patent 2075056), VKPM B-8012 (Russian patent application 2000124295), plasmid mutants described in DE Patent 3127361, plasmid mutants described by Bloom F.R. et al (The 15th Miami winter symposium, 1983, p.34), and the like.

L-arginine-producing bacteria

Examples of parent strains for deriving L-arginine-producing bacteria of the present invention include, but are not limited to, strains belonging to the genus Escherichia, such as E. coli strain 237 (VKPM B-7925) (U.S. Patent Application 2002/058315 Al) and its derivative strains harboring mutant N-acetylglutamate synthase (Russian Patent Application No. 2001112869), E. coli strain 382 (VKPM B-7926) (EPl 170358A1), an arginine-producing strain into which argA gene encoding N-acetylglutamate synthetase is introduced therein (EPl 170361 Al), and the like.

Examples of parent strains for deriving L-arginine producing bacteria of the present invention also include strains in which expression of one or more genes encoding an L- arginine biosynthetic enzyme are enhanced. Examples of such genes include genes encoding N-acetylglutamyl phosphate reductase (argC), ornithine acetyl transferase (argJ), N-acetylglutamate kinase (argB), acetylornithine transaminase (argD), ornithine carbamoyl transferase (argF), argininosuccinic acid synthetase (argG), argininosuccinic acid lyase (argH), and carbamoyl phosphate synthetase {car AB).

L-valine-producing bacteria

Example of parent strains for deriving L-valine-producing bacteria of the present invention include, but are not limited to, strains which have been modified to overexpress the UvGMEDA operon (U.S. Patent No. 5,998,178). It is desirable to remove the region of the UvGMEDA operon which is required for attenuation so that expression of the operon is not attenuated by the L- valine that is produced. Furthermore, the UvA gene in the operon is desirably disrupted so that threonine deaminase activity is decreased.

Examples of parent strains for deriving L-valine-producing bacteria of the present invention include also include mutants having a mutation of amino-acyl t-RNA synthetase (U.S. Patent No. 5,658,766). For example, E. coli VLl 970, which has a mutation in the UeS gene encoding isoleucine tRNA synthetase, can be used. E. coli VLl 970 has been deposited in the Russian National Collection of Industrial Microorganisms (VKPM) (Russia, 117545 Moscow, 1 Dorozhny Proezd, 1) on June 24, 1988 under accession number VKPM B-4411.

Furthermore, mutants requiring lipoic acid for growth and/or lacking H⁺-ATPase can also be used as parent strains (WO96/06926).

L-isoleucine-producing bacteria

Examples of parent strains for deriving L-isoleucine producing bacteria of the present invention include, but are not limited to, mutants having resistance to 6- dimethylaminopurine (JP 5-304969 A), mutants having resistance to an isoleucine analogue such as thiaisoleucine and isoleucine hydroxamate, and mutants additionally having resistance to DL-ethionine and/or arginine hydroxamate (JP 5-130882 A). In addition, recombinant strains transformed with genes encoding proteins involved in L- isoleucine biosynthesis, such as threonine deaminase and acetohydroxate synthase, can also be used as parent strains (JP 2-458 A, FR 0356739, and U.S. Patent No. 5,998,178).

2. Method of the present invention

The method of the present invention is a method for producing an L-amino acid by cultivating the bacterium of the present invention in a culture medium to produce and excrete the L-amino acid into the medium, and collecting the L-amino acid from the medium. In the present invention, the cultivation, collection, and purification of an L-amino acid from the medium and the like may be performed in a manner similar to conventional fermentation methods wherein an amino acid is produced using a bacterium.

A medium used for culture may be either a synthetic or natural medium, so long as the medium includes a carbon source and a nitrogen source and minerals and, if necessary, appropriate amounts of nutrients which the bacterium requires for growth. The carbon source may include various carbohydrates such as glucose and sucrose, and various organic acids. Depending on the mode of assimilation of the chosen microorganism, alcohol, including ethanol and glycerol, may be used. As the nitrogen source, various ammonium salts such as ammonia and ammonium sulfate, other nitrogen compounds such as amines, a natural nitrogen source such as peptone, soybean-hydrolysate, and digested fermentative microorganism can be used. As minerals, potassium monophosphate, magnesium sulfate, sodium chloride, ferrous sulfate, manganese sulfate, calcium chloride, and the like can be used. As vitamins, thiamine, yeast extract, and the like, can be used.

The cultivation is preferably performed under aerobic conditions, such as a shaking culture, and a stirring culture with aeration, at a temperature of 20 to 40 ⁰C, preferably 30 to 38 ⁰C. The pH of the culture is usually between 5 and 9, preferably between 6.5 and 7.2. The pH of the culture can be adjusted with ammonia, calcium carbonate, various acids, various bases, and buffers. Usually, a 1 to 5-day cultivation leads to accumulation of the target L-amino acid in the liquid medium.

After cultivation, solids such as cells can be removed from the liquid medium by centrifugation or membrane filtration, and then the L-amino acid can be collected and purified by ion-exchange, concentration, and/or crystallization methods.

Brief Description of Drawings

Figure 1 shows the construction of the pMWl 18-attL-Cm-attR plasmid, which is used as a template for PCR.

Figure 2 shows the relative positions of primers P 17, P 18, P21 and P22 on plasmid pMWl 18-attL-Cm-attR, which is used for PCR amplification of the cat gene.

Figure 3 shows the construction of the chromosomal DNA fragment including the inactivated csgBAC operon.

Figure 4 shows the construction of the chromosomal DNA fragment including the inactivated csgDEFG operon. Examples

The present invention will be more concretely explained below with reference to the following non-limiting Examples.

Example 1. Preparation of the PCR template and helper plasmids

The PCR template plasmid pMWl 18-attL-Cm-attR and the helper plasmid pMW- intxis-ts were prepared as follows:

(1) pMWl 18-attL-Cm-attR

The pMWl 18-attL-Cm-attR plasmid was constructed on the basis of pMWl 18- attL-Tc-attR that was obtained by ligation of the following four DNA fragments:

1) the Bglll-EcoRl fragment (114 bp) carrying attL (SEQ ID NO: 15) which was obtained by PCR amplification of the corresponding region of the E. coli W3350 (contained λ prophage) chromosome using oligonucleotides Pl and P2 (SEQ ID NOS: 16 and 17) as primers (these primers contained the subsidiary recognition sites for BgRl and EcoRl endonucleases);

2) the Pstl-HindLϊl fragment (182 bp) carrying attR (SEQ ID NO: 18) which was obtained by PCR amplification of the corresponding region of the E. coli W335O (contained λ prophage) chromosome using the oligonucleotides P3 and P4 (SEQ ID NOS: 19 and 20) as primers (these primers contained the subsidiary recognition sites for Psfl and Hindlϊl endonucleases);

3) the large Bglϊl-Hindlϊl fragment (3916 bp) of pMWl 18-ter_/raS. The plasmid pMWl 18-ter_rniδ was obtained by ligation of the following three DNA fragments:

• the large DNA fragment (2359 bp) carrying the Aatll-EcoRI fragment of pMWl 18 that was obtained as follows: pMWl 18 was digested with EcoRl restriction endonuclease, treated with Klenow fragment of DNA polymerase I, and then digested with _^4αtII restriction endonuclease;

• the small Aatll-BgRl fragment (1194 bp) of pUC19 carrying the bla gene for ampicillin resistance (Ap^R) was obtained by PCR amplification of the corresponding region of the pUC19 plasmid using oligonucleotides P5 and P6 (SEQ ID NOS: 21 and22) as primers (these primers contained the subsidiary recognition sites for _^4MI and BgIIL endonucleases);

• the small Bgϊll-Pstl fragment (363 bp) of the transcription terminator ter_rmδ was obtained by PCR amplification of the corresponding region of the E. coli MGl 655 chromosome using oligonucleotides P7 and P8 (SEQ ID NOS: 23 and 24) as primers (these primers contained the subsidiary recognition sites for BgIII and PM endonucleases); 4) the small EcoRl-Pstl fragment (1388 bp) (SEQ ID NO:25) of pML-Tc-ter_t/*rZ having the tetracycline resistance gene and the t&xjhrL transcription terminator; the pML-Tc-ter_t/zrZ plasmid was obtained in two steps:

• the pML-ter_//zrZ plasmid was obtained by digesting the pML-MCS plasmid (Mashko, S.V. et al., Biotekhnologiya (in Russian), 2001, no. 5, 3-20) with the Xbal and BamHl restriction endonucleases, followed by ligation of the large fragment (3342 bp) with the Xbal-BamHl fragment (68 bp) carrying terminator tQXJhrL obtained by PCR amplification of the corresponding region of the E. coli MG1655 chromosome using oligonucleotides P9 and PlO (SEQ ID NOS: 26 and27) as primers (these primers contained the subsidiary recognition sites for the Xbal and BamHl endonucleases);

• the pML-Tc-ter_t/zrZ plasmid was obtained by digesting the pML-ter_t/?rZ plasmid with the Kpnl and Xbal restriction endonucleases followed by treatment with Klenow fragment of DNA polymerase I and ligation with the small EcoRl~Van91l fragment (1317 bp) of pBR322 having the tetracycline resistance gene (pBR322 was digested with EcoRl and Van91l restriction endonucleases and then treated with Klenow fragment of DNA polymerase I).

E. coli W3350 is a derivative of wild type strain E. coli K-12. E. coli MG1655 (ATCC 700926) is a wild-type strain and can be obtained from American Type Culture Collection (P.O. Box 1549 Manassas, VA 20108, United States of America). The plasmids pMWl 18 and pUC19 are commercially available. The Bglϊl-EcoRl fragment carrying attL and the Bglll-Pstl fragment of the transcription terminator ter_rrnB can be obtained from the other strains of E. coli in the same manner as described above.

The pMWl 18-attL-Cm-attR plasmid was constructed by ligation of the large BamHl-Xbal fragment (4413 bp) of pMWl 18-attL-Tc-attR and the artificial DNA BgHl- Xbal fragment (1162 bp) containing the PA₂ promoter (the early promoter of the phage T7), the cat gene for chloramphenicol resistance (Cm^R), the XexjhrL transcription terminator, and attR. The artificial DNA fragment (SEQ ID NO:28) was obtained as follows: 1. The pML-MCS plasmid was digested with the Kpnl and Xbal restriction endonucleases and ligated with the small Kpnl-Xbal fragment (120 bp), which included the PA₂ promoter (the early promoter of phage T7) obtained by PCR amplification of the corresponding DNA region of phage T7 using oligonucleotides Pl 1 and P12 (SEQ ID NOS: 29 and30, respectively) as primers (these primers contained the subsidiary recognition sites for Kpnl and Xbal endonucleases). As a result, the PML-PA₂-MCS plasmid was obtained. The complete nucleotide sequence of phage T7 has been reported (J. MoI. Biol., 166: 477-535 (1983). 2. The Xbal site was deleted from pML-P_A2-MCS. AS a result, the pML-P/α- MCS(XbaT) plasmid was obtained.

3. The small BgHl-Hindlll fragment (928 bp) of PML-P_A2-MCS(^aI^") containing the PA₂ promoter (the early promoter of the phage T7) and the cat gene for chloramphenicol resistance (Cm^R) was ligated with the small Hindlll-Hindlll fragment (234 bp) of pMWl 18-attL-Tc-attR containing the ϊ&cJhrL transcription terminator and attR.

4. The required artificial DNA fragment (1156 bp) was obtained by PCR amplification of the ligation reaction mixture using oligonucleotides P9 and P4 (SEQ ID NOS: 26 and20) as primers (these primers contained the subsidiary recognition sites for Hindϊll and Xbal endonucleases).

(2) pMW-intxis-ts

Recombinant plasmid pMW-intxis-ts containing the cl repressor gene and the int- xis genes of phage λ under control of promoter PR was constructed on the basis of vector pMWPi_aJacI-ts. To construct the pMWPi_aclacI-ts variant, the Aatll-EcoRV fragment of the pMWPi_aclacI plasmid (Skorokhodova, A. Yu. et al., Biotekhnologiya (in Russian), 2004, no. 5, 3-21) was substituted with the Aatϊl-EcoRV fragment of the pMAN997 plasmid (Tanaka, K. et al., J. Bacterid., 2001, 183(22): 6538-6542; WO99/03988) bearing thenar and ori loci and the repA^ts gene (a temperature sensitive-replication origin) of the pSClOl replicon. The plasmid pMAN997 was constructed by exchanging with the Vspl-Hindlll fragment of pMAN031 (J. Bacterid., 162, 1196 (1985)) and pUC19.

Two DNA fragments were amplified using phage λ DNA ("Fermentas") as a template. The first one contained the DNA sequence from 37168 to 38046, the cl repressor gene, promoters PRM and PR, and the leader sequence of the cro gene. This fragment was PCR-amplified using oligonucleotides P13 and P14 (SEQ ID NOS: 31 and32) as primers. The second DNA fragment containing the xis-int genes of phage λ and the DNA sequence from 27801 to 29100 was PCR-amplified using oligonucleotides Pl 5 and Pl 6 (SEQ ID NOS: 33 and 34) as primers. All primers contained the corresponding restriction sites.

The first PCR-amplified fragment carrying the cl repressor was digested with restriction endonuclease CIaI, treated with Klenow fragment of DNA polymerase I, and then digested with restriction endonuclease EcoRI. The second PCR-amplified fragment was digested with restriction endonucleases EcoRI and Pstl. The pMWPi_aolacI-ts plasmid was digested with the BgM endonuclease, treated with Klenow fragment of DNA polymerase I, and digested with the Pstl restriction endonuclease. The vector fragment of pMWPlaclacI-ts was eluted from agarose gel and ligated with the above-mentioned digested PCR-amplified fragments to obtain the pMW-intxis-ts recombinant plasmid. Example 2. Construction of a strain with the inactivated csgBAC operon

1. Deletion of the csgBAC operon

A strain wherein the csgBAC operon has been deleted was constructed by the method initially developed by Datsenko, K.A. and Wanner, B.L. (Proc. Natl. Acad. Sci. USA, 2000, 97(12): 6640-6645) called "Red-driven integration". The DNA fragment containing the Cm^R marker encoded by the cat gene was obtained by PCR, using primers P17 (SEQ ID NO:35) and P18 (SEQ ID NO:36) and plasmid pMWl 18-attL-Cm-attR as a template (for construction see Example 1). Primer P17 contains both a region complementary to the 36-nt region located at the 5' end of the csgBAC operon and a region complementary to the attL region. Primer Pl 8 contains both a region complementary to the 35-nt region located at the 3' end of the csgBAC operon and a region complementary to the attR region. Conditions for PCR were as follows: denaturation step: 3 min at 95°C; profile for two first cycles: 1 min at 95°C, 30 sec at 50°C, 40 sec at 72°C; profile for the last 25 cycles: 30 sec at 95°C, 30 sec at 54°C, 40 sec at 72°C; final step: 5 min at 72⁰C.

A 1699-bp PCR product (Fig. 2) was obtained and purified in agarose gel and was used for electroporation of E. coli MGl 655 (ATCC 700926), which contains the ρKD46 plasmid having temperature-sensitive replication. The pKD46 plasmid (Datsenko, K.A. and Wanner, B.L., Proc. Natl. Acad. Sci. USA, 2000, 97(12):6640-6645) includes a 2,154- bp DNA fragment of phage λ (nucleotide positions 31088 to 33241, GenBank accession no. J02459), and contains genes of the λ Red homologous recombination system (γ, β, exo genes) under the control of the arabinose-inducible P_araB promoter. The plasmid pKD46 is necessary for integration of the PCR product into the chromosome of strain MG1655. The strain MG1655 can be obtained from American Type Culture Collection. (P.O. Box 1549 Manassas, VA 20108, U.S.A.).

Εlectrocompetent cells were prepared as follows: a night culture of E. coli MGl 655 was grown at 30°C in LB medium supplemented with ampicillin (100 mg/1) and then 100- fold diluted with 5 ml of SOB medium (Sambrook et al, "Molecular Cloning: A Laboratory Manual, Second Edition", Cold Spring Harbor Laboratory Press, 1989) supplemented with ampicillin and L-arabinose (1 mM). The obtained culture was grown with aeration at 30°C to an OD₆₀₀ of »0.6 and then was made electrocompetent by 100-fold concentrating and washing three times with ice-cold deionized H₂O. Electroporation was performed using 70 μl of cells and «100 ng of the PCR product. Cells after electroporation were incubated with 1 ml of SOC medium (Sambrook et al, "Molecular Cloning: A Laboratory Manual, Second Edition", Cold Spring Harbor Laboratory Press, 1989) at 37°C for 2.5 hours and after that were plated onto L-agar supplemented with chloramphenicol (30 μg/ml) and grown at 37°C to select Cm^R recombinants. Then, to eliminate the pKD46 plasmid, two passages on L-agar with Cm at 42°C were performed and the resulting colonies were tested for sensitivity to ampicillin.

2. Verification of the cssBAC operon deletion by PCR

The mutants having the csgBAC operon deleted and marked with the Cm resistance gene were verified by PCR. Locus-specific primers P19 (SEQ ID NO:37) and P20 (SEQ ID NO: 38) were used in PCR for the verification. Conditions for PCR verification were as follows: denaturation step: 3 min at 94⁰C; profile for the 30 cycles: 30 sec at 94°C, 30 sec at 54°C, 1 min at 72°C; final step: 7 min at 72⁰C. The PCR product obtained in the reaction with the parental csgBAC ⁺ MGl 655 strain as a template was ~ 1.5kb in length. The PCR product obtained in the reaction with the mutant MG1655 ΔcsgBAC::cat strain as a template was ~ 1.8kb in length (Fig.3).

Example 3. Production of L-threonine by E. coli B-3996-ΔcsgBAC

To test the effect of inactivation of the csgBAC operon on threonine production, DNA fragments from the chromosome of the above-described E. coli MGl 655 ΔcsgBAC::cat were transferred to the threonine-producing E. coli strain VKPM B-3996 by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the strain B-3996-ΔcsgBAC.

Both E. coli strains, B-3996 and B-3996-ΔcsgBAC, were grown for 18-24 hours at 37⁰C on L-agar plates. To obtain a seed culture, the strains were grown on a rotary shaker (250 rpm) at 32°C for 18 hours in 20x200-mm test tubes containing 2 ml of L-broth supplemented with 4% glucose. Then, the fermentation medium was inoculated with 0.21 ml (10%) of seed material. The fermentation was performed in 2 ml of minimal medium for fermentation in 20x200-mm test tubes. Cells were grown for 65 hours at 32⁰C with shaking at 250 rpm.

After cultivation, the amount of L-threonine which had accumulated in the medium was determined by paper chromatography using the following mobile phase: butanol - acetic acid - water = 4 : 1 : 1 (v/v). A solution of ninhydrin (2%) in acetone was used as a visualizing reagent. A spot containing L-threonine was cut off, L-threonine was eluted with 0.5 % water solution of CdCl₂, and the amount of L-threonine was estimated spectrophotometrically at 540 run. The results of five independent test tube fermentations are shown in Table 1. As follows from Table 1, B-3996-ΔcsgBAC caused accumulation of a higher amount of L-threonine, as compared with B-3996.

The composition of the fermentation medium (g/1) was as follows:

Glucose 80.0

(NH₄)₂SO₄ 22.0 NaCl 0.8

KH₂PO₄ 2.0

MgSO₄-7H₂O 0.8

FeSO₄-7H₂O 0.02

MnSO₄-5H₂O 0.02

Thiamine HCl 0.0002

Yeast extract 1.0

CaCO₃ 30.0

Glucose and magnesium sulfate were sterilized separately. CaCO₃ was sterilized by dry-heat at 180°C for 2 hours. The pH was adjusted to 7.0. The antibiotic was introduced into the medium after sterilization.

Table 1

Example 4. Production of L-lvsine by E. coli WC196(t>CABD2VΔcsgBAC

To test the effect of inactivation of the csgBAC operon on lysine production, DNA fragments from the chromosome of the above-described E. coli strain MG1655 ΔcsgBAC::cat can be transferred to the lysine-producing E. coli strain WC 196 (pCABD2) by Pl transduction (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain the strain WC196(pCABD2)-ΔcsgBAC. pCABD2 includes a dapA gene coding for a dihydrodipicolinate synthase having a mutation which desensitizes feedback inhibition by L-lysine, a lysC gene coding for aspartokinase III having a mutation which desensitizes feedback inhibition by L-lysine, a dapB gene coding for a dihydrodipicolinate reductase gene, and a ddh gene coding for diaminopimelate dehydrogenase (US Patent 6,040,160).

Both E. coli strains WC196(pCABD2) and WC196(ρCABD2)-ΔcsgBAC can be cultured in the L-medium containing 20 mg/1 of streptomycin at 37 °C, and 0.3 ml of the obtained culture can be inoculated into 20 ml of the fermentation medium containing the required drugs in a 500 ml-flask. The cultivation can be carried out at 37 ⁰C for 16 hours by using a reciprocal shaker at the agitation speed of 115 rpm. After the cultivation, the amounts of L-lysine and residual glucose in the medium can be measured by a known method (Biotech-analyzer AS210, manufactured by Sakura Seiki Co.). Then, the yield of L-lysine relative to consumed glucose can be calculated for each of the strains. The composition of the fermentation medium (g/1) is as follows:

Glucose 40

(NH₄)₂SO₄ 24

K₂HPO₄ 1.0

MgSO₄-7H₂O 1.0

FeSO₄-7H₂O 0.01

MnSO₄-5H₂O 0.01

Yeast extract 2.0 pH is adjusted to 7.0 by KOH and the medium is autoclaved at 115°C for 10 min. Glucose and MgSO₄ 7H₂O are sterilized separately. CaCO₃ is dry-heat sterilized at 180°C for 2 hours and added to the medium for a final concentration of 30 g/1.

Example 5. Production of L-cysteine by E. coli strain JM15(ydeD)-ΔcsgBAC

To test the effect of inactivation of the csgBAC operon on L-cysteine production, DNA fragments from the chromosome of the above-described E. coli MGl 655 ΔcsgBAC::cat can be transferred to the E. coli L-cysteine producing strain JM15(ydeD) by Pl transduction (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain the strain JM15(ydeD)-ΔcsgBAC.

E. coli strain JM15(ydeD) is a derivative of E. coli strain JMl 5 (US Patent 6,218,168) which can be transformed with DNA having the ydeD gene, which codes for a membrane protein, and is not involved in a biosynthetic pathway of any L-amino acid (US Patent 5,972,663). The strain JMl 5 (CGSC# 5042) can be obtained from The Coli Genetic Stock Collection at the E.coli Genetic Resource Center, MCD Biology Department, Yale University (http://cgsc.biology.yale.edu/).

Fermentation conditions for evaluation of L-cysteine production were described in detail in Example 6 of US Patent 6,218,168.

Example 6. Production of L-leucine by E. coli strain 57-ΔcsgBAC

To test the effect of inactivation of the csgBAC operon on L-leucine production, DNA fragments from the chromosome of the above-described E. coli strain MG1655 ΔcsgBAC::cat can be transferred to the E. coli L-leucine producing strain 57 (VKPM B- 7386, US Patent 6,124,121) and Pl transduction can be performed (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain the strain 57-pMW-ΔcsgBAC. The strain 57 has been deposited in the Russian National Collection of Industrial Microorganisms (VKPM) (Russia, 117545 Moscow, 1 Dorozhny proezd, 1) on May 19, 1997_under the accession number VKPM B-7386. Both E. coli strains 57 and 57-ΔcsgBAC, can be cultured for 18-24 hours at 37°C on L-agar plates. To obtain a seed culture, the strains can be grown on a rotary shaker (250 rpm) at 32 °C for 18 hours in 20x200 mm test tubes containing 2 ml of L-broth with 4% sucrose. Then, the fermentation medium can be inoculated with 0.21 ml (10%) seed material. The fermentation can be performed in 2 ml of minimal medium for fermentation in 20x200 mm test tubes. Cells can be grown for 48-72 hours at 32°C with shaking at 250 rpm. The amount of L-leucine can be measured by paper chromatography (liquid phase composition: butanol - acetic acid - water = 4:1:1)

The composition of the fermentation medium (g/1) is as follows (pH 7.2):

Glucose 60.0

(NEU)₂SO₄ 25.0

K₂HPO₄ 2.0

MgSO₄-7H₂O 1.0

Thiamine 0.01

CaCO₃ 25.0

Glucose and CaCO₃ are sterilized separately.

Example 7. Production of L-histidine by E. coli strain 80-ΔcsgBAC

To test the effect of inactivation of the csgBAC operon on L-histidine production, DNA fragments from the chromosome of the above-described E. coli MGl 655 ΔcsgBAC::cat can be transferred to the histidine-producing E. coli strain 80 by Pl transduction (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain the strain 80-ΔcsgBAC. The strain 80 has been described in Russian patent 2119536 and deposited in the Russian National Collection of Industrial Microorganisms (Russia, 117545 Moscow, 1 Dorozhny proezd, 1) on October 15, 1999 under accession number VKPM B-7270 and then converted to a deposit under the Budapest Treaty on July 12, 2004.

Both E. coli strains 80 and 80-ΔcsgBAC, can be cultured in L-broth for 6 hours at 29 °C. Then, 0.1 ml of obtained culture can be inoculated into 2 ml of fermentation medium in 20x200mm test tube and cultivated for 65 hours at 29 °C with a rotary shaker (350 rpm). After cultivation, the amount of histidine which accumulates in the medium can be determined by paper chromatography. The paper can be developed with a mobile phase: n- butanol : acetic acid : water = 4 : 1 : 1 (v/v). A solution of ninhydrin (0.5%) in acetone can be used as a visualizing reagent.

The composition of the fermentation medium (pH 6.0) (g/1) is as follows:

Glucose 100.0

Mameno 0.2 as total nitrogen L-proline 1.0

(NH₄)₂SO₄ 25.0

KH₂PO₄ 2.0

MgSO₄-7H₂0 1.0

FeSO₄-7H₂0 0.01

MnSO₄ 0.01

Thiamine 0.001

Betaine 2.0

CaCO₃ 60.0

Glucose, proline, betaine and CaCO₃ are sterilized separately. pH is adjusted to 6.0 before sterilization.

Example 8. Production of L-glutamate by E. coli strain VL334thrC⁺-ΔcsgBAC

To test the effect of inactivation of the csgBAC operon_on L-glutamate production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgBAC::cat can be transferred to the E. coli L-glutamate producing strain VL334thrC⁺ (EP 1172433) by Pl transduction (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain the strain VL334thrC⁺-ΔcsgBAC. The strain VL334thrC⁺ has been deposited in the Russian National Collection of Industrial Microorganisms (VKPM) (Russia, 117545 Moscow 1, Dorozhny proezd 1) on December 6, 2004 under the accession number VKPM B-8961 and then converted to a deposit under the Budapest Treaty on December 8, 2004.

Both strains, VL334thrC⁺ and VL334thrC⁺-ΔcsgBAC, can be grown for 18-24 hours at 37°C on L-agar plates. Then, one loop of the cells can be transferred into test tubes containing 2ml of fermentation medium. The fermentation medium contains glucose (60g/l), ammonium sulfate (25 g/1), KH₂PO₄ (2g/l), MgSO₄ (1 g/1), thiamine (0.1 mg/ml), L-isoleucine (70 μg/ml), and CaCO₃ (25 g/1). The pH is adjusted to 7.2. Glucose and CaCO₃ are sterilized separately. Cultivation can be carried out at 30 °C for 3 days with shaking. After the cultivation, the amount of L-glutamic acid produced can be determined by paper chromatography (liquid phase composition: butanol-acetic acid-water=4: 1:1) with subsequent staining by ninhydrin (1% solution in acetone) and further elution of the compounds in 50% ethanol with 0.5% CdCl₂.

Example 9. Production of L- phenylalanine by E. coli strain AJ12739-ΔcsgBAC To test the effect of inactivation of the csgBAC operon on L-phenylalanine production, DNA fragments from the chromosome of the above-described E. coli MGl 655 ΔcsgBAC::cat can be transferred to the phenylalanine-producing E. coli strain AJl 2739 by Pl transduction (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain strain AJ12739-ΔcsgBAC. The strain AJl 2739 has been deposited in the Russian National Collection of Industrial Microorganisms (VKPM) (Russia, 117545 Moscow, 1 Dorozhny proezd, 1) on November 6, 2001 under accession number VKPM B-8197 and then converted to a deposit under the Budapest Treaty on August 23, 2002.

Both strains, AJ12739-ΔcsgBAC and AJ12739, can be cultivated at 37°C for 18 hours in a nutrient broth, and 0.3 ml of the obtained culture can be inoculated into 3 ml of a fermentation medium in a 20x200-mm test tube and cultivated at 37 ⁰C for 48 hours with a rotary shaker. After cultivation, the amount of phenylalanine which accumulates in the medium can be determined by TLC. 10 x 15 cm TLC plates coated with 0.11 mm layers of Sorbfil silica gel without fluorescent indicator (Stock Company Sorbpolymer, Krasnodar, Russia) can be used. Sorbfil plates can be developed with a mobile phase: propan-2-ol : ethylacetate : 25% aqueous ammonia : water = 40 : 40 : 7 : 16 (v/v). A solution (2%) of ninhydrin in acetone can be used as a visualizing reagent.

The composition of the fermentation medium (g/1) is as follows:

Glucose 40.0

(NH₄)₂SO₄ 16.0

K₂HPO₄ 0.1

MgSO₄-7H₂O 1.0

FeSO₄-7H₂O 0.01

MnSO₄-5H₂O 0.01

Thiamine HCl 0.0002

Yeast extract 2.0

Tyrosine 0.125

CaCO₃ 20.0

Glucose and magnesium sulfate are sterilized separately. CaCO₃ is dry-heat sterilized at 180° for 2 hours. The pH is adjusted to 7.0.

Example 10. Production of L- tryptophan by E. coli strain SVl 64 (pGH5VΔcsgBAC

To test the effect of inactivation of the csgBAC operon on L-tryptophan production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgBAC::cat can be transferred to the tryptophan-producing E. coli strain SV164 (pGH5) by Pl transduction (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain the strain SV164(pGH5)-ΔcsgBAC. The strain SVl 64 has the trpE allele encoding anthranilate synthase and is free from feedback inhibition by tryptophan. The plasmid pGH5 harbors a mutant serA gene encoding phosphoglycerate dehydrogenase and is free from feedback inhibition by serine. The strain SVl 64 (pGH5) was described in detail in US patent 6,180,373 or European patent 0662143.

Both strains, SV164(pGH5)-ΔcsgBAC and SV164(pGH5), can be cultivated with shaking at 37 °C for 18 hours in a 3 ml of nutrient broth supplemented with 20 mg/1 of tetracycline (marker of pGH5 plasmid). 0.3 ml of the obtained cultures can each be inoculated into 3 ml of a fermentation medium containing tetracycline (20 mg/1) in 20 x 200 mm test tubes, and cultivated at 37 °C for 48 hours with a rotary shaker at 250 rpm. After cultivation, the amount of tryptophan which accumulates in the medium can be determined by TLC as described in Example 8. The fermentation medium components are set forth in Table 2, but should be sterilized in separate groups A, B, C, D, E₃ F, and H, as shown, to avoid adverse interactions during sterilization.

Table 2

The pH of solution A is adjusted to 7.1 with NH₄OH.

Example 11. Production of L-proline by E. coli strain 702ilvA-ΔcsgBAC

To test the effect of inactivation of the csgBAC operon on L-proline production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgBAC::cat can be transferred to the proline-producing E. coli strain 702ilvA by Pl transduction (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain the strain 702ilvA-ΔcsgBAC. The strain 702ilvA has been deposited in the Russian National Collection of Industrial Microorganisms (VKPM) (Russia, 117545 Moscow, 1 Dorozhny proezd, 1) on July 18, 2000 under accession number VKPM B-8012 and then converted to a deposit under the Budapest Treaty on May 18, 2001.

Both E. coli strains 702ilvA and 702ilvA-ΔcsgBAC, can be grown for 18-24 hours at 37°C on L-agar plates. Then, these strains can be cultivated under the same conditions as in Example 8.

Example 12. Production of L-arginine by E. coli strain 382-ΔcsgBAC

To test the effect of inactivation of the csgBAC operon on L-arginine production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgBAC::cat can be transferred to the arginine-producing E. coli strain 382 by Pl transduction (Miller, J.H. (1972) Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, Plainview, NY) to obtain the strain 382-ΔcsgBAC. The strain 382 has been deposited in the Russian National Collection of Industrial Microorganisms (VKPM) (Russia, 117545 Moscow, 1 Dorozhny proezd, 1) on April 10, 2000 under accession number VKPM B-7926 and then converted to a deposit under the Budapest Treaty on May 18, 2001.

Both strains, 382-ΔcsgBAC and 382, can be separately cultivated with shaking at 37 °C for 18 hours in a 3 ml of nutrient broth. 0.3 ml of the obtained cultures can each be inoculated into 3 ml of a fermentation medium in 20 x 200 mm test tubes, and cultivated at 32 °C for 48 hours on a rotary shaker.

After the cultivation, the amount of L-arginine which accumulates in the medium can be determined by paper chromatography using the following mobile phase: butanol : acetic acid : water = 4 : 1 : 1 (v/v). A solution (2%) of ninhydrin in acetone can be used as a visualizing reagent. A spot containing L-arginine can be cut off, L-arginine can be eluted with 0.5 % water solution of CdCl₂, and the amount of L-arginine can be estimated spectrophotometrically at 540 nm.

The composition of the fermentation medium (g/1) is as follows:

Glucose 48.0

(NH4)₂SO₄ 35.0

KH₂PO₄ 2.0

MgSO₄-7H₂O 1.0

Thiamine HCl 0.0002

Yeast extract 1.0 L-isoleucine 0.1

CaCO₃ 5.0

Glucose and magnesium sulfate are sterilized separately. CaCO₃ is dry-heat sterilized at 180 °C for 2 hours. The pH is adjusted to 7.0.

Example 13. Construction of a strain with the inactivated cssDEFG operon

1. Deletion of the csgDEFG operon

A strain having deletion of the csgDEFG operon was constructed by the method initially developed by Datsenko, K.A. and Wanner, B.L. (Proc. Natl. Acad. Sci. USA, 2000, 97(12): 6640-6645) called "Red-driven integration". The DNA fragment containing the Cm^R marker encoded by the cat gene was obtained by PCR, using primers P21 (SEQ ID NO:39) and P22 (SEQ ID NO:40) and plasmid pMWl 18-attL-Cm-attR as a template (for construction see Example 1). Primer P21 contains both a region complementary to the 36- nt region located at the 5' end of the csg DEFG operon and a region complementary to the attL region. Primer P22 contains both a region complementary to the 35-nt region located at the 3' end of the csgDEFG operon and a region complementary to the attR region. Conditions for PCR were as follows: denaturation step: 3 min at 95°C; profile for two first cycles: 1 min at 95°C, 30 sec at 50°C, 40 sec at 72°C; profile for the last 25 cycles: 30 sec at 95°C, 30 sec at 54⁰C, 40 sec at 72°C; final step: 5 min at 72⁰C.

A 1699-bp PCR product (Fig. 2) was obtained and purified in agarose gel and was used for electroporation of E. coli MGl 655 (ATCC 700926), which contains the ρKD46 plasmid having temperature-sensitive replication. The pKD46 plasmid (Datsenko, K.A. and Wanner, B.L., Proc. Natl. Acad. Sci. USA, 2000, 97(12):6640-6645) includes a 2,154- bp DNA fragment of phage λ (nucleotide positions 31088 to 33241, GenBank accession no. J02459), and contains genes of the λ Red homologous recombination system (γ, β, exo genes) under the control of the arabinose-inducible P_3T3B promoter. The plasmid pKD46 is necessary for integration of the PCR product into the chromosome of strain MG1655.

Electrocompetent cells were prepared as described in Example 2. Electroporation was performed using 70 μl of cells and «100 ng of the PCR product. Cells after electroporation were incubated with 1 ml of SOC medium (Sambrook et al, "Molecular Cloning: A Laboratory Manual, Second Edition", Cold Spring Harbor Laboratory Press, 1989) at 37°C for 2.5 hours and after that were plated onto L-agar supplemented with chloramphenicol (30 μg/ml) and grown at 37⁰C to select Cm^R recombinants. Then, to eliminate the pKD46 plasmid, two passages on L-agar with Cm at 42°C were performed and the obtained colonies were tested for sensitivity to ampicillin.

2. Verification of the ess DEFG operon deletion by PCR The mutants having the csgJDEFG operon deleted and marked with the Cm resistance gene were verified by PCR. Locus-specific primers P23 (SEQ ID NO:41) and P24 (SEQ ID NO:42) were used in PCR for the verification. Conditions for PCR verification were as follows: denaturation step: 3 min at 94°C; profile for the 30 cycles: 30 sec at 94°C, 30 sec at 54°C, 1 min at 72°C; final step: 7 min at 72°C. The PCR product obtained in the reaction with the parental csg_DEFG ⁺ MGl 655 strain as a template was ~ 2.4 kb in length. The PCR product obtained in the reaction with the mutant MGl 655 Δcsg DEFG: :cat strain as a template was ~1.8kb in length (Fig.4).

Example 14. Production of L-threonine by E. coli strain B-3996-ΔcsgDEFG

To test the effect of inactivation of the csgDEFG operon on threonine production, DNA fragments from the chromosome of the above-described E. coli MGl 655 ΔcsgDEFG::cat were transferred to the threonine-producing E. coli strain VKPM B-3996 by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the strain B-3996-ΔcsgDEFG.

Both E. coli strains, B-3996 and B-3996-ΔcsgDEFG, were grown for 18-24 hours at 37°C on L-agar plates. To obtain a seed culture, the strains were grown on a rotary shaker (250 rpm) at 32°C for 18 hours in 20x200-mm test tubes containing 2 ml of L-broth supplemented with 4% glucose. Then, the fermentation medium was inoculated with 0.21 ml (10%) of seed material. The fermentation was performed in 2 ml of minimal medium for fermentation in 20x200-mm test tubes. Cells were grown for 65 hours at 32°C with shaking at 250 rpm.

After cultivation, the amount of L-threonine which had accumulated in the medium was determined by paper chromatography using the following mobile phase: butanol - acetic acid - water = 4 : 1 : 1 (v/v). A solution of ninhydrin (2%) in acetone was used as a visualizing reagent. A spot containing L-threonine was cut off, L-threonine was eluted with 0.5 % water solution Of CdCl₂, and the amount of L-threonine was estimated spectrophotometrically at 540 nm. The results of five independent test tube fermentations are shown in Table 3. As follows from Table 3, B-3996-Δ csgDEFG caused accumulation of a higher amount of L-threonine, as compared with B-3996.

The composition of the fermentation medium (g/1) was as follows:

Glucose 80.0

(NH₄)₂SO₄ 22.0

NaCl 0.8

KH₂PO₄ 2.0

MgSO₄-7H₂O 0.8

FeSO₄-7H₂O 0.02 MnSO₄-5H₂O 0.02

Thiamine HCl 0.0002

Yeast extract 1.0

CaCO₃ 30.0

Table 3

Example 15. Production of L-lvsine by E. coli strain WC196fρCBAD2VΔcsgDEFG

To test the effect of inactivation of the csgDEFG operon on lysine production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgDEFG::cat can be transferred to the lysine-producing E. coli strain WC 196 (pCABD2) by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the strain WC196(pCABD2)-ΔcsgDEFG.

Both E. coli strains WC196(pCABD2) and WC196(pCABD2)-ΔcsgDEFG can be cultured in L-medium containing streptomycin (20 mg/1) at 37°C, and 0.3 ml of the obtained culture can be inoculated into 20 ml of the fermentation medium containing the required drugs in a 500-ml flask. The cultivation can be carried out at 37°C for 16 h by using a reciprocal shaker at the agitation speed of 115 rpm. After the cultivation, the amounts of L-lysine and residual glucose in the medium can be measured by a known method (Biotech-analyzer AS210 manufactured by Sakura Seiki Co.). Then, the yield of L- lysine relative to consumed glucose can be calculated for each of the strains.

The composition of the fermentation medium (g/1) is as follows:

Glucose 40

(NH₄)₂SO₄ 24

K₂HPO₄ 1.0

MgSO₄-7H₂O 1.0

FeSO₄-7H₂O 0.01

MnSO₄-5H₂O 0.01

Yeast extract 2.0

The pH is adjusted to 7.0 by KOH and the medium is autoclaved at 115⁰C for 10 min. Glucose and MgSO₄ 7H₂O are sterilized separately. CaCO₃ is dry-heat sterilized at 180⁰C for 2 hours and added to the medium for a final concentration of 30 g/1.

Example 16. Production of L-cysteine by E. coli strain JM15(ydeD>ΔcsgDEFG

To test the effect of inactivation of the csgDEFG operon on L-cysteine production, DNA fragments from the chromosome of the above-described E. coli MGl 655 ΔcsgDEFG::cat can be transferred to the E. coli L-cysteine-producing strain JM15(ydeD) by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the strain JM15(ydeD)-ΔcsgDEFG.

Example 17. Production of L-leucine by E. coli strain 57-ΔcsgDEFG

To test the effect of inactivation of the csgDEFG operon on L-leucine production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgDEFG::cat can be transferred to the E. coli L-leucine-producing strain 57 (VKPM B- 7386, US Patent 6,124,121) by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the 57-pMW- ΔcsgDEFG strain.

Both E. coli strains, 57 and 57-ΔcsgDEFG, can be cultured for 18-24 hours at 37°C on L-agar plates. To obtain a seed culture, the strains can be grown on a rotary shaker (250 rpm) at 32°C for 18 hours in 20x200-mm test tubes containing 2 ml of L-broth supplemented with 4% sucrose. Then, the fermentation medium can be inoculated with 0.21 ml of seed material (10%). The fermentation can be performed in 2 ml of a minimal fermentation medium in 20x200-mm test tubes. Cells can be grown for 48-72 hours at 32°C with shaking at 250 rpm. The amount of L-leucine can be measured by paper chromatography (liquid phase composition: butanol - acetic acid - water = 4:1:1).

The composition of the fermentation medium (g/1) (pH 7.2) is as follows:

Glucose 60.0

(NH₄)₂SO₄ 25.0

K₂HPO₄ 2.0

MgSO₄-7H₂O 1.0

Thiamine 0.01

CaCO₃ 25.0

Glucose and CaCO₃ are sterilized separately.

Example 18. Production of L-histidine by E. coli strain 80-ΔcsgDEFG To test the effect of inactivation of the csgDEFG operon on L-histidine production, DNA fragments from the chromosome of the above-described E. coli MGl 655 ΔcsgDEFG::cat can be transferred to the histidine-producing E. coli strain 80 by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the strain80-ΔcsgDEFG.

Both E. coli strains, 80 and 80-ΔcsgDEFG, can be cultured in L-broth for 6 hours at 29⁰C. Then, 0.1 ml of obtained culture can be inoculated into 2 ml of fermentation medium in a 20x200-mm test tube and cultivated for 65 hours at 29°C with shaking on a rotary shaker (350 rpm). After cultivation, the amount of histidine which accumulates in the medium can be determined by paper chromatography. The paper can be developed with a mobile phase consisting of n-butanol : acetic acid : water = 4 : 1 : 1 (v/v). A solution of ninhydrin (0.5%) in acetone can be used as a visualizing reagent.

The composition of the fermentation medium (g/1) (pH 6.0) is as follows:

Glucose 100.0

Mameno 0.2 as total nitrogen

L-proline 1.0

(NH₄)₂SO₄ 25.0

KH₂PO₄ 2.0

MgSO₄-7H₂0 1.0

FeSO₄-7H₂0 0.01

MnSO₄ 0.01

Thiamine 0.001

Betaine 2.0

CaCO₃ 60.0

Glucose, proline, betaine and CaCO₃ are sterilized separately. The pH is adjusted to 6.0 before sterilization.

Example 19. Production of L-glutamate by E. coli strain VL334thrC⁺-ΔcsgDEFG

To test the effect of inactivation of the csgDEFG operon_on L-glutamate production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgDEFG::cat can be transferred to the E. coli L-glutamate-producing strain VL334thrC⁺ (EP 1172433) by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the strain VL334thrC⁺- ΔcsgDEFG.

Both strains, VL334thrC⁺ and VL334thrC⁺-ΔcsgDEFG, can be grown for 18-24 hours at 37°C on L-agar plates. Then, one loop of the cells can be transferred into test tubes containing 2ml of fermentation medium. The fermentation medium contains glucose (60g/l), ammonium sulfate (25 g/1), KH₂PO₄ (2g/l), MgSO₄ (I g/1), thiamine (0.1 mg/ml), L-isoleucine (70 μg/ml), and CaCO₃ (25 g/1). The pH is adjusted to 7.2. Glucose and CaCO₃ are sterilized separately. Cultivation can be carried out at 30°C for 3 days with shaking. After the cultivation, the amount of L-glutamic acid which is produced can be determined by paper chromatography (liquid phase composition of butanol-acetic acid- water^: 1:1) with subsequent staining by ninhydrin (1% solution in acetone) and further elution of the compounds in 50% ethanol with 0.5% CdCl₂.

Example 20. Production of L- phenylalanine by E. coli strain AJ12739-ΔcsgDEFG To test the effect of inactivation of the csgDEFG operon on L-phenylalanine production, DNA fragments from the chromosome of the above-described E. coli MGl 655 ΔcsgDEFG::cat can be transferred to the phenylalanine-producing E. coli strain AJ12739 by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY).

Both strains, AJ12739-ΔcsgDEFG and AJ12739, can be cultivated at 37°C for 18 hours in a nutrient broth, and 0.3 ml of the obtained culture can be inoculated into 3 ml of a fermentation medium in a 20x200-mm test tube and cultivated at 37°C for 48 hours with shaking on a rotary shaker. After cultivation, the amount of phenylalanine which accumulates in the medium can be determined by TLC. The 1Ox 15 -cm TLC plates coated with 0.11 -mm layers of Sorbfil silica gel without fluorescent indicator (Stock Company Sorbpolymer, Krasnodar, Russia) can be used. The Sorbfil plates can be developed with a mobile phase consisting of propan-2-ol : ethylacetate : 25% aqueous ammonia : water = 40 : 40 : 7 : 16 (v/v). A solution of ninhydrin (2%) in acetone can be used as a visualizing reagent.

The composition of the fermentation medium (g/1) is as follows:

Glucose 40.0

(NH₄)₂SO₄ 16.0

K₂HPO₄ 0.1

MgSO₄-7H₂O 1.0

FeSO₄-7H₂O 0.01

MnSO₄-5H₂O 0.01

Thiamine HCl 0.0002

Yeast extract 2.0

Tyrosine 0.125

CaCO₃ 20.0

Glucose and magnesium sulfate are sterilized separately. CaCO₃ is dry-heat sterilized at 180° for 2 hours. The pH is adjusted to 7.0. Example 21. Production of L- tryptophan by E. coli strain SVl 64 fpGH5>ΔcsgDEFG

To test the effect of inactivation of the csgDEFG operon on L-tryptophan production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgDEFG::cat can be transferred to the tryptophan-producing E. coli strain SVl 64 (pGH5) by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the strain SV164(pGH5)-ΔcsgDEFG. Both strains, SV164(pGH5)-ΔcsgDEFG and SV164(pGH5), can be cultivated with shaking at 37°C for 18 hours in 3 ml of nutrient broth supplemented with 20 mg/1 of tetracycline (marker of pGH5 plasmid). The obtained cultures (0.3 ml each) can be inoculated into 3 ml of a fermentation medium containing tetracycline (20 mg/1) in 20 x 200-mm test tubes, and cultivated at 37⁰C for 48 hours with a rotary shaker at 250 rpm. After cultivation, the amount of tryptophan which accumulates in the medium can be determined by TLC as described in Example 8. The fermentation medium components are listed in Table 2, but should be sterilized in separate groups (A, B, C, D, E, F, and H), as shown, to avoid adverse interactions during sterilization.

Example 22. Production of L-proline by E. coli strain 702ilvA-ΔcsgDEFG

To test the effect of inactivation of the csgDEFG operon on L-proline production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔDEFG::cat can be transferred to the proline-producing E. coli strain 702ilvA by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY). The strain 702ilvA has been deposited in the Russian National Collection of Industrial Microorganisms (VKPM) (Russia, 117545 Moscow, 1 Dorozhny proezd, 1) under accession number VKPM B-8012.

Both E. coli strains 702ilvA and 702ilvA-ΔcsgDEFG, can be grown for 18-24 hours at 37⁰C on L-agar plates. Then, these strains can be cultivated under the same conditions as in Example 8.

Example 23. Production of L-arginine by E. coli strain 382-ΔcsgDEFG

To test the effect of inactivation of the csgDEFG operon on L-arginine production, DNA fragments from the chromosome of the above-described E. coli strain MGl 655 ΔcsgDEFG::cat can be transferred to the arginine-producing E. coli strain 382 by Pl transduction (Miller, J.H. Experiments in Molecular Genetics, Cold Spring Harbor Lab. Press, 1972, Plainview, NY) to obtain the strain 382-ΔcsgDEFG.

Both strains, 382-ΔcsgDEFG and 382, can be separately cultivated with shaking at 37⁰C for 18 hours in 3 ml of nutrient broth. The obtained cultures (0.3 ml each) can be inoculated into 3 ml of a fermentation medium in 20 x 200-mm test tubes and cultivated at 32°C for 48 hours on a rotary shaker.

After the cultivation, the amount of L-arginine which accumulates in the medium can be determined by paper chromatography using the following mobile phase: butanol : acetic acid : water = 4 : 1 : 1 (v/v). A solution of ninhydrin (2%) in acetone can be used as a visualizing reagent. A spot containing L-arginine can be cut off, L-arginine can be eluted with 0.5 % water solution Of CdCl₂, and the amount of L-arginine can be estimated spectrophotometrically at 540 ran.

The composition of the fermentation medium (g/1) is as follows:

Glucose 48.0

(NH₄)₂SO₄ 35.0

KH₂PO₄ 2.0

MgSO₄-7H₂O 1.0

Thiamine HCl 0.0002

Yeast extract 1.0

L-isoleucine 0.1

CaCO₃ 5.0

Glucose and magnesium sulfate are sterilized separately. CaCO₃ is dry-heat sterilized at 180 ⁰C for 2 hours. The pH is adjusted to 7.0.

Example 24. Deletion of the Cm resistance gene (cat Rene) from the chromosome of L- amino acid-producing E. coli strains.

The Cm resistance gene (cat gene) can be deleted from the chromosome of the L- amino acid-producing strain using the int-xis system. For that purpose, an L-amino acid- producing strain having DNA fragments from the chromosome of the above-described E. coli strain MG1655 ΔcsgBAC::cat or MG1655 ΔcsgDEFG::cat transferred by Pl transduction (see Examples 3-23), can be transformed with plasmid pMWts-Int/Xis. Transformant clones can be selected on the LB -medium containing 100 μg/ml of ampicillin. Plates can be incubated overnight at 30°C. Transformant clones can be cured from the cat gene by spreading the separate colonies at 37°C (at that temperature repressor Cits is partially inactivated and transcription of the int/xis genes is derepressed) followed by selection of Cm^sAp^R variants. Elimination of the cat gene from the chromosome of the strain can be verified by PCR. Locus-specific primers P25 (SEQ ID NO:43) and P26 (SEQ ID NO:44) can be used in PCR for the verification. Conditions for PCR verification can be as described above. The PCR product obtained in reaction with cells having the eliminated cat gene as a template, should be 0.2 kbp in length. Thus, the L-amino acid-producing strain with the inactivated csgBAC or csg DEFG operon and eliminated cat gene can be obtained.

While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. All the cited references herein are incorporated as a part of this application by reference.

Industrial Applicability

According to the present invention, production of L-amino acid of a bacterium of the Enterobacteriaceae family can be enhanced.

Claims

1. An L-amino acid-producing bacterium of the Enterobacteriaceae family, wherein said bacterium has been modified to abolish curli formation.

2. The bacterium according to claim 1, wherein expression of the csgBAC and/or csgDEFG operons is attenuated.

3. The bacterium according to claim 2, wherein said expression of the csgBAC and/or csgDEFG operons is attenuated by inactivation of the csgBAC and/or csgDEFG operons.

4. The bacterium according to claim 1, wherein said bacterium belongs to the genus

Escherichia.

5. The bacterium according to claim 1, wherein said bacterium belongs to the genus

Pantoea.

6. The L-amino acid-producing bacterium according to any of claims 1 to 5, wherein said

L-amino acid is selected from the group consisting of an aromatic L-amino acid and a non-aromatic L-amino acid.

7. The L-amino acid-producing bacterium according to claim 6, wherein said aromatic L- amino acid is selected from the group consisting of L-phenylalanine, L-tyrosine, and L- tryptophan.

8. The L-amino acid-producing bacterium according to claim 6, wherein said non-aromatic

L-amino acid is selected from the group consisting of L-threonine, L-lysine, L-cysteine, L-methionine, L-leucine, L-isoleucine, L-valine, L-histidine, glycine, L-serine, L- alanine, L-asparagine, L-aspartic acid, L-glutamine, L-glutamic acid, L-proline, and L- arginine.

9. A method for producing an L-amino acid comprising:

- cultivating the bacterium according to any of claims 1 to 8 in a medium, and

- collecting said L-amino acid from the medium.

10. The method according to claim 9, wherein said L-amino acid is selected from the group consisting of an aromatic L-amino acid and a non-aromatic L-amino acid.

11. The method according to claim 10, wherein said aromatic L-amino acid is selected from the group consisting of L-phenylalanine, L-tyrosine, and L-tryptophan.

12. The method according to claim 10, wherein said non-aromatic L-amino acid is selected from the group consisting of L-threonine, L-lysine, L-cysteine, L-methionine, L- leucine, L-isoleucine, L-valine, L-histidine, glycine, L-serine, L-alanine, L-asparagine, L-aspartic acid, L-glutamine, L-glutamic acid, L-proline, and L-arginine.