L-amino acid producing bacterium which has enhanced expression of at least one of the nhaA gene, the nhaB gene, the nhaR gene, the chaA gene, the mdfA gene and a method of producing L-amino acid

A method of producing an L-amino acid comprising

• I) culturing an L-amino acid-producing Escherichia coli bacterium in a medium to produce and accumulate an L-amino acid in the medium or cells of the Escherichia coli bacterium and
• II) collecting the L-amino acid from the medium or the cells,
• wherein said Escherichia coli bacterium has been modified so that Na+/H+ antiporter activity is enhanced as compared to a non-modified Escherichia coli bacterium by increasing expression of a gene selected from the group consisting of nhaA, nhaB, nhaR, chaA, mdfA, and combinations thereof,
• wherein said L-amino acid is selected from the group consisting of L-lysine, L-threonine, and combinations thereof,
• wherein the nhaA gene encodes a protein selected from the group consisting of:
• (A) a protein comprising the amino acid sequence of SEQ ID NO:
• 2, and
• (B) a protein comprising the amino acid sequence of SEQ ID NO:
• 2, but which includes substitution, deletion, insertion or addition of one to 10 amino acids, and has Na+/H+ antiporter activity,
• wherein the nhaB gene encodes a protein selected from the group consisting of:
• (C) a protein comprising the amino acid sequence of SEQ ID NO:
• 4, and
• (D) a protein comprising the amino acid sequence of SEQ ID NO:
• 4, but which includes substitution, deletion, insertion or addition of one to 10 amino acids, and has Na+/H+ antiporter activity,
• wherein the nhaR gene encodes a protein selected from the group consisting of:
• (E) a protein comprising the amino acid sequence of SEQ ID NO:
• 6, and
• (F) a protein comprising the amino acid sequence of SEQ ID NO:
• 6, but which includes substitution, deletion, insertion or addition of one to 10 amino acids, and is able to increase expression of an Na+/H+ antiporter,
• wherein the chaA gene encodes a protein selected from the group consisting of:
• (G) a protein comprising the amino acid sequence of SEQ ID NO:
• 24, and
• (H) a protein comprising the amino acid sequence of SEQ ID NO:
• 24, but which includes substitution, deletion, insertion or addition of one to 10 amino acids, and has Na+/H+ antiporter activity,
• wherein the mdfA gene encodes a protein selected from the group consisting of:
• (I) a protein comprising the amino acid sequence of SEQ ID NO:
• 26, and
• (J) a protein comprising the amino acid sequence of SEQ ID NO:
• 26, but which includes substitution, deletion, insertion or addition of one to 10 amino acids in SEQ ID NO:
• 26, and has Na+/H+ antiporter activity.