1. Field of the Invention
The present invention relates to techniques used in the field of microbial industry. More precisely, the present invention relates to a method for producing L-lysine or L-arginine by fermentation and a microorganism used in the production method.
2. Description of the Related Art
Amino acids such as L-lysine, L-glutamic acid, L-threonine, L-leucine, L-isoleucine, L-valine and L-phenylalanine are industrially produced by fermentation using microorganisms that belong to the genus Brevibacterium, Corynebacterium, Bacillus, Escherichia, Streptomyces, Pseudomonas, Arthrobacter, Serratia, Penicillium, Candida or the like. In order to improve the productivity of these microorganisms, strains isolated from nature or artificial mutants thereof have been used. Moreover, various techniques have been disclosed for increasing the L-amino acid producing abilities by using recombinant DNA techniques to enhance L-amino acid biosynthetic enzymes.
Productivities of L-amino acids have been considerably increased by breeding of microorganisms such as those mentioned above and improvements of production methods. However, in order to respond to further increase in demands in future, development of methods for more efficiently producing L-amino acids at lower cost have still been desired.
As methods for producing L-amino acids by fermentation of methanol, which is a fermentation raw material available in a large amount at a low cost, there have hitherto known methods using microorganisms that belong to the genus Achromobacter or Pseudomonas (Japanese Patent Laid-open (Kokai) No. 45-25273), Protaminobacter (Japanese Patent Publication (Kokoku) No. 49-125590), Protaminobacter or Methanomonas (Japanese Patent Laid-open No. 50-25790), Microcyclus (Japanese Patent Laid-open No. 52-18886), Methylobacillus (Japanese Patent Laid-open No. 4-91793), Bacillus (Japanese Patent Laid-open No. 3-505284) and so forth. The inventors of the present invention have so far developed methods for producing L-amino acids using Methylophilus bacteria based on breeding by artificial mutagenesis and recombinant DNA techniques (Japanese Patent Application No. 11-368097).
In recent years, there have been identified proteins that have a function of specifically excreting an L-amino acid to outside a cell of microorganism and genes therefor, and in particular, Vrljic et al. identified a gene involved in excretion of L-lysine from a Corynebacterium bacterium to outside of a cell (Vrljic M., Sahm H., Eggeling L., Molecular Microbiology 22:815–826 (1996)). This gene was designated as lysE, and it was reported that L-lysine producing ability of Corynebacterium bacteria could be improved by enhancing this gene in Corynebacterium bacteria (WO97/23597). It is also known that productivities for some L-amino acids can be improved by increasing expression amounts of amino acid excreting proteins in Escherichia coli (Japanese Patent Laid-open No. 2000-189180). For example, it is reported that productivities of cysteine, cysteine and so forth can be improved by enhancing expression of ORF306 gene in Escherichia coli (EP885962).
However, there has so far been disclosed no example of demonstrating that the excretion process of an amino acid constitutes a serious obstacle for amino acid production by fermentation of methanol using a methanol assimilating bacterium. There is also no report on any amino acid excretion gene that can provide such an excretion activity in a methanol assimilating bacterium.
Furthermore, it has not been known that the lysE gene has a function of excreting amino acids other than L-lysine.