Process for producing L-glutamic acid by fermentation

Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing alpha or beta amino acid or substituted amino acid...

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4352523, 4352528, 4351721, C12N 121, C12N 1501, C12P 1314

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active

06110714&

DESCRIPTION:

BRIEF SUMMARY
This application is filed under 35 U.S.C. 371 as the National Stage of PCT/JP96/01944, filed Jul. 12, 1996.


TECHNICAL FIELD

The present invention relates to a process for producing L-glutamic acid by fermentation. L-glutamic acid is an important amino acid as food, pharmaceutical preparations or the like.


BACKGROUND ART

L-glutamic acid has been produced by fermentation mainly using so-called coryneform L-glutamic acid-producing strains belonging to the genus Brevibacterium, Corynebacterium or Microbacterium or mutants thereof (Amino-Acid Fermentation, Gakkai Shuppan Center, pp. 195-215, 1986). The other known methods of producing L-glutamic acid by fermentation use microorganisms belonging to the genus Bacillus, Streptomyces or Penicillium (U.S. Pat. No. 3,220,929), and microorganisms belonging to the genus Pseudomonas, Arthrobacter, Serratia or Candida (U.S. Pat. No. 3,563,857). The L-glutamic acid productivity is remarkably increased by the conventional methods. However, in order to meet foreseen increased needs in the future, the development of a more inexpensive and efficient method of producing L-glutamic acid has been in demand.
There is a possibility that bacteria of the genus Escherichia will be used as excellent L-glutamic acid producing-strains in the future because of its high growth rate and advanced gene analysis. It has only been reported so far that a mutant of wild type strain Escherichia coli W, results in accumulation of L-glutamic acid in small amounts of about 2.3 g/liter (J. Biochem., vol. 50, pp. 164-165, 1961). However, recently, it has been shown that a mutant of Escherichia coli K-12, in which .alpha.-ketoglutaric acid dehydrogenase (hereinafter abbreviated as ".alpha.-KGDH) activity is deficient or reduced, exhibits high L-glutamic acid productivity [Japanese Laid-Open Patent Application (Kokai) No. 244,970/1993]. Wild type strains belonging to the genus Escherichia include strains having properties which are better than those of Escherichia coli K-12 and mutants thereof. For Example, it has been reported that Escherichia coli B exhibits higher growth rate than Escherichia coli K-12 and mutants thereof and gives a high yield of biomass based on glucose consumed (J. Biotechnology, vol. 2, pp. 191-206, 1985; and Appl. Environ. Microbiol., vol. 56, pp. 1004-1011, 1990).
It is an object of the present invention to provide an inexpensive and efficient process for producing L-glutamic acid by propagating L-glutamic acid-producing strain which belongs to the genus Escherichia.


DISCLOSURE OF THE INVENTION

The present inventors have assiduously conducted investigations on a process for producing L-glutamic acid using bacteria of the genus Escherichia, and have consequently found that a strain obtained by amplifying citrate synthase (hereinafter abbreviated as "CS") activity and phosphoenolpyruvate carboxylase (hereinafter abbreviated as "PPC") activity in a valine-sensitive strain has high L-glutamic acid-productivity. This finding has led to the completion of the present invention.
That is, the present invention is as follows.
Invention 1. A microorganism which belongs to the genus Escherichia, which exhibits valine sensitivity, and which has amplified citrate synthase activity and phosphoenolpyruvate carboxylase activity and which has L-glutamic acid-productivity.
Invention 2. A microorganism according to the Invention 1, wherein .alpha.-ketoglutaric acid dehydrogenase activity is deficient or reduced.
Invention 3. A microorganism according to any of the Inventions 1 and 2, which belongs to Escherichia coli.
Invention 4. A microorganism according to the Invention 3, which belongs to Escherichia coli B strain.
Invention 5. A microorganism according to the Invention 3, which belongs to Escherichia coli K-12 strain.
Invention 6. A process for producing L-glutamic acid by fermentation, which comprises cultivating in a liquid medium a microorganism according to any of the Inventions 1 to 5, accumulating L-glutamic acid in the broth, and recovering said L-glutamic acid.


BRIEF DESCRI

REFERENCES:
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