Process for producing L-amino acids by fermentation

Abstract: A microorganism belonging to the genus Brevibacterium or the genus Corynebacterium, which has resistance to a peptide containing glutamic acid or aspartic acid is capable of producing an L-amino acid in high yields. A process for producing an L-amino acid by culturing in a liquid medium an L-amino acid producing microorganism belonging to the genus Brevibacterium or the genus Coryne­ bacterium is provided, in which an L-amino acid producing microorganism is used, which has resistance to a peptide containing glutamic acid or aspartic acid.

Description: The present invention relates to a process for producing L-amino acids by fermentation and to microorganisms useful in this process. L-Amino acids have been widely used as seasonings, medical drugs, feed additives, chemicals, reagents and the like. L-amino acids produced by fermentation in an industrial scale are L-glutamic acid, L-lysine, L-glutamine, L-arginine, L-phenylalanine, L-alanine, L-threonine, L-isoleucine, L-histidine, L-proline, L-valine, L-serine, L-ornithine, L-citrulline, L-tyrosine, L-tryptophan and L-leucine, etc. Examples of microorganisms utilized for their production are those belonging to the genus Brevibacterium, the genus Corynebacterium, the genus Bacillus, the genus Escherichia, the genus Serratia, the genus Providencia, the genus Arthrobacter, etc. In order to industrially produce L-amino acids at low costs utilizing these various microorganisms, improved breeding of microorganism has often been used. Since the L-amino acid productivity of wild strains per se is extremely poor in many cases there have been applied methods to induce mutations. Known is a method for imparting nutrient auxotrophy, imparting analog resistance or imparting nutrient auxotrophy in combination with analog resistance by artificial mutation; or a method for potentiating a gene for amino acid biosynthesis, etc. by genetic recombination, and the like. It is important to produce L-amino acids at low costs in an industrial scale by enhancing the fermentation yield and the accumulated amount of L-amino acids. FR-A-2 491 495 describes a process for the preparation of amino acids in which a microorganism producing an amino acid and being capable of assimilating lactic acid is cultured under aerobic conditions in the presence of at least one microorganism being capable of assimilating a hydrocarbon and being capable of converting said hydrocarbon to lactic acid. The resulting amino acids are accumulated in the culture medium and recovered therefrom. JP-A-54 44 096 discloses the preparation of L-arginine by the cultivation of bacteria belonging to the genus Brevibacterium, which are resistant to 2-thiazol and deficient for L-histidine, L-proline, L-threonine, L-isoleucine, L-methionine or L-tryptophane. After cultivation of the bacteria the L-arginine is isolated from the culture medium. JP-A-74 118 891 describes the preparation of L-lysine by Corynebacterium mutants being resistant to S-2-aminoethyl-L-cystine and deficient in the histidine-, phenylalanine-, proline-, adenine-, guanine-, methionine-, and leucine-synthesis pathway. After culturing the bacterium L-lysine is recovered from the culture medium. In order to further improve the fermentation yield of L-amino acids and to develop a process for producing L-amino acids by fermentation which is advantageous from the industrial point of view, the present inventors have made extensive investigations. As a result, it has been found for the first time that by breeding strains having resistance to a peptide containing glutamic acid or aspartic acid, the yield of L-amino acids can be improved. Based on this finding, further investigations have been made and as the result, the present invention has been attained. The present invention provides a process for producing an L-amino acid which comprises culturing in a liquid medium an L-amino acid-producing microorganism belonging to the genus Brevibacterium or the genus Corynebacterium, accumulating said L-amino acid in the culture medium and collecting said L-amino acid from the culture medium, wherein the L-amino acid-producing microorganism has resistance to a peptide containing. glutamic acid or aspartic acid. There is further provided a microorganism belonging to the genus Brevibacterium or the genus Corynebacterium which is Brevibacterium flavum AJ 12418 (FERM BP-2205), Corynebacterium acetoacidophilum AJ 12419 (FERM BP-2206), Brevibacterium lactofermentum AJ 12420 (FERM BP-2207), Corynebacterium glutamicum AJ 12421 (FERM BP-2208), Brevibacterium flavum AJ 12422 (FERM BP-2209), Brevibacterium lactofermentum AJ 12423 (FERM BP-2210), Corynebacterium glutamicum AJ 12424 (FERM BP-2211), Brevibacterium flavum AJ 12425 (FERM BP-2212), Corynebacterium glutamicum AJ 12426 (FERM BP-2213), Brevibacterium flavum AJ 12427 (FERM BP-2214), Brevibacterium flavum AJ 12428 ((FERM BP-2215). Strains having resistance to at least one of them are referred to as peptide-resistant strains of the present invention. The above peptide containing glutamic acid or aspartic acid is represented by X-Glu, Glu-X, X-Asp or Asp-X, wherein X is preferably The L-amino acid produced by the method of this invention is any amino acid producible by fermentation. Examples are L-glutamic acid, L-glutamine, L-lysine, L-arginine, L-phenylalanine, L-threonin, L-isoleucine, L-histidine, L-proline, L-valine, L-serine, L-ornithine, L-citrulline, L-tyrosine, L-tryptophan and L-leucine, etc. The present invention can apply even to L-amino acids other than those exemplified herein as long as they are L-amino acids which can be produced by fermentation. The microorganism belonging to the genus Brevibacterium or the genus Corynebacterium which can be used in the present invention is a variant having the peptide resistance described above and capable of producing an L-amino acid. For obtaining the mutant of the present invention, the peptide resistance described above may be induced into parent strains shown below; alternatively, the peptide resistance may also be induced into mutants capable of producing L-amino acid. Wild strains which can be parent strains of the mutants of the present invention are bacteria belonging to the genus Brevibacterium or the genus Corynebacterium known as Coryneform L-glutamic acid producing bacteria, and are exemplified by the following bacteria. Brevibacterium flavum ATCC 14067 Brevibacterium lactofermentum ATCC 13869 Brevibacterium divaricatum ATCC 14020 Brevibacterium saccharolyticum ATCC 14066 Corynebacterium glutamicum ATCC 13032 Corynebacterium acetoacidophilum ATCC 13870 For the mutation treatment to produce mutants of the present invention from these parent strains, a conventional method such as a treatment with N-methyl-N′-nitro-N-nitrosoguanidine, etc. can be used. The isolation of the mutant of the present invention from the treated bacteria solution can be effected by screening and collecting strains which can grow in a medium containing the peptide. A concrete mutation method to produce the variant of the present invention and the relationship between the peptide concentration and growth degree of the strain are shown below. Mutation method Bacteria cells of Brevibacterium flavum ATCC 14067, which had been grown in a bouillon agar slant at 30°C for 24 hours, were suspended in M/30 phosphate buffer solution in a cell density of 10⁹/ml. To the cell suspension was added 200 µg/ml of N-methyl-N′-nitro-N-nitrosoguanidine. The mixture was maintained at 0°C for 20 minutes followed by centrifugation. The cells were inoculated on a medium having the composition shown in Table 1 and cultured at 31.5°C for 2 to 10 days. Composition of the Medium Component Content Glucose 1.0 g/dl Urea 0.2 g/dl KH₂PO₄ 0.1 g/dl MgSO₄.7H₂O 0.1 g/dl FeSO₄.7H₂O 0.002 g/dl MnSO₄.7H₂O 0.002 g/dl Biotin 100 µg/l Thiamine hydrochloride 100 µg/l Tyr-Glu 0.5 g/dl Agar 2.0 g/dl (pH 7.0) From 200 Tyr-Glu-resistant strains grown in the agar medium, Brevibacterium flavum AJ 12418 (FERM BP-2205) was obtained as a strain having high productivity of L-glutamine. By procedures similar to the above mutation, strains having more improved productivity of amino acids could be obtained using various amino acid-producing strains as the original strain. Representative examples are shown in Table 2. In addition to the improvement of bacteria capable of producing glutamine, lysine, arginine, glutamic acid, histidine, proline, isoleucine, etc. illustratively shown in Table 2, the procedure was also effective for strains producing phenylalanine, threonine, valine, ornithine, tryptophane, citrulline, leucine, tyrosine and serine. The peptide resistance of the thus obtained variants was compared with that of the parent strains. Onto a liquid medium composed of 0.5 g/dl of glucose, 0.2 g/dl of urea, 0.15 g/dl of ammonium sulfate, 0.3 l g/dl of KH₂PO₄, 0.1 g/dl of K₂HPOO₄, 0.01 g/dl of MgSO₄.7H₂O, 0.1 mg/dl of CaCl₂.2H₂O, 100 µg/l of biotin, 100 µg/l of thiamine hydrochloride, 0.002 g/dl of FeSO₄.7H₂O, 0.002 g/dl of MnSO₄.7H₂O and a peptide in the amount shown in the table and which was adjusted to pH 7.0, there was inoculated a suspension of the cells in sterile water, which had been obtained by culturing in a slant of a natural medium (1 g/dl of peptone, 1 g/dl of yeast extract and 0.5 g/dl of NaCl (pH 7.0) for 24 hours. After culturing for 24 hours, turbidity associated with the growth of bacteria was determined and the growth degree was expressed in terms of relative growth degree (%) (Tables 3 through 8). Media used for culturing such variants are conventional media containing carbon sources, nitrogen sources, inorganic ions, substances satisfying nutrient auxotrophy and, if necessary, other organic trace nutrients including vitamins, etc. As carbon sources, there are preferably used carbohydrates such as glucose, sucrose, etc., organic acids such as acetic acid, etc. As nitrogen sources, there are preferably used aqueous ammonia, ammonia gas, ammonium salts, etc. As inorganic ions, potassium ions, sodium ions, magnesium ions, phosphate ions, and the like are appropriately added to media, depending upon necessity. Incubation is preferably conducted under aerobic conditions. When the incubation is carried out while adjusting the pH of the medium to a range from 4 to 8 at a temperature of from 25 °C to 37 °C, more preferable results can be obtained. Thus, during a cultivation for 1 to 7 days, remarkable amounts of L-amino acid are produced and accumulated in the media. Subsequently using a separation method, such as ion exchange etc., crystals of L-amino acid can be obtained. The present invention is further described with reference to the following examples. Example 1 300 ml aliquots of an aqueous solution medium, comprising 10 % of glucose, 1 % of ammonium sulfate, 0.25 % of potassium primary phosphate, 0.04 % of magnesium sulfate, 0.001 % of ferrous sulfate, 350 µg/l of thiamine hydrochloride, 5 µg/l of biotin and 0.5 ml/dl of Aji-Eki (soybean protein hydrolysate) (registered trademark), pH 7.0, were separately charged in small sized glass jar fermenters. After sterilizing in a conventional manner, various L-glutamine-producing bacteria strains shown in Table 10, which had been previously grown on bouillon slants at 30 °C for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5 °C for 30 hours at 1200 rpm with aeration in an amount of 1/4 volume per minute, while keeping the pH to 6.5 with ammonia gas. The yield of L-glutamine produced and accumulated in the solution after completion of the fermentation based on glucose is shown in Table 10. Strain Property Yield of L-Glutamine Based on Glucose (%) Brevibacterium flavum ATCC 14067 (AJ 11576) wild 29.0 Brevibacterium flavum AJ 12418 Imparted with Tyr-Glu resistance 40.0 Corynebacterium acetoacidophilum ATCC 13870 wild 22.5 Corynebacterium acetoacidophilum AJ 12419 Imparted with Ala-Glu resistance 34.0 After completion of the fermentation using Brevibacterium flavum AJ 12418 the cells were removed by centrifugation from 1 liter of the solution obtained to give a supernatant. From the supernatant, L-glutamine was isolated in a conventional manner using a ion exchange resin to give 19.0 g of L-glutamine as crystals. Example 2 300 ml aliquots of an aqueous solution medium composed of 10 % of glucose, 2 % of ammonium sulfate, 0.1 % of potassium primary phosphate, 0.04 % of magnesium sulfate, 0.001 % of ferrous sulfate, 200 µg/l of thiamine hydrochloride, 500 µg/l of biotin, 5 ml/dl of Aji-Eki (registered trademark), 1 mg/dl of nicotinamide and 0.1 % of DL-alanine, pH 7.0, were separately charged in small sized glass jar fermenters. After sterilizing in a conventional manner, various L-lysine-producing bacteria strains shown in Table 11, which had been previously grown on bouillon slants at 30 °C for 48 hours, were inoculated theron. Then, incubation was carried out at 31.5 °C for 48 hours at 1200 rpm with aeration in a rate of 1/2 volume per minute, while keeping the pH at 7.0 with ammonia gas. The yield of L-lysine produced and accumulated in the solution after completion of the fermentation based on glucose is shown in Table 11. Strain Property Yield of L-Lysine Based on Glucose (%) Brevibacterium lactofermentum AJ 3445(US-A-3 929 571) AEC [(S-(2-aminoethyl)-L-cysteine] resistance 16.0 Brevibacterium lactofermentum AJ 12420 Imparted with Val-Glu resistance 31.0 Corynebacterium glutamicum AJ 3399 (JP-A-48891/1974) Met, AEC resistance 23.0 Corynebacterium glutamicum AJ 12421 Imparted with Ala-Glu resistance 32.0 The cells were removed from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium lactofermentum AJ 12420 by centrifugation to give a supernatant. From the supernatant, L-lysine was isolated in a conventional manner using an ion exchange resin to give 19.2 g of L-lysine as crystals. Example 3 300 ml aliquots of an aqueous solution medium composed of 10 % of glucose, 4 % of ammonium sulfate, 0.1 % of potassium primary phosphate, 0.04 % of magnesium sulfate, 0.001 % of ferrous sulfate, 0.001 % of manganese sulfate, 100 µg/l of thiamine hydrochloride, 100 µg/l of biotin, 5 ml/dl of Aji-Eki (registered trademark) and 0.2 % of yeast extract, pH 7.0, were separately charged in small sized glass jar fermenters. After sterilizing in a conventional manner, various L-arginine-producing bacteria strains shown in Table 12, which had been previously grown on bouillon slants at 30 °C for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5 °C for 48 hours at 1200 rpm with an aeration rate of 1/2 volume per minute, while keeping the pH to 7.0 with ammonia gas. The yield of L-arginine produced and accumulated in the solution after completion of the fermentation based on glucose is shown in Table 12. Strain Property Yield of L-Arginine Based on Glucose (%) Brevibacterium flavum AJ 3401 (US-A-3 878 044) (FERM P-1639) Gua⁻(requirement of guanine), 2-thiazolyl-alanine resistance 25.5 Brevibacterium flavum AJ 12422 (FERM BP-2209 ) Imparted with Tyr-Glu resistance 32.0 The cells were removed by centrifugation from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium flavum AJ 12422 to give a supernatant. From the supernatant, L-arginine was isolated in a conventional manner using an ion exchange resin to give 17.3 g of L-arginine as crystals. Example 4 300 ml aliquots of an aqueous solution medium comprising 10 % of glucose, 1 % of ammonium sulfate, 0.2 % of potassium primary phosphate, 0.1 % of magnesium sulfate, 0.001 % of ferrous sulfate, 0.001 % of manganese sulfate, 500 µg/l of thiamine hydrochloride, 5 µg/l of biotin and 1 ml/dl of Aji-Eki (registered trademark), pH 7.2, were separately charged in small sized glass jar fermenters. After sterilizing in an autoclave, various L-glutamic acid-producing bacteria strains shown in Table 13, which had been previously grown on bouillon slants at 30 °C for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5 °C for 48 hours at 1200 rpm with an aeration rate of 1/2 volume per minute, while keeping the pH at 7.2 with ammonia gas. The yield of L-glutamic acid produced and accumulated in the solution after completion of the fermentation based on glucose is shown in Table 13. Strain Property Yield of L-Glutami acid Based on Glucose (%) Brevibacterium lactofermentum ATCC 13869 wild strain 44.2 Brevibacterium lactofermentum AJ 12423 Imparted with Tyr-Glu resistance 49.5 Corynebacterium glutamicum ATCC 13032 wild strain 40.1 Corynebacterium glutamicum AJ 12424 Imparted with Ala-Glu resistance 46.8 The cells were removed by centrifugation from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium lactofermentum AJ 12423 to give the supernatant. From the supernatant, L-glutamic acid was isolated in a conventional manner using ion exchange resin to give 35.5 g of L-glutamic acid as crystals. Example 5 300 ml aliquots of an aqueous solution medium comprising 10 % of glucose, 0.5 % of ammonium sulfate, 0.15 % of potassium primary phosphate, 0.1 % of magnesium sulfate, 0.001 % of ferrous sulfate, 0.001 % of manganese sulfate, 300 µg/l of thiamine hydrochloride, 350 µg/l of biotin, 5 ml/dl of Aji-Eki (registered trademark) and 0.5 % of ammonium acetate, pH 7.0, were separately charged in small sized glass jar fermenters. After sterilizing in an autoclave, various L-histidine-producing bacteria strains shown in Table 14, which had been previously grown on bouillon slants at 30 °C for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5 °C for 48 hours at 1200 rpm with an aeration rate of 1/2 volume per minute, while keeping the pH at 6.5 with ammonia gas. The yield of L-histidine produced and accumulated in the solution after completion of the fermentation based on glucose is shown in Table 14. Strain Property Yield of L-Histidine Based on Glucose (%) Brevibacterium flavum AJ 3620 (JP-A-70591/1975) 2-AT(2-thiazole alanine), sulfadiazine, cobalamine resistance 7.2 Brevibacterium flavum AJ 12425 Imparted with Trp-Glu resistance 10.0 Corynebacterium glutamicum AJ 12092 (JP-A-36197/1987) 2-AT(2-thiazole alanine) resistance 5.0 Corynebacterium glutamicum AJ 12426 Imparted with Glu-His resistance 9.3 The cells were removed by centrifugation from 1 liter of the solution obtained after completion of the fermentation using Corynebacterium glutamicum AJ 12425 to give a supernatant. From the supernatant, L-histidine was isolated in a conventional manner using ion exchange resin to give 4.7 g of L-histidine as crystals. Example 6 300 ml aliquots of an aqueous solution medium comprising 10 % of glucose, 4 % of ammonium sulfate, 0.1 % of potassium primary phosphate, 0.5 % of magnesium sulfate, 0.001 % of ferrous sulfate, 0.001 % of manganese sulfate, 100 µg/l of thiamine hydrochloride, 350 µg/l of biotin, 1 ml/dl of Aji-Eki (registered trademark) and 35 mg/dl of L-isoleucine, pH 7.0, were separately charged in small sized glass far fermenters. After sterilizing in a conventional manner, various L-proline-producing bacteria strains shown in Table 15, which had been previously grown on bouillon slants at 30 °C for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5 °C for 48 hours at 1200 rpm with an aeration rate of 1/2 volume per minute, while keeping the pH at 7.0 with ammonia gas. After completion of the fermentation, the yield of L-proline produced and accumulated in the solution based on glucose is shown in Table 15. Strain Property Yield of L-Proline Based on Glucose (%) Brevibacterium flavum AJ 11512 (JP-A-2691/1982) Ile⁻, sulfaguanidine resistance 21.0 Brevibacterium flavum AJ 12427 Imparted with Tyr-Glu resistance 29.0 The cells were removed from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium flavum AJ 12 427 by centrifugation to give a supernatant. From the supernatant, L-proline was isolated in a conventional manner using ion exchange resin to give 17.5 g of L-proline as crystals. Example 7 300 ml aliquots of an aqueous solution medium composed of 10 % of glucose, 1 % of ammonium sulfate, 0.1 % of potassium primary phosphate, 0.04 % of magnesium sulfate, 0.001 % of ferrous sulfate, 0.001 % of manganese sulfate, 100 µg/l of thiamine hydrochloride, 100 µg/l of biotin and 2 ml/dl of Aji-Eki (registered trademark), pH 7.0 were separately charged in small sized glass jar fermenters. After sterilizing in a conventional manner, various L-isoleucine-producing bacteria strains shown in Table 16, which had been previously grown on bouillon slants at 30 °C for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5 °C for 48 hours at 1200 rpm with an aeration rate of 1/2 volume per minute, while keeping the pH at 7.3 with ammonia gas. The yield of L-isoleucine produced and accumulated in the solution after completion of the fermentation based on glucose is shown in Table 16. Strain Property Yield of L-Isoleucine Based on Glucose (%) Brevibacterium flavum AJ 3686 (US-A-4 656 135) AHV (α-amino-β-hydroxyvaleric acid) resistance 8.5 Brevibacterium flavum AJ 12428 Imparted with Ala-Asp resistance 13.0 The cells were removed from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium flavum AJ 12428 by centrifugation to give the supernatant. From the supernatant, L-isoleucine was isolated in a conventional manner using a ion exchange resin to give 6.5 g of L-isoleucine as crystals. According to the present invention, various L-amino acids can be obtained in a good yield.

Claims: A process for producing an L-amino acid which comprises culturing in a liquid medium an L-amino acid-producing microorganism belonging to the genus Brevibacterium or the genus Corynebacterium, accumulating said L-amino acid in the culture medium and collecting said L-amino acid from the culture medium, wherein the L-amino acid-producing microorganism has resistance to a peptide containing glutamic acid or aspartic acid. A process for producing an L-amino acid according to claim 1, wherein said peptide containing glutamic acid or aspartic acid is X-Glu, Glu-X, X-Asp or Asp-X; wherein X represents A microorganism belonging to the genus Brevibacterium or the genus Corynebacterium which is Brevibacterium flavum AJ 12418 (FERM BP-2205), Corynebacterium acetoacidophilum AJ 12419 (FERM BP-2206), Brevibacterium lactofermentum AJ 12420 (FERM BP-2207), Corynebacterium glutamicum AJ 12421 (FERM BP-2208), Brevibacterium flavum AJ 12422 (FERM BP-2209), Brevibacterium lactofermentum AJ 12423 (FERM BP-2210), Corynebacterium glutamicum AJ 12424 (FERM BP-2211), Brevibacterium flavum AJ 12425 (FERM BP-2212), Corynebacterium glutamicum AJ 12426 (FERM BP-2213), Brevibacterium flavum AJ 12427 (FERM BP-2214), Brevibacterium flavum AJ 12428 ((FERM BP-2215).

Inventors: SEKI MITSUYOSHI C O AJINOMOTO, TAKEUCHI HIROSHI C O AJINOMOTO, TSUCHIDA TAKAYASU C O AJINOMOT, UCHIBORI HARUO C O AJINOMOTO C, SEKI, MITSUYOSHI, C/O AJINOMOTO CO.INC., TAKEUCHI, HIROSHI, C/O AJINOMOTO CO.INC., TSUCHIDA, TAKAYASU, C/O AJINOMOTO CO.INC., UCHIBORI, HARUO, C/O AJINOMOTO CO.INC.
Applicants: AJINOMOTO KK, AJINOMOTO CO., INC.
Application year: 1990
Main classification: C12P13
IPC codes: C12N1, C12R1, C12P13