PROCESS FOR PRODUCING L-ISOLEUCINE BY FERMENTATION

Abstract: A process for producing L-isoleucine, which comprises culturing a microorganism belonging to the genus Brevibac­ terium or the genus Corynebacteriurn which has a methylly­ sine resistance or α-ketomalonic acid resistance and which is capable of producing L-isoleucine in a liquid medium, and obtaining the accumulated L-isoleucine from said medium.

Description: BACKGROUND OF THE INVENTION Field of the Invention L-Isoleucine is an important component for parenteral and enteral nutrition and complex amino acid preparations. The present invention involves an improvement to a process for producing L-isoleucine by fermentation. Description of the Prior Art It is known that in order to impart L-isoleucine productivity to microorganisms belonging to the genus Brevibacterium or the genus Corynebacterium , it may be sufficient for the microorganisms to have resistance to α-amino-β-hydroxyvaleric acid (hereafter simply referred to as AHV), etc. (Published Examined Japanese Patent Application 20316/73, U.S. Patent 3,767,529). It is also known that the productivity of L-isoleucine may be improved by imparting to the microorganisms, in addition to the above-mentioned chemical resistance, O-methylthreonine resistance, β-hydroxyleucine resistance or trichloroalanine resistance, and by imparting thereto auxotrophy for purine type substances or lysine, etc. (Published Examined Japanese Patent Applications 21077/76, 4629/77, 29998/81 and 3035/81, and Published Unexamined Japanese Patent Application 2687/82). From the viewpoint of industrial production, it is of importance to improve the fermentation yield or accumulation of L-isoleucine. SUMMARY OF THE INVENTION The present invention has been made to solve the foregoing problem. As a result of investigations on α hitherto known microorganism belonging to the genus Brevibacterium or the genus Corynebacterium and having L-isoleucine productivity with an attempt to improve these microorganisms and to find strains providing improved fermentation yields, it has been found that among those strains having imparted thereto resistance to methyllysine (hereafter simply referred to as ML) or a α-ketomalonic acid (hereafter simply referred to as α-KM), are found strains having L-isoleucine productivity in a higher yield than with known L-isoleucine-producing bacteria. That is, the present invention relates to a process for producing L-isoleucine, which comprises culturing a microorganism belonging to a species selected from the group consisting of Brevibacterium flavum or Corynebacterium glutamicum , having ML resistance or α-KM resistance and capable of producing L-isoleucine in a liquid medium and obtaining the accumulated L-isoleucine from said medium. DESCRIPTION OF PREFERRED EMBODIMENTS Examples of ML's of the present invention include methyllysines such γ-ML, β-ML, δ-ML, ε-ML, etc. Bacteria having resistance thereto are effective for improving L-isoleucine productivity. The microorganisms used in the present invention are mutants which belong to the genus Brevibacterium or the genus Corynebacterium , possess ML resistance or α-KM resistance and are capable of producing L-isoleucine. To obtain the mutants of the present invention, wild strains described below may first have imparted thereto L-isoleucine productivity and then have imparted thereto ML resistance or α-KM resistance; alternatively, ML resistance or α-KM resistance may be first imparted to the wild strains followed by having L-isoleucine productivity imparted thereto. Examples of the wild strains that are parent strains of the mutants are known as Coryneform L-glutamic acid-producing bacteria belonging to the species Brevibacterium flavum or the species Corynebacterium glutamicum , examples of which are shown below. Brevibacterium flavum ATCC 14067 Corynebacterium glutamicum ATCC 13032 To obtain the mutants of the present invention from these parent strains, a conventional process for mutation and induction, such as by treating the parent strains with N-methyl-N'-nitro-N-nitrosoguanidine, etc. is applicable. Separation of the mutants of the present invention from the bacteria solution obtained by mutation treatment may be carried out by collecting strains that grow on a medium containing ML or α-KM. The relationship between a specific process for mutation of the mutants of the present invention and the degree of growth of strains in the presence of γ-ML or α-KM is shown below. Process for mutation Brevibacterium flavum AJ 3686 FERM-P 2433, FERM-BP 755 (AHV resistant strain induced from ATCC 14067) and Corynebacterium glutamicum AJ 12150 FERM-P 7674, FERM-BP 756 (AHV resistant strain induced from ATCC 13032) were grown on bouillon agar slants at 30°C for 24 hours. The thus grown cells were suspended in M/30 phosphate buffer to a cell concentration of 10⁸ to 10⁹/ml. To the cell suspensions, 500 µg/ml of N-methyl-N'-nitro-N-nitrosoguanidine was added and the mixture was maintained at 30°C for 20 minutes. Then, the system was centrifuged to collect the bacteria. After the bacteria were thoroughly washed with M/30 phosphate buffer, the bacteria were inoculated on medium having the composition shown in Table 1, and were cultured at 31.5°C for 2 to 10 days. Composition of 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 γ-ML or α-KM 0.2 g/dl Agar 2.0 g/dl From the bacteria that grew in agar medium containing γ-ML, Brevibacterium flavum AJ 12149 FERM-P 7677, FERM-BP 759 (AHV resistance, γ-methyllysine resistance) and Corynebacterium glutamicum AJ 121251 FERM-P 7675, FERM-BP 757 (AHV resistance, γ-methyllysine resistance) were selected as having high productivity of L-isoleucine. Further, from the strains that grew in agar medium containing α-KM, Brevibacterium flavum AJ 12152, FERM-P 7678, FERM-BP 760 (AHV resistance, α-KM resistance) and Corynebacterium glutamicum AJ 12153, FERM-P 7676, FERM-BP 758 (AHV resistance, α-KM resistance) were obtained as strains having high productivity of L-isoleucine. The strain FERM-P was originally deposited on January 8, 1974 and the strains FERM-P 7674, FERM-P 7675, FERM-P 7676, FERM-P 7677 and FERM-P 7678 were deposited on June 22, 1984 at the Fermentation Research Institute, Agency of Industrial Sciences and Technology, Ministry of International Trade and Industry (FRI), 1-3, Migashi 1-chome, Yatabe-machi, Tsukuba-gun, Ibaragi-ken 305, Japan. These deposited strains were then converted into deposits under the Budapest Treaty on April 10, 1985, and were accorded the corresponding FERM-BP numbers. The degree of γ-ML resistance or the degree of α-KM resistance of the thus obtained variants was compared with that of the parent strains. The bacteria obtained by culturing in a natural medium (1 g/dl peptone, 1 g/dl yeast extract, 0.5 g/dl NaCl, pH 7.0) slant for 24 hours were suspended in sterilized water. The suspension was inoculated on a medium containing 0.5 g/dl glucose, 0.2 g/dl urea, 0.15 g/dl ammonium sulfate, 0.3 g/dl KH₂PO₄, 0.1 g/dl K₂HPO₄, 0.01 g/dl MgSO₄·7H₂O, 0.1 mg/dl CaCl₂·2H₂O, 100 µg/l biotin, 100 µg/l thiamine hydrochloride, 0.002 g/dl FeSO₄·7H₂O, and γ-ML or α-ML in the amount shown in Table 2, the pH of which was adjusted to 7.0. After culturing for 24 hours, the degree of growth was determined by turbidity. In most cases, the yield can be further improved by additionally imparting to the aforesaid mutants a property that is already known to improve the productivity of L-isoleucine, such as O-methylthreonine resistance, β-hydroxyisoleucine resistance or trichloroalanine resistance. The medium used for culturing such mutants is a conventional one containing carbon sources, nitrogen sources, inorganic ions, substances for satisfying the above-mentioned auxotrophy, and if necessary, vitamins and other organic trace nutrients. As carbon sources, carbohydrates such as glucose, sucrose, etc., organic acids such as acetic acid, etc. are preferred and as nitrogen sources, ammonia water, ammonia gas, ammonium salts, etc. are preferred. If necessary, potassium ions, sodium ions, magnesium ions, phosphate ions and others are appropriately added to the medium as inorganic ions. It is preferred that the cultivation be conducted under aerobic conditions. When the cultivation is carried out while adjusting the pH of the medium to 4 to 8 and the temperature to 25 to 37°C during the cultivation, more preferred results are obtained. Cultivation for 1 to 7 days under these conditions produces and accumulates marked amounts of L-isoleucine. L-isoleucine may be collected from the culture solution in a conventional manner such as using ion exchange resins, etc. The invention now being generally described, the same will be better understood by reference to the following examples which are included herein for purposes of illustration only and are not intended to be limiting of the invention or any embodiment thereof, unless specified. EXAMPLES A medium containing 10 g/dl glucose, 7 g/dl (NH₄)₂SO₄, 0.1 g/dl KH₂PO₄, 0.04 g/dl MgSO₄·7H₂O, 1 mg/dl FeSO₄·7H₂O, 1 mg/dl MnSO₄·4H₂O, CaCl₂·2H₂O, 100 µg/l thiamine hydrochloride, 100 µg/l biotin, 60 mg/dl (as the total nitrogen) soybean protein acid hydrolysate solution and 5 g/dl calcium carbonate (separately sterilized) was adjusted to a pH of 7.0, 20 ml of which was charged in a 500 ml volume-flask followed by thermal sterilization. A platinum loop of the strain shown in Table 1 was inoculated on the medium. While being maintained at 31°C, the system was shaken for 4 days. In the culture solution of each strain, L-isoleucine was accumulated in the amount shown in Table 3. AJ 12149 was cultured in a similar manner to obtain 1 liter of the culture solution. From the culture solution, the bacteria were removed by centrifugation and the supernatant was passed through a strongly acidic ion exchange resin "Diaion" SK-1B® (NH + / 4 type). After rinsing the resin with water, elution was conducted with ammonia water. Then the eluate was concentrated and from the concentrate, 17.0 g of crude L-isoleucine crystals were obtained.

Claims: A process for producing L-isoleucine by fermentation which comprises culturing a microorganism belonging to a species selected from the group consisting of Brevibacterium flavum and Corynebacterium , glutamicum , capable of producing L-isoleucine in a liquid medium, and collecting accumulated L-isoleucine from said medium, characterized in that the process is carried out by using a microorganism belonging to the species Brevibacterium flavum or Corynebacterium glutamicum lysine resistance or α-ketomalonic acid resistance. The process of Claim 1, wherein said culturing is carried out while adjusting the pH of said medium to from 4 to 8 at a temperature of from about 25 to 37°C for from 1 to 7 days. The process of Claim 1, wherein said microorganism having methyllysine resistance or α-ketomelonic acid resistance is produced by mutation of a parent strain selected from the group consisting of Brevibacterium flavum ATCC 14067 or Corynebacterium glutamicum ATCC 13032. The process of Claim 1, wherein said microorganism is resistant to a methyllysine which is γ-ML, β-ML, δ-ML, or ε-ML. The process of Claim 1, wherein said microorganism which is resistant to a methyllysine or α-ketomalonic acid is produced by treating a parent microorganism which is not resistant to a methyllysine or α-ketomalonic acid with N-methyl-N'-nitro-N-nitrosoguanidine. The process of Claim 1, wherein said microorganism is Brevibacterium flavum AJ 12149, FERM-P 7677, FERM-BP 759. The process of Claim 1, wherein said microorganism is Corynebacterium glutamicum AJ 12151, FERM-P 7675, FERM-BP 757. The process of Claim 1, wherein said microorganism is Brevibacterium flavum AJ 12152, FERM-P 7678, FERM-BP 760. The process of Claim 1, wherein said microorganism is Corynebacterium glutamicum AJ 12153, FERM-P 7676, FERM-BP 758.

Inventors: OTSUKA, NOBORU, SONODA, HIROSHI, TSUCHIDA, TAKAYASU
Applicants: AJINOMOTO CO., INC.
Application year: 1985
Main classification: C12P13
IPC codes: C12P13