Process for producing L-amino acids by fermentation

Abstract

Culturing an L-amino acid producing microorganism belonging to the genus Brevibacterium or Corynebacterium and having a resistance to a peptide containing glutamic acid or aspartic acid gives L-amino acids in high yield.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for producing L-amino acids by fermentation and microorganisms for producing L-amino acids.

2. Discussion of the Background

L-amino acids have been widely used as seasonings, medical drugs, feed additives, chemicals, reagents and the like. L-amino acids, which are produced by fermentation on an industrial scale, include 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. As microorganisms utilized for the production of L-amino acids, there are those belonging to the genus Brevibacterium, the genus Corynebacterium, the genus Bacillus, the genus Escherichia, the genus Seratia, the genus Providencia, and the genus Arthrobacter, etc.

It is important to produce L-amino acids at low costs on an industrial scale by enhancing the fermentation yield and accumulation of L-amino acids. To produce L-amino acids industrially at low costs utilizing these various microorganisms, improved breeding of microorganism has often been used. That is, the L-amino acid production of wild strains per se is extremely poor in many instances, and therefore, methods for imparting nutrient auxotrophy, imparting analog resistance or imparting nutrient auxotrophy in combination with analog resistance, through artificial mutation; or potentiating a gene for amino acid biosynthesis, etc. by genetic recombination, and the like are used to increase the L-amino acid productivity of the wild strain. However, fermentation with conventional strains does not produce L-amino acids in a sufficiently high yield.

Thus, there remains a need for a process which will produce L-amino acids by fermentation in high yield. There also remains a need for microorganisms which produce L-amino acids in high yield.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a process for producing L-amino acids in high yield by fermentation.

It is another object of the present invention to provide microorganisms which produce L-amino acids in high yield by fermentation.

These and other objects, which will become apparent during the course of the following detailed description, have been achieved by the inventors' discovery that culturing strains having a resistance to a peptide containing glutamic acid or aspartic acid of the formula x-glu, glu-x, x-asp or asp-x, in which x represents an amino acid, produces L-amino acids in improved yields.

That is, one embodiment of the present invention is a process for producing an L-amino acid, which comprises culturing an L-amino acid-producing microorganism belonging to the genus Brevibacterium or the genus Corynebacterium and having a resistance to a peptide containing glutamic acid or aspartic acid in a liquid medium, for a sufficient time to accumulate the L-amino acid in the culture, and collecting the L-amino acid from the culture.

In another embodiment, the present invention relates to L-amino acid-producing microorganisms belonging to the genus Brevibacterium or the genus Corynebacterium and having a resistance to a peptide containing glutamic acid or aspartic acid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term L-amino acid as used herein includes L-glutamic acid, L-glutamine, L-lysine, L-arginine, L-phenylalanine, L-threonine, 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 even be applied to L-amino acids other than those exemplified herein so long as they are L-amino acids which can be produced by fermentation.

Examples of the peptide of the present invention include tyr-glu, ala-glu, trp-glu, met-glu, gly-glu, glu-gly, glu-leu, glu-his, gly-asp, ala-asp, asp-gly, etc. Strains having a resistance to at least one of these are referred to as peptide-resistant strains in the present invention.

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.

To obtain the variants of the present invention, the peptide resistance described above may be induced in the parent strains described below; alternatively, the peptide resistance may also be induced in variants capable of producing an L-amino acid.

Wild strains which can be the parent strains of the variants of the present invention include bacteria belonging to the genus Brevibacterium or the genus Corynebacterium such as a Coryneform producing L-glutamic acid, 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 of these parent strains to the variants of the present invention, a conventional method such as a treatment with N-methyl-N'-nitro-N"-nitrosoguanidine, etc. can be used. Isolation of the variants of the present invention from the mutation-treated bacterial solution can be effected by collecting the strains which can grow in a medium containing the peptide.

Media used for culturing such variants are any 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 ammonia water, ammonia gas, ammonium salts, etc. As inorganic ions, potassium ions, sodium ions, magnesium ions, phosphate ions, and the like are appropriately added to the media, as required. 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, preferably 5 to 7.5, at a temperature of from 25.degree. C. to 37.degree. C., preferably 28.degree. to 34.degree. C., better results can be obtained. Thus, when the present strains are cultured for 1 to 7 days, remarkable amounts of L-amino acids are produced and accumulated in the media. Subsequently using a collecting method using an ion exchange resin, etc., yields crystals of L-amino acid.

Other features of the invention will become apparent in the course of the following descriptions of exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof.

EXAMPLES

An example for the mutation of the parent strains to the variants of the present invention and the relationship between the peptide concentration and degree of growth of the present strains are shown below.

Method for Mutation.

Bacterial cells of Brevibacterium flavum ATCC 14067, which has been grown in a bouillon agar slant at 30.degree. C. for 24 hours, were suspended in M/30 phosphate buffer solution at a cell density of 10.sup.9 / ml. To the cell suspension was added 200 .mu.g/ml of N-methyl-N'-nitro-N"-nitrosoguanidine. The mixture was maintained at 0.degree. 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.degree. C. for 2 to 10 days.

TABLE 1______________________________________Composition of MediumComponent Content______________________________________Glucose 1.0 g/dlUrea 0.2 g/dlKH.sub.2 PO.sub.4 0.1 g/dlMgSO.sub.4.7H.sub.2 O 0.1 g/dlFeSO.sub.4.7H.sub.2 O 0.002 g/dlMnSO.sub.4.7H.sub.2 O 0.002 g/dlBiotin 100 .mu.g/lThiamine hydrochloride 100 .mu.g/ltyr--glu 0.5 g/dlAgar 2.0 g/dl (pH 7.0)______________________________________

From 20 tyr-glu-resistant strains grown in the agar medium, Brevibacterium flavum AJ 12418 (FERM BP-2205) was obtained and characterized as having high productivity of L-glutamine.

By procedures similar to the mutation above, 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 present process is also effective for phenylalanine, threonine, valine, ornithine, tryptophan, 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 1 g/dl of KH.sub.2 PO.sub.4, 0.1 g/dl of K.sub.2 HPO.sub.4, 0.01 g/dl of MgSO.sub.4 .multidot.7H.sub.2 O, 0.1 mg/dl of CaCl.sub.2 .multidot.2H.sub.2 O, 100 .mu.g/l of biotin, 100 .mu.g/l of thiamine hydrochloride, 0.002 g/dl of FeSO.sub.4 .multidot.7H.sub.2 O, 0.002 g/dl of MnSO.sub.4 .multidot.7H.sub.2 O and the peptide in the amounts shown in Tables 3-9 and adjusted to a pH of 7.0, there were inoculated suspensions of each of the cells in sterile water, which were obtained by culturing in natural medium (1 g/dl of peptone, 1 g/dl of yeast extract and 0.5 g/dl of NaCl, pH 7.0) in slants for 24 hours. After culturing for 24 hours, the turbidity associated with the growth of bacteria was determined and the degree of growth is expressed in terms of relative growth degree (%) in Tables 3 through 9.

TABLE 2______________________________________ Strain Having Peptide Improved YieldAmino Acid Parent Strain Resistance Based On Glucose______________________________________Glutamine Brevibacterium tyr--glu Brevibacterium flavum flavum AJ 12418 ATCC 14067 (FERM BP-2205) Corynebacterium ala--glu Corynebacterium acetoacidophilum acetoacidophilum ATCC 13870 AJ 12419 (FERM BP-2206)Lysine Brevibacterium val--glu Brevibacterium lactofermentum lactofermentum AJ 3445 AJ 12420 (FERM P-1944) (FERM BP-2207) Corynebacterium ala--glu Corynebacterium glutamicum glutamicum AJ 3399 AJ 12421 (FERM P-1615) (FERM BP-2208)Arginine Brevibacterium tyr--glu Brevibacterium flavum flavum AJ 3401 AJ 12422 (FERM P-1642) (FERM BP-2209)Glutamic acid Brevibacterium tyr--glu Brevibacterium lactofermentum lactofermentum ATCC 13869 AJ 12423 (FERM BP-2210) Corynebacterium ala--glu Corynebacterium glutamicum glutamicum ATCC 13032 AJ 12424 (FERM BP-2211)Histidine Brevibacterium trp--glu Brevibacterium flavum flavum AJ 3620 AJ 12425 (FERM P-2316) (FERM BP-2212) Corynebacterium glu--his Corynebacterium glutamicum glutamicum AJ 12092 AJ 12426 (FERM P-7273) (FERM BP-2213)Proline Brevibacterium tyr--glu Brevibacterium flavum flavum AJ 11512 AJ 12427 (FERM P-5332) (FERM BP-2214)Isoleucine Brevibacterium ala--asp Brevibacterium flavum flavum AJ 3686 AJ 12428 (FERM P-2433) (FERM BP-2215)______________________________________ TABLE 3______________________________________ PeptideGln tyr--glu (%) ala--glu (%)Strain 0 0.05 0.1 0.3 0 0.05 0.1 0.3______________________________________Brevibacterium 100 85 45 0flavumATCC 14067Brevibacterium 100 100 100 72flavumAJ 12418Corynebacterium 100 70 30 0acetoacidophilumATCC 13870Corynebacterium 100 100 100 65acetoacidophilumAJ 12419______________________________________ TABLE 4______________________________________ PeptideLys* val--glu (%) ala--glu (%)Strain 0 0.05 0.1 0.3 0 0.05 0.1 0.3______________________________________Brevibacterium 100 95 80 10lactofermentumAJ 3445Brevibacterium 100 100 100 90lactofermentumAJ 12420Corynebacterium 100 50 10 0glutamicumAJ 3399(FERM P-1615)Corynebacterium 100 100 100 100glutamicumAJ 2421______________________________________ *When Corynebacterium glutamicum was used, 15 mg/dl of methionine was supplemented. TABLE 5______________________________________ PeptideArg* tyr--glu (%)Strain 0 0.05 0.1 0.3______________________________________Brevibacterium flavum 100 100 30 0AJ 3401Brevibacterium flavum 100 100 100 95AJ 12422______________________________________ *Liquid medium was supplemented with 5 mg/dl of guanine. TABLE 6______________________________________ PeptideGlu tyr--glu (%) ala--glu (%)Strain 0 0.05 0.1 0.3 0 0.05 0.1 0.3______________________________________Brevibacterium 100 78 142 0lactofermentumATCC 13869Brevibacterium 100 100 95 80lactofermentumAJ 12423Corynebacterium 100 75 40 0glutamicumATCC 13032Corynebacterium 100 100 100 94glutamicumAJ 12424______________________________________ TABLE 7______________________________________ PeptideHis trp--glu (%) glu--his (%)Strain 0 0.05 0.1 0.3 0 0.05 0.1 0.3______________________________________Brevibacterium 100 100 75 36flavumAJ 3620Brevibacterium 100 100 100 100flavumAJ 12425Corynebacterium 100 100 96 55glutamicumAJ 12092Corynebacterium 100 100 100 98glutamicumAJ 12426______________________________________ TABLE 8______________________________________ PeptidePro* tyr--glu (%)Strain 0 0.05 0.1 0.3______________________________________Brevibacterium flavum 100 90 30 0AJ 11512Brevibacterium flavum 100 100 95 60AJ 12427______________________________________ *Liquid medium was supplemented with 15 mg/dl of isoleucine. TABLE 9______________________________________ PeptideIle ala--asp (%)Strain 0 0.05 0.1 0.3______________________________________Brevibacterium flavum 100 70 20 0AJ 3686Brevibacterium flavum 100 100 98 70AJ 12428______________________________________ Example 1.

An aqueous solution medium having a composition of 10% of glucose, 1% of ammonium sulfate, 0.25% of potassium primary phosphate (KH.sub.2 PO.sub.4), 0.04% of magnesium sulfate, 0.001% of ferrous sulfate, 350 .mu.g/l of thiamine hydrochloride, 5 .mu.g/l of biotin and 0.5 ml/dl of Aji-Eki.RTM. which is a soybean protein hydrolysate which accelerates the growth of L-amino acid-producing microorganisms and shortens the required culture time, at pH 7.0, was charged in an amount of 300 ml into separate small sized glass jar fermenters. After sterilizing in a conventional manner, the various L-glutamine-producing bacterial strains shown in Table 10, which had been previously grown in bouillon slants at 30.degree. C. for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5.degree. C. for 30 hours at 1200 rpm at an aeration rate of 1/4 volume per minute, while keeping the pH at 6.5 by the addition of ammonia gas. After completion of the fermentation, the yield of L-glutamine produced and accumulated in the solution based on glucose was determined and is shown in Table 10.

TABLE 10______________________________________ Yield of L-Glutamine Based onStrain Property Glucose (%)______________________________________Brevibacterium Wild 29.0flavum AJ 14067Brevibacterium Imparted with 40.0flavum AJ 12418 tyr--glu resistanceCorynebacterium Wild 22.5acetoacidophilumATCC 13870Corynebacterium Imparted with 34.0acetoacidophilum ala--gluAJ 12419 resistance______________________________________

The cells were removed from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium flavum AJ 12418 by centrifugation to give a supernatant. From the supernatant, L-glutamine was isolated in a conventional manner using an ion exchange resin to give 19.0 g of L-glutimine as crystals.

Example 2.

An aqueous solution medium having a composition 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 .mu.g/l of thiamine hydrochloride, 500 .mu.g/l of biotin, 5 ml/dl of Aji-Eki.RTM., 1 mg/dl of nicotinamide and 0.1% of DL-alanine, at pH 7.0, was charged in an amount of 300 ml into separate small sized glass jar fermenters. After sterilizing in a conventional manner, the various L-lysine-producing bacterial strains shown in Table 11, which had been previously grown in bouillon slants at 30.degree. C. for 48 hours, were inoculated thereon. Then, incubation was carried out at 31.5.degree. C. for 48 hours at 1200 rpm at an aeration rate of 1/2 volume per minute, while keeping the pH at 7.0 by the addition of ammonia gas. After completion of the fermentation, the yield of L-lysine produced and accumulated in the solution based on glucose was determined and is shown in Table 11.

TABLE 11______________________________________ Yield of L-Lysine Based onStrain Property* Glucose (%)______________________________________Brevibacterium AEC resistance 16.0lactofermentumAJ 3445Brevibacterium Imparted with 31.0lactofermentum val--glu resistanceAJ 12420Corynebacterium met, AEC resistance 23.0glutamicumAJ 3399Corynebacterium Imparted with 32.0glutamicum ala--glu resistanceAJ 12421______________________________________ *AEC = S(aminoethyl)-cystein.

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.

An aqueous solution medium having a composition 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 .mu.g/l of thiamine hydrochloride, 100 .mu.g/l of biotin, 5 ml/dl of Aji-Eki.RTM. and 0.2% of yeast extract, at pH 7.0, was charged in an amount of 300 ml into separate small sized glass jar fermenters. After sterilizing in a conventional manner, the various L-arginine-producing bacterial strains shown in Table 12, which had been previously grown in bouillon slants at 30.degree. C. for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5.degree. C. for 48 hours at 1200 rpm at an aeration rate of 1/2 volume per minute, while keeping the pH at 7.0 by the addition of ammonia gas. After completion of the fermentation, the yield of L-arginine produced and accumulated in the solution based on glucose was determined and is shown in Table 12.

TABLE 12______________________________________ Yield of L-Arginine Based onStrain Property Glucose (%)______________________________________Brevibacterium gua.sup.-, 2-thiazolyl- 25.5flavum AJ 3401 alanine resistance(FERM P-1642)Brevibacterium Imparted with 32.0flavum AJ 12422 tyr--glu(FERM BP-2209) resistance______________________________________

The cells were removed from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium flavum AJ 12422 by centrifugation 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.

An aqueous solution medium having a composition of 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 .mu.g/l of thiamine hydrochloride, 5 .mu.g/l of biotin and 1 ml/dl of Aji-Eki.RTM., at pH 7.2, was charged in an amount of 300 ml into separate small sized glass jar fermenters. After sterilizing in an autoclave, the various L-glutamic acid-producing bacterial strains shown in Table 13, which had been previously grown in bouillon slants at 30.degree. C. for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5.degree. C. for 48 hours at 1200 rpm at an aeration rate of 1/2 volume per minute, while keeping the pH at 7.2 by the addition of ammonia gas. After completion of the fermentation, the yield of L-glutamic acid produced and accumulated in the solution based on glucose was determined and is shown in Table 13.

TABLE 13______________________________________ Yield of L-glutamic Acid Based onStrain Property Glucose (%)______________________________________Brevibacterium Wild 44.2lactofermentumATCC 13869Brevibacterium Imparted with 49.5lactofermentum tyr--gluAJ 12423 resistanceCorynebacterium Wild 40.1glutamicumATCC 13032Corynebacterium Imparted with 46.8glutamicum ala--gluAJ 12424 resistance______________________________________

The cells were removed from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium lactofermentum AJ 12423 by centrifugation to give a supernatant. From the supernatant, L-glutamic acid was isolated in a conventional manner using an ion exchange resin to give 35.5 g of L-glutamic acid as crystals.

Example 5.

An aqueous solution medium having a composition of 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 .mu.g/l of thiamine hydrochloride, 350 .mu.g/l of biotin, 5 ml/dl of Aji-Eki.RTM. and 0.5% of ammonium acetate, at pH 7.0, was charged in an amount of 300 ml into separate small sized glass jar fermenters. After sterilizing in an autoclave, the various L-histidine-producing bacterial strains shown in Table 14, which had been previously grown in bouillon slants at 30.degree. C. for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5.degree. C. for 48 hours at 1200 rpm at an aeration rate of 1/2 volume per minute, while keeping the pH at 6.5 by the addition of ammonia gas. After completion of the fermentation, the yield of L-histidine produced and accumulated in the solution based on glucose was determined and is shown in Table 14.

TABLE 14______________________________________ Yield of L-Histidine Based onStrain Property Glucose (%)______________________________________Brevibacterium 2-AT, sulfadiazine, 7.2flavum AJ 3620 cobalamine resistanceBrevibacterium Imparted with 10.0flavum AJ 12425 trp--glu resistanceCorynebacterium 2-AT resistance 5.0glutamicumAJ 12092Corynebacterium Imparted with 9.3glutamicum glu--his resistanceAJ 12426______________________________________

The cells were removed from 1 liter of the solution obtained after completion of the fermentation using Corynebacterium glutamicum AJ 12426 by centrifugation to give a supernatant. From the supernatant, L-histidine was isolated in a conventional manner using an ion exchange resin to give 4.7 g of L-histidine as crystals.

Example 6.

An aqueous solution medium having a composition of 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 .mu.g/l of thiamine hydrochloride, 350 .mu.g/l of biotin, 1 ml/dl of Aji-Eki.RTM. and 35 mg/dl of L-isoleucine, at pH 7.0, was charged in an amount of 300 ml into separate small sized glass jar fermenters. After sterilizing in a conventional manner, the various L-proline-producing bacterial strains shown in Table 15, which had been previously grown in bouillon slants at 30.degree. C. for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5.degree. C. for 48 hours at 1200 rpm at an aeration rate of 1/2 volume per minute, while keeping the pH at 7.0 by the addition of ammonia gas. After completion of the fermentation, the yield of L-proline produced and accumulated in the solution based on glucose was determined and is shown in Table 15.

TABLE 15______________________________________ Yield of L-Proline Based onStrain Property Glucose (%)______________________________________Brevibacterium ile.sup.-, sulfaguanidine 21.0flavum AJ 11512 resistanceBrevibacterium Imparted with 29.0flavum AJ 12427 tyr--glu resistance______________________________________

The cells were removed from 1 liter of the solution obtained after completion of the fermentation using Brevibacterium flavum AJ 12427 by centrifugation to give a supernatant. From the supernatant, L-proline was isolated in a conventional manner using an ion exchange resin to give 17.5 g of L-proline as crystals.

Example 7.

An aqueous solution medium having a composition 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 .mu.g/l of thiamine hydrochloride, 100 .mu.g/l of biotin and 2 ml/dl of Aji-Eki.RTM., at pH 7.0, was charged in an amount of 300 ml into separate small sized glass jar fermenters. After sterilizing in a conventional manner, the various L-isoleucine-producing bacterial strains shown in Table 16, which had been previously grown in bouillon slants at 30.degree. C. for 24 hours, were inoculated thereon. Then, incubation was carried out at 31.5.degree. C. for 48 hours at 1200 rpm at an aeration rate of 1/2 volume per minute, while keeping the pH at 7.3 by the addition of ammonia gas. After completion of the fermentation, the yield of L-isoleucine produced and accumulated in the solution based on glucose was determined and is shown in Table 16.

TABLE 16______________________________________ Yield of L-Isoleucine Based onStrain Property* Glucose (%)______________________________________Brevibacterium AHV resistance 8.5flavum AJ 3686Brevibacterium Imparted with 13.0flavum AJ 12428 ala--asp resistance______________________________________ *AHV = amino-hydroxy-valeric acid.

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 a supernatant. From the supernatant, L-isoleucine was isolated in a conventional manner using an ion exchange resin to give 6.5 g of L-isoleucine as crystals.

Thus, as shown by the results given above, according to the present invention, various L-amino acids can be obtained in a good yield.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A process for producing an L-amino acid, which comprises culturing a mutant L-amino acid producing microorganism belonging to a genus selected from Brevibacterium and Corynebacterium which is resistant to a dipeptide at a concentration of 0.3% in a liquid medium for a time sufficient to produce said L-amino acid; and

recovering said L-amino acid produced wherein

1) L-glutamine is produced from a tyr-glu resistant mutant of Brevibacterium flavum ATCC 14067 or an ala-glu resistant mutant of Corynebacterium acetoacidophilum ATCC 13870;

2) L-lysine is produced from a val-glu resistant mutant of Brevibacterium lactofermentum ATCC 13869 or an ala-glu resistant mutant of Corynebacterium glutamicum ATCC 13032;

3) L-arginine is produced from a tyr-glu resistant mutant of Brevibacterium flavum ATCC 14067;

4) L-glutamic acid is produced from a tyr-glu resistant mutant of Brevibacterium lactofermentum ATCC 13869 or an ala-glu resistant mutant of Corynebacterium glutamicum ATCC 13032;

5) L-histidine is produced from a trp-glu resistant mutant of Brevibacterium flavum ATCC 14067 or a glu-his resistant mutant of Corynebacterium glutamicum ATCC 13032;

6) L-proline is produced by a tyr-glu resistant mutant of Brevibacterium flavum ATCC 14067; and

7) L-isoleucine is produced from an ala-asp resistant mutant of Brevibacterium flavum ATCC 14067, and

wherein said mutant microorganism is obtained by mutation of a parent strain, and said microorganism produces the L-amino acid in an amount greater than the amount produced by the parent strain.

2. The process of claim 1, wherein said L-amino acid producing microorganism is obtained by contacting the parent strain with N-methyl-N'-nitro-N-nitrosoguanidine.

3. A process for producing an L-amino acid, which comprises culturing a mutant L-amino acid producing microorganism belonging to the genus Brevibacterium which is resistant to a dipeptide at a concentration of 0.3% in a liquid medium for a time sufficient to produce said L-amino acid; and

recovering said L-amino acid produced, wherein the amino acid is L-glutamine, the mutant microorganism is a tyr-glu resistant mutant of Brevibacterium flavum ATCC 14067, the mutant microorganism is obtained by mutation of a parent strain, and the mutant microorganism produces the L-amino acid in an amount greater than the amount produced by the parent strain.

4. The process of claim 3, wherein said L-amino acid producing microorganism is obtained by contacting the parent strain with N-methyl-N'-nitro-N-nitrosoguanidine.