Method for producing L-glutamic acid by fermentation

Abstract

Mutants of the genus Brevibacterium or Coryne-bacterium resistant to a respiratory inhibitor or ADP phosphorylation inhibitor produced L-glutamic acid in a high yield, when they are cultured aerobically in an aqueous culture medium.

Description

FIELD OF THE INVENTION

This invention relates to a method for producing L-glutamic acid by fermentation.

DESCRIPTION OF THE PRIOR ART

L-Glutamic acid has been produced by fermentation using a microorganism of the genus Brevibacterium or Corynebacterium. Various attempts have been done to improve the productivity of the known glutamic acid producing strains by artificial mutation techniques. Examples of such artificial mutants are mutants of Brevibacterium resistant to S-2-amino-ethyl-cysteine (Japanese Published Unexamined Patent Application No. 126877/1975, mutants of Brevibacterium and Corynebacterium resistant to fluorocitric acid, ketomalonic acid, .alpha.-amino-.beta.-hydroxyvaleric acid, DL-threoninehydroxamate, 2-amino-3-phosphopropionic acid or 5-aminolevulinic acid, (Japanese Published Unexamined Patent Application No. 89045/1979), mutants of Brevibacterium and Corynebacterium sensitive to lysozyme (Japanese Published Unexamined Patent Application No. 122794/1979), mutant of Brevibacterium and Corynebacterium having reduced activity of pyruvic acid dehydrogenase (Japanese Published Unexamined Patent Application No. 21762/1980), mutants resistant to glutamic acid or glutamic acid-analogue of Brevibacterium or Corynebacterium (Japnese Published Unexamined Patent Application No. 21763/1980), and mutants of Brevibacteirum resistant to 2,6-pyridine-dicarboxylic acid (Japanese Published Unexamined Patent Application No. 21764/1980).

SUMMARY OF THE INVENTION

It is now found that mutants of the genus Brevibacterium or Corynebacterium resistant to a respiratory inhibitor or ADP phosphorylation inhibitor produce L-glutamic acid in an improved yield.

Now, it is provided a method for producing L-glutamic acid which comprises culturing in an aqueous culture medium a mutant of the genus Brevibacterium or Corynebacterium which is resistant to a resipiratory inhibitor or ADP phosphorylation inhibitor, and recovering L-glutamic acid accumulated in the resulted culture liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The respiratory inhibitors of this invention inhibit, as is well known, respiration of the microorganisms, and then their growth. The examples of the respiratory inhibitors are malonic acid, potassium cyanid, sodium azide, sodium arsenite.

The ADP phosphorylation inhibitors inhibit the phosphorylation of ADP (adenosine diphosphate) of microorganisms, and production of ATP (adenosine triphosphate), and then their growth. ADP phosphorylation inhibitors include uncouplers, which inhibit coupling reaction in respiratory chain, such as 2,4-dinitrophenol, hydroxylamine and arsenic, and energy trasfer inhibitors, which inhibit energy transferring reaction such as guanidine.

Specimens of the mutants of this invention are:

Brevibacterium lactofermentum AJ 11426 (FERM-P 5123, NRRL B-12211), (malonic acid) Brevibacterium flavum AJ 11427 (FERM-P 5124, NRRL B-12203), (malonic acid) Corynebacterium glutamicum AJ 11441 (FERM-P 5138, NRRL B-12210), (malonic acid) Brevibacterium lactofermentum AJ 11428 (FERM-P 5125, NRRL B-12212), (sodium azide) Brevibacterium lactofermentum AJ 11429 (FERM-P 5126, NRRL B-12213), (potassium cyanid) Brevibaterium flavum AJ 11430 (FERM-P 5127, NRRL B-12204), (potassium cyanid) Corynebacterium glutamicum AJ 11431 (FERM-P 5128, NRRL B-12207), (potassium cyanid) Brevibacterium lactofermentum AJ 11432 (FERM-P 5129, NRRL B-12214), (sodium arsenite) Brevibacterium lactofermentum AJ 11433 (FERM-P 5130, NRRL B-12215), (2,4-dinitrophenol) Brevibacterium flavum AJ 11434 (FERM-P 5131, NRRL B-12205), (2,4-dinitrophenol) Brevibacterium lactofermentum AJ 11435 (FERM-P 5132, NRRL B-12216), (hydroxylamine hydrochloride) Corynebacterium glutamicum AJ 11436 (FERM-P 5133, NRRL B-12208), (hydroxylamine hydrochloride) Brevibacterium lactofermentum AJ 11437 (FERM-P 5134, NRRL B-12217), (arsenic) Brevibacterium lactofermentum AJ 11438 (FERM-P 5135, NRRL B-12218), (guanidine) Brevibacterium flavum AJ 11439 (FERM-P 5136, NRRL B-12206), (guanidine) Corynebacterium glutamicum AJ 11440 (FERM-P 5137, NRRL B-12209), (guanidine)

The mutants of Brevibacterium flavum, Brevibacterium lactofermentum and Corynebacterium glutamicum were derived from the parent strains, Brevibacterium flavum ATCC 14067, Brevibacterium lactofermentum ATCC 13869 and Corynebacterium glutamicum ATCC 13032, respectively. Brevibacterium divaricatum ATCC 14020, Brevibacterium saccharoliticum ATCC 14066, Corynebacterium acetoacidophilum ATCC 13870, and other glutamic acid-producing bacteria of the genera Corynebacterium and Brevibacterium can be used as the parent strains.

The parent strains can be mutated to obtain the mutants of this invention by a conventional manner such as UV-radiation X-ray radiation, exposure to a mutagen. For instance, the parent strain is mutated by exposing to 250 .mu.g/ml N-nitro-N'-methyl-N-nitrosoguanidine at 30.degree. C. fof 20 minutes.

Inhibitory action to the growth of the mutants of this invention and their parents in the presence of the respective inhibitors to which the mutants resist was tested and the results are shown in Tables 1, 2 and 3. As can be seen in Tables 1, 2 and 3, the growth of the mutants of this invention was less inhibited than that of their parents by the inhibitors.

The determination of growth was performed by the following way; the medium containing 1 g/dl yeast extract, 1 g/dl peptone, 0.5 g/dl sodium chloride and 2 g/dl agar of pH 7.0 was sterilized at 120.degree. C. for 15 minutes, and was poured into plates. The plates were inoculated with the microorganisms, which had been cultured on meat extract agar slant for 24 hours and had been suspended into sterilized water. The inoculum size was 10.sup.5 .about.10.sup.6 cells per plate. A paper disk containing the amount of inhibitor shown in each Table was placed on each plate. Growth around the paper disk was observed after 16 to 48 hours incubation of the plates at 30.degree. C.

In Tables "++", "+" and "-" show that good growth, poor growth and scarce growth were observed around the disk, respectively.

TABLE 1______________________________________inhibitor indisk(mg/ml) Growth______________________________________ ATCC AJ ATCC AJ ATCC AJmalonic acid 13869 11426 14067 11427 13032 11441______________________________________1 ++ ++ ++ ++ + +3 .+-. ++ .+-. ++ - +5 - + - + - +10 - + - - - -______________________________________ ATCC AJ ATCC AJ ATCC AJKCN 13869 1429 14067 11430 13032 11431______________________________________0.1 + ++ + ++ + +0.3 .+-. + + + + .+-. +0.5 - + - + - +0.8 - - - - - -______________________________________ ATCC AJNaN.sub.3 13869 11428______________________________________ 0.01 .+-. + 0.05 - +0.1 - -0.5 - -______________________________________ ATCC AJNa.sub.3 AsO.sub.3 13869 11432______________________________________0.5 ++ +++1.0 - ++5.0 - +10 - -______________________________________ TABLE 2__________________________________________________________________________2,4-Di-nitro Growth Hydro- Growth Growthphenol ATCC AJ ATCC AJ xylamine ATCC AJ ATCC AJ Arsenic ATCC AJ(mg/ml) 13869 11433 14067 11434 HCl(mg/ml) 13869 11435 13032 11436 (mg/dl) 13869 11437__________________________________________________________________________0.1 ++ ++ ++ ++ 0.5 ++ ++ ++ ++ 1 ++ ++0.5 + ++ .+-. ++ 1.0 - ++ + ++ 3 + ++0.8 - + + + 3.0 - + - + 5 - +1.0 - - - - 5.0 - - - - 10 - +__________________________________________________________________________ TABLE 3______________________________________GrowthGuanidine ATCC AJ ATCC AJ ATCC AJ(mg/ml) 13869 11438 14067 11439 13032 11440______________________________________1 ++ ++ ++ ++ + +3 - ++ - ++ - +5 - + - + - -10 - - - - - -______________________________________

The effect of respiratory inhibitor on NADH oxidation of the mutants resistant to respiratory inhibitor and their parents was tested, and the results are shown in Table 4.

NADH oxidation activity was determined by the following manner: Ten ml batches of reaction mixture containing 500 .mu.moles of phosphate buffer (pH 7.5), 6 .mu.moles of NADH, a certain volume of cell extract of the test strain and the amount of respiratory inhibitor shown in Table 4 were kept airtight in vessels having oxygen sensor "Beckman model 777", stirred, and held at 32.degree. C. NADH oxidation activity was determined based on the decreasing rate of the partial pressure of oxygen, It was observed that the NADA oxidation activity of AJ 11429, AJ 11430 and AJ 11431 was less reduced by the inhibitors shown in Table 4 than that of their parents.

TABLE 4__________________________________________________________________________ Relative activity of NADH oxidationInhibitor conc. ATCC AJ ATCC AJ ATCC AJadded (mg/ml) 13869 11429 14067 11430 13032 11431__________________________________________________________________________malonic acid 5 40 70 35 75 20 75KCN 0.5 0 85 0 75 0 65NaN.sub.3 0.05 0 50 0 60 0 75Na.sub.3 AsO.sub.3 1.0 15 90 25 95 10 80none -- 100 100 100 100 100 100__________________________________________________________________________

Respiration activity and ADP phosphorylation activity of the mutant resistant to ADP phosphorylation inhibitor and their parent were determined in the presence of uncoupler (Table 5) or energy transfer inhibitor (Table 6).

Determination of respiration activity and ADP phosphorylation activity was carried out as follows:

RESPIRATION ACTIVITY

Test strains were cultured for 20 hours in a medium containing, per milliliter, 36 mg glucose, 2 mg urea, 1 mg KH.sub.2 PO.sub.4, 0.4 mg MgSO.sub.4.7H.sub.2 O, 10 .mu.g FeSO.sub.4.7H.sub.2 O, 8 .mu.g MnSO.sub.4.4H.sub.2 O, 5 .mu.l soybean acid-hydrolysate, 0.1 .mu.g thiamine.HCl, and 0.0025 .mu.g biotin, Cells in the resulted culture liquids were harvested, washed twice with 0.5% NaCl, and suspended in 1/15 M phosphate buffer of pH 7.5. The cell suspension was shaken at 28.degree. C. for 3 hours, and 0.5 ml of the resting cell suspension was put into 2 ml of a reaction mixture containing 100 .mu.moles of phosphate buffer of pH 7.5, 100 .mu.moles of glucose and the amount of the inhibitor shown in Table 5 or 6. The reaction mixture was held at 32.degree. C. for 3 hours, and oxygen uptake was measured with warburg manometer.

ADP PHOSPHORYLATION ACTIVITY

The resting cells mentioned above were dried at a room temperature and dried further in a phosphorus pentoxide desiccator under a vacuum overnight. Fifty mg of the dried cells were put into 2 ml of a reaction mixture containing 10 .mu.moles ADP, 200 .mu.moles glucose 250 .mu.moles phosphate buffer, 5 .mu.moles MgCl.sub.2.6H.sub.2 O and the amount of the inhibitor shown in Table 5 or 6. The reaction mixture was held at 30.degree. C. for 3 hours, and then heated in boiling water for 3 minutes. ATP formed in the reaction mixture was determined colorimetrically.

TABLE 5__________________________________________________________________________ Relative activityUnconpler conc. Activity ATCC AJ ATCC AJ ATCC AJadded (mg/ml) determined 13869 11433 14067 11434 13032 11436__________________________________________________________________________2,4-dini- 0.5 repiration 125 160 145 145 135 140trophenol ADP phospho- 0 65 0 70 0 50 rylationhydroxyla- 1.0 respiration 130 175 120 150 135 160mine ADP phospho- 0 50 0 65 0 45 rylationarsenic 5.0 respiration 130 160 145 160 140 160 ADP Phospho- 0 50 0 70 0 45 rylationnone -- repiration 100 100 100 100 100 100 ADP phospho- 100 100 100 100 100 100 rylation__________________________________________________________________________ TABLE 6__________________________________________________________________________Relative activity conc. Activity ATCC AJ ATCC AJ ATCC AJInhibitor (mg/ml) determined 13869 11438 14067 11439 13032 11440__________________________________________________________________________guanidine 3 respiration 100 110 100 110 100 100 ADP phospho- 0 85 15 80 10 75 rylationnone -- respiration 100 100 100 100 100 100 ADP phospho- 100 100 100 100 100 100 rylation__________________________________________________________________________

From these experiments, it was observed that ADP phosphorylation activity of both of the mutants resistant to uncoupler and mutant resistant to energy transfer inhibitor was less decreased by uncoupler or energy transfer inhibitor than that of their parents.

The mutants of this invention are cultured to produce L-glutamic acid by conventional manner. Namely, the cultivation is carried out under an aerobic condition at a temperature in the range from 30.degree. C. to 40.degree. C. The culture medium employed in this invention contains carbon sources, nitrogen sources and inorganic ions as in conventional medium.

Preferred carbon sources are carbohydrates (sucrose, glucose, fructose and crude materials containing the carbohydrates such as cane molasses beet molasses and starch hydrolyzate), acetic acid, and ethanol. Most preferred nitrogen sources are urea, gaseous ammonia and aqueous ammonia.

L-Glutamic acid thus accumulated in the resulted culture liquid can be recovered also by conventional manner.

EXAMPLE 1

Twenty milliliter batches of a culture medium containing, per milliliter, 36 mg glucose, 2 mg urea, 1 mg KH.sub.2 PO.sub.4, 0.4 mg MgSO.sub.4.7H.sub.2 O, 10 .mu.g FeSO.sub.4.7H.sub.2 O, 8 .mu.g MnSO.sub.4.4H.sub.2 O, 0.1 .mu.g thiamine.HCl, 0.0025 .mu.g biotin and 5 .mu.l soy protein hydrolyzate, were placed in 500 ml shaking flasks, and sterilized at 115.degree. C. for 10 minutes.

The microorganisms listed in Table 7 below were inoculated in the culture media and cultured at 31.5.degree. C. with shaking. During the cultivation, a small portion of urea solution (containing 450 mg/ml urea) was fed to the fermentation media to maintain the pH of the fermentation media at from 6.5 to 8.0.

After 30 hours' cultivation, the amounts of L-glutamic acid shown in Table 7 were accumulated.

EXAMPLE 2

An aqueous medium was prepared to contain, per milliliter, 100 mg (as sugar) of cane molasses, 1.0 mg KH.sub.2 PO.sub.4, 1.0 mg MgSO.sub.4.7H.sub.2 O, and 0.1 .mu.g thiamine.HCl, adjust to pH 7.0, 30 ml batches of the medium were placed in 500 ml flasks and heated to sterilize.

The microorganisms listed in Table 8 were inoculated in the media and cultured at 31.5.degree. C. with shaking. During the cultivation, an urea solution containing 400 mg/ml urea was fed in the medium so as to maintain the pH of the medium at 6.5.about.8.0. When the optical density at 562 m.mu. of a 26 times dilution of the culture medium reached 0.3, 0.5 mg/ml polyoxyethylenesorbitanmonopalmitate were added to the medium.

After 36 hours' of the cultivation, the amounts of L-glutamic acid shown in Table 8 were accumulated.

TABLE 7______________________________________ L-Glutamic acidMicroorganism tested accumulated (g/l)______________________________________ATCC 13869 16.2ATCC 14067 15.0ATCC 13032 15.5AJ 11426 17.5AJ 11427 17.0AJ 11428 17.8AJ 11429 17.8AJ 11430 18.2AJ 11431 17.5AJ 11432 18.0AJ 11433 17.5AJ 11434 17.0AJ 11435 18.0AJ 11436 17.2AJ 11437 16.9AJ 11438 18.0AJ 11439 18.0AJ 11440 17.5AJ 11441 17.8______________________________________ TABLE 8______________________________________ L-Glutamic acidmicroorganism tested accumulated (g/l)______________________________________AJ 11426 52.0AJ 11427 49.5AJ 11429 51.5AJ 11430 50.3AJ 11431 51.0AJ 11433 50.9AJ 11434 50.3AJ 11435 51.5AJ 11436 50.8AJ 11438 52.9AJ 11439 52.0AJ 11440 52.5AJ 11441 50.8______________________________________

Claims

1. A method for producing L-glutamic acid by fermentation which comprises aerobically culturing in aqueous culture medium a mutant of the genus Brevibacterium or Corynebacterium of which ADP phosphorylation is less inhibited than its parent strain by ADP phosphorylation inhibition, and recovering L-glutamic acid accumulated in the resulting culture liquid, wherein the mutant is selected from the group consisting of:

Corynebacterium glutamicum NRRL B-12210

Brevibacterium lactofermentum NRRL B-12212

Brevibacterium lactofermentum NRRL B-12213

Brevibacterium flavum NRRL B-12204

Corynebacterium glutamicum NRRL B-12207

Brevibacterium lactofermentum NRRL B-12214

Brevibacterium lactofermentum NRRL B-12215

Brevibacterium flavum NRRL B-12205

Brevibacterium lactofermentum NRRL B-12216

Corynebacterium glutamicum NRRL B-12208

Brevibacterium lactofermentum NRRL B-12217

Brevibacterium lactofermentum NRRL B-12218

Brevibacterium flavum NRRL B-12206

Corynebacterium glutamicum NRRL B-12209.

2. The method of claim 1 wherein said mutant is resistant to sodium azide, potassium cyanid, sodium arsenite, 2,4-dinitrophenol, hydroxylamine hydrochloride, arsenic or guanidine.

3. The method of claim 1, wherein the mutant is Brevibacterium lactofermentum NRRL B-12212 which is resistant to sodium azide.

4. The method of claim 1, wherein the mutant is Brevibacterium lactofermentum NRRL B-12213 which is resistant to potassium cyanid.

5. The method of claim 1, wherein the mutant is Brevibacterium flavum NRRL B-12204 which is resistant to potassium cyanid.

6. The method of claim 1, wherein the mutant is Brevibacterium lactofermentum NRRL B-12214 which is resistant to sodium arsenite.

7. The method of claim 1, wherein the mutant is Brevibacterium lactofermentum NRRL B-12215 which is resistant to 2,4-dinitrophenol.

8. The method of claim 1, wherein the mutant is Brevibacterium flavum NRRL B-12205 which is resistant to 2,4-dinitrophenol.

9. The method of claim 1, wherein the mutant is Brevibacterium lactofermentum NRRL B-12216 which is resistant to hydroxylamine hydrochloride.

10. The method of claim 1, wherein the mutant is Brevibacterium lactofermentum NRRL B-12217 which is resistant to arsenic.

11. The method of claim 1, wherein the mutant is Brevibacterium lactofermentum NRRL B-12218 which is resistant to guanidine.

12. The method of claim 1, wherein the mutant is Brevibacterium flavum NRRL B-12206 which is resistant to guanidine.

13. The method of claim 1, wherein the mutant is Corynebacterium glutamicum NRRL B-12210 which is resistant to malonic acid.

14. The method of claim 1, wherein the mutant is Corynebacterium glutamicum NRRL B-12207 which is resistant to potassium cyanid.

15. The method of claim 1, wherein the mutant is Corynebacterium glutamicum NRRL B-12208 which is resistant to hydroxylamine hydrochloride.

16. The method of claim 1, wherein the mutant is Corynebacterium glutamicum NRRL B-12209 which is resistant to guanidine.