Method for producing L-proline by fermentation
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method for producing L-proline by fermentation. 
     2. Description of the Prior Art 
     Hitherto, an isoleucine or arginine requiring mutant of the genus Brevibacterium or Corynebacterium (Japanese Published Examined Patent Application No. 11751/1968), an isoleucine requiring and sulfaguanidine resistant mutant of the genus Brevibacterium or Corynebacterium (Japanese Published Examined Patent Application No. 4015/1976) and a histidine and methionine requiring mutant of the genus Bacillus or Esterichia (Jananese Published Examined Patent Application No. 1198/1969) have been known as L-proline producing microorganisms. 
     SUMMARY OF THE INVENTION 
     We have now found excellent L-proline producing mutants belonging to the genus Brevibacterium, Corynebacterium or Microbacterium which are resistant to DL-3,4-dehydroproline. 
     The present invention thus provides a method for producing L-proline by fermentation which comprises culturing an L-proline producing mutant belonging to the genus Brevibacterium or Corynebacterium and resistant to DL-3,4-dehydroproline (hereinafter referred to as DP) in a culture medium, and recording the L-proline accumulated in the culture medium. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Examples of the mutants used in this invention are as follows: 
     Brevibacterium lactofermentum AJ 11225 (FERM-P 4370) (NRRLB-11421) 
     Brevibacterium flavum AJ 11226 (FERM-P 4371) (NRRLB-11422) 
     Corynebacterium glutamicum AJ 11227 (FERM-P 4372) (NRRLB-11423) 
     Microbacterium ammoniaphilum AJ 11228 (FERM-P 4373) (NRRLB-11424) 
     FERM-P numbers are the accession numbers of the Fermentation Research Institute, Agency of Industrial Science and Technology, Ministry of International Trade and Industry, at 2-go, 5-ban, 5-chome, Inagehigashi, Chiba-shi, Japan, and NRRL numbers are the accession numbers of the Northern Utilization Research and Development Division, U.S. Department of Agriculture, Peoria, Ill. 
     The mutants as mentioned above are derived from the parent strains of the genus Brevibacterium or Corynebacterium or Microbacterium which are known to produce L-proline, or wild strains of the genus Brevibacterium or Corynebacterium such as Brevibacterium lactofermentuum ATCC 13869, Brevibacterium flavum ATCC 14067, Brevibacterium divaricatum ATCC 14020, Brevibacterium roseum ATCC 13825, Corynebacterium glutamicum (Micrococcus glutamicus) ATCC 13032, Corynebacterium acetoacidophilum ATCC 13870, and Corynebacterium acetoglutamicum ATCC 15806 
     The growth of the parent strains are inhibited by DP, but the inhibition is suppressed by L-proline partly or completely. 
     The manner to induce the mutants of this invention from the parent strains is conventional such as exposing the parent strain to 2000 μg/ml N-methyl-N&#39;-nitro-N-nitrosoguanidine at 0° C. for 20 minutes. 
     When the mutants of this invention have additional characteristics such as nutritional requirement or resistance to other drugs, usually they produce higher amounts of L-proline. 
     The experimental data of the relative growth of the mutants mentioned above in a medium containing DP are shown in Table 1 (The relative growth in a medium free from DP is shown as 100). 
     The relative growth shown in Table 1 is determined as follows: The microorganisms had been previously cultured for 24 hours at 30° C. on an agar slants containing 1.0 g/dl peptone, 1.0 g/dl yeast extract and 0.5 g/dl NaCl. Each one loopful inoculum of the cells on the agar slants was transferred to a culture medium of pH 7.0 containing 2.0 g/dl glucose, 1.0 g/dl ammonium sulfate 0.25 /dl urea, 0.1 g/dl KH 2  PO 4 , 0.04 g/dl MgSO 4 .7H 2  O, 1 mg/dl FeSO 4 .7H 2  O, 1 mg/dl MnSO 4 .7H 2  O, 20 μg/dl thiamine.HCl, 5 μg/dl biotin, and the amount of DP shown in Table 1. 
     
                       Table 1                                                     
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                relative growth                                           
                DP concentration                                          
Microorganisms    0      0.25   0.5  1.0  2.0                             
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Brevibacterium lactofermentum                                             
2256 (ATCC 13869) 100    47     32   15   10                              
Brevibacterium lactofermentum                                             
AJ 11225          100    100    98   88   80                              
Brevibacterium flavum                                                     
AJ 3416 (FERM-P 1681)                                                     
                  100    42     16    5    5                              
Brevibacterium flavum                                                     
AJ 11226          100    100    73   63   42                              
Corynebacterium glutamicum                                                
ATCC 13032        100    53     28   15   11                              
Corynebacterium glutamicum                                                
AJ 11227          100    99     99   85   72                              
Microbacterium ammoniaphilum                                              
ATCC 15354        100    38     33   13   10                              
Microbacterium ammoniaphilum                                              
AJ 11228          100    99     87   87   75                              
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     For the cultivation of Brevibacterium flavum AJ 3416 and AJ 11226 both of which require L-isoleucine for growth, 500 μg/ml of L-isoleucine were further contained in the culture medium. After 24 hours cultivation at 30° C. with shaking, the growth was determined by measuring the optical density of the aqueous culture medium. The results are shown in Table 1. 
     As a method to produce L-proline using the mutants of the present invention it is possibly to apply any known method used for the production of L-proline. The culture media are conventional media containing carbon sources, nitrogen sources, inorganic salts and, where required, other minor organic nutrients such as vitamins and amino acids. As the carbon source, carbohydrates such as beet or cane molasses and starch hydrolyzate, organic acids such as acetic acid and alcohols such as ethanol can be used. Nitrogen sources are, for example, gaseous ammonia, aqueous ammonia, ammonium salts, and urea. 
     Cultivation is carried out under an aerobic condition at a temperature in the range from 20° C. to 40° C. During the cultivation, the pH of the medium is preferably maintained at 6 to 9. The cultivation is continued for 20 to 100 hours. 
     L-proline accumulated in the resultant culture liquid can be recovered by any known methods such as by using ion-exchange resin. 
    
    
     Having now generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified. 
     EXAMPLE 1 
     Twenty ml batches of a culture medium of pH 7.0, containing 10 g/dl glucose, 0.1 g/dl KH 2  PO 4 , 0.08 g/dl MgSO 4 .7H 2  O, 100 μg/dl thiamine HCl, 0.1 ml/dl soybean protein hydrolyzate, 6.0 g/dl (NH 4 ) 2  SO 4 , 1 mg/dl FeSO 4 .7H 2  O, 1 mg/dl MnSO 4 .4H 2  O, 450 μg/l biotin, and 5.0 g/dl CaCO 3  were plased in 500 ml shaking flasks, and heated for sterilization. Each batch of the medium was inoculated with Brevibacterium lactofermentum AJ 11225, and shaken at 30° C. for 72 hours. 
     L-Proline was produced in the resultant culture liquids in the amount of 22.5 g/l. 
     EXAMPLE 2 
     Brevibacterium flavum AJ 3416 FERM-P 1681 (L-isoleucine requiring mutant) which is not resistant to DP and Brevibacterium flavum AJ 11226 which is resistant to DP and which had been derived from AJ 3416 are cultured by the manner shown in Example 1 in the medium shown in Example 1 further containing 150 mg/l L-isoleucine. AJ 11226 produced 36.2 g/l L-proline, while AJ 3416 produced 32.3 g/l L-proline. 
     EXAMPLE 3 
     Corynebacterium glutamicum AJ 11227 was cultured by the manner shown in Example 1 and produced 12.0 g/l L-proline. 
     EXAMPLE 4 
     Microbacterium ammoniaphilum AJ 11228 was cultured by the manner shown in Example 1 and produced 3.3 g/l L-proline. 
     Having now fully described this invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention set forth herein.