SUMMARY: Growth of NC1B 7581 in a simple chemically defined medium was inhibited by D-glutamate above 0.01 mg ml; equimolar L-glutamate prevented this inhibition. When DL-glutamate (2 mg ml) was present in the medium (with glycerol as the main carbon source), organisms grew exponentially until all the L-isomer had disappeared; growth then stopped for about 24 h during which there was a transient appearance of D-glutamine in the medium. Throughout the first stationary phase the concentration of D-glutamate in the medium fell continuously and when it was less than 0.01 mg ml there was a second phase of growth. Exponential phase organisms growing without glutamate contained only 4 mM-glutamate in the free amino acid pool. During the first stationary phase with DL-glutamate added to the medium, the concentration of glutamate (all D-isomer) was 47 mM in the pool. Of four other strains of tested, only one was sensitive to D-glutamate. From strain 7581 a D-glutamate-resistant substrain was easily developed. Among other amino acids added singly to the defined medium, only D- (and L-) serine was inhibitory to all five strains examined. Inhibition of 7581 by D-glutamate was prevented by single addition of several amino acids, each of which could act as a sole source of nitrogen for growth.


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