Excretion of alpha-keto acids by strains of Streptomyces venezuelae.

Cultures of Streptomyces venezuelae released acidic metabolites during nitrogen-limited growth on glucose. The main products were pyruvic acid and alpha-ketoglutaric acid. Variation in the extent of acid production was observed; spores of the parental strain 13s gave approximately 10% of low-producing colonies when plated on acid-base indicator medium. Examination of one low producer, strain PC 51-5, showed that differences in acid production became apparent only in low-glucose media containing manganese. In both strains PC 51-5 and 13s, uptake of alpha-keto-[5-14C]glutaric acid occurred by diffusion and no marked differences in permeability to alpha-ketoglutarate were detected. However, differences were observed in the activity of alpha-ketoglutarate dehydrogenase. In cultures of strain PC 51-5, the specific activity of the enzyme increased throughout growth, whereas in the parental strain activity decreased and could not be detected in older mycelium. Loss of enzyme activity was accompanied by excretion of alpha-ketoglutaric acid and failure to assimilate the product after glucose exhaustion. The results suggest that accumulation of pyruvic and alpha-ketoglutaric acids in S. venezuelae cultures grown in glucose-containing media may be due to regulatory suppression of the dehydrogenases by this carbon source.