SUMMARY: The half-maximal growth rate of a streptomycin-dependent mutant of B on limiting concentrations of dihydrostreptomycin varied with the nature (but not with the initial concentration) of the carbon source. It was highest with gluconate, lower with glucose and glycerol and lowest with lactate. Glucose-sensitive enzymes (acetohydroxy acid synthetase, fumarase, aconitase, citrate synthase and isocitric dehydrogenase) were specifically repressed by antibiotic limitation. Parallelism was observed between decreasing dihydrostreptomycin concentration, decreasing growth rate and increasing catabolite repression of certain glucose-sensitive enzymes. The results are not incompatible with the hypothesis that the primary site of action of dihydrostreptomycin in the dependent organism is an anabolic process (e.g. protein synthesis). However, the growth-limiting effect of antibiotic deprival appears to be augmented by catabolite repression.


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