ACETOLACTATE FORMATION BY STREPTOMYCIN MUTANTS OF ESCHERICHIA COLI

Abstract

The activity of the enzyme system which forms acetolactate in Escherichia coli was found to be greater at both pH 6 and at pH 8 in streptomycin-dependent mutants than in the parent sensitive cultures. The activity of the acetolactate-forming system was observed to be lower in a streptomycin-sensitive revertant than in the dependent E. coli culture from which it was derived by back-mutation. The activity of the acetolactate-forming system from streptomycin-resistant (indifferent) mutants was within the range found for streptomycin-sensitive cultures and was not affected by growth in medium containing dihydrostreptomycin. It was concluded from these observations that excretion of L-valine by streptomycin-dependent E. coli was a consequence of the elevated acetolactate-forming activity of these mutants. To explain the (apparently specific) elevation of the acetolactate-forming system in streptomycin-dependent cells, it was postulated that the antibiotic functioned as a de-repressor while pyruvate functioned as the specific enzyme inducer.