Effects of Streptomycin in Bacterial Cultures Growing at Different Rates; Interaction with Bacterial Ribosomes in vivo

Growth‐inhibitory effects of streptomycin and dihydrostreptomycin are influenced by initial growth rates of treated cultures. Growth rates were varied by medium composition and by temperature. A given change in initial growth rate brought about by temperature change produced a larger effect on the decline in growth rate under the influence of the antibiotic, than did a similar variation in initial growth rate brought about by differences in medium composition. These effects of growth conditions on the growth‐inhibitory action of the antibiotics could not be accounted for by effects on intracellular accumulation. It is concluded that interaction of intracellular streptomycin or dihydrostreptomycin with ribosomes must be restricted to a certain stage in the cycle of ribosome function. Such restriction of effective interaction to the free 30 S ribosomal subunits would fit all observations. It suggests that the antibiotic effect of streptomycin and dihydrostreptomycin may be due to combination with specific sites on the 30 S ribosomal subunits which are not accessible during peptide synthesis by the fully functional ribosome‐messenger RNA‐transfer RNA complex.