On the basis of aminoglycoside-dependent growth of mutants from E. coli: Physiological studies

Summary

A physiological analysis was carried out of a mutant of Escherichia coli dependent on dihydrostreptomycin or streptomycin for growth. The extent of growth of the mutant was proportional to the external drug concentration up to an optimal value above which growth was inhibited. When cultures were deprived of dihydrostreptomycin, growth became linear, the rate of this linear growth depending on the concentration of the antibiotic present before the withdrawal. Addition of ethanol increased the rate of linear growth. This linear growth was characterized by the following events: (i) In addition to ribosomal precursor particles a substantial quantity of mature 70S ribosomes was synthesized; (ii) these newly synthesized ribosomes were active since the total protein synthesis capacity increased albeit noncoordinately with the increase of total RNA and cell mass; (iii) in the course of linear growth cells lost their sensitivity to other aminoglycosides (‘phenotypic masking’) irrespective of whether or not ethanol was present; ethanol was found only to accelerate this process; (iv) there was a progressive disturbance of the balanced synthesis of cellular proteins; many proteins were synthesized at rates different from those characteristic of exponentially growing cells; other proteins were no longer synthesized, and some proteins, not present before, appeared.

The results support the notion that the growth-limiting effect of withdrawal of streptomycin from the culture of a streptomycin-dependent strain is that ribosomes are synthesized that due to altered functional properties are no longer able to maintain balanced synthesis of cellular proteins in the absence of the drug.