Phenotypic suppression in Escherichia coli by chloramphenicol and other reversible inhibitors of the ribosome.

Antibiotics that interfere reversibly with various aspects of ribosomal function (chloramphenicol, tetracycline, erythromycin, and spectinomycin) are shown to antagonize, at barely inhibitory concentrations, the inhibitory effect of low concentrations of streptomycin (SM) on the growth of Escherichia coli. Paradoxically, these compounds can also replace SM in supporting the growth of conditionally SM-dependent mutants. Chloramphenicol produced about as much phenotypic suppression as SM in SM-sensitive strains, but less than that attainable with high concentrations of SM in resistant strains. The antagonism to SM inhibition and the phenotypic suppression appear to be specific for those growth inhibitors that act on the ribosome. Since inhibitors of the 50S subunit of the ribosome (chloramphenicol, erythromycin) are as active as inhibitors of the 30S subunit, it is suggested that phenotypic suppression by borderline concentrations of ribosome inhibitors does not necessarily depend on an alteration of the recognition region of the ribosome. Alternatively, partial inhibition of the ribosomes might change the environment in a way that would influence the frequency of misreading. Phenotypic suppression by a low concentration of SM as well as by chloramphenicol was found to depend on the presence of a trace of the required growth factor.