The consequences for cell envelope integrity of Escherichia coli K-12 of the inhibition of protein synthesis by a variety of means have been examined. Protein synthesis was blocked by the antibiotics chloramphenicol and streptomycin, by amino acid starvation of an amino acid auxotroph, and by inactivation of temperature-sensitive aminoacyl transfer ribonucleic acid synthetase and ribosomal mutations. Closely similar morphological and physiological effects were found irrespective of the means by which protein synthesis was blocked. Scanning electron microscopy revealed a spectrum of changes after protein inhibition, with granular material derived from cells and spheroplasts commonly seen. Streptomycin caused additional changes manifested in a collapsed appearance of treated cells. Measurements of the release of lipopolysaccharide from the cell surface, alterations in outer membrane penetrability, and lysis of lysozyme-ethylenediaminetetraacetic acid-treated cultures also showed that the various inhibitory treatments all had similar effects on cell envelope properties. The close correspondence between the effects seen with antibiotic-treated cultures and those in which protein synthesis inhibition was achieved by use of mutants indicates that the effects of chloramphenicol and streptomycin on the cell envelope are indirect consequences of ribosomal block, rather than due to multiple sites of action of the antibiotics.
Bacterial Outer Membrane Proteins Cell Membrane Permeability