Involvement of the relA gene in the autolysis of Escherichia coli induced by inhibitors of peptidoglycan biosynthesis

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Abstract
It is generally assumed that inhibitors of peptidoglycan biosynthesis do not kill nongrowing bacteria. An exceptional case is reported here. The addition of chloramphenicol to amino acid-deprived cultures of relA+ strains of Escherichia coli which were treated with beta-lactam antibiotics, D-cycloserine, or moenomycin resulted in lysis. This phenomenon is termed chloramphenicol-dependent lysis. To be effective, chloramphenicol had to be present at its minimum growth-inhibitory concentration (or higher). Analogs of chloramphenicol which did not bind to ribosomes were completely ineffective. Amino acid deprivation was actually not required to demonstrate chloramphenicol-dependent lysis, and cultures treated with growth-inhibitory levels of chloramphenicol alone were lysed when challenged with inhibitors of peptidoglycan synthesis. Peptidoglycan synthesis has been shown previously to be under stringent (relA+) control, and chloramphenicol is known to be an antagonist of stringent control. Thus, it is proposed that the mechanism of chloramphenicol-dependent lysis is based on the ability of chloramphenicol to relax peptidoglycan synthesis in nongrowing relA+ bacteria. This is also consistent with the observation that treatment of amino acid-deprived relA mutants with inhibitors of peptidoglycan synthesis resulted in lysis, i.e., without the mediation of chloramphenicol.