Temperature-sensitive autolysis-defective mutants of Escherichia coli

Abstract

Two independently isolated temperature-sensitive autolysis-defective mutants of Escherichia coli LD5 (thi lysA dapD) were characterized. The mutants were isolated by screening the survivors of a three-step enrichment process involving sequential treatments with bactericidal concentrations of D-cycloserine, benzylpenicillin, and D-cycloserine at 42°C. Cultures of the mutants underwent autolysis during β-lactam treatment, D-cycloserine treatment, or diaminopimelic acid deprivation at 30°C. The same treatments at 42°C inhibited growth but did not induce lysis of the mutants. The minimum inhibitory concentrations of selected β-lactam antibiotics and D-cycloserine were identical for the parent and mutant strains at both 30 and 42°C. Both mutants failed to form colonies at 42°C, and both gave rise to spontaneous temperature-resistant revertants. The revertants exhibited the normal lytic response when treated with D-cycloserine and β-lactams or when deprived of diaminopimelic acid at 42° C. The basis for the autolysis-defective phenotype of these mutants could not be determined. However, a nonspecific in vitro assay for peptidoglycan hydrolase activity in cell-free extracts indicated that both mutants were deficient in a peptidoglycan hydrolase. Both mutations were localized to the 56- to 61-min region of the E. coli chromosome by F' complementation.