Temperature-sensitive autolysis-defective mutants of Escherichia coli

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Abstract
Two independently isolated temperature-sensitive autolysis-defective mutants of E. coli LD5 (thi lysA dapD) were characterized. The mutants were isolated by screening the survivors of a 3-step enrichment process involving sequential treatments with bactericidal concentrations of D-cycloserine, benzylpenicillin and D-cycloserine at 42.degree. C. Cultures of the mutants underwent autolysis during .beta.-lactam treatment, D-cycloserine treatment or diaminopimelic acid deprivation at 30.degree. C. The same treatments at 42.degree. C inhibited growth but did not induce lysis of the mutants. The minimum inhibitory concentrations of selected .beta.-lactam antibiotics and D-cycloserine were identical for the parent and mutant strains at 30 and 42.degree. C. Both mutants failed to form colonies at 42.degree. C; both gave rise to spontaneous temperature-resistant revertants. The revertants exhibited the normal lytic response when treated with D-cycloserine and .beta.-lactams or when deprived of diaminopimelic acid at 42.degree. C. The basis for the autolysis-defective phenotype of these mutants could not be determined. 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 56-61-min region of the E. coli chromosome by F'' complementation.