Temperature-sensitive beta-lactam-tolerant mutants of Escherichia coli

Seven temperature-sensitive penicillin-tolerant mutants of Escherichia coli strain LD5 (thi lysA dapD) were isolated and characterized. Treatment with beta-lactams caused lysis of the mutants at 30 degrees C. Although growth of the mutants at 42 degrees C was inhibited by beta-lactams, no lysis occurred. The mutants were also slightly tolerant to D-cycloserine at 42 degrees C but lysed readily when deprived of diaminopimelate or when treated with moenomycin. The minimum inhibitory concentrations of various antibiotics were the same for the mutants and their parent. The mutations conferring penicillin tolerance were phenotypically suppressed in the presence of a variety of compounds which may act as chaotropic or antichaotropic agents. No defects in penicillin-binding proteins and peptidoglycan hydrolases were detected. Temperature-resistant revertants of the mutants were no longer tolerant to penicillin-induced autolysis at 42 degrees C. The mutations in five isolates were localized to the 56 to 61 min region of the E. coli linkage map and to the 44 to 51 min region in the case of two other isolates.