Cell division in Echerichia coli : the involvement of the peptidoglycan

The role of the cell envelope in cell division has been examined using mutants of Escherichia coli which are temperature-sensitive in the process of cell division. These mutants grow normally at 30 C but exhibit morphological changes at 42 C. Two assays for peptidoglycan-specific autolytic enzymes have been developed. One depends on the prevention of synthesis of autolytic enzymes using chloramphenicol, while the autolytic capacity is determined by observing the rate of cell lysis in the presence of low levels of ampicillin. The second assay is based on the in vitro release of specific radioactive fragments from peptidoglycan previously labelled with radioactive diaminopimelic acid. The majority of cells in an exponential population of E. coli B/r/l are not lysed by penicillin if chloramphenicol is added. However, larger cells are particularly susceptible to lysis. Three types of lysis have been defined by observing rates of lysis of synchronous cultures at different ages and at different growth rates: (A) lysis associated with cross-wall formation during cell division; (B) lysis associated with initiation and segregation of the replication of DNA; and (C) lysis associated with general expansion of the cell wall. Filamentous mutants of E. coli which segregate DNA exhibit lysis in excess of type C while filaments formed by inhibition of DNA synthesis exhibit lysis only of type C. The autolytic enzymes of E. coli appear to be tightly bound to localized areas of the cell envelope as determined by the in vitro assay. Qualitative differences between the autolytic activities of normal cells and of filaments formed by inhibition of DNA synthesis are described.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat