Peptidoglycan biosynthesis in a thermosensitive division mutant of Escherichia coli

Peptidoglycan biosynthesis during a bacterial division cycle was investigated in the thermosensitive division mutant Escherichia coli PAT 84 Synchronous cell division of this organism was initiated by a shift down from restrictive to permissive growth temperature. Cells harvested at different times after a shift down of temperature served as representatives of the various stages during cell division. These cells were made permeable to peptidoglycan nucleotide-sugar precursors by pretreatment with ether and were found capable of catalyzing the polymerization of externally added precursors as well as the covalent attachment of the newly synthesized peptidoglycan strands to those preexisting in the cell wall. Differences were observed in the rats of peptidoglycan synthesis and in the extent of peptide side-chain corss-linkage at the various stages of division. Nonseptate filaments, formed at the restrictive temperature, incorporated significantly more peptidoglycan which was more cross-linked than in normally dividing cells grown at the permissive temperature. Quantitative analyses of the carboxypeptidase and transpeptidase reactions in cells at different stages of division were performed and the inhibitory effect of a number of beta-lactam antibiotics was investigated. Of special significance was the finding that low doses of penicillin or growth at restrictive temperature, which did not affect transpeptidation, partially inhibited the carboxypeptidase activity. This inhibition was paralleled by an increase in incorporation of newly synthesized peptidoglycan into the preexisting cell wall. We therefore propose that carboxypeptidase activity regulates the availability of peptidoglycan precursor(s) for attachment to the preexisting peptidoglycan by transpepidation.