Peptidoglycan turnover during growth recovery after chloramphenicol treatment in a Dap-Lys-mutant of Bacillus megaterium.

The study of diaminopimelic acid (DAP) incorporation and turnover during growth recovery in chloramphenicol-treated (CMP-treated) Bacillus megaterium cells showed that two kinds of turnover occurred. A low acid-soluble turnover appeared as soon as growth resumed in bacteria labeled before the CMP treatment and at the middle of the first generation in those labeled during the treatment. The acid-insoluble turnover appeared only at the beginning of the second generation of growth resumption in bacteria labeled before CMP addition and at the beginning of the third generation in those labeled during the CMP treatment. The acid-soluble release observed during the period of cell wall thinning is too low to account for the decrease of the wall thickness and the acid-insoluble loss appears after this period. When bacteria were transferred into partially spent medium instead of fresh culture medium the acid-insoluble release started to appear half a generation sooner. Electron microscopic observations showed that in this case, large scales detached from the cell wall. This activity of wall degradation was not observed when the partially spent medium was previously heated for 10 min at 100 degree C. The persistence of a thick wall on cell ends during the first generation does not reflect an absence of growth sites because their labeling on autoradiographs is high. Rather, it seems to be due to a low lytic activity at the poles.