Fast lysis of Escherichia coli filament cells requires differentiation of potential division sites

Periodic activation of zonal peptidoglycan (murein) synthesis at division in Escherichia coli has been reported recently. Zonal synthesis is for septum formation, whereas elongation of the cell sacculus is performed diffuse insertion of precursors. Zonal synthesis can be triggered in ftsA, and ftsI (pbpB) division mutants growing as filaments at the restrictive temperature, but not in ftsZ mutant strains. The lytic response to beta-lactams cells able or unable to periodically trigger a zonal mode of murein could be substantially different. Therefore, we investigated the response to the bacteriolytic beta-lactam cefsulodin of ftsZ and ftsI mutants growing at restrictive (42 degreesC) temperature. The ftsI cells lysed early and quickly after addition of the antibiotic. Sacculi of lysed cells were transversely cut in a sharp way. In contrast the ftsI strain lysed late and slowly after addition of antibiotic and sacculi showed a generalized weakening of the murein and extended breaks with a frayed appearance. No transversely cut sacculi comparable to those seen in the ftsl samples were found. Our results support that beta-lactam-induced lysis occurs preferentially at division sites because of the activation of zonal murein synthesis at the initiation of septation.