Division-associated changes in membrane viscosity of Escherichia coli

Septum formation is initiated by the FtsZ ring assembly in the middle of rod-shape bacteria. The mechanism which determines the division site in the membrane and makes it recognizable by FtsZ is still unknown. We have recently demonstrated that the putative division membrane domains can be visualized by a fluorescent membrane probe (Fishov and Woldring, Mol. Microbiol., 1999) and that these domains can be dissipated by interrupting the process of coupled transcription and translation of proteins (Binenbaum et al., Mol. Microbiol., 1999). Here, we examined the membrane dynamics of Escherichia coli during division and after a reversible division arrest. Anisotropy of DPH fluorescence, used as an indicator of membrane dynamics (viscosity), correlated with the rate of division in synchronous cells. It decreased during filamentation caused by drugs or by temperature, but not in the ftsZ mutant and when DNA replication was blocked by nalidixic acid. Based on previous data, we incline to interpret these results as reflecting formation and dissipation of putative membrane domains marking the division sites; domains are formed by partitioning nucleoids and dissipate while used for constriction or after the nucleoids have been segregated too far in a filament.