A two-step model of FtsZ-ring disassembly in Bacillus subtilis.

UNLABELLED: Bacillus subtilis grows and divides by binary fission, directed by medial localization of cell division protein FtsZ. Disruption of either the Min system or EzrA results in aberrant FtsZ positioning. Here we compare FtsZ dynamics in cells disrupted for either MinD or EzrA when grown in microfluidic channels. Here we show that cells lacking MinD or EzrA appear to be similarly defective in Z-ring disassembly after septation, but play different roles as simultaneous disruption results in a synergistic defect in division. Moreover, we account for a low frequency of minicell formation in the absence of EzrA, as MinD but not EzrA is necessary for removal of ZapA from polar Z-rings. Finally, overexpression of MinCD results inhibits division through pervasive Z-ring disassembly but appears to concentrate ZapA through localized sequestration. Combined, our results indicate a closer relationship between MinCD and ZapA than previously recognized and show that Z-ring disassembly can be genetically separated into discrete steps. We propose a two-step model for Z-ring disassembly that mirrors the assembly process, such that after and/or during septation, the Z-ring separately decondenses and protofilaments are disassembled to monomers for recycling.

IMPORTANCE: Bacteria divide by polymerizing and condensing the cell division protein FtsZ, and encode a suite of proteins that control FtsZ spatial localization. Here we compare two FtsZ regulatory proteins MinD and EzrA in the bacterium Bacillus subtilis and find that are required for the disassembly of FtsZ after division at two different steps. Based on our results, we propose a two-step model of Z-ring disassembly where FtsZ protofilaments are decondensed and depolymerized separately. Finally, most regulators of FtsZ tend to be considered from the standpoint of Z-ring assembly and we assert that Z-ring disassembly, and monomer recycling, is just as important for timely division.