The Min System Disassembles FtsZ Foci and Inhibits Polar Peptidoglycan Remodeling in Bacillus subtilis

Abstract

A microfluidic system coupled with fluorescence microscopy is a powerful approach for quantitative analysis of bacterial growth. Here, we measure parameters of growth and dynamic localization of the cell division initiation protein FtsZ in Bacillus subtilis. Consistent with previous reports, we found that after division, FtsZ rings remain at the cell poles, and polar FtsZ ring disassembly coincides with rapid Z-ring accumulation at the midcell. In cells mutated for minD, however, the polar FtsZ rings persist indefinitely, suggesting that the primary function of the Min system is in Z-ring disassembly. The inability to recycle FtsZ monomers in the minD mutant results in the simultaneous maintenance of multiple Z-rings that are restricted by competition for newly synthesized FtsZ. Although the parameters of FtsZ dynamics change in the minD mutant, the overall cell division time remains the same, albeit with elongated cells necessary to accumulate a critical threshold amount of FtsZ for promoting medial division. Finally, the minD mutant characteristically produces minicells composed of polar peptidoglycan shown to be inert for remodeling in the wild type. Polar peptidoglycan, however, loses its inert character in the minD mutant, suggesting that the Min system not only is important for recycling FtsZ but also may have a secondary role in the spatiotemporal regulation of peptidoglycan remodeling. IMPORTANCE Many bacteria grow and divide by binary fission in which a mother cell divides into two identical daughter cells. To produce two equally sized daughters, the division machinery, guided by FtsZ, must dynamically localize to the midcell each cell cycle. Here, we quantitatively analyzed FtsZ dynamics during growth and found that the Min system of Bacillus subtilis is essential to disassemble FtsZ rings after division. Moreover, a failure to efficiently recycle FtsZ results in an increase in cell size. Finally, we show that the Min system has an additional role in inhibiting cell wall turnover and contributes to the “inert” property of cell walls at the poles.

Noc Corrals Migration of FtsZ Protofilaments during Cytokinesis in Bacillus subtilis

“…4C and D; Fig. S2E), as had been observed with cells mutated for the Min system (27). Instead, the medial delay time, defined as the time between cell division and appearance of the next Z-ring, was negative, as future rings were formed by splitting from a Z-ring soon after coalescence ( Fig.…”

“…To explore Z-ring dynamics, 100 cells each were chosen at random from the wild type and noc mutant and tracked through the course of division (27). Four events were sequentially measured, i.e., the appearance of an FtsZ ring, accumulation of FtsZ to peak intensity, cell division, and disappearance of the FtsZ ring, and used to calculate seven division parameters.…”

“…In the noc mutant, however, a subpopulation of protofilaments escapes the cytokinetic ring, travels over the chromosome, and arrives at the future site of cell division earlier than in the wild type. Nevertheless, the cell cycle is largely unperturbed, as Z-ring maturation requires a combination of de novo FtsZ synthesis and Min-mediated monomer recycling, and the rest of the division machinery relocates on time (27). Moreover, overexpression of ZapA compensated for the absence of Noc, perhaps by restricting FtsZ migration through increased protofilament cross-linking.…”

“…Here, we used a programmable microfluidic device with an integrated microchannel array (26,27) to monitor B. subtilis FtsZ dynamics in the presence and absence of Noc during chemostatic growth. Our data suggest that rather than functioning as an inhibitor of Z-ring formation, Noc functions as an inhibitor of FtsZ migration.…”

The division defect of aBacillus subtilis minD nocdouble mutant can be suppressed by Spx-dependent and Spx-independent mechanisms

“…[40][41][42][43][44][45] Polar localization is related to Min function, and in the case of B. subtilis, the FtsZ ring remains after division is completed and requires the Min system for depolymerization such that in the absence of Min, FtsZ rings persist at the polar location indefinitely. [46][47][48][49][50][51] Constitutive maintenance of multiple Z-rings and the inability to recycle FtsZ monomers puts an increased emphasis on de novo FtsZ synthesis for division, and competition between the multiple rings for FtsZ recruitment results in elongated cells. [51][52][53][54] Finally, recruitment of FtsZ to the persistent polar FtsZ rings eventually gives rise to polar division events and the generation of anucleoid minicells.…”