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 find that after division FtsZ rings remain at the cell pole, and 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 maintenance of multiple Z-rings simultaneously, that are restricted by competition for newly synthesized FtsZ. Whereas the parameters of FtsZ dynamics change in the minD mutant, the overall cell cycle remains the same, albeit with elongated cells necessary to accumulate a threshold concentration 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 not only is the Min system important for recycling FtsZ but also may have a secondary role in the regulation of peptidoglycan remodeling. IMPORTANCEMany bacteria grow and divide by binary fission in which a mothercell 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 analyze FtsZ dynamics during growth and find 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.