Department of Chemistry, Indiana University Bloomingtongrid.411377.7, Bloomington, Indiana, USA.
Department of Biology, Indiana University Bloomingtongrid.411377.7, Bloomington, Indiana, USA.
J Bacteriol. 2021 Aug 20;203(18):e0024921. doi: 10.1128/JB.00249-21.
During growth, bacteria increase in size and divide. Division is initiated by the formation of the Z-ring, a ring-like cytoskeletal structure formed by treadmilling protofilaments of the tubulin homolog FtsZ. FtsZ localization is thought to be controlled by the Min and Noc systems, and here we explore why cell division fails at high temperature when the Min and Noc systems are simultaneously mutated. Microfluidic analysis of a double mutant indicated that FtsZ formed proto-Z-rings at periodic interchromosome locations but that the rings failed to mature and become functional. Extragenic suppressor analysis indicated that a variety of mutations restored high temperature growth to the double mutant, and while many were likely pleiotropic, others implicated the proteolysis of the transcription factor Spx. Further analysis indicated that a Spx-dependent pathway activated the expression of ZapA, a protein that primarily compensates for the absence of Noc. In addition, an Spx-independent pathway reduced the length of the cytokinetic period, perhaps by increasing divisome activity. Finally, we provide evidence of an as-yet-unidentified protein that is activated by Spx and governs the frequency of polar division and minicell formation. Bacteria must properly position the location of the cell division machinery in order to grow, divide, and ensure each daughter cell receives one copy of the chromosome. In Bacillus subtilis, cell division site selection depends on the Min and Noc systems, and while neither is individually essential, cells fail to grow at high temperature when both are mutated. Here, we show that cell division fails in the absence of Min and Noc, due not to a defect in FtsZ localization but rather to a failure in the maturation of the cell division machinery. Suppressor mutations that restored growth were selected, and while some activated the expression of ZapA via the Spx stress response pathway, others appeared to directly enhance divisome activity.
在生长过程中，细菌会增大并分裂。分裂是由 Z 环的形成引发的，Z 环是由微管同源物 FtsZ 的踏车原丝形成的环状细胞骨架结构。FtsZ 的定位被认为是由 Min 和 Noc 系统控制的，在这里我们探讨了当 Min 和 Noc 系统同时突变时，为什么细胞分裂在高温下失败。微流控分析表明，双突变体中的 FtsZ 周期性地在染色体间位置形成原 Z-环，但这些环未能成熟并发挥功能。外显子抑制因子分析表明，各种突变恢复了双突变体在高温下的生长，虽然许多可能是多效的，但其他突变则暗示了转录因子 Spx 的蛋白水解。进一步的分析表明，Spx 依赖的途径激活了 ZapA 的表达，ZapA 主要补偿了 Noc 的缺失。此外，Spx 独立的途径缩短了细胞分裂周期，可能通过增加分裂体的活性来实现。最后，我们提供了证据表明，一种尚未确定的蛋白质被 Spx 激活，并控制着极分裂和小型细胞形成的频率。细菌必须正确定位细胞分裂机制的位置，才能生长、分裂，并确保每个子细胞都能获得一份染色体。在枯草芽孢杆菌中，细胞分裂位点的选择取决于 Min 和 Noc 系统，尽管这两个系统都不是必需的，但当它们都突变时，细胞在高温下无法生长。在这里，我们表明，在 Min 和 Noc 缺失的情况下，细胞分裂失败不是由于 FtsZ 定位的缺陷，而是由于细胞分裂机制的成熟失败。恢复生长的抑制突变被选择，虽然一些通过 Spx 应激反应途径激活了 ZapA 的表达，但其他突变似乎直接增强了分裂体的活性。
