Bacterial cell division and the septal ring

Abstract

Cell division in bacteria is mediated by the septal ring, a collection of about a dozen (known) proteins that localize to the division site, where they direct assembly of the division septum. The foundation of the sep-tal ring is a polymer of the tubulin-like protein FtsZ. Recently, experiments using fluorescence recovery after photobleaching have revealed that the Z ring is extremely dynamic. FtsZ subunits exchange in and out of the ring on a time scale of seconds even while the overall morphology of the ring appears static. These findings, together with in vitro studies of purified FtsZ, suggest that the rate-limiting step in turnover of FtsZ polymers is GTP hydrolysis. Another component of the septal ring, FtsK, is involved in coordinating chromosome segregation with cell division. Recent studies have revealed that FtsK is a DNA translocase that facilitates decatenation of sister chromosomes by TopIV and resolution of chromosome dimers by the XerCD recombinase. Finally, two murein hydrolases, AmiC and EnvC, have been shown to localize to the septal ring of Escherichia coli , where they play an important role in separation of daughter cells. Scope of this review This MicroReview opens with a whirlwind tour of cell division in Escherichia coli. To keep it short and to the point, I have made some oversimplifications and relied almost exclusively on citations to a collection of review articles rather than the original studies. The remainder of the review is devoted to a more detailed and critical look at a few questions that have been the focus of several recent studies. (i) How do the proteins that comprise the septal ring work together during cytokinesis? One step towards answering this question is to identify protein-protein interactions among the division proteins. I will summarize what is known about this topic and suggest reasons why progress has been slow. (ii) How does FtsZ drive cytoki-nesis? Although the answer remains elusive, recent experiments suggest the rate-limiting step in turnover of the FtsZ polymer is GTP hydrolysis. I will speculate on the implications that this has for the ability of FtsZ to generate force. (iii) How is septum assembly coordinated with partitioning of chromosomes to daughter cells? At least three mechanisms by which FtsK prevents the septum from closing on the chromosomes like a guillotine have been elucidated. I will describe these activities, and briefly compare FtsK with a similar protein, SpoIIIE, involved in sporulation in Bacillus subtilis. (iv) How are daughter cells separated? Two peptidoglycan hydrolases, AmiC and EnvC, have recently been shown to localize to the septal ring and play an important role in this process in E. coli.

FtsZ and the division of prokaryotic cells and organelles

“…Once assembled, the Z ring recruits several membrane-associated proteins that are essential for cell division 2 (FIG. 5).…”

FisB mediates membrane fission during sporulation in Bacillus subtilis

“…It has been proposed that protein components of the cell division machinery could catalyze fission (Sharp and Pogliano 1999;Liu et al 2006;de Boer 2010;Fleming et al 2010). Alternatively, it has been suggested that cell wall synthesis on the outside of the cell could force the constricting membranes into close proximity, ultimately leading to fission (Weiss 2004;Judd et al 2005;Meyer et al 2010). To date, no protein has been directly implicated in this fission reaction.…”

The Escherichia coli datA site promotes proper regulation of cell division

“…It is crucial that the two daughter nucleoids are segregated into each half of the cell, so that each daughter cell receives a copy of the genetic material and that none of the nucleoids are trapped in the septum. To ensure this, cell division and chromosome segregation are highly regulated processes involving a number of different proteins (see Egan & Vollmer, 2013;Harry et al, 2006;and Weiss, 2004, for reviews), the most studied being FtsZ. This protein polymerizes to form a ring-like structure at the site of division and serves as a scaffold for recruitment of other division proteins (Bi & Lutkenhaus, 1991).…”