Recent advances in understanding how rod-like bacteria stably maintain their cell shapes

Abstract

Cell shape and cell volume are important for many bacterial functions. In recent years, we have seen a range of experimental and theoretical work that led to a better understanding of the determinants of cell shape and size. The roles of different molecular machineries for cell-wall expansion have been detailed and partially redefined, mechanical forces have been shown to influence cell shape, and new connections between metabolism and cell shape have been proposed. Yet the fundamental determinants of the different cellular dimensions remain to be identified. Here, we highlight some of the recent developments and focus on the determinants of rod-like cell shape and size in the well-studied model organisms Escherichia coli and Bacillus subtilis.

Keywords: B.subtilis; E.coli; bacterial functions; bacterial metabolism; bacterial physiology; cell shape; cell size; rod-like.

Figure 1.. Schematic representation of the prevailing mechanisms of cell-wall synthesis in rod-shaped bacteria.

( A) Illustration of a rod-shaped cell indicating the rod complex, hydrolases, and class A penicillin-binding proteins (aPBPs) during cell growth (peptidoglycan [PG] elongation) and of the divisome during cell division (PG constriction). Despite decades of research on bacterial cell-wall growth, there are still many open questions about the factors that can actively influence PG assembly and cell growth, such as metabolism, mechanical stresses, and cell shape. ( B) Inset showing the major cell-wall synthesis machineries recently suggested to work partially independently : (i) the processively moving rod complex containing the transglycosylase RodA, the transpeptidase PBP2, and circumferentially oriented MreB filaments and (ii) the bi-functional aPBPs. Hydrolases may be actively engaged in cell-wall cleavage during cell-wall synthesis. Questions remain of how hydrolases interact with the rod complex or aPBPs or both. ( C) aPBPs are activated through outer membrane (OM) lipoproteins LpoA and LpoB. This interaction could provide a mechanism to sense pore sizes in the cell wall to direct PG synthesis. ( D) Division in rod-shaped bacteria is guided by treadmilling FtsZ filaments that are oriented along the circumference of the constricting cell. IM, inner membrane.