Regulation of cell size and volume in bacteria
Prof. Sven van Teeffelen, Institut Pasteur, Paris
Rod-like bacteria such as Escherichia coli control their macroscopic cylindrical shape with high precision by expanding and remodeling their cell envelope, in particular the peptidoglycan cell wall, a mesh of covalently bond sugar strands and peptide bonds. Many of the major components required for cell-wall expansion are known. However, only recently have we gained first insights into their spatio-temporal regulation. Specifically, we found that the bacterial cytoskeleton MreB is physically coupled to cell-wall synthesis and that MreB rotates continuously around the cell axis, which reflects the processive insertion of new sugar strands into the cell wall. However, recent experiments in Escherichia coli by us and by others show that the cell-wall synthesizing enzymes move diffusively in the cell envelope and are thus not part of a stable processively moving complex that had previously been hypothesized. I will present results from single-molecule tracking microscopy showing that these enzymes undergo multi-state confined diffusion, which could reveal both different states of enzymatic activities and facilitated diffusion to guarantee processive cell-wall synthesis at a high rate.
While the shape of the newly forming cell is governed by the localization of cell-wall modifying enzymes, the rate of cell-volume expansion is governed by enzyme activity and enzyme abundance – through a combination of transcriptional, translational, and post-translational regulation. Even in constant environmental conditions bacterial physiology (in particular, growth rate) varies significantly from cell to cell. Yet, different cellular functions such as volume regulation function reliably. If time permits I will present how the levels of different proteins involved in growth and cell-volume regulation are differentially temporally regulated as a function of the fluctuating instantaneous single-cell growth rate and how this might contribute to robust adaptation to noisy single-cell physiology.