Cell Size Regulation Through Tunable Geometric Localization of the Bacterial Actin Cytoskeleton

Abstract

Virtually all cells have the ability to adjust their size in response to environmental cues, yet relatively little is known about the molecular factors responsible for tuning cell size or the mechanisms through which they reconfigure cellular dimensions. In the rod-shaped bacterium Escherichia coli, the actin-like protein MreB localizes in a curvaturedependent manner and spatially coordinates cell-wall insertion to maintain cell shape across changing environments. Here, we demonstrate that the MreB-binding protein RodZ regulates the biophysical properties of MreB filaments and thereby alters the spatial patterning of cell-wall growth to modulate cell size. The relative expression levels of MreB and RodZ changed in a manner commensurate with variations in growth rate and cell width, and single-cell analyses demonstrated that RodZ systematically alters the curvature-based localization of MreB and cell width in a manner dependent on the concentration of RodZ. We identified MreB mutants that we predict using molecular dynamics simulations to alter the bending properties of MreB filaments at the molecular scale in a manner similar to RodZ binding, and showed that these mutants rescue rod-like shape in the absence of RodZ alone or in combination with wild-type MreB. Together, our results show that E. coli controls its shape and dimensions by differentially regulating RodZ and MreB expression, highlighting the rich capacity for precise coordination of cell-shape changes with environmental conditions by exploiting cytoskeletal molecular biophysics.