The mechanics of bacterial cell shape

Abstract

Cell shape is crucial for bacterial motility, proliferation, adhesion, and survival. How bacteria maintain their diverse shapes is largely unknown, and unraveling the mechanisms underlying cell shape requires an understanding of the physics of growth and form. In the first part of this dissertation, I show that the spatial coupling of growth to regions of high mechanical strain can explain the plastic response of cells to bending and theoretically predict the rate at which bent cells straighten. The predicted rate is consistent with experiments in which filamentous Escherichia coli cells straighten after being bent in doughnut-shaped microchambers, implicating mechanical strain sensing as an important component of robust shape regulation. In the second part of this dissertation, I examine a key protein involved in cell wall synthesis, MreB, at the subcellular level. By modeling the mechanics and dynamics of MreB filaments bound to curved membranes, I show that micron-scale localization of MreB can arise from nanometer-scale filament properties alone, a result which has significant implications on rod shape morphogenesis. In the final part of this dissertation, I model the mechanics of bacterial cell lysis, or rupture, and show that this mechanical model elucidates the lysis dynamics of single E. coli cells. Taken together, these results demonstrate how subcellular-scale dynamics and cellular-scale elasticity dictate and constrain growth in bacteria.