Bending forces plastically deform growing bacterial cell walls

TL;DR

This study reveals that bacterial cell walls respond elastically to transient forces but deform plastically during growth, with mechanical stresses regulating cell-wall synthesis and shape maintenance in bacteria.

Contribution

The paper introduces a combined experimental and theoretical framework showing mechanical stresses influence bacterial cell-wall growth and shape, supported by a single dimensionless parameter.

Findings

Bacterial cells exhibit elastic behavior under transient forces.

Cells deform plastically during active wall synthesis.

A single parameter predicts cell response across conditions.

Abstract

Cell walls define a cell shape in bacteria. They are rigid to resist large internal pressures, but remarkably plastic to adapt to a wide range of external forces and geometric constraints. Currently, it is unknown how bacteria maintain their shape. In this work, we develop experimental and theoretical approaches and show that mechanical stresses regulate bacterial cell-wall growth. By applying a precisely controllable hydrodynamic force to growing rod-shaped Escherichia coli and Bacillus subtilis cells, we demonstrate that the cells can exhibit two fundamentally different modes of deformation. The cells behave like elastic rods when subjected to transient forces, but deform plastically when significant cell wall synthesis occurs while the force is applied. The deformed cells always recover their shape. The experimental results are in quantitative agreement with the predictions of the theory of dislocation-mediated growth. In particular, we find that a single dimensionless parameter, which depends on a combination of independently measured physical properties of the cell, can describe the cell's responses under various experimental conditions. These findings provide insight into how living cells robustly maintain their shape under varying physical environments.