MreB, A Prokaryotic Actin Homologue, Contributes To Cell Stiffness In E. Coli

Abstract

Genetic and microscopy studies have shown that the newly discovered bacterial cytoskeleton is essential for the maintenance of cell shape in many prokaryotes. Moreover, the localization of different components of the cytoskeleton correlates with the localization of cell-wall-synthesis enzymes and of newly added cell-wall material. These correlations suggest that the cytoskeleton controls cell shape by regulating the location of cell-wall synthesis. However, whether the cytoskeleton also applies mechanical forces inside of cells is unknown. To address this issue, a quantitative measurement of the role of cytoskeletal proteins in cell mechanics is needed.We used an optical trap to measure the elasticity of live E. coli cells. Upon the addition of A22, a drug that promotes the disassembly of MreB filaments, cells become significantly weaker in their resistance to cell bending. This effect is reversible, and cells recover wild-type stiffness when A22 is removed from the environment. Our results show that MreB, a bacterial actin homologue, contributes as much to the stiffness of a cell as the peptidoglycan cell wall. This is the first direct evidence that the bacterial cytoskeleton contributes to the mechanical integrity of a cell in much the same way as it does in eukaryotes.