Bacterial Elongation

Most bacterial cells are surrounded by a rigid cell wall. This protective and highly crosslinked structure prevents the cell from lysing due to its high internal turgor pressure. As bacterial cells accumulate biomass, they must coordinate growth of the cytoplasm with growth of the cell wall. They must adapt quickly to sudden changes in the quality of their external environment. In the rod-shaped Gram-positive organism Bacillus subtilis, all of these processes must also be organized spatially to produce and maintain a rodlike shape with a constant width.

We study the molecular mechanisms by which the spatial and temporal coordination of cell wall growth and synthesis is achieved. Tracking fluorescently tagged MreB (a bacterial actin), we observed synthesis-dependent circumferential motion of MreB puncta.

We showed that this spatially organized MreB motion is abolished when rod shape is disrupted, and that filaments of MreB preferentially align perpendicular to the long axis of rod-shaped spheroplasts, suggesting that circumferential MreB motion results from alignment to a preferred membrane curvature.

Working more directly with the enzymes responsible for cell wall synthesis, we helped show that glycan polymerization is mediated by two distinct classes of proteins – namely, the class A penicillin binding proteins and the SEDS family of proteins.

Further work has shown that these different classes of enzymes have distinct effects on the architecture of the cell wall due to a distinct spatial organization and regulation – increasing levels of circumfrentially moving glycan polymerases relative to diffusely moving glycan polymerases results in thinner cells, and the reverse experiment produces wider cells.

Current work in the lab focuses on understanding what role cell wall hydrolases play in cell wall growth, and on understanding how cells coordinate their rates of cell wall growth and cytoplasmic growth.