Jeff Errington (Newcastle University - Centre for Bacterial Cell Biology)
The cell wall is a defining structure of bacterial cells. It provides a protective outer shell and is crucial in pathogenesis as well as the target for important antibiotics. Synthesis of the wall is organised by cytoskeletal proteins homologous to tubulin (FtsZ) and actin (MreB). Because all major branches of the bacterial lineage possess both wall and cytoskeleton, these were probably present in the last common ancestor of the bacteria. L-forms are unusual variants of bacteria that lack the wall and are found in various specialised habitats, possibly responsible for a range of chronic and persistent diseases. We have developed a model system for studying the L-form state in Bacillus subtilis (Leaver et al., 2009, Nature 457, 849-53; Dominguez-Cuevas et al., 2012, Mol Microbiol 83, 52-66; Mercier et al., 2012, Cell Reports 1, 417-23). Unexpectedly, we found that proliferation of L-forms is completely independent of the normally essential FtsZ or MreB cytoskeletal systems and instead occurs by a remarkable membrane blebbing or tubulation process. Results of wide ranging genetic experiments are consistent with the notion that L-form proliferation is based on membrane dynamics, largely driven by biophysical effects. L-forms may provide an interesting model for considering how primitive cells proliferated before the invention of the cell wall. The results also suggest that invention of the cell wall was a pivotal step in the evolution of cellular life.