Shapeshifting to Survive: Shape Determination and Regulation in Caulobacter crescentus

Bacterial cell shape is a genetically encoded and inherited feature that is optimized for efficient growth, survival, and propagation of bacteria. In addition, bacterial cell morphology is adaptable to changes in environmental conditions. Work in recent years has demonstrated that individual features of cell shape, such as length or curvature, arise through the spatial regulation of cell wall synthesis by cytoskeletal proteins. However, the mechanisms by which these different morphogenetic factors are coordinated and how they may be globally regulated in response to cell cycle and environmental cues are only beginning to emerge. Here, we have summarized recent advances that have been made to understand morphology in the dimorphic Gram-negative bacterium Caulobacter crescentus. Caulobacter cell shape arises through spatiotemporal regulation of cell wall synthesis. Cell width, length, curvature, and stalk formation are the major shape attributes for Caulobacter cells, and are regulated by the MreB, FtsZ, crescentin, and bactofilin cytoskeletons, respectively. Though independently regulated, these shape features are coordinated in time and space. Caulobacter length and stalk formation are cell-cycle regulated through transcriptional, translational, and proteolytic control, as well as through post-translational modifications and spatial regulation. Starvation, stationary phase, and other stresses promote distinct morphological adaptations to facilitate survival. The mechanisms of shape adaptation are mostly unclear, but include transcriptional responses to environmental signals. Quantitative principles describe shape homeostasis in Caulobacter.