Examination of bacterial growth, cell shape maintenance, DNA segregation, and death in Caulobacter crescentus

Abstract

Despite their long-standing role as comparatively simple model organisms, bacteria undergo very complex physiological processes. Their growth depends on the coordinated action of the peptidoglycan remodeling complexes, which include biosynthetic transpeptidases and transglycosylases as well as hydrolytic enzymes. While the roles of transpeptidases in specific modes of bacterial growth are well understood, this dissertation addresses the contribution of transglycosylases to the peptidoglycan synthesis in Caulobacter. We find that tranglycosylases are largely redundant, but the loss of CC0252 leads to a general defect in cell wall integrity. The remodeling complexes themselves are spatially controlled by the three-dimensional arrangements of cytoskeletal structures within the cells. In particular, elongation of most rod-shaped bacteria requires the actin homolog MreB, but despite the central importance of MreB to cell shape maintenance and viability, its regulation is poorly understood. We report the identification of MbiA, a small protein that genetically and biochemically interacts with MreB and whose overexpression mimics the MreB loss-of-function phenotype while also perturbing MreB localization. Bacterial chromosome segregation is also a complex, multistep process. We show that it progresses through several phases involving polar release of the origin, its slow initial motion, and the fast late motion dependent on the action of the polymer-forming ATPase ParA. Finally, we find that upon DNA damage, Caulobacter induces a BapE endonuclease and activates an apoptotic-like response, demonstrating the ability to undergo a process long thought to be the sole purview of eukaryotes.