| Caulobacter crescentus populations are composed of cells of two distinct morphologies: the motile, flagellated swarmer cell, and the sessile, adherent stalked cell. With each cell cycle, a stalked cell asymmetrically divides giving rise to a swarmer cell, which will ultimately differentiate into a stalked cell to begin the cycle anew. Caulobacter can be recovered from aquatic, oligotrophic niches as free swimming swarmer cells, or as part of a multicellular biofilm community comprised of both cell types. The sessile: motile switch achieved with each cell cycle permits newly-fledged swarmers to remain part of a maturing biofilm, or, when local resources are insufficient, to disperse and scavenge. It is not known how biofilms mitigate local resource competition. Chapter II proposes a strategy for population control within the Caulobacter biofilm subpopulation under glucose limitation. Transcriptional profiling performed on cells grown in continuous culture, modeling oligotrophic levels of glucose availability, points to a stalked cell-specific defense response that invokes a novel signaling pathway. Evidence indicates adherent stalked cells induce a cell defense response to prevent unsustainable growth in a dense biofilm.;Critical to both single and multicellular life strategies, biogenesis of the flagellum is a well-studied differentiation process in Caulobacter. Flagellar components have been resolved into four classes based on the sequential pattern by which they are assembled. A trans-acting hierarchy regulates the temporal expression of the flagellar component classes requiring that a complete complement of genes from an earlier class must be translated prior to expression of genes in the successive class. A late assembly checkpoint employs post-transcriptional regulator, FlbT, which represses flagellin translation until the hook structure is assembled. Chapter III is a reprint of article, The conserved flaF gene has a critical rote in coupling flagellin translation and assembly in Caulobacter crescentus, which originally appeared in Molecular Microbiology. This manuscript investigates the regulatory role of the gene just 3' to flbT, flaF. Analysis of flagellin mRNA abundance and stability, as well as phenotypic comparisons of Delta flaF and DeltaflaF DeltaflbT strains indicate that FlaF is a positive regulator of flagellin translation and secretion, and operates in conjunction with FlbT. |
