The Dimorphic Life Cycle ofCaulobacterand Stalked Bacteria

Abstract

The development of stalked bacteria like Caulobacter is an integral part of cell growth and occurs in each cell division cycle. This chapter introduces the life cycle of stalked bacteria and then focuses on the best-studied example, Caulobacter crescentus. Recent progress in understanding the regulation of stalk and holdfast synthesis and of cell division are reviewed. The holdfast, the adhesion organelle that allows Caulobacter to attach to surfaces, appears at the tip of nascent stalks during swarmer cell differentiation. Phosphate starvation dramatically induces stalk synthesis in Caulobacter, whereas starvation for nitrogen can block the differentiation of swarmer cells. Caulobacter cells undergo drastic morphological changes when cultured in stationary phase for an extended period. The isolation of mecillinam-resistant short-stalked mutants of Caulobacter also suggests that penicillin binding proteins (PBPs) play an important role in stalk synthesis. The increase in surface-to-volume ratio caused by stalk elongation during phosphate starvation is thought to allow Caulobacter cells to take up phosphate and other nutrients more efficiently. The holdfast is an adhesive organelle, found at the tips of stalks in Caulobacter, which mediates attachment to substrates. The study of bacterial development has had a major impact on one’s understanding of the bacterial cell.