
Full text loading...
22 Developmental Control in Caulobacter crescentus: Strategies for Survival in Oligotrophic Environments, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815677/9781555814205_Chap22-1.gif /docserver/preview/fulltext/10.1128/9781555815677/9781555814205_Chap22-2.gifAbstract:
In stalked alphaproteobacteria such as Caulobacter crescentus, Asticcacaulis biprosthecum, and Hyphomicrobium neptunium, development is not triggered by environmental changes but is a consequence of normal progression through the cell cycle. In contrast to M. xanthus and B. subtilis, the oligotrophic C. crescentus has adopted a different strategy to cope with almost constant famine. First, the production of a chemotactically competent swarmer cell allows dispersal towards more nutritionally rich environments. Second, the successive synthesis of a flagellum, pili, and holdfast at the same pole of the cell optimizes attachment of swarmer cells to surfaces, thus improving the cell’s access to nutrients absorbed to surfaces. Finally, once attached tightly to a surface by its holdfast, the cell synthesizes a stalk, which dramatically improves nutrient uptake in the diffusion-limited environment where C. crescentus typically lives. This chapter focuses on the mechanisms of surface adhesion and stalk function, as well as how the overall developmental cycle is controlled. Differentiation is an essential process for adhesion of C. crescentus to surfaces. The stalk is an extension of the cell wall and membranes devoid of ribosomes, DNA, and cytoplasmic proteins. The stalk is transected perpendicularly by crossbands synthesized during each round of cell division, which may serve to compartmentalize the stalk from the cell body. A complex signal transduction pathway ensures that polar development, DNA replication, and cell division are coordinated. The new pole remains marked until late in cell division when TipN moves from the pole to the site of division.
Full text loading...
The cell cycle of C. crescentus. Each round of cell division produces a stalked cell and a motile swarmer cell. The swarmer cell must differentiate into a stalked cell prior to undergoing cell division.
Diagram of the stages of C. crescentus adhesion. From left to right, a swarmer cell approaches a substrate so that the pili and/or the flagellum binds the surface; weak attachment persists transiently, during which time the pili retract until tight attachment forms, mediated by the holdfast.
Nutrient uptake model of stalk function in C. crescentus. Two nonexclusive models are proposed to explain nutrient uptake by the stalk. The periplasmic diffusion model illustrates nutrients binding to periplasmic receptors and being transported to the cell body through the periplasm, where they can then be taken up by the cell. The stalk core diffusion model shows the possibility of nutrients binding to periplasmic receptors and then being taken into the core of the stalk by transport proteins. The nutrients would then diffuse into the cell body. The available experimental data support the periplasmic diffusion model. Reprinted from Molecular Microbiology (Wagner and Brun, 2007) with permission of the publisher.
Regulatory pathway controlling cell division and polar development in C. crescentus. Sensor kinases and response regulators, along with other factors, coordinate polar development with cell cycle progression. Figure adapted from Biondi et al. ( Biondi et al., 2006 a).