Replicative senescence in Caulobacter crescentus

Replicative senescence has been reported in Caulobacter crescentus, a bacterium in which cytokinesis is intrinsically asymmetrical. The bacterium can freely swim in water and this free swimming cell represents the swarmer cell. The swarmer cell is non-reproductive, but after a period of free swimming, it gets differentiated to a sessile reproductive stalked cell. The stalked cell remains attached to the substrate but produces progeny swarmer cells which then separates from the stalked cells and begin free swimming.

Ackerman et al. (2003) studied the replicative senescence in Caulobacter crescentus by using microscopy flow chambers in which the stalked cells were attached to the chamber while the swarmer cells produced from the stalked cells were removed by the medium flowing through the chamber. They noticed that, as the stalked cells gave rise to more progenies, their rate of division slowed and finally stopped completely. However, the progenies produced, i.e. the swarmer cells, were rejuvenated offspring. Moreover, those progenies produced towards the end were indistinguishable from any of the young cells produced earlier in the experiment in terms of cell division time. These experiments proved that the stalked cells undergo senescence and that their reproductive output decreases with increasing aging. However, the major difference was that, unlike S. cerevisiae, S. pombe, or D. melanogaster, the progenies from both the older and younger mother cells were rejuvenated offspring and indistinguishable from each other. i.e. older bacterium produces only young bacterium.

Next- Stewart et al. (2005) model of replicative senescence in E.coli

Ackermann et al. (2003). Senescence in a bacterium with asymmetric division. Science 300(5627), 1920.