Caption for image: “What is true for E. coli is true for the elephant.” Quote by Jacques Monod. This false color image shows a growing microcolony of E. coli, where the cells are colored by age (in numbers of divisions). The oldest cells are red, and the youngest blue. Photograph by Eric Stewart and Stefanie Timmermann, Inserm U571, Faculté de Médecine Necker Enfants-Malades, Paris, France.
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Can organisms such as bacteria age? The assumption has been that cells that divide symmetrically do not age and are functionally immortal. In a study published in the premier open-access journal PLoS Biology Eric Stewart and colleagues have now overturned this idea by analyzing repeated cycles of reproduction in Escherichia coli, a bacteria that reproduces without a juvenile phase and with an apparently symmetric division - revealing that these bacteria, like other organisms, have not escaped mortality.

E. coli reproduces by dividing in the middle. Each resultant cell inherits an old end or pole and a new pole, which contain slightly different components, so although they look the same, they are physiologically asymmetrical. At the next division, one cell inherits the old pole again (plus a brand new pole), while the other cell inherits a not-quite-so-old pole and a new pole. Thus, Stewart and co-workers reasoned, an age in divisions can be assigned to each pole and hence to each cell. The researchers used automated time-lapse microscopy to follow all the cell divisions in 94 colonies, each grown from a single fluorescently labeled E. coli cell. In all, the researchers built up a lineage for 35,049 cells in terms of which pole--old or new--each cell had inherited at each division during its history. They found that the cells inheriting old poles had a reduced growth rate, decreased rate of offspring formation, and increased risk of dying compared with the cells inheriting new poles. Thus, the "old pole" cell is effectively an aging parent repeatedly producing rejuvenated offspring.

Stewart and his colleagues conclude that no life strategy is immune to the effects of aging and suggest that this may be because immortality is too costly or is mechanistically impossible. This may be bad news for people who had hoped that advances in science might eventually lead to human immortality. Nevertheless, E. coli should now provide an excellent genetic platform for the study of the fundamental mechanisms of cellular aging and so could provide information that might ameliorate some of the unpleasantness of the human aging process.

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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