A Bacterial Kind of Aging

acteria are sometimes honored with a few lines in books and reviews on aging as an example of organisms that do not age.This is because binary fission of bacteria has been assumed to proceed with a nonconservative dispersion of both undamaged and damaged constituents, such that there are no adult forms of bacterial cells and the bacterial population is not age structured.However, some authors have expressed different views; for example, Partridge and Barton [1] consider asymmetry in simple unicellular systems and how this might develop into aging, and Tom Kirkwood [2] argues, on theoretical grounds, that damage segregation could be selected for in simple unicellular systems dividing by binary fission, and that sibling-specific deterioration may confer a selective advantage.Indeed, recent reports lend experimental support to this notion and point to mandatory aging also being a part of the life history of bacteria.These reports include the demonstration that cells of an Escherichia coli population exhibit markedly different loads of damaged proteins [3].This damage heterogeneity does not follow a simple normal distribution but rather indicates that the population consists of two discrete populations with respect to damage; a damage-enriched and a low-damage population [3].Moreover, the low-damage cells remain reproductively competent, whereas damage-enriched cells become genetically dead (non-culturable) [3].In addition, and most importantly, bacterial cells have been shown to exhibit signs of replicative aging, or loss of fitness, in a sibling-specific manner during exponential growth; i.e., a cumulative loss of fitness in one sibling lineage that could be argued to serve as a ''mother-type'' lineage, similar to that of the budding yeast Saccharomyces cerevisiae [4,5].