Conditional and replicative senescence in Escherichia coli

Analysis of the molecular mechanisms underlying the cellular degeneration of bacteria in stationary phase (known as conditional senescence) reveals interesting similarities with the aging process of higher organisms. These similarities include the role of self-inflicted oxidative damage and the importance of protein quality control systems in retarding senescence. In addition, recent data suggests that Escherichia coli cells display signs of replicative senescence, or loss of fitness, during exponential growth and that this phenomenon targets the ‘older’ cells. Thus, bacterial physiology might entail both conditional and mandatory aging processes.