In nature, bacteria can survive for long periods in non-growing stationary states. Some species of bacteria survive by forming spores but non-spore-forming bacteria, including Escherichia coli, survive in the stationary phase. Gross changes in morphology and physiology occur in the stationary-phase bacteria and concomitantly a state of increased resistance against various stresses is established. The stationary-phase adaptation of E. coli has only recently begun to be investigated at the molecular level.