Adaptation d’Escherichia coli à la phase stationnaire
During colonization of the human colon, E. coli may enter stationary phase as a result of Pi starvation. Pi-starved cells are exposed to oxidative agents and weak acids produced during aerobic glucose metabolism. E. coli may survive prolonged incubation as a result of the induction by RpoS of the poxB and gadB genes. The PoxB shunt prevents the synthesis of H2O2, and GadB neutralizes acetic acid by consuming glutamate and protons. However, rpoS mutants can survive by growing in stationary phase on acetic acid and Pi excreted by dying cells. E. coli K-12 can evolve rapidly, thereby generating mutants that eventually overtake the population during prolonged incubation in the absence of glutamate. Evolved strains carry several mutations, including rpoS mutations, which allow cells to express a growth under Pi starvation (GPS) phenotype. We are in the process of determining the nature of the evolved mutations, the changes in metabolic pathways, and the mechanisms of adaptive mutagenesis triggered in Pi-starved cells.