Genome-wide mutational diversity in Escherichia coli population evolving in prolonged stationary-phase

Prolonged stationary-phase is an approximation of natural environments presenting a range of stresses. Survival in prolonged stationary-phase requires alternative metabolic pathways for survival. This study describes the repertoire of mutations accumulating in starving E. coli populations in lysogeny broth. A wide range of mutations accumulate over the course of one month in stationary-phase. SNPs constitute 64% of all mutations. A majority of these mutations are non-synonymous and are located at conserved loci. There is an increase in genetic diversity in the evolving populations over time. Computer simulations of evolution in stationary phase suggest that the maximum frequency obtained by mutations in our experimental populations can not be explained by neutral drift. Moreover there is frequent genetic parallelism across populations suggesting that these mutations are under positive selection. Finally functional analysis of mutations suggests that regulatory mutations are frequent targets of selection.