RT Journal Article SR Electronic T1 Sex overrides mutation in Escherichia coli colonizing the gut JF bioRxiv FD Cold Spring Harbor Laboratory SP 384875 DO 10.1101/384875 A1 N. Frazão A1 A. Sousa A1 M. Lässig A1 I. Gordo YR 2018 UL http://biorxiv.org/content/early/2018/08/07/384875.abstract AB Bacteria evolve by mutation accumulation in laboratory experiments, but the tempo and mode of evolution in natural environments are largely unknown. Here we show, by experimental evolution of E. coli in the mouse gut, that the ecology of the gut controls bacterial evolution. If a resident E. coli strain is present in the gut, an invading strain evolves by rapid horizontal gene transfer; this mode precedes and outweighs evolution by point mutations. An epidemic infection by two phages drives gene uptake and produces multiple co-existing lineages of phage-carrying (lysogenic) bacteria. A minimal dynamical model explains the temporal pattern of phage epidemics and their complex evolutionary outcome as generic effects of phage-mediated selection. We conclude that phages are an important eco-evolutionary driving force – they accelerate evolution and promote genetic diversity of bacteria.One Sentence Summary Bacteriophages drive rapid evolution in the gut.