Costs and benefits of high mutation rates: Adaptive evolution of bacteria in the mouse gut

We have shown that bacterial mutation rates change during the experimental colonization of the mouse gut. A high mutation rate was initially beneficia l because it allowed faster adaptation, but this benefit disappeared once a daptation was achieved. Mutator bacteria accumulated mutations that. althou gh neutral in the mouse gut, are often deleterious in secondary environment s. Consistently, the competitiveness of mutator bacteria is reduced during transmission to and re-colonization of similar hosts. The short-term advant ages and long-term disadvantages of mutator bacteria could account for thei r frequency in nature.