Evolution of high mutation rates in experimental populations of E. coli

Abstract

Most mutations are likely to be deleterious, and so the spontaneous mutation rate is generally held at a very low value¹. Nonetheless, evolutionary theory predicts that high mutation rates can evolve under certain circumstances^2,3,4. Empirical observations have previously been limited to short-term studies of the fates of mutator strains deliberately introduced into laboratory populations of Escherichia coli^5,6,7, and to the effects of intense selective events on mutator frequencies in E. coli⁸. Here we report the rise of spontaneously originated mutators in populations of E. coli undergoing long-term adaptation to a new environment. Our results corroborate computer simulations of mutator evolution in adapting clonal populations⁴, and may help to explain observations that associate high mutation rates with emerging pathogens⁹ and with certain cancers¹⁰.