Data from: High mutation rates limit evolutionary adaptation in Escherichia coli

Mutation is fundamental to evolution, because it generates the genetic
variation on which selection can act. In nature, genetic changes often
increase the mutation rate in systems that range from viruses and bacteria
to human tumors. Such an increase promotes the accumulation of frequent
deleterious or neutral alleles, but it can also increase the chances that
a population acquires rare beneficial alleles. Here, we study how up to
100-fold increases in Escherichia coli’s genomic mutation rate affect
adaptive evolution. To do so, we evolved multiple replicate populations of
asexual E. coli strains engineered to have four different mutation rates
for 3000 generations in the laboratory. We measured the ability of evolved
populations to grow in their original environment and in more than 90
novel chemical environments. In addition, we subjected the populations to
whole genome population sequencing. Although populations with higher
mutation rates accumulated greater genetic diversity, this diversity
conveyed benefits only for modestly increased mutation rates, where
populations adapted faster and also thrived better than their ancestors in
some novel environments. In contrast, some populations at the highest
mutation rates showed reduced adaptation during evolution, and failed to
thrive in all of the 90 alternative environments. In addition, they
experienced a dramatic decrease in mutation rate. Our work demonstrates
that the mutation rate changes the global balance between deleterious and
beneficial mutational effects on fitness. In contrast to most theoretical
models, our experiments suggest that this tipping point already occurs at
the modest mutation rates that are found in the wild.