Coevolution with viruses drives bacterial mutations
Bacteria with greatly elevated mutation rates (mutators) are frequently found in natural and laboratory populations, and are often associated with clinical infections. Although mutators may increase adaptability to novel environmental conditions, they are also prone to the accumulation of deleterious mutations. The long-term maintenance of high bacterial mutation rates is therefore likely to be driven by rapidly changing selection pressures, in addition to the possible slow transition rate by point mutation from mutators to non-mutators. One of the most likely causes of rapidly changing selection pressures is antagonistic coevolution with parasites.
This paper examines whether coevolution with viral parasites could drive the evolution of bacterial mutation rates in laboratory populations of the bacterium Pseudomonas fluorescens. After fewer than 200 bacterial generations, 25% of the populations coevolving with phages had evolved 10- to 100-fold increases in mutation rates owing to mutations in mismatch-repair genes; no populations evolving in the absence of phages showed any significant change in mutation rate. Furthermore, mutator populations had a higher probability of driving their phage populations extinct, strongly suggesting that mutators have an advantage against phages in the coevolutionary arms race. Given their ubiquity, bacteriophages may play an important role in the evolution of bacterial mutation rates.
The most probable explanation for this result is that mutator alleles hitch-hike with the beneficial phage resistance mutation they generated. The ubiquity of bacteriophages suggests that they may play a pivotal role in explaining why mutators persist at relatively high frequencies in many natural bacterial populations. As such, targeting phage populations may weaken selection for mutator bacteria in clinical infections. This study provides the first direct experimental evidence that a mechanism that increases genetic variation can be individually advantageous when coevolving with parasites.
Coevolution with viruses drives the evolution of bacterial mutation rates
Nature 450: 1079 (2007)
