Coevolution with viruses drives the evolution of bacterial mutation rates
Bacteria with greatly elevated mutation rates (mutators) are frequently found in natural and laborator 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. Here we show 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. (doi:10.1038/nature06350)
Posted on 
December 12th, 2007 by 
Simon Greenhill
2 Responses to “Coevolution with viruses drives the evolution of bacterial mutation rates”
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Email Henry Updates to Me
December 13th, 2007 at 8:19 am
[...] Bacteria mutates more quickly when with viruses (especially phages) (tags: biology evolution science technology) [...]
December 19th, 2007 at 2:26 pm
First rule of science - do the mathematics. If you calculate the values of the supposed “disadvantages of mutation” over all values of probability of survival and not only the stable normal range you will note that at low rates of survivability (caused by phages, or anything else) the disadvantages of mutation become progressively smaller until they are smaller than the advantages. Hence any organism that treats being pushed to the limits of extinction as a stimulus to increased mutation will tend to gain advantages and leave more descendants - which is the ultimate test in evolution. Active mutation, as opposed to the passive forms considered in the popular but essentially irrelevant neo-Darwinian theories, is subject to natural selection. The organisms that mutate most appropriately in response to a specific stress gain most advantage and leave most descendants. After a few billion years of selection the forms of active mutation utilised by bacteria are spectacularly more effective at producing genetic novelties appropriate to the presenting problems than any form of random mutation.
Evolution of species is also an active process. A thriving population of a species is under no pressure to evolve, it is only the failing species that have to evolve or become extinct. Since the failing species have an example before them, the thriving species, of a genome that is more appropriate to the (presumably changed) environment there is no difficulty in determining the preferred direction of evolution. All that is required is a mechanism, and this is provided by lateral gene transfer - the acquisition by a species which cannot survive in a given environment of genes from a species that can.