Bacteria are different – the dynamics of genome content

Bacteria show startling variation in the composition of their genomes, such that isolates of the same named species may vary by as much as 10% of the genes present, which are termed the ‘accessory’ genome. This is often thought to be a consequence of natural selection, both on the organisms, and the genes themselves, which may behave as selfish actors. However much of the observed variation may be explained by a simple, neutral model that allows bacteria to take up DNA from other members of the same species, which is often observed in nature. This may be used to estimate ecological overlap of species clusters, by the amount they have diverged. Finally, there is evidence that negative frequency dependent selection on a subset of genes may explain features of population structure, and be useful in predicting population dynamics in response to vaccination.