THE POPULATION-GENETICS OF BACTERIA

Electrophoretic studies have shown that bacterial populations are highly variable, but that particular clones are found repeatedly. Even if it is assumed that large-scale recombination is rare, and if allowance is made for the sub-divided nature of bacterial populations, these two observations (high variability and clonal population structure) can only be reconciled in a simple model by assuming an unrealistically small effective population size. This paper therefore considers a more complex model, incorporating hitch-hiking (the fixation of favourable alleles in the absence of recombination), localized recombination (the transfer between related strains of short regions of DNA), and ecotypic structure (the adaptation of different clones to different habitats).