The population structure of pathogenic bacteria

The structure of bacterial populations affects their potential to cause disease and respond to human interventions, and we can infer some of that structure from species differences in nucleotide diversity. If there is no natural selection, mutation rate and effective population size determine nucleotide diversity. Mutation rate will not usually influence species differences in nucleotide diversity. In some species an elevated mutation rate may signal that the species has undergone recent rapid evolutionary change. Recombination does not affect effective population size but does determine the effect that natural selection has on the system. Selective sweeps will eliminate diversity, while diversifying selection maintains diversity. When there is little or no recombination, selection will strongly influence nucleotide diversity generally. When there is much recombination, selection will only influence nucleotide diversity locally. Thus, the nucleotide diversity (both local and genomic) gives us information about how pathogens have adapted to changing conditions.