Recombination and clonality in natural populations of Escherichia coli.

Bacteria such as Escherichia coli have been commonly viewed as being primarily clonal organisms. As such, the genetic variation within clones was thought to be almost exclusively the result of the mutational process. This conclusion has recently been challenged by data from DNA sequencing studies of natural isolates that are incompatible with a primarily clonal structure. Molecular population genetic analyses of these data, including gene genealogical comparisons, have raised the possibility of a much more complex population structure that may encompass relatively frequent recombination, recurrent selective sweeps and extensive ecological population subdivision.