Fine-scale diversity and extensive recombination in a quasisexual bacterial population occupying a broad niche

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Science  29 May 2015:
Vol. 348, Issue 6238, pp. 1019-1023
DOI: 10.1126/science.aaa4456

Quasi-sexual microbe populations

Astonishing levels of fine-scale microbial diversity have been uncovered by DNA sequencing of natural populations. How this diversity is shaped and maintained and what its environmental or clinical implications might be is unclear. Using custom-made advanced statistical methods, Rosen et al. analyzed the evolutionary structure of a photosynthetic bacterium that grows in the hot springs of Yellowstone Park (see the Perspective by Desai and Walczak). The populations behaved neither as clones nor “ecotypes” but more like sexual organisms. These cyanobacteria have high recombination rates that maintain diversity and prevent selective sweeps that would otherwise reduce diversity.

Science, this issue p. 1019; see also p. 977


Extensive fine-scale genetic diversity is found in many microbial species across varied environments, but for most, the evolutionary scenarios that generate the observed variation remain unclear. Deep sequencing of a thermophilic cyanobacterial population and analysis of the statistics of synonymous single-nucleotide polymorphisms revealed a high rate of homologous recombination and departures from neutral drift consistent with the effects of genetic hitchhiking. A sequenced isolate genome resembled an unlinked random mixture of the allelic diversity at the sampled loci. These observations suggested a quasisexual microbial population that occupies a broad ecological niche, with selection driving frequencies of alleles rather than whole genomes.

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