Potential link between selection for high GC content and repair of double strand breaks in prokaryotic genomes

Genomic GC content varies widely among microbes for reasons unknown. While mutation bias partially explains this variation, prokaryotes near-universally have a higher GC content than predicted solely by this bias. Debate surrounds the relative importance of the remaining explanations of selection versus biased gene conversion favoring GC alleles. Some environments (e.g. soils) are associated with a high genomic GC content of their inhabitants, which implies that this content may be a selective adaptation to a particular habitat. Here, we report a novel association between the presence of the non-homologous end joining DNA double- strand break repair pathway and GC content; this observation suggests that high GC content may be an adaptation to facilitate repair of double strand breaks when homologous recombination is not possible. We discuss potential mechanisms accounting for the observed association, and provide preliminary evidence that sites experiencing high rates of double-strand breaks are under selection for increased GC content relative to the genomic background.