The Contribution of Genetic Recombination to CRISPR Array Evolution.
Bottom Line: Genetic recombination has been proposed to accelerate adaptation by combining beneficial mutations that arose in independent lineages.However, for most species under study, we find that CRISPR evolution is shaped mainly by spacer acquisition and loss rather than recombination.Since the evolution of spacer content is characterized by a rapid turnover, it is likely that recombination is not beneficial for improving phage resistance in the strains under study, or that it cannot be detected in the resolution of intraspecies comparisons.
Affiliation: Institute of General Microbiology, Christian-Albrechts-University Kiel, Germany email@example.com.Show MeSH
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Mentions: The observed stable ratios can be the result of either a constant rate of deletions and recombination events or a constant rate of deletions and the ensuing proximal deletions. To distinguish between these two alternatives, we performed additional perturbations of the original data sets. Simulated deletions are introduced into the data sets where the number of successive spacers being deleted is randomly chosen from the observed distribution of deletion length in the respective data set (supplementary table S1, Supplementary Material online). We define artificial deletions as the deletions that are inferred in the data sets following the perturbation. This analysis reveals that increasing the number of simulated deletions in the data set results in an increased number of artificial deletions (fig. 6). However, only a minority of the simulated deletions is detectable, with a ratio of artificial to simulated deletions ranging from 0.12 (S. agalactiae) to 0.3 (S. thermophilus) (fig. 6 and table 3; supplementary fig. S3, Supplementary Material online).Fig. 6.—
Affiliation: Institute of General Microbiology, Christian-Albrechts-University Kiel, Germany firstname.lastname@example.org.