Contrasting inter-and intraspecies recombination patterns in the "harveyi clade" vibrio collected over large spatial and temporal scales

Recombinationplaysanimportant role in thedivergenceofbacteria, but thefrequencyof interspecies andintraspecies recombination events remains poorly understood. We investigated recombination events that occurred within core genomes of 35 Vibrio strains (family Vibrionaceae, Gammaproteobacteria), from six closely related species in the so-called "Harveyi clade." The strains were selected from a collection of strains isolated in the last 90 years, fromvarious environments worldwide.Wefound a close relationship between the number of interspecies recombination events within core genomes of the 35 strains and the overall genomic identity, as inferred fromcalculations of the average nucleotide identity. The relationship between theoverall nucleotide identity andthe number of detected interspecies recombination events was comparable when analyzing strains isolated over 80 years apart, from different hemispheres, or from different ecologies, as well as in strains isolated from the same geographic location within a short time frame. We further applied the same method of detecting recombination events to analyze 11 strains of Vibrio campbellii, and identified disproportionally high number of intraspecies recombination events within the core genomes of some, but not all, strains. The high number of recombination events was detected between V. campbellii strains that have significant temporal (over 18 years) and geographical (over 10,000 km)differences in theirorigins of isolation. Resultsof this study reveal aremarkablestabilityofHarveyi clade species, and give clues about the origins and persistence of species in the clade.