High genetic diversity of Vibrio cholerae in the European lake Neusiedler See is associated with intensive recombination in the reed habitat and the long-distance transfer of strains.

Coastal marine Vibrio cholerae populations usually exhibit high genetic diversity. To assess the genetic diversity of abundant V. cholerae non-O1/non-O139 populations in the Central European lake Neusiedler See, we performed a phylogenetic analysis based on recA, toxR, gyrB and pyrH loci sequenced for 472 strains. The strains were isolated from three ecologically different habitats in a lake that is a hot-spot of migrating birds and an important bathing water. We also analyzed 76 environmental and human V. cholerae non-O1/non-O139 isolates from Austria and other European countries and added sequences of seven genome-sequenced strains. Phylogenetic analysis showed that the lake supports a unique endemic diversity of V. cholerae that is particularly rich in the reed stand. Phylogenetic trees revealed that many V. cholerae isolates from European countries were genetically related to the strains present in the lake belonging to statistically supported monophyletic clades. We hypothesize that the observed phenomena can be explained by the high degree of genetic recombination that is particularly intensive in the reed stand, acting along with the long distance transfer of strains most probably via birds and/or humans. Thus, the Neusiedler See may serve as a bioreactor for the appearance of new strains with new (pathogenic) properties.

Vibrio cholerae in an Historically Cholera-Free Country.

We report the autochthonous existence of Vibrio cholerae in coastal waters of Iceland, a geothermally active country where cholera is absent and has never been reported. Seawater, mussel, and macroalgae samples were collected close to and distant from sites where geothermal activity causes a significant increase in water temperature during low tides. V. cholerae was detected only at geothermal-influenced sites during low-tides. None of the V. cholerae isolates encoded cholera toxin (ctxAB) and all were non-O1/non-O139 serogroups. However, all isolates encoded other virulence factors that are associated with cholera as well as extra-intestinal V. cholerae infections. The virulence factors were functional at temperatures of coastal waters of Iceland, suggesting an ecological role. It is noteworthy that V. cholerae was isolated from samples collected at sites distant from anthropogenic influence, supporting the conclusion that V. cholerae is autochthonous to the aquatic environment of Iceland.