Multilocus Sequence Analysis of the Marine Bacterial Genus Tenacibaculum Suggests Parallel Evolution of Fish Pathogenicity and Endemic Colonization of Aquaculture Systems

The genusTenacibaculum , a member of the familyFlavobacteriaceae , is an abundant component of marine bacterial ecosystems that also hosts several fish pathogens, some of which are of serious concern for marine aquaculture. Here, we applied multilocus sequence analysis (MLSA) to 114 representatives of most known species in the genus and of the worldwide diversity of the major fish pathogenTenacibaculum maritimum . Recombination hampers precise phylogenetic reconstruction, but the data indicate intertwined environmental and pathogenic lineages, which suggests that pathogenicity evolved independently in several species. At lower phylogenetic levels recombination is also important, and the speciesT. maritimum constitutes a cohesive group of isolates. Importantly, the data reveal no trace of long-distance dissemination that could be linked to international fish movements. Instead, the high number of distinct genotypes suggests an endemic distribution of strains. The MLSA scheme and the data described in this study will help in monitoringTenacibaculum infections in marine aquaculture; we show, for instance, that isolates from tenacibaculosis outbreaks in Norwegian salmon farms are related toT. dicentrarchi , a recently described species.