Large genomic, functional, and phenotypical diversity of Janthinobacterium associated with Atlantic salmon fry

Members of the genus Janthinobacterium are widespread and found in soil and freshwater ecosystems, but also in the skin of humans, fish, and amphibians. They are known for producing violacein, and they typically have antifungal properties. In amphibians, Janthinobacterium spp. protect their hosts against fungal infections. We examined the diversity of five Janthinobacterium strains isolated from the skin and rearing water of Atlantic salmon fry by phenotypic characterization and comparative genomics. Although their 16S rRNA gene sequences were almost identical, their phenotypes were highly dissimilar, and only two of the species consistently produced violacein. Genomic analyses revealed that they represented five species, and phylogenetic analysis suggested that only one was closely related to a previously described species (Janthinobacterium tructae ^T). All strains possessed the Janthinobacterium quorum sensing system, while three harbored genes of the AHL QS system. They had great potential for producing secondary metabolites, and one carried putative genes of the antibiotic tropodithietic acid, previously described in the marine Phaeobacter. Interestingly, they all carried putative genes for heterotrophic carbon fixation. Furthermore, they had the genetic potential for chemotaxis and motility; compatible with a host-associated lifestyle. Gnotobiotic experiments confirmed that they were able to colonize yolk sac fry of Atlantic salmon.