Comparative Genomics Analysis of the Fish Pathogen Rahnella aquatilis KCL-5 Reveals Potential Multidrug Resistance and Virulence Properties.

The genus Rahnella has been isolated from human, fish, and water environments. We recently reported on the isolation and genomic identification of a novel pathogen R. aquatilis strain KCL-5 from crucian carp Carassius auratus. To investigate the evolution of bacterial virulence and resistance properties of R. aquatilis, comparative genomics analyses were performed for genus Rahnella strains including R. aquatilis, R. variigena, R. bruchi, and R. victoriana. This analysis provides up-to-date information on genus Rahnella genomic diversity, including comparative analyses of virulence and resistance, synteny, single-nucleotide polymorphisms, average nucleotide identity, core-genes, gene families, and genomic islands. The sister species to R. aquatilis is R. victoriana, and closer R. victoriana than with other Rahnella sp. Multiple genes encoding functions that likely contribute to antimicrobial resistance and pathogenic factors were identified by comparative genome analysis, including multidrug resistance efflux pump, adherence, invasion, and secretion systems. To our knowledge, this is the first report to provide a more detailed insight into the comparative genomic characteristics of Rahnella spp., contributing to the understanding of its diversity and evolution, as well as concerning the virulence of R. aquatilis.