Comparative genomics provides new insights into pathogenesis of spotting disease causative bacteria in farmed Strongylocentrotus intermedius

The bacterial genus Vibrio includes major pathogens of spotting disease in sea urchins. However, information concerning spotting disease causative Vibrio species is still lacking in regard to genetic features, classification biomarkers, and evolutionary relationships. The current study provides complete genome descriptions of two Vibrio strains (named HD-1 and HD-2) isolated from diseased Strongylocentrotus intermedius farmed in coastal areas of northern China. Comparative genomics analysis results showed that: (1) genomes of both the HD-1 and HD-2 were divided into two chromosomes; the HD-1 genome contained more genes compared to HD-2, and the number of plasmids in HD-1 was less than that in HD-2; (2) there were 464 and 401 potential virulence factors identified in the HD-1 and the HD-2 genomes, respectively. The results of laboratory-based artificial infection experiments identified more potential virulence factors (such as T3SS- and T4SS-related virulence factors) specific to the HD-1 genome, indicating a higher infection efficiency of HD-1 compared to HD-2; (3) Phylogeny and collinearity analyses indicated the intra-taxa diversity and evolutionary distance between HD-1 and HD-2. All of the observations in this study not only enrich current knowledge of genetic information for the genus Vibrio, but they also reveal the infection efficiency variation, intra-taxa diversity, and evolutionary relationships of spotting disease causative Vibrio species in sea urchins.