Comparative Genomic Analysis of a Novel sp. Isolated from an Ulcer Disease Event in Atlantic Salmon ().

Ulcer diseases are a recalcitrant issue at Atlantic salmon () aquaculture cage-sites across the North Atlantic region. Classical ulcerative outbreaks (also called winter ulcer disease) refer to a skin infection caused by . However, several bacterial species are frequently isolated from ulcer disease events, and it is unclear if other undescribed pathogens are implicated in ulcer disease in Atlantic salmon. Although different polyvalent vaccines are used against , ulcerative outbreaks are continuously reported in Atlantic salmon in Canada. This study analyzed the phenotypical and genomic characteristics of sp. J383 isolated from internal organs of vaccinated farmed Atlantic salmon displaying clinical signs of ulcer disease. Infection assays conducted on vaccinated farmed Atlantic salmon and revealed that sp. J383 causes a low level of mortalities when administered intracelomic at doses ranging from 10-10 CFU/dose. sp. J383 persisted in the blood of infected fish for at least 8 weeks at 10 and 12 °C. Clinical signs of this disease were greatest 12 °C, but no mortality and bacteremia were observed at 16 °C. The sp. J383 genome (5,902,734 bp) has two chromosomes of 3,633,265 bp and 2,068,312 bp, respectively, and one large plasmid of 201,166 bp. Phylogenetic and comparative analyses indicated that sp. J383 is related to , with 93% identity. Furthermore, the phenotypic analysis showed that there were significant differences between sp. J383 and other spp, suggesting J383 is a novel species adapted to cold temperatures.