First isolation, pathogenicity, and draft genome sequences of Lactococcus garvieae serotype III from cobia Rachycentron canadum.

Abstract

Lactococcus garvieae causes lactococcosis in several marine-cultured fish species in Japan. A new L. garvieae serotype III was recently identified in diseased striped jack Pseudocaranx dentex, yellowtail Seriola quinqueradiata, and amberjack S. dumerili. Herein, we report the first isolation of L. garvieae serotype III isolates LC2313 and LC2323 from cage-cultured cobia Rachycentron canadum. Naturally diseased fish exhibited clinical signs of hemorrhagic eyes and a curved spine. An infectivity trial on cobia using the LC2323 isolate revealed 30% mortality by intramuscular injection at doses of 105 or 107 CFU fish-1, while 50-60% mortalities were observed by intraperitoneal injection at the same infectious doses. Both the LC2313 and LC2323 isolates caused up to 100% mortality in yellowtail and amberjack during 14 d of observation. The draft genomes of LC2313 and LC2323 were 1951432 and 1953218 bp, respectively, with G+C contents of 38.9% for both isolates. A total of 1867 coding sequences were predicted for LC2313 and 1872 for LC2323 with 12 phage-related genes each. The core-genome sequence alignment indicated a close relationship between these isolates and the recently identified L. garvieae serotype III from amberjack and striped jack. Taken together, these results demonstrate the pathogenicity of L. garvieae serotype III in susceptible fish species, highlighting the need for awareness regarding disease transmission among fish species.