Comparative genome analyses of three serotypes of Lactococcus bacteria isolated from diseased cultured striped jack (Pseudocaranx dentex)

Abstract

Lactococcosis, caused by members of the genus Lactococcus, represents a devastating disease inducing mass mortalities and economic losses in many fish species worldwide. The present work aimed to compare the whole genome sequences of three different serotypes of Lactococcus garvieae isolated from diseased cultured striped jack (Pseudocaranx dentex) in Ehime prefecture, Japan. The three serotypes showed different virulence in the challenge test using Japanese amberjack (Seriola quinqueradiata). The genome sequencing revealed that two of the strains (serotype I and serotype III) were identified as L. garvieae, while the third strain (serotype II) was identified as L. formosensis. The chromosome sizes of the three serotypes ranged from 1.9 to 2.0 Mb; the GC content ranges were 38.2 to 38.9%; and the numbers of predicted protein‐coding sequences (CDSs) were from 1922 to 1959. Only the serotype II harbours two plasmids, sizes of around 14 kb and 9 kb. The detected virulence factors varied among the different serotypes with some shared factors like adherence, anti‐phagocytosis, secretion system, toxin (haemolysin), serum resistance, antimicrobial resistance and others. The genomes also contained factors responsible for resistance to toxic compounds. The genome of the serotype III tended to encode more prophage regions than the other serotypes.

Genetic Characterization of Lactococcus spp. Isolated from Brazilian Native Fish Species

“…Fragments measuring 285 bp correspond to serotype I, while fragments measuring 1,285 bp correspond to serotype II [15]. Using this methodology, serotype I was detected in diseased Anguilla anguilla, Oncorhynchus mykiss, Paralichthys olivaceus, Pseudocaranx dentex, Rachycentron canadum, Seriola quinqueradiata, Seriola dumerili, and Trachinotus blochii [15,16,25,[47][48][49]. On the other hand, serotype II was detected in Pseudocaranx dentex, Seriola quinqueradiata, Seriola dumerili and Seriola lalandi [15,50].…”

“…Our study showed that L. garvieae and L. petauri strains were classified as serotype I, while the isolates of L. formosensis were characterized as serotype II (Figure 2). In addition, one isolate that was previously classified as serotype II [50] was recently described as belonging to L. formosensis [47]. Furthermore, we performed an in silico PCR, using java web tools [51], for all the complete genomes (I4/60, GenBank accession number: GCA_023822125.1; 122061, GCA_002355575.1; and MS200408A, GCA_030295725.1) and the reference genome (NBRC 109475, GCA_018403745.1) of L. formosensis strains, with taxonomy checked on the NCBI database, and also found an expected PCR product size of 1,285 bp.…”