Emerging bacterial fish pathogen Lactococcus garvieae RTCLI04, isolated from rainbow trout (Oncorhynchus mykiss): Genomic features and comparative genomics.

Lactococcus garvieae is one of the emerging zoonotic bacterial pathogen, causes fatal hemorrhagic septicemia in cultured fish species, animals and humans, worldwide. Here, we report the genomic features of whole-genome sequence (WGS) of L. garvieae strain RTCLI04, recovered from lower intestine of farmed rainbow trout, Oncorhynchus mykiss in the northwest Himalayan region India. The genome of L. garvieae RTCLI04 is a single circular chromosome of 2,054,885 base pairs (bp), which encodes 1993 proteins and has G + C content of 39%. The bioinformatics analysis of WGS of RTCLI04, confirmed the presence of 51 tRNAs genes (including two pseudogenes), six rRNAs genes (four genes for 5S rRNA; one gene for 16S rRNA and one gene for 23S rRNA), five virulent domains, and twenty eight different genetic pathways. A Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) finder tool indicates that three different CRISPR and one cas system with common spacer was present in the genome of L. garvieae RTCLI04. Pan-genome analysis of RTCLI04 and all the other reference L. garvieae strains shows that pan-genome of this bacterium consisted of 2239 putative protein-coding genes in which 1850 genes are core gene, 389 genes are dispensable gene, and 221 genes are unique to RTCLI04. L. garvieae RTCLI04 lacks genomic island of 16.5 Kb capsule gene cluster. In addition, 39 virulence-associated genes (VAGs) including hly1,-2,-3; PavA, PsaA; eno; LPxTG containing surface proteins 1, 2, 3 and 4; pgm, sod and 29 antimicrobial resistant genes (ARGs) including mefE (clindamycin), srmB (lincomycin), dfrA26 (trimethoprim), gyrB (nalidixic acid), arr-3 (rifampin), otrB (tetracycline), aac(6)-Ic (tobramycin), IrgB (penicillin), mecA (oxacillin), vanRB (vancomycin) and mfpA (fluoroquinolone) were also predicted in the genome of L. garvieae RTCLI04. Our study provides new insight into understanding the virulence mechanism, antimicrobial resistance, and development of effective therapeutic measures against L. garvieae during a disease outbreak in aquaculture.