Complete Genome Sequences and Pathogenicity Analysis of Two Red Sea Bream Iridoviruses Isolated from Cultured Fish in Korea

Abstract

In Korea, red sea bream iridovirus (RSIV), especially subtype II, has been the main causative agent of red sea bream iridoviral disease since the 1990s. Herein, we report two Korean RSIV isolates with different subtypes based on the major capsid protein and adenosine triphosphatase genes: 17SbTy (RSIV mixed subtype I/II) from Japanese seabass (Lateolabrax japonicus) and 17RbGs (RSIV subtype II) from rock bream (Oplegnathus fasciatus). The complete genome sequences of 17SbTy and 17RbGs were 112,360 and 112,235 bp long, respectively (115 and 114 open reading frames [ORFs], respectively). Based on nucleotide sequence homology with sequences of representative RSIVs, 69 of 115 ORFs of 17SbTy were most closely related to subtype II (98.48–100% identity), and 46 were closely related to subtype I (98.77–100% identity). In comparison with RSIVs, 17SbTy and 17RbGs carried two insertion/deletion mutations (ORFs 014R and 102R on the basis of 17SbTy) in regions encoding functional proteins (a DNA-binding protein and a myristoylated membrane protein). Notably, survival rates differed significantly between 17SbTy-infected and 17RbGs-infected rock breams, indicating that the genomic characteristics and/or adaptations to their respective original hosts might influence pathogenicity. Thus, this study provides complete genome sequences and insights into the pathogenicity of two newly identified RSIV isolates classified as a mixed subtype I/II and subtype II.

Whole‐genome analysis of red sea bream iridovirus spread in 2021 in Japan provided epidemiological and viral traits insight

“…RSIV is a double‐stranded DNA virus that belongs to the family Iridoviridae and the genus Megalocytivirus . The length of RSIV genome is ~112 kbp, and the RSIV whole‐genome sequence was first reported in 2002 in an isolate from Ehime Prefecture, Japan (Kurita et al, 2002), after which other genomic sequences of isolates in India (Puneeth et al, 2021) and Korea (Jeong et al, 2021) were continuously reported.…”

“…AP017456.1), can be used for more detailed classification of the RSIV group of megalocytiviruses (Sakseepipad et al, 2021). As the genome sequences of RSIV were analysed, Jeong et al (2021) discovered mutations that may affect viral virulence on protein‐coding regions of two RSIV isolated in Korea in 2017 compared with each other and previously reported RSIV genomes.…”

A New Cell Line Derived from the Caudal Fin of the Dwarf Gourami (Trichogaster lalius) and Its Susceptibility to Fish Viruses

“…Various fish viruses were inoculated into DGF cells to evaluate their susceptibility to viruses. The viruses used in this experiment are as follows: red sea bream iridovirus (RSIV, 17RbGs strain; isolated from rock bream; [ 25 ]), infectious spleen and kidney necrosis virus (ISKNV, PGIV strain; isolated from pearl gourami; [ 7 ]), viral hemorrhagic septicemia virus (VHSV; isolated from olive flounder; [ 26 ]), hirame rhabdovirus (HIRRV; ATCC, VR-1391), and spring viraemia of carp virus (SVCV, SVCV-K1 strain; isolated from common crap; [ 27 ]); nervous necrosis virus (NNV, RGNNV-type; isolated from sea bass; [ 26 ]). The infectivity titer of the virus was measured by TCID 50 assay using DGF, epithelioma papulosum cyprini (EPC), and E11 cell lines for megalocytiviruses (RSIV and ISKNV), rhabdoviruses (VHSV, HIRRV, and SVCV), and NNV, respectively.…”