Propagations of grouper (Epinephelus sp.) viruses in a new fibroblast-like cell line from orange spotted grouper (E. coioides) brain

Abstract Viral nervous necrosis virus (VNNV) and both ranavirus-type and megalocytivirus-type grouper iridoviruses (GIV-R and GIV-M, respectively) are three main viral causative agents in grouper industry. Although many grouper cell lines have been developed, very few studies showed that these three grouper viruses could proliferate well in the same host cellular system. In this study, propagations of grouper original VNNV, GIV-R and GIV-M were carried out in a newly established grouper brain (GB11) cell line. The result showed that both GNNV and GIV-R could propagate efficiently in GB11 cells, whereas GIV-M could maintain persistently moderate propagations, which were evidenced strongly by cytopathic effect (CPE) observation, transmission electron micrographs analysis and persistent viral titer measurements. Western-blotting analysis showed that polyclonal antibodies against GNNV capsid protein and GIV-R major capsid protein, and a mouse monoclonal antibody against GIV-M could strongly recognize the corresponding infected GB11 cells with GNNV, GIV-R and GIV-M, respectively, which also supported that three grouper viruses could replicate well in GB11 cells. Artificial infection showed that GB11-cultured GNNV, GIV-R and GIM-M resulted in 73.3%, 93.3% and 100% cumulative mortalities ( n  = 30) in the same juvenile hybrid grouper ( E. fuscoguttatus × E. lanceolatus ) infection model, respectively. Moreover, the highly lethal infection of GB11-cultured GIV-M was confirmed furtherly by histopathology and immunohistochemistry analysis. Collectively, our study provides robust experimental evidences that GB11 is a potential cellular material suitable for the study of grouper original VNNV, GIV-R as well as GIV-M.