Interference of the life cycle of grouper nervous
necrosis virus (GNNV), a member of the Nodaviridae, genus Betanodavirus, by snakehead retrovirus (SnRV) has been studied in vitro.
SGF-1, a new fish cell line that is persistently infected with SnRV, was induced by inoculating SnRV into the grouper fin cell line GF-1. Culture supernatants and cell pellets from both GNNV-infected
SGF-1 and GF-1 cells were collected and employed for virus productivity analysis. The yields of GNNV
RNA and
capsid protein in GNNV-infected
SGF-1 cells were similar to those in GNNV-infected GF-1 cells. However, when GF-1 cells were used for titration, the titre of the culture supernatant from GNNV-infected
SGF-1 cells was much higher than that from GNNV-infected GF-1 cells. The titration result suggested that SnRV enhanced the
infection or cytopathic effect (CPE) of GNNV during GNNV and SnRV
coinfection of the GF-1 cell titration system, although SnRV cannot induce any CPE in GF-1 cells alone, nor can it increase the yield of GNNV after GNNV
superinfection of
SGF-1 cells. Moreover, GNNV
cDNA was detected in both the pellet and the supernatant from GNNV-infected
SGF-1 cells. This result indicated that SnRV reverse-transcribed the GNNV single-stranded genomic
RNA into
cDNA during GNNV
superinfection of
SGF-1 cells and created a new
cDNA stage in the life cycle of the fish nodavirus.