Complete genomic sequence of a reovirus isolated from grass carp in China

Abstract

A reovirus was isolated from sick grass carp in Guangdong, China in 2009, and tentatively named 'grass carp reovirus Guangdong 108 strain' (GCRV-GD108). This reovirus was propagated in grass carp snout fibroblast cell line PSF with no obvious cytopathic effects. Its genome was 24,703bp in length with a 50% G+C content and 11 dsRNA segments encoding 11 proteins instead of 12 proteins. It has been classified as an Aquareovirus (AQRV). Sequence comparisons showed that it possessed only 7 homologous proteins to grass carp reovirus (GCRV) (with 17.6-45.8% identities), but 9 homologous proteins to mammalian orthoreoviruses (MRV) (with 15-46% identities). GCRV-GD108 lacked homology to VP7, NS4&NS5 and NS3 of GCRV, while it had sigma1 and sigma NS homology to MRV. VP2 of GCRV-GD108 shared high amino acid sequence identity (44-47%) with AQRVs, whereas VP5 did not exhibit much identity (24-25%) to AQRVs. Conserved terminal sequences, 5'-GUAAUUU and UUCAUC-3', were found in all of the 11 genomic segments of GCRV-GD108 at the 5' and 3' non-coding regions (NCRs) of the segments. The 5' NCRs of GCRV-GD108 was similar to GCRV, but differed from other species of AQRV or Orthoreoviruses (ORV). Phylogenetic analysis of coat proteins belonging to Reoviridae, VP1-VP6, showed that GCRV-GD108 clustered with AQRVs and grouped with ORVs, suggesting that GCRV-GD108 belonged to the genus Aquareovirus but was distinctive from any known species of AQRV. Morphological and pathological analyses, and genetic characterization of GCRV-GD108 suggested that it may be a new species of AQRV and it was more closely related with ORVs than other AQRVs. In addition, RT-PCR analysis of diseased grass carp samples collected from different regions of China indicated that these viruses displayed high similarities to each other (95.3-99.4%). They also shared high sequence similarities to GCRV-GD108 (96.7-99.4%), indicating that GCRV-GD108 is representative of the prevalence strain in southern China.