Abstract
The advancement of high throughput sequencing has greatly facilitated the exploration of viruses that infect marine hosts. For example, a number of putative virus genomes belonging to the Totiviridae family have been described in crustacean hosts. However, there has been no characterization of the most newly discovered putative viruses beyond description of their genomes. In this study, two novel double-stranded RNA (dsRNA) virus genomes were discovered in the Atlantic blue crab (Callinectes sapidus) and further investigated. Sequencing of both virus genomes revealed that they each encode RNA dependent RNA polymerase proteins (RdRps) with similarities to toti-like viruses. The viruses were tentatively named Callinectes sapidus toti-like virus 1 (CsTLV1) and Callinectes sapidus toti-like virus 2 (CsTLV2). Both genomes have typical elements required for −1 ribosomal frameshifting, which may induce the expression of an encoded ORF1–ORF2 (gag-pol) fusion protein. Phylogenetic analyses of CsTLV1 and CsTLV2 RdRp amino acid sequences suggested that they are members of two new genera in the family Totiviridae. The CsTLV1 and CsTLV2 genomes were detected in muscle, gill, and hepatopancreas of blue crabs by real-time reverse transcription quantitative PCR (RT-qPCR). The presence of ~40 nm totivirus-like viral particles in all three tissues was verified by transmission electron microscopy, and pathology associated with CsTLV1 and CsTLV2 infections were observed by histology. PCR assays showed the prevalence and geographic range of these viruses, to be restricted to the northeast United States sites sampled. The two virus genomes co-occurred in almost all cases, with the CsTLV2 genome being found on its own in 8.5% cases, and the CsTLV1 genome not yet found on its own. To our knowledge, this is the first report of toti-like viruses in C. sapidus. The information reported here provides the knowledge and tools to investigate transmission and potential pathogenicity of these viruses.
Highlights
With the wide application of generation sequencing (NGS), a huge number of virus genomes have been described from studies of metagenomes and viromes
Five genera are officially recognized by the International Committee on Taxonomy of Viruses (ICTV), including Totivirus, Victorivirus, Giardiavirus, Leishmaniavirus, and Trichomonasvirus (King et al, 2011; Wickner et al, 2011)
Viruses belonging to the genera Totivirus and Victorivirus mainly infect fungi, whereas those in the genera Giardiavirus, Leishmaniavirus, and Trichomonasvirus are present in parasitic protozoa and do not appear to cause cytopathic effects (Ghabrial and Suzuki, 2009; Goodman et al, 2011)
Summary
With the wide application of generation sequencing (NGS), a huge number of virus genomes have been described from studies of metagenomes and viromes. An increasing number of toti-like virus sequences have been revealed by metagenomic studies, but further characterization and investigation are lacking (Shi et al, 2016). Viruses of the Totiviridae family have a non-segmented, double-stranded RNA (dsRNA) genome, with two open reading frames (ORFs) encoding the putative capsid protein (Cp) and the RNA dependent RNA polymerase (RdRp). Most virions in this family are isometric with no projections, and are ∼40 nm in diameter (Wickner et al, 2011). Five genera are officially recognized by the International Committee on Taxonomy of Viruses (ICTV), including Totivirus, Victorivirus, Giardiavirus, Leishmaniavirus, and Trichomonasvirus (King et al, 2011; Wickner et al, 2011). Two genera were proposed recently, including Artivirus which infect arthropod and fish hosts (Zhai et al, 2010), and Insevirus which infect insect hosts (Zhang et al, 2018)
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