Abstract
Multiple enveloped viruses with rod-shaped nucleocapsids have been described, infecting the epithelial cell nuclei within the hepatopancreas tubules of crustaceans. These bacilliform viruses share the ultrastructural characteristics of nudiviruses, a specific clade of viruses infecting arthropods. Using histology, electron microscopy and high throughput sequencing, we characterise two further bacilliform viruses from aquatic hosts, the brown shrimp (Crangon crangon) and the European shore crab (Carcinus maenas). We assembled the full double stranded, circular DNA genome sequences of these viruses (~113 and 132 kbp, respectively). Comparative genomics and phylogenetic analyses confirm that both belong within the family Nudiviridae but in separate clades representing nudiviruses found in freshwater and marine environments. We show that the three thymidine kinase (tk) genes present in all sequenced nudivirus genomes, thus far, were absent in the Crangon crangon nudivirus, suggesting there are twenty-eight core genes shared by all nudiviruses. Furthermore, the phylogenetic data no longer support the subdivision of the family Nudiviridae into four genera (Alphanudivirus to Deltanudivirus), as recently adopted by the International Committee on Taxonomy of Viruses (ICTV), but rather shows two main branches of the family that are further subdivided. Our data support a recent proposal to create two subfamilies within the family Nudiviridae, each subdivided into several genera.
Highlights
Few viruses infecting marine invertebrates have been formally characterised with most tentatively assigned to families based upon morphological, developmental and replicative characteristics within the host cell [1]
Gene order is poorly conserved among nudivirus genomes [4], to date 31 core genes have been identified as being shared amongst all members of the Nudiviridae, including homologs of several baculovirus core genes [8,9]
Utilizing the new latinized binominal method for the naming of virus species, we propose the virus species Gammanudivirus cracrangoni and Gammanudivirus camaenasi, with the common names Crangon crangon nudivirus (CcNV) and Carcinus maenas nudivirus (CmNV), respectively, to be used in the rest of this manuscript
Summary
Few viruses infecting marine invertebrates have been formally characterised with most tentatively assigned to families based upon morphological, developmental and replicative characteristics within the host cell [1] This was largely due to the lack of crustacean cell lines for culturing viral infections, but with the recent development and increasing availability of high-throughput sequencing technologies comprehensive descriptions facilitate classifications and taxonomic placement of novel viruses, at least to family level [2,3]. Nudiviruses infect a wide array of arthropods and exhibit nuclear replication They have double-stranded, circular DNA genomes ranging in size between 96 and 232 kbp. Endogenous viral elements (EVEs) derived from nudiviruses have been reported to be incorporated into the genomes of multiple arthropod species [14,15,16,17]
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