A novel class of herpesvirus with bivalve hosts

Abstract

Ostreid herpesvirus 1 (OsHV-1) is the only member of the Herpesviridae that has an invertebrate host and is associated with sporadic mortality in the Pacific oyster (Crassostrea gigas) and other bivalve species. Cryo-electron microscopy of purified capsids revealed the distinctive T=16 icosahedral structure characteristic of herpesviruses, although the preparations examined lacked pentons. The gross genome organization of OsHV-1 was similar to that of certain mammalian herpesviruses (including herpes simplex virus and human cytomegalovirus), consisting of two invertible unique regions (U L , 167?8 kbp; U S , 3?4 kbp) each flanked by inverted repeats (TR L /IR L , 7?6 kbp; TR S /IR S , 9?8 kbp), with an additional unique sequence (X, 1?5 kbp) between IR L and IR S . Of the 124 unique genes predicted from the 207 439 bp genome sequence, 38 were members of 12 families of related genes and encoded products related to helicases, inhibitors of apoptosis, deoxyuridine triphosphatase and RING-finger proteins, in addition to membrane-associated proteins. Eight genes in three of the families appeared to be fragmented. Other genes that did not belong to the families were predicted to encode DNA polymerase, the two subunits of ribonucleotide reductase, a helicase, a primase, the ATPase subunit of terminase, a RecB-like protein, additional RING-like proteins, an ion channel and several other membrane-associated proteins. Sequence comparisons showed that OsHV-1 is at best tenuously related to the two classes of vertebrate herpesviruses (those associated with mammals, birds and reptiles, and those associated with bony fish and amphibians). OsHV-1 thus represents a third major class of the herpesviruses. INTRODUCTIONViruses are assigned to the family Herpesviridae on the basis of morphological criteria and have been identified in a wide range of vertebrates and one invertebrate, the Pacific oyster, Crassostrea gigas (Minson et al., 2000). The vertebrate herpesviruses fall into two major phylogenetic groups. Those in the first group have mammalian or avian hosts and are classified into three subfamilies (Alphaherpesvirinae, Betaherpesvirinae and Gammaherpesvirinae) that share extensive genetic relationships . Reptilian herpesviruses probably also belong among the Alphaherpesvirinae (Nigro et al., 2004;Quackenbush et al., 1998;Une et al., 2000;Yu et al., 2001). Viruses in the second group infect amphibians or bony fish and again are interrelated (Bernard & Mercier, 1993;Davison, 1998; Davison et al., 1999). Genetic evidence for a common evolutionary origin for the two groups is tenuous, however, since not a single herpesvirus-specific gene is detectably conserved in both. The only completely sequenced lower vertebrate herpesvirus, channel catfish virus (CCV), does share a few genes with the higher vertebrate group, but these have counterparts in other organisms (Davison, 1992). The conserved gene that comes closest to being herpesvirus specific encodes the putative ATPase subunit of the terminase, an enzyme complex involved in p...

Metagenomic analysis indicates that stressors induce production of herpes-like viruses in the coral Porites compressa

“…Although herpesviruses were once considered exclusively vertebrate diseases, members of the ostreid Herpesviridae are known to infect and kill invertebrates, specifically industrially cultured bivalves (64). The genomes of these shellfishinfecting herpesviruses contain few gene sequences in common with their vertebrate counterparts.…”

Antiviral immunity in marine molluscs

“…Genes encoding the apoptotic machinery are highly conserved in molluscs , but the role of the apoptosis system in molluscan immunity has received little attention . The large number of apoptosis inhibitors encoded in the genomes of OsHV-1, AVNV and AbHV (Davison et al, 2005;Ren et al, 2013;Savin et al, 2010) implies apoptosis may represent an important antiviral response of molluscs and warrants further investigation.…”

“…Since this time, herpes-like viruses have been described in other species of oyster (Burge et al, 2006;Hine et al, 1992;Renault et al, 1994), scallops (Arzul et al, 2001a;Ren et al, 2013) and clams (Renault et al, 2001). The virus has been purified from naturally infected Crassostrea gigas larvae (Le Deuff & Renault, 1999) and its genome entirely sequenced (Davison et al, 2005). Several genotypes of OsHV-1 have been detected by conventional PCR, targeting a specific area of the genome (Arzul et al, 2001b;Martenot et al, 2011;Segarra et al, 2010).…”

Herpèsvirus et herpèsviroses humaines

“…(HHV) 6,7, Les similitudes dans les processus moléculaires et pathologiques ne signifient pas qu'il existe des homologies étendues sur le plan moléculaire entre tous les herpèsvirus. Malgré les similitudes structurales évoquées plus haut, les homologies génétiques entre OsHV-1 et HSV-1 sont extrêmement ténues, au point d'avoir fait longuement discuter l'appartenance de la première espèce virale à l'ensemble des herpèsvirus (Davison et al 2005). De même, les protéines EBNA1 et LANA qui exercent des fonctions très comparables pour le maintien de la latence de deux gammaherpèsvirus humains, le virus Epstein-Barr (EBV) et l'herpèsvirus humain 8 (HHV-8) respectivement, sont très différentes dans leur structure primaire, bien que probablement beaucoup plus proches dans leur structure tridimensionnelle (Hu et al 2002).…”