Morphological diversity of virus-like particles within the surface microlayer of scleractinian corals

Abstract

Transmission electron microscopy was employed to determine the morphological diversity of virus-like particles (VLPs) associated with the coral surface microlayer (CSM) of Acropora muricata and Porites spp. from the Great Barrier Reef, Australia. VLPs were assigned to one of 17 sub-groups within 5 major morphological groups including tailed bacteriophages, polyhedral, filamentous and lemon-shaped VLPs. Polyhedral VLPs in the 30 to 60 nm size class dominated the CSM of A. muricata and Porites spp., comprising 29.4 and 26.9% of total VLPs, respectively. Tailed bacteriophages comprised < 6% of total VLPs within the CSM of both A. muricata and Porites spp. Filamentous VLPs (FVLPs) of varying lengths and widths accounted for up to 19.9% of total CSM VLPs, with no significant difference between the CSM samples and overlying water. Unique VLPs, which could not be classified into any known viral morphological group, accounted for 1.2 to 11.7% of total VLPs within the CSM and were absent from overlying water. While some exchange of VLPs likely occurred between the CSM and overlying water, our results suggest that the majority of CSM morphotypes were specific to the CSM micro-niche. The similarity of many of these VLPs to previously described viruses suggests that a range of potential hosts exist in the CSM, including bacteria, archaea, cyanobacteria, fungi, algae (possibly including zooxanthellae) and the coral animal. Research on coral-microbial interactions and their role in coral health and functioning is in its infancy and the present study provides important information on the largely unstudied viral component of the coral microbiota.

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

“…In addition to our datasets, transmission electron micrographs (TEM) and sequences from the Nematostella genome and hydra EST project provide further evidence that Cnidarians, not just corals, are hosts for herpes-like viruses. Corals contain large enveloped icosahedral virions morphologically similar to the Herpesviridae (28,29). Herpesvirus essential genes are also present in Cnidarian genomes (28,51,52).…”

“…Corals contain large enveloped icosahedral virions morphologically similar to the Herpesviridae (28,29). Herpesvirus essential genes are also present in Cnidarian genomes (28,51,52). Within the Nematostella draft genome, alkaline exonucleases, herpes major outer envelope proteins, herpes DNA primases, herpes ubiquitin-specific proteases as well a herpes surface glycoprotein and transcription activation factor were identified (Table S4).…”

“…While the identity of these VLPs has yet to be established, an increase in viral particles within dinoflagellates has been hypothesized to be responsible for symbiont loss during bleaching (25)(26)(27). VLPs also have been identified visually on several species of scleractinian corals, specifically: Acropora muricata, Porites lobata, Porites lutea, and Porites australiensis (28). Based on morphological characteristics, these VLPs belong to several viral families including: tailed phages, large filamentous, and small (30-80 nm) to large (Ͼ100 nm) polyhedral viruses (29).…”

Bacterial and viral dynamics during a mass coral spawning period on the Great Barrier Reef

“…Alternatively, ) from different oligotrophic and eutrophic marine environments. FCM = flow cytometry; TEM = transmission electron microscopy; ND = not determined detachment of reef and coral surface-associated VLPs (Davy & Patten 2007) when water is advected through the reef framework may have indirectly contributed to increased water column viral loads. In contrast, bacterial abundances appeared to be less affected by tidal flushing and more responsive to the input of labile organic matter from the spawning event.…”

Dynamics of nutrients, total organic carbon, prokaryotes and viruses in onboard incubations of cold-water corals

“…Wilson et al, 2005;Danovaro et al, 2008) and lytic phages of coral pathogens have been isolated (Efrony et al, 2007). The morphological diversity of viruses in coral mucus and in the holobiont is high (Davy and Patten, 2007;Patten et al, 2008a) and a high diversity was also shown by viral metagenomics of the holobiont (Marhaver et al, 2008). There is also some in situ evidence that viral abundance increases close to corals (Patten et al, 2006;Seymour et al, 2005).…”