Abstract
Stony corals (Scleractinia) are marine invertebrates that form the foundation and framework upon which tropical reefs are built. The coral animal associates with a diverse microbiome comprised of dinoflagellate algae and other protists, bacteria, archaea, fungi and viruses. Using a metagenomics approach, we analysed the DNA and RNA viral assemblages of seven coral species from the central Great Barrier Reef (GBR), demonstrating that tailed bacteriophages of the Caudovirales dominate across all species examined, and ssDNA viruses, notably the Microviridae, are also prevalent. Most sequences with matches to eukaryotic viruses were assigned to six viral families, including four Nucleocytoplasmic Large DNA Viruses (NCLDVs) families: Iridoviridae, Phycodnaviridae, Mimiviridae, and Poxviridae, as well as Retroviridae and Polydnaviridae. Contrary to previous findings, Herpesvirales were rare in these GBR corals. Sequences of a ssRNA virus with similarities to the dinornavirus, Heterocapsa circularisquama ssRNA virus of the Alvernaviridae that infects free-living dinoflagellates, were observed in three coral species. We also detected viruses previously undescribed from the coral holobiont, including a virus that targets fungi associated with the coral species Acropora tenuis. Functional analysis of the assembled contigs indicated a high prevalence of latency-associated genes in the coral-associated viral assemblages, several host-derived auxiliary metabolic genes (AMGs) for photosynthesis (psbA, psbD genes encoding the photosystem II D1 and D2 proteins respectively), as well as potential nematocyst toxins and antioxidants (genes encoding green fluorescent-like chromoprotein). This study expands the currently limited knowledge on coral-associated viruses by characterising viral composition and function across seven GBR coral species.
Highlights
Reef-building corals are keystone taxa of coral reefs; they are responsible for the deposition of a three-dimensional calcium-carbonate framework that constitutes the reef, and are the ecosystem’s main primary producers (Muscatine, Mccloskey & Marian, 1981)
The diversity and functional roles of other groups of symbionts within these holobiont communities are poorly studied. This is true for viruses, i.e., the eukaryotic viruses, archaeal viruses, and bacteriophages, whose identity and diversity is still largely undescribed for many coral species
This study characterised the viral diversity across seven coral species of the central Great Barrier Reef (GBR) and provided taxonomic and functional information with an additional comparison of viral communities that exist in seawater sampled in the GBR
Summary
Reef-building corals are keystone taxa of coral reefs; they are responsible for the deposition of a three-dimensional calcium-carbonate framework that constitutes the reef, and are the ecosystem’s main primary producers (Muscatine, Mccloskey & Marian, 1981). The diversity and functional roles of other groups of symbionts within these holobiont communities are poorly studied This is true for viruses, i.e., the eukaryotic viruses, archaeal viruses, and bacteriophages, whose identity and diversity is still largely undescribed for many coral species. While previous studies have assessed the taxonomic composition of DNA viruses in corals, insights into RNA virus assemblages and viral functional genes are scarce. We utilize the recently developed computational pipeline HoloVir (Laffy et al, 2016) to describe the viral taxonomic diversity and gene function based on DNA and RNA viromes of seven scleractinian coral species and their surrounding seawater from the central GBR
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