Abstract
The coral-Symbiodinium association is a critical component of coral reefs as it is the main primary producer and builds the reef's 3-dimensional structure. A breakdown of this endosymbiosis causes a loss of the dinoflagellate photosymbiont, Symbiodinium, and/or its photosynthetic pigments from the coral tissues (i.e., coral bleaching), and can lead to coral mortality. Coral bleaching has mostly been attributed to environmental stressors, and in some cases to bacterial infection. Viral lysis of Symbiodinium has been proposed as another possible cause of some instances of coral bleaching, but this hypothesis has not yet been experimentally confirmed. In this study, we used coral virome data to develop a novel PCR-based assay for examining the presence and diversity of a single-stranded RNA (ssRNA) virus by targeting its major capsid protein (MCP) gene. Illumina sequence analysis of amplicons obtained with novel primers showed 99.8% of the reads had the closest taxonomic affinity with the MCP gene of the virus, Heterocapsa circularisquama RNA virus (HcRNAV) known to infect dinoflagellates, indicating that dinorna-like viruses are commonly associated with corals on the Great Barrier Reef. A phylogenetic analysis of MCP gene sequences revealed strong coral species specificity of viral operational taxon units (OTUs). This assay allows a relatively easy and rapid evaluation of the presence and diversity of this particular viral group and will assist in enhancing our understanding of the role of viral lysis in coral bleaching.
Highlights
A balanced microbiome is essential for the health and functioning of corals (Rohwer et al, 2002; Thompson et al, 2014; Blackall et al, 2015)
SISPA-amplified DNA and the major capsid protein (MCP) amplicon were successfully synthesized for A. tenuis, F. fungites, G. fascicularis, P. cylindrical, and P. damicornis from Orpheus Island, PCR amplication failed for A. hyacinthus, G. aspera and A. millepora
Of the 354,795 unique sequences obtained from 11 coral colonies, 99.8% showed closest taxonomic affiliation with the single-stranded RNA (ssRNA) dinorna-like virus, Heterocapsa circularisquama RNA virus (HcRNAV) (GenBank: LC120626.1) based on a BLASTx search to viral RefSeq NCBI
Summary
A balanced microbiome is essential for the health and functioning of corals (Rohwer et al, 2002; Thompson et al, 2014; Blackall et al, 2015). Abundance of VLPs increased in freshly isolated Symbiodinium under similar stressors (Wilson et al, 2001; Davy et al, 2006; Lohr et al, 2007; Lawrence et al, 2014) Consistent with these observations, metagenomic studies have revealed an increased abundance of viral sequences in metagenomes obtained from heat stressed corals (Vega Thurber et al, 2008, 2009; Littman et al, 2011) and Symbiodinium (Correa et al, 2013; Levin et al, 2016)
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