Abstract
Corals that naturally thrive under extreme conditions are gaining increasing attention due to their importance as living models to understand the impact of global warming on world corals. Here, we present the first metagenomic study of viral communities in corals thriving in a thermally variable water body in which the temperature fluctuates between 11 and 39°C in different seasons. The viral assemblages of two of the most abundant massive (Porites harrisoni) and branching (Acropora downingi) corals in offshore and inshore reef systems in the northern Arabian Gulf were investigated. Samples were collected from five reef systems during summer, autumn and winter of 2011/2012. The two coral viromes contain 12 viral families, including 10 dsDNA viral families [Siphoviridae, Podoviridae, Myoviridae, Phycodnaviridae, Baculoviridae, Herpesviridae, Adenoviridae, Alloherpesviridae, Mimiviridae and one unclassified family], one-ssDNA viral family (Microviridae) and one RNA viral family (Retroviridae). Overall, sequences significantly similar to Podoviridae were the most abundant in the P. harrisoni and A. downingi viromes. Various morphological types of virus-like particles (VLPs) were confirmed in the healthy coral tissue by transmission electron microscopy, including large tailless VLPs and electron-dense core VLPs. Tailed bacteriophages were isolated from coral tissue using a plaque assay. Higher functional gene diversity was recorded in A. downingi than in P. harrisoni, and comparative metagenomics revealed that the Gulf viral assemblages are functionally distinct from Pacific Ocean coral viral communities.
Highlights
The field of coral virology remains in its infancy (Correa et al, 2016)
A. downingi and P. harrisoni nubbins were collected by SCUBA from two inshore locations, including the Qit’at Benaya [28.6164◦ N, 48.4289◦ E] and Qit’at Alzor reefs [28.7607◦ N, 48.3912◦ E], and three offshore locations, including the Umm Al Maradim Island [28.6851◦ N, 48.6568◦ E], Kubbar Island [29.0754◦ N, 48.4926◦ E] and Qaro Island [28.8161◦ N, 48.7747◦ E] reef systems (Figure 1)
110,866,698 bp and 141,093,140 bp of raw read data were generated from A. downingi and Porites harrisoni, respectively, and an average of 21% of the reads were quality trimmed
Summary
The field of coral virology remains in its infancy (Correa et al, 2016). Coral viruses remain the least-studied constituent of the coral holobiont, despite the fact that they are expected to infect and modulate all other members of the holobiont (for a review, see Vega Thurber and Correa, 2011). All available information about coral viruses is derived from studies performed on corals thriving in conditions of pristine warm water, where temperatures range between 16 and 32◦C (Marhaver et al, 2008; Vega Thurber et al, 2008; Correa et al, 2013, 2016; Weynberg et al, 2014) and any increase or decrease in temperature outside the range causes coral to perish (Jokiel and Coles, 1990; Hoegh-Guldberg, 1999). No information is available about the viruses of corals that thrive naturally under extreme conditions, such as those dominating the Arabian Gulf.
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