Viral communities associated with healthy and bleaching corals

Abstract

The coral holobiont is the integrated assemblage of the coral animal, its symbiotic algae, protists, fungi and a diverse consortium of Bacteria and Archaea. Corals are a model system for the study of symbiosis, the breakdown of which can result in disease and mortality. Little is known, however, about viruses that infect corals and their symbionts. Here we present metagenomic analyses of the viral communities associated with healthy and partially bleached specimens of the Caribbean reef-building coral Diploria strigosa. Surprisingly, herpes-like sequences accounted for 4-8% of the total sequences in each metagenome; this abundance of herpes-like sequences is unprecedented in other marine viral metagenomes. Viruses similar to those that infect algae and plants were also present in the coral viral assemblage. Among the phage identified, cyanophages were abundant in both healthy and bleaching corals and vibriophages were also present. Therefore, coral-associated viruses could potentially infect all components of the holobiont--coral, algal and microbial. Thus, we expect viruses to figure prominently in the preservation and breakdown of coral health.

Fig. 1

Epifluorescent micrographs of samples before and after viral particle isolation. DsH = Diploria strigosa – Healthy, DsB = Diploria strigosa – Bleaching. Samples were stained with SYBR Gold nucleic acid stain and visualized under epifluorescence at 1000×. A. and C. Whole coral blastate from (A) DsH and (C) DsB. Visible are abundant virus-like particles (VLPs, white arrows), as well as intact microbial cells and autofluorescent zooxanthellae (black arrows). B. and D. Purified viruses from (B) DsH and (D) DsB. VLPs are visible (white arrows) in addition to autofluorescence of coral GFP-like proteins. Scale bar represents approximately 5 μm and applies to all four panels.

Fig. 2

Alignment of coral virus sequences to alphaherpesvirus genomes. Each dot represents the location of an individual metagenome sequence based on its best tblastx hit (E-value < 0.001) to the virus genome. Shown are the five alphaherpesviruses with the most hits.