Metagenomic analysis indicates that stressors induce production of herpes-like viruses in the coral Porites compressa - PubMed (original) (raw)

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

Rebecca L Vega Thurber et al. Proc Natl Acad Sci U S A. 2008.

Abstract

During the last several decades corals have been in decline and at least one-third of all coral species are now threatened with extinction. Coral disease has been a major contributor to this threat, but little is known about the responsible pathogens. To date most research has focused on bacterial and fungal diseases; however, viruses may also be important for coral health. Using a combination of empirical viral metagenomics and real-time PCR, we show that Porites compressa corals contain a suite of eukaryotic viruses, many related to the Herpesviridae. This coral-associated viral consortium was found to shift in response to abiotic stressors. In particular, when exposed to reduced pH, elevated nutrients, and thermal stress, the abundance of herpes-like viral sequences rapidly increased in 2 separate experiments. Herpes-like viral sequences were rarely detected in apparently healthy corals, but were abundant in a majority of stressed samples. In addition, surveys of the Nematostella and Hydra genomic projects demonstrate that even distantly related Cnidarians contain numerous herpes-like viral genes, likely as a result of latent or endogenous viral infection. These data support the hypotheses that corals experience viral infections, which are exacerbated by stress, and that herpes-like viruses are common in Cnidarians.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

A) Percentages of best similarities (tBLASTx, e ≤10−6) to 19 families of viruses in each individual coral-associated viral metagenome: Time Zero (open circles), Aquarium Control (filled circles), Temperature (red triangles), pH (blue diamonds), Nutrient (green arrows), and DOC (orange hexagons). (B) Predicated host ranges across each metagenome, with libraries containing vertebrate (light gray) and invertebrate (black bars) associated viral sequences and plant (white bars) and algal (dark-gray bars) viruses. Blue bars represent similarity to viral genomes that are associated with Protists.

Fig. 2.

Fig. 2.

Coverage of selected Herpesviridae genomes and other marine associated viral genomes. Libraries were combined and sequences analyzed for similarity (tBLASTx e ≤10−6) to a boutique database of 2,020 fully sequenced eukaryotic viral genomes collected from the National Center for Biotechnology Information. Genomes were separated into 2,500 base pair bins. (A–C) Broad and high fold coverage was found for many mammalian associated Herpesviridae genomes, such as a suid herpesvirus (A) and 2 cercopithecine/macaque herpesviruses (B and C). (D–F) Low and uneven coverage was found for the symbiont associated chlorella phycodnavirus (D), a coccolithophorid virus (E), and a fish iridovirus (F).

Fig. 3.

Fig. 3.

Herpes-like viral sequence abundance across two 64-h experiments. (A and B) Real-time PCR on a putative herpes-like virus thymidylate synthetase gene was conducted on all temporal samples collected during the original metagenomic experiment (A) and samples from a second experiment conducted 1 year later (B). In the original experiment, coral specimens were exposed to thermal (5° C above ambient), dissolved organic carbon (25 mg·mL−1 glucose), nutrient (10 μM nitrate, nitrite, phosphate, and ammonium), and pH (1.7 units below ambient) stress for 64 hours. (B) In the second 2007 experiment, corals were acclimated to the tanks for 2 weeks before treatment with stressor, thermal stress was an elevation of seawater temperature 3°C, acidity stress was a 0.2 unit reduction of ambient pH, and samples were collected at 0, 4, and 64 h.

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