Coral Dinoflagellate's have gone VIRAL!

A healthy coral consists of a symbiosis between the coral animal and a bacterium, for example dinoflagellate algae. A coral can also consist of microbes from Archaea or fungi which exist on the mucosal layer. In a healthy reef ecosystem different corals consist of different combinations of host and symbiont genotypes. The different phenotypes expressed from these different combinations contributes to the survivability of the reef, corals having variability in their tolerances to; temperature, light, growth rates, and disease resistance. Coral bleaching is a major environmental issue, the causes of which have been attributed to long term environmental stress or bacterial induced. Much work has also been done on the effects of viruses on bleaching which is still currently inconclusive. Thus far there is evidence that indicates herpes-like viruses target the coral animal, but less is known if any viruses target the dinoflagellate partner within the holobiont.

In this study they looked for evidence for viral infection in the symbiotic dinoflagellate Symbiodinium within the Montastraea cavernosa coral through generating a cDNA library from a Symbiodinium culture and comparing this with isolated DNA from Symbiodinium within a heat-stressed coral and a normal coral. It was found that large DNA viruses associate with both the free-living algae as well as the symbiont within the coral, which is the first genomic evidence of this. Viral transcripts were found which are similar to known viruses which infect planktonic dinoflagellate’s, suggesting that novel viruses target symbiotic dinoflagellate’s. More research is needed to expand upon the known viromes for marine ecosystems as shown by the identification of novel dsDNA and ssRNA viruses within this study. If these viruses’ are lytic to the dinoflagellate partner then they are an important factor when assessing coral health.

This paper was intriguing in its approach to isolating viral cDNA librarys, although the accuracy of the data could have been improved by increasing the number of samples pyrosequenced, as for both heat-stressed and control corals N=1. Despite this, the paper does highlight another aspect to the assessment of coral health which can be further studied.

Correa, A.M.S., Welsh, R.M. & Thurber, R.L.V. (2013) Unique nucleocytoplasmic dsDNA and þssRNA viruses are associated with the dinoflagellate endosymbionts of corals. The ISME journal 7, 13-27.