Preliminary analysis of the viral influence on the holobiont of Elkhorn coral, Acropora palmata, in the context of temperature associated white pox disease
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Caribbean Elkhorn coral, Acropora palmata, has experienced a severe decline in recent years due in large part to white pox disease. This disease is associated with elevated water temperature, but the exact mechanisms that determine coral survival remain undiscovered. While Serratia marcescens has been identified as a causative agent, many questions remain unknown, particularly concerning the influence of bacteriophages. For instance, the viral community might act as an accessory immune system for Elkhorn, as hypothesized by the hologenome theory. To study the viral component of A. palmata and white pox disease, I determined the concentration of viruses and bacteria in mucus from healthy corals, mucus from diseased corals, water above healthy corals, water above diseased corals, and white pox lesions at two reefs in the Florida Keys before (25oC) and after (30oC) the summer warm period, which is correlated to higher incidence of disease. Concentration increased with temperature in mucus but not water, and white pox lesions contained lower concentrations of bacteria and mucus than mucus from healthy and diseased colonies. Coral mucus also had a higher proportion of virus to bacteria than the surrounding water. I isolated and characterized two novel phages of S. marcescens, which are the first two known phages for S. marcescens PDR60, and can be used for controlled laboratory studies on the phage influence on disease. I found evidence to support interaction between phage isolates and S. marcescens and the reef environment, which lends support for phage influence in white pox disease through mechanisms predicted by the hologenome theory and by the bacteriophage adherence to mucus model.