| Summary: | The coral holobiont is a complex assemblage of the coral animal and microbial organism. Coral mucus harbours distinct microbial communities and bacteria living in the coral mucus play a major role in the survival of corals. While several studies have assessed their importance in protecting their coral hosts from disease, very little is known about the response of these bacteria to climate change. One of the major consequences of climate changes are enhanced ocean temperatures which lead to coral bleaching. Another major cause of coral bleaching is the increased amount of anthropogenic carbon dioxide (CO2) which leads to a phenomenon called ocean acidification. In both cases, very little its known about how bacteria living in the coral mucus react to the changing conditions. In a laboratory-based experiment, we assessed the impact of temperature and carbon dioxide elevation on mucus-associated bacteria in Trachyphyllia geoffroyi, Euphyllia ancora and Corallimorphs sp. Fragments of the selected corals were placed into tanks and exposed to enhanced concentrations of CO2 and temperature in a series of experiments. Coral mucus samples were collected on a weekly basis and CO2 concentrations monitored using a Fourier-Transform Infrared (FTIR) trace gas analyzer. Potential changes in the coral mucus-associated bacteria communities were monitored by (a) culture based and (b) molecular approaches. Mucus samples were cultured weekly and bacterial isolates identified using Sanger sequencing. Furthermore, fingerprinting methods such as Denaturing Gel Gradient Electrophoresis (DGGE) and Ribosomal Intergenic Spacer analysis (RISA) were applied to monitor changes in the microbial communities. Enzymatic properties (amylase, caseinase, gelatinase and phospholipase) of the coral mucus-associated bacteria were also assessed to identify potential pathogenic bacteria. Significant shifts were detected in all three corals. For Trachyphyllia geoffroyi, Euphyllia ancora and Corallimorphs sp., When the temperature and carbon dioxide were maintained around 25°C to 28°C and 500 ppm, Vibrio sp., Bacillus sp. and Pseudomonas sp. were found but as temperature increases up to 29°C, Bacillus sp. started to dominate. However, when both temperature and carbon dioxide were rised up to stressful conditions for the corals, Vibrio sp. dominated the corals mucus layers. Lastly, the isolation of bacteriophage that has the ability to cause a plaque in the Bacteriophage Plaque Assay when tested against selected potential pathogens was also identified. The species identified are phylogenetically 96% similar to Enterobacteriophage reference strain, which are potential bacteriophages for the inhibition of marine pathogens. There were shifts in Trachyphyllia geoffroyi, Euphyllia ancora and Corallimorphs sp. mucus-associated bacteria community when temperature and carbon dioxide content of the corals surrounding changes.
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