Bacteria-Mediated Coral Disease Resistance

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Corals are increasingly threatened by disease induced mortality, and the risk of infection may be increased by elevated sea surface temperature either by promoting pathogen growth or virulence, reducing host resistance to infection, or a combination of both. This project will investigate the hypothesis that coral-associated bacteria mediate disease resistance through bacteria-bacteria interactions and this resistance mechanism is altered by elevated temperatures. The project tests three hypotheses related to the bacteria mediated resistance hypothesis: (1) Antagonistic interactions among coral-associated bacteria limit pathogen colonization and proliferation within the mucus layer. Antagonistic interactions among bacteria affect the diversity and spatial distribution of bacteria in marine pelagic and epibiotic communities, in part by preventing some bacteria from entering the established community. Analogous processes in the coral surface mucus layer will be examined with laboratory assays and in situ experiments using cultivable bacteria, combined with fluorescent in situ hybridization, phylotype-specific PCR, and denaturing gradient gel electrophoresis to assess non-cultivable bacteria. (2) Elevated temperature alters bacterial growth rates and bacteria-bacteria antagonism, facilitating pathogen colonization and proliferation. Growth rates are a fundamental force influencing bacteria community dynamics and can influence the relative abundance of phylotypes within a community. Temperature can affect growth rate as well as bacterial antibiotic production, thus altering the outcome of bacteria-bacteria interactions. Culture-dependent and -independent techniques will be used to explore bacteria-bacteria interactions on corals exposed to various temperature treatments and temporal samples of permanently tagged corals on the reef. (3) Other members of the coral-associated microbial community (e.g., eukaryotic grazers, viruses) impact the abundance and dynamics of coral-associated bacteria, potentially altering disease resistance. The coral mucus habitat contains not only prokaryotes but eukaryotic grazers and viruses. These predators strongly influence bacteria communities in the water column and their role is proposed to be analogous in the coral mucus layer. The intellectual merit of this project lies in the integration of coral reef ecology and microbial ecology to address fundamental questions regarding coral health and disease. Both culture-dependent and-independent techniques will be utilized to examine the ecological interactions of cultivable bacteria and assess dynamics of the whole community. The work is timely and imperative given the declining status of coral reefs and predictions of future decline. The broader impacts of this project include integration of research and education by developing seminars for the Professional Development Series for Education Staff at the Birch Aquarium at Scripps (La Jolla, CA). Participation of under-represented groups will be encouraged through 1) international coral disease workshops in the Philippines and East Africa facilitated in conjunction with the World Bank / Global Environment Fund Coral Reef Targeted Disease Research Group, 2) Mentoring of undergraduate students from the University of Guam, and 3) Developing a curriculum to engage minority high school students with ocean sciences and mentoring a team of minority high school students for the National Ocean Sciences Bowl.