Intellectual Merit: An ever-growing variety of diseases, including some demonstrably caused by bacteria, are decimating reef-building corals in many places around the globe. Corals are open systems persistently exposed to a great diversity of exogenous bacteria in the overlying seawater and attached to sinking particles. Furthermore, as coastal development continues to expand, increasing eutrophication, there is increasing concern that endogenous bacteria among the normal coral associated community could proliferate to become opportunistic pathogens causing tissue damage and coral death. How corals resist bacterial invasions is a complex issue, one critical aspect being the ability of endogenous bacteria to resist colonization and proliferation of potential pathogens.
Despite great strides in recent years uncovering the remarkable genetic diversity of coral-associated bacteria, mitigation and management of coral diseases remains hampered by a lack of understanding of in situ ecological interactions within the microbial community and with exogenous bacteria that underlie coral health and disease. Bacterial attachment and proliferation are critical steps in the infection process, thus inhibiting or preventing colonization and proliferation of pathogens is fundamental to disease resistance.
Recent research by the investigator demonstrates that corals exposed to organic matter enrichment can become colonized by potential pathogens, but the communities can rebound from such perturbations. Conducting in vitro studies, the investigator found that bacteria-bacteria antagonism is common among coral isolates which suggests it may be a mechanism to resist community shifts and pathogen colonization. It could thus drive resilience within coral-associated microbial communities. In this project the investigator will test these interactions in an in situ context.
Microbes are critical for the functioning of coral ecosystems at the global scale and, therefore, it is essential that a mechanistic understanding of microbial interactions at the microscale be attained. The following hypotheses will be tested which are designed to elucidate the ecological mechanisms by which bacterial colonization and proliferation in the coral mucus layer (CML) are prevented by microbial interactions: 1) Bacterial community homeostasis in the CML is maintained through the exclusion of potential colonizers 2) Microspatial organic matter hotspots within the coral mucus layer, particularly surrounding zooxanthallae, create loci of intense growth and antagonism 3) Spatially dispersed organic matter inputs overwhelm microscale hotspots and enable pathogens to colonize the CML
Broader Impacts: This project simultaneously improves our fundamental understanding of coral associated microbial ecology and provides a necessary scientific basis for marine resource management decisions. Public education, at both the local and international levels, is a key component of the routine activities of all participating researchers, and these activities will prosper from inclusion of cutting-edge ecological findings generated by this research. Additionally, three postdoctoral researchers (two full time and one at two months per year) and one graduate student will receive training from the integrated research and education activities supported through this renewal.
Coral reefs are considered to be one of the most biodiverse ecosystems in the world. Healthy reefs function as a finely tuned system, which excel at capturing and recycling nutrients in nutrient poor (oligotrophic) waters, and their intricate three-dimensional structure allows for niche partitioning that supports spectacular biodiversity and biological productivity. Numerous stressors, including mismanagement of fisheries, coastal pollution, and warming ocean waters have placed corals into a threatened state, with the majority of coral mortality arising from bacterial infection and subsequent disease. We have been working towards gaining a better understanding of the mechanisms that are responsible for coral resilience to disease. Our hypothesis is that bacteria-bacteria "antagonism", or the ability for certain bacteria to outcompete others (including the pathogenic bacteria), plays a fundamental role in coral health. Important to coral survival is their ability to prevent and remove unwanted "pathogenic" bacteria from their surface, a sticky mucus layer, which provides protection to the coral. Our findings suggest that corals are able to shed bacteria through their surface mucus layer, getting rid of unwanted potential pathogens. This discovery was made using a powerful microscope capable of capturing real-time video. In addition to this newly applied video microscopy technique, we’ve also developed a new method for counting bacteria within the mucus layer. This enables scientist to quantity the abundance of bacteria – an important technique when studying disease. To test the hypothesis that bacteria-bacteria antagonism plays a role in coral disease resilience our lab has been able to sequence the genome of two types of bacteria that exhibit very strong antagonism towards other microbes. This antagonism may prove important for "symbiotic", or beneficial microbes ability to prevent pathogenic bacteria from colonizing it. Our most recent findings give insight into the potential molecules called "secondary metabolites" used by these microbes, and we also investigated the enzymes used for breaking down nutrients to digestible molecules, which may allow some microbes to be more successful then others. We suspect that the ability of one microbe to outcompete another within the coral mucus layer is fundamental for the corals selection of symbiotic over pathogenic bacteria. Insight gained by our research, coupled with the methods we have developed, should prove valuable for the field of studies relating to coral reef health and disease. Several publications have resulted from this award and more are in preparation – we list below: M. Garren and F. Azam, "New Method for Counting Bacteria Associated with Coral Mucus", APPLIED AND ENVIRONMENTAL MICROBIOLOGY, p. 6128, vol. 76, (2010). Published, 10.1128/AEM.01100-1 M. Garren and F. Azam, "Corals shed bacteria as a potential mechanism of resilience to organic matter enrichment", The ISME Journal, p. 1159, vol. 6, (2011). Published, 10.1038/ismej.2011.180 M. Garren and F. Azam, "New directions in coral reef microbial ecology", Environmental Microbiology, p. 833, vol. 14, (2011). Published, 10.1111/j.1462-2920.2011.02597 K. L. Rypien, E. E. Allen, S. J. Nam, W. Fenical, P. R. Jensen, K. Penn, F. Azam. Genomic insights into life on a coral: Genome comparison of coral-associated Pseudoalteromonas luteoviolacea and P. flavipulchra. In preparation Y. Zhou, R. Guillemette, F. Azam, "Hydrolytic enzyme activity of mucus and seawater associated with the coral Orbicella annularis". In preparation
