Abstract:  Increasing seawater temperatures represent a major challenge to the health of the world’s coral reefs, particularly in light of evidence that bleaching and diseases have contributed to significant loss of both key reef organisms and coral cover. Corals shape their microbial partners, creating complex holobiont associations thought to be vital in maintaining coral health. However, what factors structure coral microbial associations remain a mystery. The cycling of sulfur and nitrogen compounds within the holobiont are increasingly being recognised as driving many of these coral microbial associations and have important consequences for coral health and the subsequent resilience of coral reefs. For example, diazotrophic bacteria appear specific to coral species with the three dominant groups of diazotrophic bacteria (67% of total retrieved sequences) found in three different coral species closely related to species belonging to the Rhizobia, a group of diazotrophic bacteria that can only accomplish nitrogen fixation after establishing symbiosis in the roots of host plants. In addition an extensive overlap is observed between bacterial species associated with corals and species implicated in the degradation of dimethylsulfoniopropionate (DMSP) to dimethylsulfide (DMS), two key compounds in the global sulfur cycle. Shifts in coral associated microbiota are indicators and implicated in contributing to reduced coral fitness. For example, temperature stress causes shifts in coral associated microbial communities, with a metagenomic approach demonstrating a shift in the microbial community away from autotrophy and an increase in virulence associated genes during a bleaching period. To date however most coral-microbial studies consider the coral as a whole entity rather than a number of unique physiochemical microhabitats that support different bacterial communities. We are now at the stage where the toolbox available for coral studies allows us to probe for the specific functional role of the microorganisms within niche microhabitats of the coral holobiont. This allows a finer understanding of the role microorganisms have in coral biology and how environmental stresses can influence all partners of the holobiont. This presentation will provide an overview of the research currently being undertaken investigating coral bacterial communities, highlighting where the field is currently heading.

Biography:  Dr David Bourne is a Research Scientists at the Australian Institute of Marine Science. He has been involved in a number of research themes at AIMS including marine microbes for drug discovery and the microbial dynamics in aquaculture (Rock Lobster) larval rearing systems. More recently his work is solely focused on understanding microbial interactions with corals. This work is divided essentially into two areas, the first investigating the normal microbial communities associated with corals and their functional roles in maintaining coral fitness. The second research focus is to elucidate pathogens and mechanism of disease onset in corals and the implications this has on a stressed reef ecosystem in light of climate change being a major driver of coral reef degradation.