Hobart

Seminar Abstract

Friday 5 November 2010, 11.30am (Tas time)
CSIRO Auditorium, Hobart

David Bourne
Research Scientist
Australian Institute of Marine Science

Corals and their associated microbiota: Implications for health, bleaching and disease

Global warming and increased sea surface temperatures present a major challenge to the health of the world’s coral reefs, particularly in light of evidence that bleaching and disease outbreaks have contributed to significant loss of both key reef organisms and coral cover. Studies have demonstrated that corals shape their microbial partners, creating complex holobiont associations thought to be vital in maintaining coral health. This presentation will provide an overview of the research currently being undertaken investigating coral bacterial communities and their implication for the health of corals, highlighting some of the challenges, pitfalls and successes along the road.

What factors structure coral microbial associations remain a mystery? Cycling of sulfur and nitrogen compounds are being investigated as driving many of these coral microbial associations and having important consequences for coral health and the subsequent resilience of coral reefs. For example, diazotrophic bacteria appear specific to coral species with the two most abundant groups of diazotrophic bacteria 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 was 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. Interestingly, when exploring publically available metagenome datasets, genes implicated in DMSP metabolism are abundant in the viral component of coral-reef-derived metagenomes, indicating that viruses can act as reservoirs for such genes.

Shifts in coral associated microbiota are indicators and implicated in contributing to reduced coral fitness. During a natural bleaching event on the Great Barrier Reef, the normal microbial community shifted with increases in temperature and colony bleaching correlated with distinct changes in the microbial community. A metagenomic approach was adapted to investigate how bleaching affected the microbial functional component of the holobiont during this natural bleaching event. Vibrios have been implicated in a number of coral diseases including bleaching, often as a response to compromised health and changing environmental parameters. The role of virulence factors in the onset of coral disease is currently one area of active study to provide insights into the molecular mechanisms of bacterial infection in coral and the risk that increasing sea surface temperatures will enhance pathogen virulence. A quantitative PCR (qPCR)-based V. coralliilyticus detection assay has been was successfully developed and validated when targeting the pathogen within the complex coral holobiont. Such an assay represents a novel approach to coral disease diagnosis and provides a useful tool to allow coral pathogen detection, pathogen load monitoring, and identification of pathogen sources, vectors, and reservoirs. Investigations of another coral disease, black band disease, has demonstrated the importance of increases in both light and temperature in enhancing progression of the microbial mat implicated in coral death. These environmental factors are also important in driving shifts in the complex microbial community with increase in sulfate-reducing bacteria within the lesion particularly facilitating the pathogenesis of BBD.

Seminar recording

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Location:
CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
Andrew Meijers, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5335
Natalie Kelly, (Biology/Modelling seminars) CSIRO Marine and Atmospheric Research 0438 452 483
Jillian Enraght-Moony, (seminar administrator) CSIRO Marine and Atmospheric Research (03) 6232 5320
Communications Manager, Antarctic Climate and Ecosystems CRC (03) 6226 7888
Tracey Cochrane, Institute for Marine and Antarctic Studies (IMAS), University of Tasmania (03) 6226 2937

Last updated 26/11/10