Coral associated bacteria and their potential role in the sulfur cycle.

Marine bacteria play a central role in the degradation of DMSP to DMS and acrylic acid. This DMS that is produced is important in areas such as cloud formation. It has recently been found that some scleractinian corals contain high levels of DMSP and DMS, associated to the symbiotic algae they possess. This raises questions about the role that coral reefs play in the cycling of sulfur (Raina et al., 2009).

Most of the DMSP produced in coral ecosystems is released to the surrounding area. It has been estimated that other types of bacteria degrade 50-80% of the DMS produced, however that pathways and degradation are poorly understood. The coral associated with bacterial communities are very diverse.

A study done by Raina et al., (2009) investigates the potential of DMSP, DMS and acrylic acid as a driver of coral associated microbial community. They used these compounds as a sole carbon source to isolate bacteria from 2 coral species and then compared these to coral associated microbiota.

The coral species used by Raina et al., (2009) were Acropora millepora and Montipora aequiluberulata. They collected 3 colonies of each species from the Great Barrier Reef. 3 types of sample were taken from these corals; these included tissue slurry, mucus slurry and crushed skeletal material. There were 5 replicates for each of these sample types for both species. As mentioned earlier, the carbon sources used were DMSP, DMS and acrylic acid. The control used was made up of basal medium and the carbon source only. DNA extraction was carried out on single strain liquid cultures using an extraction kit and then PCR carried out to amplify bacteria and DMSP (Raina et al., 2009).

4 genera of bacteria, Roseobacter, Spongiobacter, Vibrio and Alteromonas, isolated on agar possessing either DMSP or DMS as a carbon source made up the majority of clones from coral tissue and mucus. M.aequiluberulata was cotained 28% Roseobacter sp, whilst A.millepora contained 59% Spongiobacter genus. Vibrio species were associated with DMS and acrylic acid enrichment and were often found in coral mucus. This finding suggests that they may be a natural part of coral ecosystems. Results gained show that DMSP, DMS and acrylic acid can be used as a nutrient source for bacteria associated with coral reefs (Raina et al., 2009).

There is some evidence for species-specificity, however this is poorly understood. Overall, the potential of DMS, DMSP and acrylic acid as a role in structuring coral microbe communities is an area that has been little investigated (Raina et al., 2009).

This study is a very good starting point for investigating bacteria that can metabolise the sulfur compounds previously mentioned. It would be interesting for further studies to be carried out in order to get a more complete spectrum of the bacteria that can metabolise these compounds. Raina et al., (2009) sees this study as being a possible perquisite for looking into coral health.

Raina, JB., Tapiolas, D., Willis, B., Bourne, D.. (2009). Coral-Associated Bacteria and Their Role in the Biogeochemical Cycling of Sulfur. Applied and Environmental Microbiology. 75, 3492-3501