Microbes associated with coral mucus and their potential role as an antibiotic

It is a well-known fact that there has been a significant decrease in coral populations worldwide (Harvell et al., 1999).

A study done by Ritchie (2006), looked at the mucus layer formed by the Elkhorn coral Acropora palmata. This species is highly susceptible to environmental stressors. The mucus layer is known to protect the corals from stressors in such ways as presenting a physical barrier, removal of microbes via ingestion and sloughing etc. However, little is known about the use of this mucus layer as a protector against disease.

This study by Ritchie (2006) looked at whether the coral mucus layer gives coral antibiotic resistance due to the bacteria associated with it providing antibiotic activity. An experimental approach was also used to look at the potential of mucus as a selection medium for coral symbionts. A symbiont in this case refers to bacteria that benefits from the coral mucus, whilst also benefitting the coral.

12 colonies of A.palmata were used. Bacteria samples were taken from the mucus and then diluted in seawater, plated on glycerol artificial seawater agar and kept at 24°C. Potentially invasive microbes were introduced which were known to be related to coral disease. Antibiotic producing corals were selected for and mucus associated bacteria were then used to test for the production of anti-bacterial compounds.

A.palmata has been documented as one of the worst affected corals worldwide, now listed as a threatened species. The study done by Ritchie (2006) shows the mucus from A.palmata can provide antibiotic resistance against gram positive and negative bacteria, a variety of microbes and from a pathogen associated with white pox disease. A.palmata associate with bacteria that can produce some sort of antibiotic resistance, showing that microbes play a key role in the protective properties of the mucus. It also has a role in the control of the associated microbes. A very interesting result showed that mucus collected at periods of increased sea surface temperature showed a decrease in antibiotic activity, suggesting temporal variability in mucus protection against stressors (Ritchie 2006).

This variability in antibiotic resistance due to temporal and spatial variability would be a very interesting subject for future work to look into (Ritchie, 2006). This is obviously a very important and current topic due to corals becoming subject to immediate environmental stressors. Therefore it would be very interesting to look at how the antibiotic activity varies under different conditions in order to predict possible effects on natural populations. The fact that the environmental stressors are only going to become more intense only makes this subject of more importance.

Ritchie,K. (2006) Regulation of microbial populations by coral surface mucus and mucus-associated bacteria. Marine Ecology Progress Series. 322 , 1-14.

Harvell, C., Kim, K., Burkholder, J., Colwell, R., Epstein, P., Grimes, D., Hoffmann, E., Lipp, E., Osterhaus, A., Overstreet, R., Porter, J., Smith, G., Vasta, G. (1999). Emerging Marine Diseases: Climate Links and Anthropogenic Factors. Science. 285, 1505-1510.