Characterization of Microbial Communities within the Surface Mucopolysaccharide Layer of Corals via Metabolic Profiling
Coral species secrete a surface mucopolysaccharide layer (SML) that provides a rich environment in which microbes reside. There is evidence to support that these surface microbes may be involved in disease protection as well as evidence that there may be a shift in community composition under stressful conditions which could result in increased susceptibility to disease.1 However, their role is not well understood. This is partially due to a difficulty in characterization of these extensive communities as many techniques that have been applied (i.e., cultures, molecular methods) are cost-prohibitive and time-consuming.
As part of a much larger project involving coral restoration in the Florida Keys using colonies derived from aquacultured fragments, we attempted to characterize the metabolic diversity of the surface microbiota of seven species of Atlantic Scleratinia using BiOLOG® EcoPlates. These are commercially available microplates that provide a selection of carbon-based substrates for use in determining the metabolic profile of a given bacterial community. They do not provide the ability to identify individual bacterial strains present within a sample; however, they do provide information regarding the functional structure of microbial communities. Furthermore, they do not require isolation and maintenance of bacterial cultures nor do they involve extensive preparation or supplies.
One of the goals of the large-scale coral restoration project was to determine if survival and growth of reintroduced fragments was affected by various culture techniques. Therefore, project corals were cultured under three separate culture conditions--an artificial seawater, recirculating system in a greenhouse; a land-based, natural seawater flow-through system; and an open ocean ("control") site. We addressed two separate questions: 1) do surface microbial communities shift during times of disease; and 2) will these populations also shift depending upon their culture conditions?
Using methods described by Gil-agudelo et al (2006)2, the SML of the parent coral colonies was sampled at the time of fragmentation (April 2006). Ten fragments of each species were transported to their respective culture condition site in May 2006. After a six-month period in culture (November 2006), samples of the SML from two fragments of each species from the two land-based aquaculture sites were obtained. A visual health assessment and health certification process was performed at this time as well, and those fragments that passed inspection were then "planted" on the open ocean site with the "control" fragments in December 2006. Planting involves using marine epoxy to adhere a cement disc, which supports the coral fragment, to a prepped site on the reef free of all other benthic organisms. Samples from the control species were also obtained at the time of planting. Additional samples are to be obtained in March 2007 after a 3-month period on the open ocean site.
Microbial community analyses from all sampling periods are still pending. Preliminary data involving the identification of individual bacterial strains from healthy and diseased samples suggest that a shift in the microbial community does occur (Matysczak and Berzins, pers. comm.). Results from this study will hopefully indicate whether or not a community shift also occurs under different culture conditions.
1. Ritchie KB. 2006. Regulation of Microbial Populations by Coral Surface Mucus and Mucus-Associated Bacteria. Marine Ecology Progress Series, 322:1-14.
2. Gil-agudelo DL, L Ali-hassan, K Kim, GW Smith. 2006. Characterization of Coral Surface Microbiota Using Metabolic Profiling. Proceedings of the 10th International Coral Reef Symposium, 1:149-152.