Characterization and Comparison of Bacterial Communities of Native Caribbean Stony Corals.
Supervisors: Aschwin Hillebrand Engelen, Tania Aires (CCMAR)
Coral reefs provide ecosystem services including increasing fish and biodiversity, boosting tourism and the local economy, providing coastal protection and offering numerous biotechnological products. Rapid ocean warming and acidification have put coral reefs in danger of rapid decline due to bleaching and disease. There is therefore a need to study and devise ways to increase the resilience of coral reefs from future bleaching and disease, and aid in their recovery. Coral microbiomes play a large role in regulating coral health. Corals manipulate their microbiomes to select the symbionts to serve their requirements in a particular environment. The study of coral microbiomes is of interest to determine core microbiomes and identify key microorganisms that serve important environmental functions within the coral holobiont. Identifying coral-associated bacteria that are potential Beneficial Microorganisms for Corals (pBMCs) could be useful in coral probiotics to help corals survive future thermal stress events which would otherwise lead to bleaching or disease. In this study, the microbiomes of two Porites coral species from the Caribbean were characterized by culture-dependent techniques. The microbiomes of the two congeneric coral species were compared and found to differ in bacterial species. Culture media influenced the cultivable microbiome: the minimal medium (R2A Agar) provided a higher bacterial diversity than the nutrient-rich medium (Marine Agar). The 103 bacterial OTUs covered three phyla covering four classes and twelve genera which were identified based on 16S rRNA sequencing. A selection of isolates was studied for their potential as BMCs. No antagonistic activity was found to be expressed by the selected OTUs. The production of reactive oxygen species (ROS)-scavenging enzyme catalase of the coral-associated bacterial OTUs was found to vary among bacterial species and even between strains; species of Kocuria, Pseudoalteromonas, and Staphylococcus produced high amounts of catalase across a temperature range of 25 to 32°C. While this study allowed the isolation of a number of coral-associated bacteria from Porites species and their functional assessment, it is evident from the findings of this study that further research is required into improving the cultivability of coral-associated bacteria.

Keywords: coral reef; microbiome; BMC; probiotic; antagonism; catalase