Bacterial communities of talang-talang reef and their potential role in coral defense

Complex microbial communities are known to have significant influence over coral reef ecosystems. The Talang-Satang region is situated off the coast of Sematan and is especially important as it is one of the most diverse ecosystems found off Sarawak. Interestingly, the Talang-talang reef thrives at above-average temperatures of 28-30 °C throughout the year. Through isolation and identification (16S rDNA) of native microbes from the coral, surface mucus layer (SML), as well as the surrounding sediment and waters, we were able to determine the species composition and abundance of the ctilturable bacteria in the coral reef ecosystem. Isolates found attached to the coral are mostly related to Vibrio spp., presumably attached to the mucus from the water column and surrounding sediment. Pathogenic Vibrio spp. and Bacillus spp. were dominant amongst the isolates from the water column and sediment. Known coral pathogens responsible for coral bleaching, V. coralliilyticus and V. shilonii, were isolated from the coral SML and sediment samples respectively. Coral SML isolates are found to be closely related to known nitrogen fixers and antibiotic producers with tolerance towards elevated temperatures and heavy metal contamination. The presence of type I modular polyketides synthase (PKS) genes responsible for clinical and economical macrolide polyketides production, and non-ribosomal peptide synthetase (NRPS) genes with the ability to produce immunosuppressant cyclosporine and other antibiotics were screened using specific PKS and NRPS primers. This specialized microbiota may be important for protecting the corals from pathogens by occupying entry niches and/ or through the production of secondary metabolites (i.e. antibiotics). The community from the coral SML were tested against each other at 28, 30 and 32 °C, and were found to exhibit antimicrobial properties under normal temperatures while pathogenic strains appear more toxic at elevated temperatures. Our results highlight the potential of bacteria associated with the coral SML in producing antibiotics and also indicate their important role in the coral defence