Recent research has suggested that many emerging diseases are caused by opportunistic pathogens derived from populations present in the environment. An underlying assumption of this hypothesis is that non-pathogenic microbes harbor the genetic potential to become pathogenic if the opportunity arises. This project will address this question by comparing, using metabolomics and metagenetics, two cyanobacterial-dominated microbial mat communities, one that is a pathogenic biofilm and one that is based on autotrophy in an extreme environment. Microbial communities in extreme environments are considered to be primitive in an evolutionary context and have been studied intensively as analogues to early life on Earth. Microbial mats in a hot spring contain the same major microorganisms to the genus level as the pathogenic microbial consortium known as black band disease (BBD) of corals. Furthermore, the overall physicochemical structure and major physiological organization of the two systems are identical. Despite the identical taxonomic/physiological structure of the two populations, they are very different in terms of trophic structure. The hot-spring mats are photoautotrophic with two energy sources: light, which powers cyanobacterial photosynthesis, and sulfide dissolved in the geothermal source waters, which powers sulfur chemolithotrophy. The BBD mats, which also contain photosynthesizing cyanobacteria, are fueled by organic carbon (the coral host tissue) as well as sulfide produced by sulfate-reducing BBD bacteria that, in turn, grow on coral-derived organic carbon. This project will use an evolutionary context and comparative approach to construct metabolic networks for both systems based on complementary metabolomics and metagenetics, a comparison of the genetic potential (genomics data) with targeted metabolites (metabolomics data) and an assessment of differences in metabolites between the ancient photoautotrophic based community and the modern pathogenic community. The health of coral reefs is now of global concern. This study will enhance existing knowledge by investigating the underlying potential for natural microbial communities to evolve pathogenicity. Research will include training of minority and female undergraduate and graduate students who will assist in the proposed research. All participating institutions are active in the recruitment and training of underrepresented groups. Florida International University is a doctoral-degree granting minority institution that is ranked first in the US among four year colleges for awarding bachelor's and master's degrees to Hispanic students, and first in awarding degrees to underrepresented minorities in STEM disciplines. The results of this study will be presented at national and international meetings, including the biannual scientific meetings of the Association of Marine Laboratories of the Caribbean (AMLC). The AMLC has science/education representatives and members from over 30 Caribbean/Latin American countries.