This study will investigate the physiology and ecology of thermophilic, nitrate-reducing microorganisms at deep-sea hydrothermal vents. Since the microbial contribution to the nitrogen cycle at deep-sea hydrothermal vents remains largely unknown, this study is designed to fill this gap. Recent studies revealed the occurrence of novel thermophilic microorganisms that couple the reduction of nitrate with autotrophic CO2 fixation in marine geothermal environments. The ecological significance of such a microbial community at deep-sea vents is twofold: 1) these organisms contribute to the primary productivity by fixing CO2, and 2) their nitrate respiratory metabolism (namely, the reduction of NO3- to NO2-, N2, or NH4+) imply that nitrogen is conserved within the vent system and is recycled into the vent nitrogen cycle. This research will integrate novel cultivation and molecular techniques with stable isotope analyses to explore the physiology of nitrate-reducing microorganisms, and to assess their functional diversity and activity. By establishing a link between physiology, phylogeny and activity, this study will contribute to our understanding of the ecological relevance of nitrate-reducing organisms at deep-sea vents, as well as their contribution to both the carbon and nitrogen cycling. This research will also contribute to the expansion of the database of genes relevant to CO2 fixation and NO3- reduction, allowing for the improvement of detection tool for monitoring these microbial processes in the environment. Training opportunities will be offered to one graduate student and several undergraduate students, and educational and outreach activities associated with several NSF-sponsored programs (e.g., the Mid-Atlantic Center for Ocean Science Education Excellence and the Student Experiments at Sea) will be supported as well.
