Recent advances in molecular microbial ecology have overturned canonical paradigms of the marine nitrogen cycle. Estimates of global nitrogen fixation are regularly revised upward, the non-traditional bacterial denitrification pathway known as anammox is now thought to be responsible for a significant portion of global denitrification, and the discovery of ammonia-oxidizing Archaea necessitates a reevaluation of the contribution of traditional nitrifying bacteria to the global nitrogen cycle. While environmental gene sequencing and geochemical studies were critical to these discoveries, much of this new understanding could not have been gained without the aid of studies on representative organisms in pure culture. Since their discovery in 1992, the ecological role of mesophilic marine Archaea has remained a mystery due in large part to the lack of a cultured representative. A mesophilic marine Crenarchaea is now available in culture along with several lines of evidence that this and many other pelagic marine Crenarchaea oxidize ammonia to obtain the energy needed to sustain autotrophic carbon fixation. The distribution of marine Crenarchaea and their genes encoding ammonia-oxidizing enzymes, suggests that these organisms are responsible for the oxidation of a significant portion of the ocean's reduced nitrogen pools. This project will examine the rate and efficiency of Archaeal ammonia-oxidation, and the relative role of Bacteria and Archaea in ammonia-oxidation. The project uniquely combines culture work, molecular biology, organic geochemistry and field investigations into one of the first studies of the role of marine Crenarchaea in the biogeochemical cycling of nitrogen. Graduate and undergraduate students will gain expertise in an interdisciplinary research project, combining cutting edge methods in microbiology, molecular biology and biomarkers, and the PIs will interact with a recently funded and soon to be established COSEE center at their home institution.
