Project: Quantifying the role of Group I Crenarchaeota in the marine nitrogen cycle using cultures and environmental monitoring of ammonia oxidation, 16S rRNA genes and lipid biomarkers

Project Summary
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 our 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.

We now have a mesophilic marine Crenarchaea 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.

Here we propose to begin to better understand the physiological capabilities, distribution and quantitative significance of ammonia-oxidizing Crenarchaea. Our group is uniquely positioned to launch a comprehensive set of studies that will use cutting edge techniques to answer the following questions:
1) What factors control the rate and efficiency of Archaeal ammonia-oxidation?

2) What is the relative role of Bacteria and Archaea in ammonia-oxidation in the marine environment?

3) How can biomarkers be used to detect and assess the physiological status of living ammonia-oxidizing Bacteria and Archaea?

Our study 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.