N-172. Combined Geochemical and Molecular Analyses of Crenarchaeal Assemblages in Columbia River Sediments

H. M. Simon, J. T. Nurmi, P. G. Tratnyek;
Oregon Hlth. & Sci. Univ., Beaverton, OR.

Recent research suggests that nonthermophilic members of the archaeal subdivision Crenarchaeota play major roles in global biogeochemical cycles. Research on the ecological functions of these organisms has been carried out mainly in marine habitats, while substantially less is known about their roles in freshwater ecosystems. We are investigating the metabolic properties of these novel archaea and the microhabitats they occupy in riverine sediments using a combination of precise microanalytical techniques, sensitive and quantitative molecular phylogenetic methods, and classical culturing. We anticipate that correlation of geochemical profiles with the diversity, abundance and distribution of different members of the crenarchaeal assemblage will lead to testable predictions about their metabolic functions and ecological roles. Several reports have documented the abundance of ammonia oxidizing archaea in marine and soil habitats. We tested the hypothesis that nonthermophilic crenarchaeotes, including those that putatively oxidize ammonia, colonize Columbia River sediments. Geochemical and microbiological profiles were generated vertically through sediment subcores collected from two different Columbia River sites. Using PCR and primers specific for the SSU rRNA genes of nonthermophilic crenarchaeotes, we discovered a diverse assemblage of these archaea in freshwater sediments. Initial results suggest that there were depth-dependent changes in the composition and abundance of members of the crenarchaeal assemblage, and that some of the differences may relate to redox potential. The putative archaeal amoA gene was also detected, indicating the potential for ammonia oxidation by riverine crenarchaeotes. Results support the idea that diversity, distribution and abundance of nonthermophilic crenarchaeotes can be coupled to geochemical profiles in subcore sediment fractions, and that this approach will yield new information about archaeal ecology.