Physiological Diversity of Marine Crenarchaea


Karen Casciotti, Chemistry

Grant Funded 2009
Marine Crenarchaeota comprise up to 40% of the deep ocean bacterioplankton, and by some
estimates represent the most abundant cell type on the planet. However, of these some 1028 cells,
only a single marine species exists in culture. This isolate along with and metagenomic data
from the environment suggest these organisms play a significant role in the global cycling of C
and N, and may even represent a new phylum within the Domain Archaea. However, no
cultures yet exist from the open ocean. Over the course of nearly two years, our laboratory has
established three enrichment cultures of planktonic Archaea from the Pacific Ocean that actively
oxidize ammonia (NH3) to nitrite (NO2
-)—the first step of nitrification and a key reaction in the
global N cycle. Support for this proposal will allow for the continued maintenance, enrichment,
and physiological characterization of these rare resources. Our first objective will be to
characterize the basic physiology of these organisms with regard to temperature optima and
substrate affinity, allowing us to gain insight into the mechanisms responsible for their numerical
dominance in both marine and terrestrial systems. Our second objective will be to examine the
biochemistry of ammonia oxidation in these enrichments by determining the isotopic systematics
of archaeal nitrification. This information will have far-reaching implications for the
interpretation of isotopic distributions of nitrate in the ocean. Lastly, continued maintenance of
these enrichments will allow us to pursue outside funding for genomic characterization to help
answer lingering questions about the placement of ammonia-oxidizing Archaea on the tree of