Project: Direct Identification and Characterization of Marine Heterotrophic Nitrogen Fixers by Stable Isotope Probing

Description from NSF award abstract:
The nitrogen cycle in the ocean is extremely complex and it continues to yield surprises. Knowledge gained in this project will directly contribute to resolving an unsettled and important question regarding the sources of nitrogen in the oceans because imbalances in nitrogen budgets have raised questions on how well we have quantified all nitrogen inputs and removal. While nitrogen-fixing cyanobacteria have long been recognized as important contributors to nitrogen fixation in the oceans heterotrophic nitrogen-fixing bacteria (HNFB) are a poorly characterized, but potentially important, component of the marine nitrogen-fixing community. Using advanced methodologies, this project will develop the means to obtain a new understanding of novel, active, HNFB in the ocean. The identification of these organisms and the assessment of their phylogenetic diversity and biogeochemical significance will provide important insights about their role in the marine nitrogen cycle. The project will develop a novel stable isotope probing (SIP) methodology coupled with high-throughput sequencing. SIP exploits the uptake of isotopically enriched substrates into nucleic acids (e.g., DNA) while high-throughput sequencing should allow the identification of nitrogen-fixing bacteria generally, and HNFB specifically, so that the principal investigator can directly link the biogeochemistry of nitrogen with the phylogeny of those nitrogen-fixers. The objective of this project is to provide a proof of concept effort and identify important HNFB lineages using this novel approach and begin to develop quantitative estimates for the contribution of HNFB populations to marine nitrogen-fixation and the nitrogen cycle.

The primary data repository for sequence data from this project is the European Nucleotide Database. All information on sequence numbers ERS980492 and ERS980611 from this project can be found there.

See the related project "New Approaches to New Production" (N-SPOT), funded by OCE-1437310 and OCE-1437458, a field effort studying the N cycle at the San Pedro Timeseries (SPOT) station off the coast of Los Angeles.