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

University Of Southern California, Los Angeles CA

Investigators

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. This project will foster the development of a graduate student who will work on all aspects of the project for his PhD and the work will be presented at science conferences and in public outreach venues. Undergraduates will also work on the project under the guidance of the graduate student and principal investigator. The participants will also engage with the USC Young Researchers Program (YRP), which recruits high school students from diverse and underprivileged local schools for summer research experiences. Students will be guided in the laboratory-based aspects of this project, and present their work at an YRP symposium. The principal investigator will also continue to participate in science curriculum development workshops of the Center for Ocean Sciences Education Excellence-West program.