Award: OCE-2124712

Nitrogen is an essential nutrient for all life. In the ocean, nitrogen can limit the growth of phytoplankton, the photosynthetic microbes that form the base of the food web and sequester carbon in the ocean. Phytoplankton primarily use nitrogen in the form of nitrate and ammonia to build the macromolecules that form cells and to produce a variety of small organic molecules that perform important metabolic functions in cells. Phytoplankton contain a large reservoir of these nitrogen-containing molecules. When phytoplankton excrete or release these metabolites into the ocean, other microorganisms can consume them and convert them back to carbon dioxide, ammonia and nitrate, restarting the cycle. Despite their recognized importance in the marine nitrogen cycle, few or no studies have characterized the full array of organic molecules produced by microorganisms  in the ocean, their concentrations or production rates due to the analytical challenge to measure these types of small molecules in the environment.

This study employed a newly developed method for measuring small polar metabolites to fill knowledge gaps in our understanding of how small nitrogen-bearing metabolites flow through the organic nitrogen pool and microbial communities. Our field studies and laboratory experiments support the hypothesis that small polar metabolites are important components of the dynamic dissolved organic nitrogen pool in the ocean. We demonstrate this by measuring the concentration, production rate, and uptake kinetics of homarine and other abundant nitrogen-containing metabolites in the ocean. For homarine, we identified the genes, enzymes and organisms responsible for its consumption and degradation. Using homarine and glycine betaine, we showed that competition for similar types of compounds within microbial communities controls their concentration and cycling in the environment. Other key findings include some of the first comprehensive measurements of the suite of metabolites called osmolytes throughout the ocean and experiments to trace their production and consumption through a variety of isotope labeling experiments.  The combination of approaches used in the work proposed here are a model for envisioning the flow of nitrogen containing molecules through marine microbial ecosystems.

Our study contributed to the creation of an open-source metabolite database and data processing pipeline that will serve the broader field of metabolomics, a growing area in environmental, engineering, and medical sciences. This collaboration also promoted the careers of several graduate students and a postdoc as well as an early career professor at a primarily undergraduate institution (PUI). Undergraduates from both institutions contributed to the project development and implementation, local cruises on the R.V. Carson, lab work, and dissemination of results. This research was integrated into a curriculum-based research experience for undergraduates (CURE) designed for a Genetics course at the PUI, University of Puget Sound. Students in this course participated directly in the genetic research by isolating and sequencing the genome of homarine-degrading bacteria. Results from this work were  disseminated through peer reviewed open source publications and presentations to the scientific community and the general public.

Last Modified: 12/29/2025
Modified by: Oscar Abraham Sosa