Project: Collaborative Research: Characterizing microbial transformation of marine DOM at the molecular level using untargeted metabolomic

NSF Abstract:

Dissolved organic matter is an important component of the global carbon cycle. Dissolved organic matter provides food and energy for microbes living in the ocean and influences microbial diversity. Microbes convert some dissolved organic matter to CO2 (respiration) whereas other forms of dissolved organic matter are altered by microbial processes and persist in the ocean. Thus, it is important to understand how microbes change dissolved organic matter composition and reactivity. This project will examine the chemical structure of dissolved organic matter to identify: 1) molecules that fulfill carbon demand (biomass produced minus losses from respiration) and 2) transformation processes that result from microbial activity. The project will combine lab experiments and field studies at the Moorea Coral Reef Long Term Ecological Research site. The project will support training for three graduate students in marine biogeochemistry. Undergraduate training is aimed at sustained mentoring of underrepresented minority (URM) students. Undergraduates will be recruited from existing programs at Minority Serving Institutions at San Diego State University and the University of Hawaiʻi at Mānoa. Undergraduates will participate in the Scripps Institution of Oceanography SURF Research Experiences for Undergraduates program, where they will conduct research in marine chemistry. The goal is to provide a mentoring approach that can successfully overcome roadblocks to URM engagement in STEM and increase retention of these students in marine science.

This work will combine field and lab studies using advanced molecular-level chemical characterization tools to explore how bacteria alter the composition and bioreactivity of organic compounds dissolved in seawater. Additionally, this project will develop informatics-based tools to identify a larger proportion of chemical structures in marine dissolved organic matter (DOM) than is currently possible using traditional approaches. The project will use tandem mass spectrometry and networking techniques to comprehensively classify organic compounds into molecular families and determine common chemical transformations. Then, using a well-developed field-based experimental ecosystem to produce diverse labile DOM pools the research team will track microbial transformation using expression of hydrolytic enzymes and measure selection for particular microbial taxa and metabolisms. This approach defines the reactivity of individual molecules and broader compound classes participating in carbon fluxes that underpin DOM-microbe interactions. Field surveys conducted within the Moorea Coral Reef Long Term Ecological Research program will explore methods to track transformation of specific molecules in the environment and validate experimental observations of compound classes that appear to accumulate as semi-labile DOM. By integrating laboratory and field experiments and oceanographic surveys with the refinement of analytical tools for untargeted metabolomics, this project will characterize the fate of reactive DOM in the ocean.

Overview:

Microbial respiration in the ocean is centered on the reactivity of complex pools of marine organic matter (hundreds of thousands of different molecules) and is a crucial component of upper ocean C cycling. The proposed research has two major objectives: one is to generate an inventory of labile molecules in dissolved organic matter (DOM), and the second is to classify widespread transformations of marine DOM that are relevant for producing semi-labile DOM in natural ecosystems. Achieving these objectives requires bridging organic chemistry and microbiology methodologies to link microbially relevant molecular transitions through the DOM pool. By integrating laboratory and field experiments and oceanographic surveys paired with the refinement of analytical tools for untargeted metabolomics and metatranscriptomics, we propose to characterize the fate of reactive DOM. A key product of this research is a refined mechanistic understanding of DOM-microbe interactions through the quantification of major microbially-mediated chemical transformations and metabolic pathways that influence the postproduction processing of DOM.