New Proteomic Windows into the Marine Nitrogen Cycle

Jacob Waldbauer1, Maureen Coleman2 and Lichun Zhang1, (1)University of Chicago, Geophysical Sciences, Chicago, IL, United States, (2)University of Chicago, Chicago, IL, United States
Nitrogen assimilation by marine microbes is one of the largest fluxes in the global N cycle. Most N in microbial cells resides in proteins, making quantitative understanding of how microbes use nitrogen anabolically – to build which proteins under which circumstances, and for which metabolic purposes – central to marine N biogeochemistry. Proteomics, the mass spectrometry-based identification and quantification of proteins and their properties (such as chemical modifications, isotopic compositions, noncanonical translation, and subcellular localizations), is a key tool in generating this molecular-level picture of microbial N utilization. We present novel quantitative and isotope-labeling proteomics methodologies, as well advances in de novo peptide sequencing and database searching for metaproteomics. These enable broad-coverage, high-precision protein expression quantification in both laboratory and field samples, as well as tracking of biosynthetic incorporation of N into specific protein components of cellular metabolism. With examples from isolated marine microbes, planktonic virus-host systems, and field studies, we illustrate how these techniques afford new insights into marine nitrogen biogeochemistry.