Collaborative Research: Relating detrital peptide sequences to particulate organic matter diagenetic histories

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Biological, chemical, and physical processes alter recently deposited marine sediments. During this alteration, commonly referred to as early diagenesis, the quantity and composition of organic matter is changed which influences key components of the marine carbon cycle. In this study, researchers will use analytical techniques to evaluate the geochemistry of peptides during early diagenesis, and develop methods for assessing the role bacteria play. This research is important because organic molecules such as peptides influence degradation rates and the fate of carbon and nitrogen in the ocean, and therefore have broad relevance for understanding the geochemical cycling of these key nutrients. The project will also involve research opportunities for undergraduate and graduate students, as well as encourage diversity in the next generation of ocean scientists by providing summer internship opportunities for female middle school students from underrepresented communities (Project COOL).Most diagenetic indices for evaluating how "far along" organic matter is in its early diagenesis are based on amino acid compositions. Total hydrolyzable amino acid compositions indicate, in a coarse manner, organic matter degradation status, bioavailability, and source. Further development of amino acids as tools to assess geochemical processes requires including the wealth of information held within the peptide chains, information that is currently lost during hydrolysis. A powerful approach to sequencing detrital peptides is the application of tandem mass spectroscopy followed by de novo sequencing. In this project, researchers will use de novo sequencing to evaluate peptide and protein geochemistry during early diagenesis, and to develop a peptidoglycan-specific quantification method that allows utilization of the unique peptidoglycan peptide structures found in different bacteria. Specific actions to be taken under this project include (1) applying de novo sequencing to a set of well-characterized archive samples, (2) conducting a set of sorption experiments to evaluate the propensity for different detrital peptides to adhere to mineral surfaces and be protected from degradation, and (3) developing a quantitative method for measuring peptidoglycan peptides. By comparing detrital peptides to other known quantities of the sample set, relationships between organic matter diagenesis and peptide source, sequence, and preservation will be assessed.