Collaborative Research: Peptide Deamination as a Source of Refractory Dissolved Organic Matter in Marine Sediments

海洋中的溶解有机物（DOM）是地球上最大的碳库之一。大部分DOM具有高度的抗降解性（难降解）和老化性，但海洋中难降解DOM积累的性质和原因是海洋碳循环尚未解决的谜团之一。虽然海洋沉积物已被证明是一个全球性的重要来源DOM的海洋，沉积物DOM动态和海洋DOM循环之间的联系仍然难以捉摸，因为信息是缺乏的分子组成和反应性的孔隙水DOM。 为了填补这一知识空白，本项目将解决沉积物中难降解DOM是如何产生的以及底栖DOM在水体中的命运的问题。 该研究将侧重于蛋白质/肽动力学和沉积物DOM循环之间的关系，研究肽脱氨基作用作为大陆边缘沉积物中产生难降解和14 C-贫化DOM的重要途径。将通过对在各种氧化还原条件下收集的沉积物岩心进行地球化学剖面分析，并在受控实验室条件下进行长期沉积物培养研究，来实现这些目标。这项工作的核心是结构解析和定量的完整和脱氨基的肽在孔隙水DOM使用国家的最先进的分析技术。 这项研究将有助于更好地了解当今的碳循环如何运作，以及它在未来可能如何应对。拟议的工作将使用几种方法将研究和教育结合起来。所有的PI都定期将他们的研究融入他们的课程中，从入门本科到高级研究生课程，并将继续在这里这样做。 所有三个PI还致力于吸引妇女和代表性不足的少数民族学生。海洋沉积物是全球海洋溶解有机物（DOM）的重要来源。 然而，沉积物DOM动态和海洋DOM循环之间的联系仍然难以捉摸，因为信息的分子组成和孔隙水DOM的反应性是缺乏的。 为了帮助填补这一知识空白，该项目将解决沉积物中难降解DOM是如何产生的以及底栖DOM通量在水柱中的命运的问题。 这项研究探索了一个新的和潜在的变革性想法，即沉积物中肽的脱氨基作用是海水中难降解和14 C耗尽的DOM的来源。这一想法不仅与大多数海水溶解的有机氮以酰胺形式存在的事实相一致，而且与最近关于深海耐火DOM中普遍存在含氮配方的报道相一致。中心假设将通过自下而上（分子水平DOM分析）和自上而下（批量水平元素和同位素分析，以及数值模拟）方法的独特组合进行测试。这项工作将包括对在各种氧化还原条件下收集的沉积物岩心进行地球化学剖面分析，并在受控实验室条件下进行长期沉积物培养研究。 在拟议的工作的核心是结构解析和定量的完整和脱氨基的肽在孔隙水DOM使用国家的最先进的液相色谱-质谱系统（超高效液相色谱耦合到Orbitrap融合Tribrid质谱仪），预计将提供前所未有的丰富的分子水平的信息孔隙水DOM。拟议的工作将导致有机物分解和底栖DOM循环的机械理解的提高，并阐明现代海洋和沉积物的碳和氮循环之间的连接，因为它们涉及到形成难降解DOM。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Dissolved organic matter (DOM) in the ocean is one of the largest carbon reservoirs on Earth. Much of this DOM is highly resistant to degradation (refractory) and aged, but the nature and reasons behind the accumulation of refractory DOM in the ocean is one of the unresolved mysteries of the marine carbon cycle. While marine sediments have been shown to be a globally important source of DOM to the ocean, the connection between sediment DOM dynamics and the oceanic DOM cycle remains elusive, because information is lacking on the molecular composition and reactivity of pore water DOM. To fill this knowledge gap, this project will address the question of how refractory DOM is produced in sediments and the fate of benthic DOM in the water column. The research will focus on the relationship between protein/peptide dynamics and sediment DOM cycling, examining peptide deamination as an important pathway for the production of refractory and 14C-depleted DOM in continental margin sediments. These objectives will be met through a combination of geochemical profiling of sediment cores collected across a range of redox conditions, and long-term sediment incubation studies conducted under controlled laboratory conditions. At the heart of this proposed work is structural elucidation and quantification of intact and deaminated peptides in pore-water DOM using state-of-the-art analytical techniques. The study will help better understand how the present-day carbon cycle operates, as well as how it may respond in the future. The proposed work will integrate research and education using several approaches. All PIs routinely integrate their research into their classes, which range from introductory-undergraduate to advanced-graduate courses and will continue to do so here. All three PIs are also committed to engaging women and underrepresented minority students. Marine sediments are a globally important source of dissolved organic matter (DOM) to the ocean. However, the connection between sediment DOM dynamics and the oceanic DOM cycle remains elusive because information about the molecular composition and reactivity of pore water DOM is lacking. To help fill this knowledge gap, this project will address the question of how refractory DOM is produced in sediments and the fate of the benthic DOM flux in the water column. The proposed study explores a novel and potentially transformative idea that deamination of peptides in sediments is a source of refractory and 14C-depleted DOM in seawater. This idea is consistent not only with the fact that the majority of seawater dissolved organic nitrogen occurs in amide form, but also with recent reports about the widespread occurrence of nitrogen-bearing formulas in deep-sea refractory DOM. The central hypothesis will be tested through a unique blend of bottom-up (molecular level DOM analyses) and top-down (bulk-level elemental and isotopic analyses, and numerical modeling) approaches. This work will involve a combination of geochemical profiling of sediment cores collected across a range of redox conditions, and long-term sediment incubation studies conducted under controlled laboratory conditions. At the heart of the proposed work is structural elucidation and quantification of intact and deaminated peptides in pore-water DOM using a state-of-the-art liquid chromatography-mass spectrometry system (ultra-high performance liquid chromatography coupled to an Orbitrap Fusion Tribrid Mass Spectrometer), which is expected to provide an unprecedented wealth of molecular-level information about pore water DOM. The proposed work will lead to an improved mechanistic understanding of organic matter decomposition and benthic DOM cycling and shed light on the connections between the modern-day oceanic and sedimentary carbon and nitrogen cycles as they relate to the formation of refractory DOM.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.