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。这种DOM大部分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的未解之谜之一。虽然海洋沉积物已被证明是海洋DOM的全球重要来源，但沉积物DOM动力学与海洋DOM循环之间的联系仍然难以捉摸，因为缺乏关于孔隙水DOM的分子组成和反应性的信息。为了填补这一知识空白，该项目将解决沉积物中难降解DOM是如何产生的问题，以及水柱中底栖DOM的命运。研究将重点关注蛋白质/多肽动力学与沉积物DOM循环之间的关系，研究多肽脱胺作用是大陆边缘沉积物中难降解和缺14c DOM产生的重要途径。这些目标将通过在一系列氧化还原条件下收集的沉积物岩心的地球化学剖面和在受控实验室条件下进行的长期沉积物孵化研究相结合来实现。这项工作的核心是利用最先进的分析技术对孔隙水DOM中的完整和脱氨肽进行结构阐明和定量。这项研究将有助于更好地了解当今的碳循环是如何运作的，以及它在未来的反应。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通常都会将他们的研究融入到他们的课堂中，从本科入门到高级研究生课程，这里也将继续这样做。这三所私立学校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质（DOM）的重要来源。然而，由于缺乏孔隙水DOM的分子组成和反应性信息，沉积物DOM动力学与海洋DOM循环之间的联系仍然难以捉摸。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是如何产生的问题，以及水柱中底栖DOM通量的命运。该研究探索了一种新颖且具有潜在变革意义的观点，即沉积物中多肽的脱氨作用是海水中难降解和14c耗尽的DOM的来源。这一观点不仅与大多数海水溶解有机氮以酰胺形式存在的事实相一致，而且与最近关于在深海难熔DOM中广泛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（整体水平元素和同位素分析以及数值模拟）方法的独特混合来验证。这项工作将包括在一系列氧化还原条件下收集的沉积物岩心的地球化学剖面，以及在受控实验室条件下进行的长期沉积物孵化研究。这项工作的核心是利用最先进的液相色谱-质谱系统（超高性能液相色谱与Orbitrap融合三重质谱联用）对孔隙水DOM中的完整和脱胺肽进行结构解析和定量分析，预计将提供前所未有的丰富的孔隙水DOM分子水平信息。拟议的工作将导致对有机物分解和底栖DOM循环的机制理解的改进，并阐明现代海洋和沉积碳和氮循环之间的联系，因为它们与难降解DOM的形成有关。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.