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的大部分高度耐降解(难降解)和老化，但难降解DOM在海洋中积累的性质和原因是海洋碳循环中尚未解开的谜团之一。虽然海洋沉积物已被证明是海洋DOM的全球重要来源，但由于缺乏关于孔隙水DOM的分子组成和反应活性的信息，沉积物DOM动力学与海洋DOM循环之间的联系仍然难以捉摸。为了填补这一知识空白，该项目将解决在沉积物中如何产生难熔DOM以及底栖生物DOM在水柱中的去向的问题。这项研究将侧重于蛋白质/多肽动力学与沉积物DOM循环的关系，考察多肽脱氨作用是大陆边缘沉积物中难降解和14C枯竭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分析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。这项拟议工作的核心是利用最先进的分析技术对孔隙水DOM中完整和脱氨基的多肽进行结构阐明和定量。这项研究将有助于更好地理解当前的碳循环是如何运作的，以及它未来可能会如何应对。拟议的工作将使用几种方法将研究和教育结合起来。所有的专业人士都会常规地将他们的研究融入到他们的课程中，从本科入门课程到高级研究生课程，并将在这里继续这样做。所有三家私人投资机构也都致力于吸引妇女和代表不足的少数族裔学生。海洋沉积物是海洋中溶解有机物(DOM)的全球重要来源。然而，由于缺乏关于孔隙水DOM的分子组成和反应活性的信息，沉积物DOM动力学和海洋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，该项目将解决在沉积物中如何产生难熔DOM的问题，以及底栖DOM通量在水柱中的去向。这项拟议的研究探索了一种新的、具有潜在变革性的想法，即沉积物中的多肽脱氨是海水中难降解和14C耗尽的DOM的来源。这一观点不仅与大多数海水中溶解的有机氮以酰胺形式存在这一事实相一致，而且与最近关于深海耐火DOM中普遍存在含氮公式的报道是一致的。中心假设将通过自下而上(分子水平的DOM分析)和自上而下(整体水平的元素和同位素分析，以及数值模拟)的独特混合方法来检验。这项工作将结合在一系列氧化还原条件下收集的沉积物岩心的地球化学特征，以及在受控实验室条件下进行的长期沉积物孵化研究。拟议工作的核心是使用最先进的液-质联用系统(超高性能液相色谱与Orbitrap Fusion三联质谱仪耦合)来阐明和定量孔隙水DOM中完整和脱氨基的多肽的结构，预计这将提供关于孔隙水DOM的前所未有的丰富的分子水平信息。拟议的工作将导致对有机物分解和海底DOM循环的更好的机械理解，并阐明现代海洋和沉积碳和氮循环之间的联系，因为它们与难处理DOM的形成有关。该奖项反映了NSF的法定使命，并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，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.