Sources and Biogeochemical Cycling of Intact Membrane Lipids in the Upper Ocean

细胞膜构成了上层海洋中10-25%的碳生物量。浮游细胞的这些重要结构成分主要由完整的极性脂质（ipl）组成，并且从上层海洋输出的有机碳中有很大一部分来自ipl。分析IPLs的主要工具是气相色谱（GC）分析其组成脂肪酸。这种方法为浮游生物的特定群体提供了许多有价值的脂肪酸生物标志物。然而，GC对与较大的IPL分子相关的巨大程度的结构多样性不敏感，因为脂肪酸必须在GC分析之前从极性“头基”中切割出来。在这个项目中，伍兹霍尔海洋研究所的研究人员将研究上层海洋中的ipl，目的是明确回答以下两个研究问题：1。上层海洋中存在的主要ipl类别是否具有特定的分类学或功能定义的生物来源？2. 上层海洋中主要种类的ipl的周转速度是否与它们赖以产生的生物质的周转速度一致？研究小组将采用新的高效液相色谱/质谱（HPLC/MS）方法，使IPLs能够在保持完整形式的情况下进行鉴定和定量。这种方法揭示了上层海洋中广泛而未被认识的IPL分子多样性。这些ipl的来源生物在很大程度上是未知的，这表明我们对上层海洋碳循环的理解存在重大差距。此外，ipl作为一种新的生物地球化学示踪剂对特定的浮游微生物群具有巨大的潜力。该项目将涉及三种不同的方法：首先，使用HPLC/MS来表征浮游生物主要分类类群中ipl的分布。这些群体通过流式细胞术从北大西洋和北太平洋的四次巡航中收集的天然海水中分离出来。其次，在这些巡航中，团队将进行孵化，以将13c标记的二氧化碳和有机化合物追踪到特定的IPL分子中。这些信息将使我们能够约束功能定义的ipi来源。最后，他们将使用同位素示踪剂孵育来靶向ipl的头基团，从而确定完整分子的周转率。这一信息将用于确定ipl是活的还是衰老的生物量的信号。这项工作将产生几个更广泛的影响。首先，拟议的项目将构成麻省理工学院/WHOI联合项目学生论文研究的核心。该学生将参与项目的各个方面。其次，将从海洋学代表性不足的群体中招募一名学生参与本项目。WHOI少数民族奖学金计划吸引了全国最聪明的本科生的申请，WHOI已经同意为我们提议的项目专门支持一个夏季少数民族奖学金。

Cell membranes make up 10-25% of the carbon biomass in the upper ocean. These important structural components of planktonic cells are dominated by intact polar lipids (IPLs), and a significant fraction of the organic carbon that is exported from the upper ocean is derived from IPLs. The primary tool for analyzing IPLs has been the gas chromatographic (GC) analysis of their constituent fatty acids. This approach has provided many valuable fatty acid biomarkers for specific groups of planktonic organisms. Yet GC is insensitive to an immense degree of structural diversity associated with the larger IPL molecules since fatty acids must be cleaved from polar "headgroups" prior to GC analysis. In this project, researchers at the Woods Hole Oceanographic Institution will study IPLs in the upper ocean with the goal of definitively answering the following two research questions: 1. Do the major classes of IPLs present in the upper ocean have specific taxonomically- or functionally-defined biological sources? 2. Do the major classes of IPLs in the upper ocean turnover at rates that are consistent with those of the living biomass from which they are derived? The research team will apply new high performance liquid chromatography/mass spectrometry (HPLC/MS) methods that allow IPLs to be identified and quantified while still in intact form. This approach has revealed a broad and unrecognized diversity of IPL molecules in the upper ocean. The source organisms of these IPLs are largely unknown, representing a significant gap in our understanding of the upper ocean carbon cycle. Furthermore, IPLs have an immense potential as new biogeochemical tracers for specific groups of microbial plankton. The project will involve three distinct approaches: First, HPLC/MS be used to will characterize the distribution of IPLs in major taxonomic groups of plankton. These groups isolated by flow cytometry from natural seawater collected during four cruises in the North Atlantic and North Pacific. Second, on these cruises the team will conduct incubations to trace 13C-labeled CO2 and organic compounds into specific IPL molecules. This information will allow us to constrain functionally-defined sources of IPLs. Last, they will use isotope tracer incubations to target the headgroups of IPLs and thereby determine the turnover rates of the intact molecules. This information will be used to establish whether IPLs are a signal of living or senescent biomass. This work will have several broader impacts. First, the proposed project will constitute the heart of an MIT/WHOI Joint Program student's dissertation research. This student will be involved in all aspects of the project. Second, a student will be recruited from a group underrepresented in oceanography to participate in this project. The WHOI Minority Fellowship Program draws applications from the brightest undergraduates in the country and WHOI has agreed to support a summer Minority Fellowship specifically for our proposed project.