DINOTROPHY: Deuterium in Organic Biomarkers: A new tool to investigate the role of Marine Mixotrophy in the Global Carbon Cycle

漂浮在海洋中的海洋微生物（浮游生物）产生了我们呼吸的氧气的50%。它们的活动有助于维持大气中氧气和二氧化碳的平衡。这种生产大部分是由称为原生生物的真核生物（非细菌）微生物进行的。科学传统上将这些海洋原生生物分为两类：一类是类似于微观植物（自养生物），直接从阳光中获取能量;另一类是类似于微观动物（异养生物），通过食用其他微生物获取能量。然而，最近，科学家们开始认识到，许多海洋原生生物在同一个细胞中联合收割机自养和异养（摄食）活动（兼养）。混合营养改变了海洋食物网的功能，并通过增加海洋光合作用影响海洋从大气中清除二氧化碳（应对气候变化）的能力。这一发现颠覆了海洋科学世纪的认识，但也提出了一个严峻的挑战;传统的方法是针对自养或异养，在单独的生物体，我们缺乏方法来确定混合营养活动。该项目将开发一种新的工具来应对这一关键挑战。我们的研究团队已经在英国、法国和瑞士建立了一个广泛的跨学科网络。我们的团队之前已经证明，植物和细菌中产生的化合物（例如脂质）的氢同位素特征对异养和自养的平衡非常敏感。该项目将扩大对海洋微生物使用类似方法产生的化合物的调查。我们将通过测量甲藻产生的特定化合物的氢同位素组成，来针对一组特别重要的兼养原生浮游生物-甲藻。具体来说，我们将研究氢同位素分馏机制（在分子水平上，即“位点特异性”），并试图建立海洋脂质生物标志物的氢同位素特征（也被用作分子化石）作为一种新的工具来研究腰鞭毛虫在现代和过去的海洋中的行为以及混合营养对全球碳循环的影响。该项目的核心通过结合微生物培养和尖端化学分析（包括质谱和核磁共振光谱），还将产生一个独特的数字生物化学模型，该模型将详细识别负责同位素特征的化学步骤。通过这样做，该项目还培养了一个新的跨学科小组，在化学，同位素地球化学和海洋生态学方面具有独特的技能，致力于扩大我们对海洋微生物及其在地球系统中的作用的了解。

Marine microscopic organisms drifting in the oceans (plankton) produce 50% of the oxygen we breath. Their activity helps maintain the balance of oxygen and carbon dioxide in the atmosphere. Much of this production is undertaken by eukaryote (non-bacterial) microbes called protists. Science has traditionally separated these marine protists between those akin to microscopic plants (autotrophs), getting their energy directly from the sunlight, or akin to microscopic animals (heterotrophs), getting their energy by eating other microbes. Recently, however, scientists have come to appreciate that many marine protists combine both autotrophic and heterotrophic (feeding) activities in the same single cell (mixotrophy). Mixotrophy alters marine food web functioning and affects the capacity of the oceans to remove carbon dioxide (counter climate change) from the atmosphere by increasing marine photosynthesis. This revelation overturns a century of understand in marine science, but also presents a severe challenge; traditional methods are targeted at autotrophy or heterotrophy, in separate organisms and we lack methods to determine mixotrophic activity. This project will develop a new tool to tackle this critical challenge. The high interest met in developing this project has already created a wide interdisciplinary network across the United Kingdom, France and Switzerland.Our team have previously shown that hydrogen isotopic signature of compounds produced in plants and bacteria (for instance into lipids) is uniquely sensitive to the balance of heterotrophy and autotrophy. This project will extend this investigation for compounds produced by marine microorganisms using similar approaches. We will target a particularly important group of mixotrophic protist plankton, the dinoflagellates, by measuring the hydrogen isotopic composition of specific compounds produced by dinoflagellates. Specifically, we will investigate the hydrogen isotope fractionation mechanisms (at molecular level, i.e. "site-specific") during biosynthesis of organic compounds and seek to establish the hydrogen isotope signature of marine lipids biomarkers (also used as molecular fossils) as a novel tool to investigate the behaviours of dinoflagellates in modern and past oceans and the impact of mixotrophy on the global carbon cycle.The core of the project will also produce of a numerical biochemical model uniquely possible by combining microorganism cultures and cutting-edge chemical analyses (including Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy) that will identify in detail the chemical steps responsible for the isotopic signature. By doing so, the project is also fostering a new cross-disciplinary group uniquely skilled in chemistry, isotope biogeochemistry and marine ecology dedicated to extend our knowledge of the marine microorganisms and their role on the Earth System.