Basin-scale distribution and activity of deep-sea protists in the North Atlantic Ocean

对深海水体中真核微生物的分布和生态知之甚少。这些微生物大多是以细菌为食的小型异养鞭毛虫，而细菌的生物量反过来又由从表面输入的溶解和颗粒有机物质提供燃料。本研究旨在了解真核微生物（即原生生物）在大流域水文和化学性质变化背景下的分布。主要的假设是，原生生物的丰度和分类组成是深海系统有机碳输入强度和类型（颗粒或溶解）的敏感指标。将收集针对北大西洋主要水团的垂直剖面样本。此外，深海样品将在压力下回收，并在四个新设计的恒化系统中在原位压力和温度下孵育。这些培养物将在压力下进行次取样，并检查营养浓度，以及监测室中原核生物和原生生物的丰度。使用相同的压力采样器进行短期孵育，研究人员将通过调查主动进食荧光标记细菌的生物比例来探索深海原生生物的活动。他们将使用荧光原位杂交和传统染色相结合的方法枚举深海原生生物，并将使用电子显微镜支持分类分类。具有图像分析能力的半自动荧光显微镜将用于扫描主要过滤区域并探测通常低于其他方法检测极限的稀有微生物。在实验室实验中，研究人员将利用新建成的培养系统，模拟下沉颗粒沉入深渊时所暴露的温度和压力变化，研究真核原生生物的压力效应。智力优势：深海是地球上最大的栖息地。在生命的三个领域（即细菌、古细菌和真核生物）中，真核生物的部分在这种环境下的微生物领域中基本上被忽视了。新的分子方法首次使我们不仅可以准确地枚举原生生物，而且可以根据它们的分类关系对它们进行分类。研究人员有了一个强大的工具，可以更好地了解深海原生生物的作用，并将它们作为有机物质输入水平的敏感指标。原生生物还可以控制下沉颗粒上的细菌数量，从而影响再矿化率。由于深海在许多方面与地表水不同（高压、低温、食物资源稀缺、黑暗），深海原生生物为解决生理学、生态学和进化领域的重大研究问题提供了极好的模式生物。更广泛的影响：这是老道明大学和荷兰海洋研究所之间的合作研究成果。技术和思想的交流对院校和学生培训都有好处。深海研究为海洋课程提供了一个迷人的教学工具。压力室将被纳入奥德道明大学本科生和研究生的生物海洋学核心课程，以便让他们在探索压力对生物和生化过程的影响方面获得实践经验。生物过程与深海中的碳储存高度相关。在一个温室气体在大气中积聚并导致气候变化的时代，海洋长期吸收和储存大气中大量多余碳的能力对社会至关重要。这项研究的数据将通过伍兹霍尔的国家海洋碳和生物地球化学（OCB）数据库和综合海洋生物地球化学和生态系统研究（IMBER）框架共享。我们将为诺福克市首屈一指的海洋博物馆和解说中心Nauticus计划举办的关于海洋微生物作用的永久性展览做出贡献，展览的标题是“看不见的世界——微生物海洋学的领域”。

Little is known about the distribution and ecology of eukaryotic microbes of the deep sea water column. Most of these microbes are small heterotrophic flagellates that feed on bacteria, where biomass in turn is fueled by the input of dissolved and particulate organic material from the surface. This study seeks to understand the distribution of eukaryotic microbes (i.e., protists) in the context of large, basin scale variations in hydrographic and chemical properties. The main hypothesis is that the abundance and taxonomic composition of protists serve as sensitive indicators of the strength and type (particulate or dissolved) of input of organic carbon into the deep ocean system. Samples in vertical profiles targeting major water masses across the North Atlantic will be collected. In addition, deep sea samples will be retrieved under pressure and incubated at in situ pressure and temperature in four newly designed chemostat systems. These cultures will be sub-sampled under pressure and examined for nutrient concentration, as well as for the purpose of monitoring the abundance of both prokaryotes and protists in the chambers. Using the same pressure samplers in short-term incubations, the investigators will explore the activity of deep sea protists by investigating the proportion of actively feeding organisms on fluorescently labeled bacteria. They will enumerate deep sea protists using a combination of fluorescence in situ hybridization and traditional staining methods, and will support taxonomic classifications using electron microscopy. Semi-automated epifluorescence microscopy with image analysis capabilities will be used to scan major filter areas and probe for rare microbes that normally fall below detection limits of other methods. In laboratory experiments, the investigators will use the newly built culture system to study pressure effects of eukaryotic protists while simulating temperature and pressure changes that sinking particles are exposed to when they sink to the abyss. Intellectual merit: The deep ocean is the largest habitat on earth. Among the three domains of life (i.e., Bacteria, Archaea and Eukarya), the eukaryotic fraction has largely been ignored in the microbial realm of this environment. New molecular methods make it possible, for the first time, to not only accurately enumerate protists but also to classify them according to their taxonomic affiliation. The investigators have a powerful tool to better understand the role of protists in the deep sea and to use them as sensitive indicators for the level of input of organic material. Protists may also control bacterial populations on sinking particles and thereby influence remineralization rates. As the deep sea differs in many ways from surface water (high pressure, low temperature, scarce food resources, darkness), deep sea protists provide excellent model organisms to address major research questions in the areas of physiology, ecology and evolution. Broader impacts: This is a collaborative research effort between Old Dominion University and the Netherlands Institute of Sea Research. The exchange of technology and ideas will benefit both institutions and student training. Deep sea research provides a fascinating teaching tool for marine courses. The pressure chambers will be incorporated into the biological oceanography core course for undergraduate and graduate students at Old Dominion University in order to give them hands-on experience in the exploration of pressure effects on biological and biochemical processes. Biological processes are highly relevant for carbon storage in the deep sea. The ocean's capacity to take up and store large amounts of excess carbon from the atmosphere over long time periods is of utmost importance to society in an era in which greenhouse gases accumulate in the atmosphere and lead to climate change. Data of this research will be shared via the national Ocean Carbon and Biogeochemistry (OCB) data repository at Woods Hole and through the Integrated Marine Biogeochemistry and Ecosystem Research (IMBER) framework. We will contribute to a planned permanent exhibit on the role of marine microbes at Nauticus, a premier maritime museum and interpretative center in Norfolk, with the title "Invisible world - the realm of microbial oceanography".