Exploring the physiological and ecological basis of mixotrophy in marine food webs

海洋浮游植物约占全球初级生产量的一半，尽管受到季节性或慢性营养物质的限制。为了应对这种情况，许多浮游植物通过混合营养来补充他们的营养需求，这涉及到以细菌或其他藻类为食。海洋中这些微小的金星捕蝇器是海洋微生物食物网的主要参与者，但我们对它们何时觅食以及它们的食物如何与光合作用平衡知之甚少。这项研究将阐明环境和细胞因素如何控制混合营养，以及混合营养和光合作用如何整合到整体新陈代谢中。虽然了解混合营养在海洋食物网中的生态作用是这项工作的中心，但这项研究的结果也将通过确定摄食和光合作用之间的潜在权衡来阐明混合营养的进化。这项工作将涉及与西菲尔教育基金会合作，这是一个海洋科学素养和教育计划，以设计一个教育单位，强调海洋微生物食物网中混合营养的重要性，并将利用乘船旅行和课堂活动来传播这些概念。来自代表性不足群体的本科生将在伍兹霍尔海洋研究所(少数民族奖学金计划)接受培训，以及当地的高中暑期学生，进行关于混合营养物的实验室研究。这项研究还将为博士后科学家提供培训和职业发展。混合营养是指将一定程度的吞噬和光养结合在一起的物种，代表了一系列不同的生态相互作用以及细胞和代谢适应。虽然混合营养通常被认为是正常的例外，但混合营养在海洋食物网中很常见，在营养含量低或有限的时期为浮游植物提供更大的生态适应性，同时稳定食物网。许多混合营养体的叶绿素与碳的比例很低，这往往使它们成为光养竞争对手。反过来，觅食使这些物种实现了最大限度的增长，同时在某些情况下也消除了它们的竞争对手。其他混合营养体是强烈的光养竞争者，只有在营养严重受限的情况下才取食。这项研究将确定导致海洋浮游植物摄食的细胞和环境因素，以及异质营养和光合作用的不同代谢如何在细胞内整合。这项研究将包括以实验室为基础的模式甲藻和金藻培养实验。利用显微镜、生理学、蛋白质组学和代谢组学的方法，这项工作将检验关于混合营养不良的最终原因和后果的假说。主要目标是确定1)诱导混合营养的环境控制，2)猎物质量对捕食者选择的作用，3)混合营养的细胞和分子控制，以及4)营养同化和综合代谢。利用这些不同的研究方法，这项工作将产生对几种混合营养生物的全面看法，并为混合营养的细胞、生态和进化方面提供新的见解。这一研究结果将加深我们对混合营养在海洋浮游植物中的生理和生态作用的理解，并为实验室和现场研究这一过程提供迫切需要的分子标记。

Marine phytoplankton are responsible for about half of global primary production despite being seasonally or chronically nutrient limited. To cope with this, many phytoplankton supplement their nutritional needs through mixotrophy, which involves feeding on bacteria or other algae. These microscopic Venus Fly Traps of the ocean are major players in marine microbial food webs, yet we know so little about when they feed and how their eating is balanced with photosynthesis. This research will shed light on how environmental and cellular factors control mixotrophy, and how mixotrophy and photosynthesis are integrated in the overall metabolism. While understanding the ecological role of mixotrophy in ocean food webs is center to this work, results from this study will also shed light on the evolution of mixotrophy by identifying potential tradeoffs between feeding and photosynthesis. This work will involve collaboration with The Zephyr Education Foundation, a marine science literacy and education program, to design an educational unit to emphasize the importance of mixotrophy in marine microbial food webs, and will utilize boat trips and classroom activities in order to communicate these concepts. Undergraduate students from underrepresented groups will be trained at the Woods Hole Oceanographic Institution (minority fellowship program), as well as local high school summer students, to perform lab research on mixotrophs. This research will also provide training and career development for a postdoctoral scientist. Mixotrophy refers to species that combine some level of phagotrophy and phototrophy, and represents a diverse array of ecological interactions and cellular and metabolic adaptations. While often perceived as an exception to the norm, mixotrophy is commonplace in marine food webs, affording phytoplankton greater ecological fitness during periods of low or limiting nutrients while stabilizing food webs. Many mixotrophs have a low chlorophyll: carbon ratio, which tends to make them poor phototrophic competitors. In turn, feeding allows these species to achieve maximum growth while in some cases also eliminating their competitors. Other mixotrophs are strong phototrophic competitors, and only feed when severely nutrient limited. This research will determine the cellular and environmental factors that lead to feeding by marine phytoplankton, and how the contrasting metabolisms of heterotrophy and photosynthesis are integrated within a cell. This research will involve laboratory-based experiments on model dinoflagellate and chrysophyte cultures. Using microscopy, physiology, proteomics and metabolomics approaches, this work will test hypotheses about the ultimate causes and consequences of mixotrophy. The major objectives are to determine 1) environmental controls for inducing mixotrophy, 2) the role of prey quality on predator selection, 3) cellular and molecular controls of mixotrophy, and 4) nutrient assimilation and integrated metabolism. Using these various research approaches, this work will produce a comprehensive view of several mixotrophs and provide new insights into cellular, ecological, and evolutionary aspects of mixotrophy. Results from this research will improve our understanding of the physiological and ecological role of mixotrophy in marine phytoplankton, and provide much needed molecular markers for studying this process in both the laboratory and field.