Collaborative Research: Role of small-sized protists in the microbial loop with emphasis on interactions between mixotrophic protists and picocyanobacteria

原生生物主要是单细胞真核微生物，包括藻类和原生动物。它们无处不在，种类繁多，是海洋食物网的主要贡献者。确定它们的分类特征以及它们对碳和营养循环（碳和矿物质在环境中不断发生化学变化并重新融入生物体）的贡献程度是本研究的主要目标之一。此外，调查人员将研究它们如何应对环境变化，这是海洋学中最重要和最具挑战性的问题之一。回答这些问题对于理解海洋环境中的生物如何相互作用并对海洋的健康和生产力做出贡献至关重要。该项目的主要目标是研究小型原生生物与非常微小的蓝藻（也称为picocyanobacteria）之间的生物相互作用，蓝藻是海洋中最丰富的光合生物。这些研究将在海洋环境和实验室实验环境中进行。考虑到这方面的知识有限，本项目计划的工作有望有重要和令人兴奋的发现。两位早期职业女性科学家将领导这个项目。此外，一名博士后、一名研究生和至少三名本科生暑期实习生将参与拟开展的研究活动。主要研究人员将创建一个强有力的公共宣传项目，让中学生参与与海洋科学相关的实践活动，并将与美国自然历史博物馆的教育部合作制作一段视频。这段视频将总结拟议研究的主要发现。它可以在学校和非正式的学习环境中使用，包括公众可以通过博物馆的科学公报网页在互联网上访问。单细胞真核微生物或原生生物，虽然在数量上远远超过了picocyanobacteria（原绿球藻和聚藻球菌），但它们对海洋碳生物量和初级生产力的贡献很大，部分原因是它们的细胞尺寸更大。此外，小型浮游原生生物可以通过放牧调节picocyanobacteria丰度。该项目的主要目标是在野外和实验室环境中研究浮游微纳米真核生物与微蓝藻的生物相互作用。将使用最先进的方法，包括荧光活化细胞分选、同位素和荧光染色标记以及下一代分子测序，进行一系列现场和培养实验，以实现研究目标。在操作上，该项目围绕两个目标进行：目标1是通过测量主要微生物群的初级生产、细菌、混合营养和磷吸收来评估小型原生生物对碳和养分循环的贡献，并评估养分有效性在控制混合营养中的作用。目的2将重点评估以picocyanobacteria为食的小型原生生物的分布和多样性，并进一步评估营养有效性在混合营养原生生物中的作用。为了达到这些目标，将在不同的环境中进行实地实验：北太平洋亚热带环流（含磷丰富，以原绿球藻为主）。（ALOHA）和地中海西北部(缺磷，主要是在Sta。DYFAMED)。利用模型原生生物和花青菌的补充实验将在实验室中使用控制培养进行。这项工作将为海洋微生物真核生物的系统发育多样性和功能提供重要的新信息，重点是它们作为picoyanobacteria Prochlorococcus和Synechococcus的捕食者（吞噬、混合营养）和竞争对手的生态作用。

Protists are mostly single-celled, eukaryotic microorganisms, including algae and protozoans. They are ubiquitous, diverse, and major contributors in oceanic food webs. Determining their taxonomic identity and the extent to which they contribute to carbon and nutrient cycles (whereby carbon and minerals are continuously changed chemically in the environment and reincorporated in living organisms) are among the major goals of this study. Moreover, the investigators will study how they respond to environmental change, one of the most important and challenging current problems in oceanography. Answering these questions is fundamental to understanding how living organisms in the ocean environment interact with one another and contribute to the health and productivity of the ocean. The main goal of the project is to investigate biotic interactions of small-sized protists with very tiny cyanobacteria also known as picocyanobacteria, which represent the most abundant photosynthetic organisms in the ocean. These studies will be done both in ocean environments and in laboratory experimental settings. Considering the limited knowledge on this topic, the work planned in this project promises important and exciting discoveries. Two early career female scientists will lead this project. In addition, one postdoctoral scholar, one graduate student, and at least three undergraduate summer interns will participate in the proposed research activities. The principal investigators will create a strong public outreach program that will engage middle school students in hands-on activities related to ocean sciences, and will produce a video in collaboration with the Education Department at the American Museum of Natural History. The video will summarize the major findings of the proposed research. It can be used in schools and in informal learning settings, including access by the public on the Internet through the Museum's Science Bulletins web page.Single-celled eukaryotic microorganisms or protists, though largely outnumbered by picocyanobacteria (Prochlorococcus and Synechococcus), contribute significantly to ocean carbon biomass and primary productivity, partially by virtue of their larger cell size. In addition, small planktonic protists can regulate picocyanobacteria abundance through grazing. The main goal of this project is to investigate biotic interactions of planktonic pico- and nano-sized eukaryotes with picocyanobacteria, both in the field and in laboratory settings. A set of field- and culture-based experiments will be conducted, using state-of-the-art methodologies, including fluorescence-activated cell sorting, isotope and fluorescent stain labeling, and next-generation molecular sequencing to address the research objectives. Operationally, this project is structured around two objectives: Objective 1 is to assess the contribution of small protists to carbon and nutrient cycling through measurement of primary production, bacterivory, mixotrophy and phosphorus uptake in major microbial groups, and evaluate the role of nutrient availability in controlling mixotrophy. Objective 2 will focus on assessing the distribution and diversity of small-sized protists that feed on picocyanobacteria and further evaluate the role of nutrient availability among the protists that are mixotrophic. To reach these objectives field-based experiments will be conducted in contrasted environments: the North Pacific subtropical gyre (phosphorus replete, dominated by Prochlorococcus at Sta. ALOHA) and the North West Mediterranean sea (phosphorus deplete, dominated by Synechococcus at Sta. DYFAMED). Complementary experiments using model protists and picocyanobacteria will be conducted using controlled cultures in the lab. The work will provide critical new information on the phylogenetic diversity and function of marine microbial eukaryotes, with emphasis on their ecological role as predators (phagotrophy, mixotrophy) on, and competitors with, the picoyanobacteria Prochlorococcus and Synechococcus.