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

原生生物大多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，是海洋食物链中的主要贡献者。确定它们的分类特征以及它们对碳和营养循环(即碳和矿物质在环境中不断发生化学变化并在生物体内重新结合)的贡献程度是这项研究的主要目标之一。此外，研究人员将研究他们如何应对环境变化，这是当前海洋学中最重要和最具挑战性的问题之一。回答这些问题对于了解海洋环境中的生物如何相互作用并为海洋的健康和生产力做出贡献是至关重要的。该项目的主要目标是研究小型原生动物与非常微小的蓝藻(又称微囊藻)之间的生物相互作用。微囊藻代表着海洋中最丰富的光合作用生物。这些研究将在海洋环境和实验室实验环境中进行。考虑到对这一主题的了解有限，该项目计划的工作有望带来重要而令人兴奋的发现。两位职业生涯早期的女科学家将领导这一项目。此外，一名博士后学者、一名研究生和至少三名本科生暑期实习生将参加拟议的研究活动。主要调查人员将创建一个强有力的公共推广项目，让中学生参与与海洋科学有关的实践活动，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中的研究的主要发现。它可用于学校和非正式学习环境，包括公众通过博物馆的科学简报网页访问互联网。虽然单细胞真核微生物或原生生物的数量远远超过微蓝细菌(原氯球菌和聚球藻)，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较大。此外，小型浮游原生动物还可以通过放牧调节微囊藻的丰度。该项目的主要目标是在野外和实验室环境中研究浮游微微和纳米真核生物与微囊藻的生物相互作用。将进行一系列基于现场和培养的实验，使用最先进的方法，包括荧光激活的细胞分选、同位素和荧光染色标记，以及下一代分子测序，以解决研究目标。在操作上，该项目围绕两个目标构建：目标1是通过测量主要微生物类群的初级生产、细菌、混合营养和磷吸收来评估小型原生动物对碳和养分循环的贡献，并评估营养可获得性在控制混合营养中的作用。目标2将重点评估以微蓝细菌为食的小型原生生物的分布和多样性，并进一步评估营养物质在混合营养原生生物中的作用。为了实现这些目标，将在不同的环境中进行实地实验：北太平洋副热带环流(磷丰富，在STA以原氯球菌为主)。Aloha)和西北地中海(缺磷，在Sta以聚球藻为主。DYFAMED)。使用模型原生生物和苦味蓝藻的补充实验将在实验室使用受控培养进行。这项工作将提供关于海洋微生物真核生物系统发育多样性和功能的关键新信息，重点是它们作为微微细菌原氯球菌和聚球藻的捕食者(吞噬、混合营养)及其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.