Collaborative Research: Understanding the Role of Picocyanobacteria in the Marine Silicate Cycle

智力优势：研究人员将追踪他们发现的聚藻属的海洋picocyanobacteria大量积累硅，以评估这些生物对海洋中生物源二氧化硅循环的贡献。长期以来，海洋学家一直认为硅藻是控制海洋中二氧化硅循环的主要海洋生物。然而，最近，从野外样本中对picocyanobacterian细胞进行的单细胞分析令人惊讶地显示，在聚藻球菌中存在大量的硅。在两个系统中，聚球菌对生物硅的贡献通常与活硅藻相媲美。此外，生物源二氧化硅粒度分馏表明，高达25%的生物源二氧化硅可存在于微浮游粒径分馏中。鉴于在世界上大部分地区，花青菌主导着浮游植物生物量和初级生产？这些发现提出了关于控制全球海洋二氧化硅循环的因素的重要问题，以及对生物成因二氧化硅测量、颗粒物质中的Si: N比、硅酸盐和硝酸盐损耗比的正确解释。它还表明，花青菌种群可能受到以前未知的限制其生产力。该项目将包括实验室和现场组成部分。由于细胞Si在野外采集的样品和实验室菌株之间存在很大差异，因此实验室组件将记录Si摄取和细胞Si浓度的变异性，同时确定生理和系统发育因素在这种变异性中发挥的作用。研究人员将使用已经有基因组序列的聚球菌菌株。实验室实验将1)使用32Si放射性示踪剂摄取实验来评估适应不同硅酸盐水平的聚球菌菌株之间Si含量和Si摄取动力学的变异性程度；2)使用分离技术、密度离心、电子显微镜和x射线吸收光谱来表征细胞内硅的分布和细胞内的化学性质。3)利用已发表基因组的生物信息学分析，确定是否可以基于系统发育关系预测硅的摄取，确定参与蓝藻硅代谢的候选基因，并开发可能与细胞硅含量相关的群落结构探针。在百慕大大西洋时间序列（BATS）地点进行的实地工作将评估聚藻球菌和硅藻在一年中通常以前者为主的时候对地表水中总生物源二氧化硅的贡献。现场测量将包括生物源二氧化硅生物量和硅摄取的大小分异，基于同步加速器的x射线荧光显微镜，以及聚球菌组合的系统发育组成。更广泛的影响：该项目有可能推动我们对海洋硅循环理解的重大范式转变。此外，一名博士生将在石溪接受培训。每个PI将为一些从事原创研究项目的本科生提供研究经验，作为REU计划的一部分或作为本科生论文的基础。石溪大学本科生的研究项目由本科生研究和创意活动（URECA）项目的夏季研究资金支持，并利用其非常多样化的学生群体。调查人员还将通过几个寄宿项目吸引有前途的高中学生，这些项目是pi过去参与的一部分。其中包括毕格罗大学的BLOOM项目和斯托尼布鲁克大学的西蒙斯夏季研究奖学金项目。PI与一所地区高中（Brentwood）保持着持续的关系，该高中的少数民族学生比例很高。PI Twining参与了毕格罗大学的咖啡科学项目。贝恩斯将通过科学和数学教育中心（CESAME）赞助的开放科学之夜（Open Science Nights）开展类似的推广活动。最后，PI Baines将与CESAMEs的教师教育项目合作，目的是将生物海洋学纳入K-12课程。克劳斯和布热津斯基将把浮游植物生态学的各个方面纳入UCSB的海洋课堂计划，该计划每年为18,000多名K-12学生带来UCSB的海洋研究生活。

INTELECTUAL MERIT: The investigators will follow-up on their discovery of significant accumulation of silicon by marine picocyanobacteria of the genus Synechococcus to assess the contribution of these organisms to the cycling of biogenic silica in the ocean. Oceanographers have long assumed that diatoms are the dominant marine organisms controlling the cycling of silica in the ocean. Recently, however, single-cell analyses of picocyanobacterial cells from field samples surprisingly revealed the presence of substantial amounts of silicon within Synechococcus. The contribution of Synechococcus to biogenic silica often rivaled that of living diatoms in the two systems examined. Moreover, size fractionation of biogenic silica indicates that up to 25% of biogenic silica can exist in the picoplanktonic size fraction. Given that picocyanobacteria dominate phytoplankton biomass and primary production over much of the world?s ocean, these findings raise significant questions about the factors controlling the marine silica cycle globally, as well as the proper interpretation of biogenic silica measurements, Si: N ratios in particulate matter, and ratios of silicate and nitrate depletion. It also suggests that picocyanobacterial populations may be subject to previously unknown constraints on their productivity.The project will have both laboratory and field components. Because cellular Si varies substantially among the field-collected samples and laboratory strains so far analyzed, the laboratory component will document variability in Si uptake and cellular Si concentrations, while determining what role physiological and phylogenetic factors play in this variability. The investigators will use strains of Synechococcus for which there are already genome sequences. Laboratory experiments will 1) use 32Si radiotracer uptake experiments to assess the degree of variability in Si content and Si uptake kinetics among strains of Synechococcus acclimated to different levels of silicate, 2) characterize the intracellular distribution and chemistry of silicon within cells using fractionation techniques, density centrifugation, electron microscopy and x-ray absorption spectroscopy, and 3) use bioinformatic analyses of published genomes to determine whether uptake of Si can be predicted based on phylogenetic relationships, to identify candidate genes involved in cyanobacterial Si metabolism, and to develop probes for community structure that can be related to cellular Si content. Field work at the Bermuda Atlantic Time Series (BATS) site will assess the contribution of Synechococcus and diatoms to total biogenic silica in surface waters at times of the year when the former are typically dominant. Field measurements will include size fractionation of biogenic silica biomass and Si uptake, and synchrotron-based x-ray fluorescence microscopy, and the phylogenetic composition of the Synechococcus assemblage.BROADER IMPACTS: This project has the potential to drive a major paradigm shift in our understanding of the marine silicon cycle. In addition, one PhD student will be trained at Stony Brook. Each PI will provide research experience to a number of undergraduates working on original research projects for credit, as a part of an REU program or as the basis for undergraduate theses. Stony Brook research programs for undergraduates are supported with summer research money from the Undergraduate Research and Creative Activities (URECA) program, and draw on its very diverse student body. The investigators will also engage promising high school level students through several residential programs that the PIs have been a part of in the past. These include the BLOOM program at Bigelow and the Simons Summer Research Fellowship Program at Stony Brook. The PI has continuing relationship with a regional high school (Brentwood) with a high proportion of underrepresented minorities. PI Twining is involved in the Café Scientifique program at Bigelow. Baines will engage in similar outreach through the Center for Science and Mathematics Education (CESAME) sponsored Open Science Nights. Finally, PI Baines will cooperate with CESAMEs teacher education programs, with the aim of incorporating biological oceanography into K-12 curricula. PIs Krause and Brzezinski will incorporate aspects of phytoplankton ecology into UCSB's Oceans to Classroom Program that brings marine research at UCSB to life for over 18,000 K-12 students each year.