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

内部优点：研究人员将跟踪他们发现的聚球藻属海洋微蓝细菌大量积累硅的情况，以评估这些生物对海洋中生物硅循环的贡献。海洋学家长期以来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，从现场样品的picocyanobacterial细胞的单细胞分析，令人惊讶地发现聚球藻内存在大量的硅。聚球藻对生物硅的贡献往往可以与两个系统中的活硅藻相媲美。此外，生物二氧化硅的粒度分级表明，高达25%的生物二氧化硅可以存在于微微碳酸盐粒度级中。鉴于微蓝细菌在世界上大部分地区的浮游植物生物量和初级生产中占主导地位？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大问题，以及对生物二氧化硅测量结果的正确解释，颗粒物中的Si：N比率以及硅酸盐和硝酸盐消耗的比率。它还表明，微蓝细菌种群的生产力可能受到以前未知的限制。由于细胞硅之间的实地收集的样品和实验室菌株，到目前为止分析的差异很大，实验室组件将记录在硅的吸收和细胞硅浓度的变化，同时确定什么样的生理和系统发育因素在这种变化中发挥作用。 研究人员将使用已经有基因组序列的聚球藻菌株。实验室实验将1）使用32 Si放射性示踪剂摄取实验来评估适应不同水平硅酸盐的聚球藻菌株之间Si含量和Si摄取动力学的变化程度，2）使用分级分离技术、密度离心、电子显微镜和X射线吸收光谱表征细胞内硅的细胞内分布和化学，和3）使用已发表的基因组的生物信息学分析来确定是否可以基于系统发育关系来预测Si的吸收，以鉴定参与蓝藻Si代谢的候选基因，并开发可以与细胞Si含量相关的群落结构的探针。在百慕大大西洋时间序列（BATS）现场的实地工作将评估聚球藻和硅藻对沃茨中生物硅总量的贡献，在一年中聚球藻占主导地位的时候。现场测量将包括生物硅生物量和硅吸收的大小分级，和同步加速器为基础的X射线荧光显微镜，和系统发育组成的聚球藻assembly.BROADER IMPLEMENTARY：这个项目有可能推动一个重大的范式转变，在我们的海洋硅循环的理解。此外，一名博士生将在斯托尼布鲁克接受培训。每个PI将提供研究经验，以一些本科生工作的原始研究项目的信贷，作为一个REU计划的一部分，或作为本科论文的基础。斯托尼布鲁克的本科生研究项目由本科生研究与创意活动（URECA）项目的夏季研究资金支持，并利用其多元化的学生群体。调查人员还将通过PI过去参与的几个住宅项目吸引有前途的高中生。其中包括毕格罗大学的布卢姆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与一所代表性不足的少数民族比例很高的地区高中（布伦特伍德）保持着持续的关系。PI Twining参与了毕格罗的咖啡馆科学计划。贝恩斯将通过科学与数学教育中心（CEESTO）赞助的开放科学之夜进行类似的推广活动。最后，PI贝恩斯将与CESAME的教师教育计划合作，目的是将生物海洋学纳入K-12课程。PI Krause和Brzezinski将把浮游植物生态学的各个方面纳入UCSB的“海洋到课堂”计划，该计划每年为超过18，000名K-12学生带来UCSB的海洋研究。

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.