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

智力优势：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，对现场样品中的苦味酸细菌细胞进行的单细胞分析意外地发现聚球藻中存在大量的硅。聚球藻对生物硅的贡献通常与所研究的两个系统中活硅藻的贡献相媲美。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浮游生物的粒度分数中。鉴于微蓝细菌主导着世界上大部分海域的浮游植物生物量和初级生产力--S海洋，这些发现提出了一些重要的问题，即全球海洋二氧化硅循环的控制因素，以及对生物成因二氧化硅测量结果、颗粒物中硅氮比以及硅酸盐和硝酸盐耗竭比的正确解释。它还表明，苦味细菌种群可能会受到以前未知的生产力限制。该项目将包括实验室和现场两个部分。由于到目前为止所分析的现场采集的样本和实验室菌株之间的细胞硅差异很大，实验室组成部分将记录硅吸收和细胞硅浓度的差异，同时确定生理和系统发育因素在这种差异中所起的作用。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放射性示踪剂吸收实验来评估适应不同硅酸盐水平的聚球藻之间硅含量和硅吸收动力学的变异程度；2)使用分级技术、密度离心法、电子显微镜和X射线吸收光谱来表征细胞内硅的分布和化学；以及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硅的吸收，以确定参与蓝藻硅代谢的候选基因，并开发与细胞硅含量相关的群落结构的探针。百慕大大西洋时间序列(BATS)现场工作将评估聚球藻和硅藻在一年中通常以聚球藻和硅藻为主的时间段对地表水中生物成因二氧化硅总量的贡献。现场测量将包括生物硅生物量和硅吸收的粒度分级，基于同步加速器的X射线荧光显微镜，以及聚球藻组合的系统发育组成。BROADER影响：该项目有可能推动我们对海洋硅循环的重大范式转变。此外，一名博士生将在石溪大学接受培训。每个PI将为一些本科生提供研究经验，这些本科生从事原创研究项目以获得学分，作为REU计划的一部分或作为本科论文的基础。石溪大学的本科生研究项目由本科生研究和创意活动(URECA)项目的暑期研究资金支持，并吸引了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生，这些项目过去一直是PI的一部分。这些项目包括毕格罗的布鲁姆项目和石溪大学的西蒙斯夏季研究奖学金项目。国际和平协会与一所地区高中(布伦特伍德)保持着持续的关系，这所学校的少数民族比例很高。皮特宁参与了毕格罗咖啡馆的科学咖啡项目。贝恩斯将通过科学和数学教育中心(CESAME)赞助的开放式科学之夜开展类似的外联活动。最后，Pi Baines将与CESAMES教师教育方案合作，目的是将生物海洋学纳入K-12课程。PiS Krause和Brzezinski将把浮游植物生态学的各个方面融入到UCSB的海洋到课堂计划中，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.