In situ Pico-Cyanobacterial Growth Rates in the Sargasso Sea Based on Cell-Specific rRNA Measurements

微浮游单细胞蓝藻原绿球藻和聚藻球菌占世界海洋总体初级产量的很大一部分。尽管这两个类群的系统发育和生态关系密切，但它们各自的林分存量在地理、季节和垂直尺度上往往呈负相关。本项目将(1)开发一种方便、可靠的方法来测量原绿球藻和聚藻球菌自然种群的原位生长速度，(2)将该方法与更传统的生长速度测量相结合，在野外应用，以阐明马尾藻海中这些种群的动态调节因素。本项目将利用流式细胞术测定群体特异性核糖体RNA （rRNA）含量来估计原绿球藻和聚球藻种群的原位生长速度。全细胞杂交与荧光标记的16S rRNA靶向肽核酸探针将用于测量细胞rRNA。最近的研究表明，当归一化为蛋白质或光散射（作为细胞生物量的代表）时，rRNA是实验室中许多海洋聚球菌菌株生长速度的有用指标。本研究打算扩大这一初步工作，包括更多样化的聚球菌菌株以及具有代表性的原绿球藻菌株，在一系列环境相关条件下生长。一旦在实验室中建立了细胞rRNA指数和生长速率之间的关系，该方法将通过与更传统（也更繁琐）的生长速率测量同时应用在现场进行测试。通过对原绿球藻和聚球藻在生物量优势条件下的生长速度的分析，阐明生理因素和食物网过程在调节所观察到的分布模式中的相对重要性。最终，这将使我们更好地理解构成浮游植物群落的力量，并将提高我们预测环境变化对这些群落的影响的能力。此计划将为本科生提供参与海洋研究游船的机会，以加强本科教育。感兴趣的海洋科学专业（以及相关领域的学生）将参加一个学期的研讨会课程，涵盖海洋学的相关主题。那些成功完成课程的学生将有机会在乔治亚大学的梅梅斯特期间参加游轮活动，他们将获得研究学分。这种经历将帮助有前途的学生欣赏生物海洋学的多样性和严密性，了解环境科学家提出问题和设计研究以回答这些问题的过程，体验执行和解释此类研究的固有局限性，并以令人兴奋和有意义的方式了解生物海洋学过程。该项目还将通过支持专门用于分析生态相关微生物的流式细胞仪的操作来加强研究生教育。研究生将获得这种仪器的实际操作经验，这是在典型的员工操作的流式细胞仪设备中无法获得的。

The picoplanktonic unicellular cyanobacteria Prochlorococcus and Synechococcus are responsible for a significant fraction of the overall primary production in the world's oceans. Despite the close phylogenetic and ecological relationship of these two groups, their respective standing stocks are often inversely related on geographic, seasonal, and vertical scales. This project will (1) develop a convenient and robust method for measuring the in situ growth rates of natural populations of Prochlorococcus and Synechococcus, and (2) apply this method in the field in combination with more tradition growth rate measures in order to clarify the factors that are responsible for regulating the dynamics of these populations in the Sargasso Sea. This project will utilize flow cytometrically-determined group-specific ribosomal RNA (rRNA) content to estimate the in situ growth rates of Prochlorococcus and Synechococcus populations. Whole-cell hybridizations with fluorescently labeled 16S rRNA-targeted peptide nucleic acid probes will be used to measure cellular rRNA. Recent research has shown that when normalized to protein or light scatter (as a proxy for cell biomass), rRNA is a useful index of growth rate in a number of marine Synechococcus strains in the laboratory. This study intends to expand this initial work to include a greater diversity of Synechococcus strains as well as representative Prochlorococcus strains, growing under a range of environmentally relevant conditions. Once the relationship between cellular rRNA indexes and growth rate is established in the laboratory, the approach will be tested in the field by simultaneous application with more traditional (and more cumbersome) growth rate measurements. By so analyzing the growth rates of Prochlorococcus and Synechococcus under contrasting conditions of biomass dominance, the relative importance of physiological factors and food web processes in regulating the observed patterns of distribution will be clarified. Ultimately, this will lead to a better understanding of the forces that structure phytoplankton communities in general, and will increase our ability to predict the effects of environmental changes on these communities. This project will enhance undergraduate education by serving as a vehicle to provide undergraduate students with the opportunity to participate in oceanographic research cruises. Interested Marine Sciences majors (and students in related fields) will enroll in a semester-long seminar course covering relevant topics in oceanography. Those students who successfully complete the course will be given the opportunity to participate in a cruise during the University of Georgia's Maymester, for which they will receive research credit. This experience would help promising students appreciate the diverse and rigorous nature of biological oceanography, understand the process by which environmental scientists frame questions and design studies to answer them, experience the limitations inherent in carrying out and interpreting such studies, and learn about biological oceanographic processes in an exciting and meaningful way. The project will also enhance graduate education by supporting the operation of a flow cytometer devoted exclusively to the analysis of ecologically relevant microbes. Graduate students will gain the sort of hands-on experience with this instrumentation that is unavailable in typical staff-run flow cytometry facilities.