Marine Synechococcus Ecotypes: Seasonal and Spatial Distributions of Physiological and Genetic Diversity

该项目将探索海洋蓝藻聚球藻的遗传和生理多样性，它们是世界少营养海洋初级生产的主要贡献者。除了在营养稀少的海洋中发挥作用外，聚球藻还可以在中营养和富营养的水域中发现。这与近缘关系密切的原氯球菌属的成员形成了鲜明的对比，后者仅限于亚热带开阔的海洋。目前尚不清楚聚球藻范围的扩大是否反映了该属所有菌株更广泛的生理耐受性，或者是存在专门适应更高营养和更低温度条件的生态型。在聚球藻群落如何应对全球气候变化或沿海水域富营养化等环境条件变化方面，这些替代情景具有非常不同的影响。在这个项目中，这一问题将通过两种方式解决，一是通过表征多种聚球菌的生理学特征，二是通过测定全球各地水样中这些基因的季节性丰度。现已确定，海洋聚球藻由多个(七个或更多)不同的遗传谱系组成。这些谱系中有三个与特定的生理特性(运动性、显色适应和缺乏藻联胆素)有关，第四个谱系由一株不能利用硝酸盐作为氮源的菌株组成。然而，与其他三种基因型相关的生理学还没有确定。为了开始了解聚球藻的所有基因类型对可能影响其生长和分布的因素的生理反应，在这个项目中，每个遗传分支的几个代表性菌株正在一系列光照、温度和氮源中生长。一些证据表明，自然界中存在更多的遗传谱系，但尚未被培养出来。为了进一步探索这一点，通过16S-23S核糖体RNA内转录间隔区(ITS)的末端限制性片段长度多态性和序列分析，研究了大西洋和太平洋远洋聚球藻种群和华盛顿州普吉特湾沿海种群的遗传多样性。利用这些序列和那些已经从聚球藻分离株中确定的序列，将设计出针对每个遗传分支的特异引物。这些引物将用于对来自相同三种环境的一组月度样本进行实时定量聚合酶链式反应，以量化每种基因类型在两个年度周期内的丰度。这个项目将直接涉及一名研究生和一名或多名本科生。在普吉特湾建立一个研究项目，通过华盛顿大学海洋学院的高级野外课程，为更多的本科生提供参与的机会。此外，有关普吉特湾聚球藻分布和动态的数据将与华盛顿州生态部共享，并纳入普吉特湾食品网络模型。最终，研究聚球藻的全球分布和种群动态，结合测量每种基因型在一系列物理条件下的生长的实验，将提供对生态型分化和生理可塑性在确定这些分布方面的相对重要性的洞察。

This project will explore the genetic and physiological diversity of the marine cyanobacteria Synechococcus, which are major contributors to primary production in the world's oligotrophic oceans. In addition to its role in the oligotrophic oceans, Synechococcus can also be found in mesotrophic and eutrophic waters. This is in sharp contrast to the members of the closely related genus Prochlorococcus that are restricted to the subtropical open oceans. At present it is not clear if the increased range of Synechococcus reflects a broader physiological tolerance by all the strains of this genus, or the existence of ecotypes that are specifically adapted to higher nutrient and colder temperature conditions. These alternate scenarios have very different implications in terms of how the Synechococcus community may respond to changes in environmental conditions such as global climate change or eutrophication of coastal waters. In this project, this question is being addressed two ways, by characterizing the physiology of multiple genotypes of Synechococcus, and by determining the seasonal abundances of these genotypes in water samples from around the globe. It has been established that marine Synechococcus consists of a number (seven or more) of genetically distinct lineages. Three of these lineages are specifically associated with a characteristic physiology (motility, chromatic adaptation and lack of phycourobilin), and a fourth consists of a single strain which is incapable of utilizing nitrate as a nitrogen source. However, the physiologies associated with the other three genotypes have not yet been determined. To begin to understand physiological responses of all of the genotypes of Synechococcus to factors that are likely to influence their growth and distributions, in this project, several representative strains of each genetic clade are being grown in a range of light levels, temperatures and nitrogen sources. Several lines of evidence suggest that additional genetic lineages exist in nature but have not yet been cultivated. To explore this further, the genetic diversity in open ocean Synechococcus populations in the Atlantic and Pacific and coastal populations in Puget Sound, Washington are being examined by terminal Restriction Fragment Length Polymorphism and sequencing analyses of the 16S-23S ribosomal RNA internal transcribed spacer (ITS). Using these sequences and those already determined from Synechococcus isolates, primers will be designed that are specific for each of the genetic clades. These primers will be used in real-time quantitative PCR in a set of monthly samples from the same three environments to quantify the abundance of each genetic type over two annual cycles. This project will directly involve a graduate student and one or more undergraduate students. Establishing a research program in Puget Sound is providing opportunities for additional undergraduate involvement through the UW School of Oceanography senior field course. In addition, data on Synechococcus distributions and dynamics in Puget Sound will be shared with the Washington State Department of Ecology and incorporated into a Puget Sound food web model. Ultimately, examining the global distribution and population dynamics of Synechococcus in conjunction with experiments measuring the growth of each genotype under a suite of physical conditions will provide insights into the relative importance of ecotypic differentiation and physiological plasticity in determining these distributions.