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

该项目将探索海洋蓝藻聚藻球菌的遗传和生理多样性，这是世界上低营养海洋初级生产的主要贡献者。除了在低营养海洋中发挥作用外，聚珠球菌也可以在中营养和富营养水域中发现。这与密切相关的原绿球藻属的成员形成鲜明对比，原绿球藻属的成员仅限于亚热带开阔的海洋。目前尚不清楚是否聚珠球菌的增加范围反映了该属所有菌株更广泛的生理耐受性，或者存在专门适应更高营养和更冷温度条件的生态型。就聚珠球菌群落如何应对环境条件的变化（如全球气候变化或沿海水域的富营养化）而言，这些替代情景具有非常不同的含义。在这个项目中，这个问题是通过两种方式解决的，一种是通过描述聚珠球菌的多种基因型的生理特征，另一种是通过确定这些基因型在全球水样中的季节性丰度。已经确定，海洋聚囊球菌由若干（七种或更多）遗传上不同的谱系组成。其中三个谱系与特定的生理特征（运动性、颜色适应性和缺乏藻胆素）有关，而第四个谱系由单个菌株组成，该菌株不能利用硝酸盐作为氮源。然而，与其他三种基因型相关的生理机制尚未确定。为了开始了解所有基因型的聚珠球菌对可能影响其生长和分布的因素的生理反应，在本项目中，每个遗传支系的几个代表性菌株正在一系列光照水平、温度和氮源中生长。几条线索的证据表明，自然界中存在额外的遗传谱系，但尚未被培育出来。为了进一步探讨这一点，我们通过末端限制性片段长度多态性和16S-23S核糖体RNA内部转录间隔（ITS）的测序分析，研究了大西洋和太平洋开放海洋聚球菌种群以及华盛顿普吉特海湾沿海种群的遗传多样性。利用这些序列和已经从聚球菌分离物中确定的序列，将设计针对每个遗传支系的特异性引物。这些引物将用于实时定量PCR，对来自相同三个环境的一组月度样本进行实时定量PCR，以在两个年度周期内量化每种遗传类型的丰度。该项目将直接涉及一名研究生和一名或多名本科生。在普吉特海湾建立一个研究项目，通过西澳大学海洋学院的高级实地课程，为更多的本科生提供了参与的机会。此外，普吉特海湾的聚球菌分布和动态数据将与华盛顿州生态部门共享，并纳入普吉特海湾食物网模型。最后，研究聚珠球菌的全球分布和种群动态，并结合测量每种基因型在一系列物理条件下的生长的实验，将提供对生态分化和生理可塑性在决定这些分布中的相对重要性的见解。

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.