Regulation of Population Dynamics of Prochlorococcus and Synechococcus Ecotypes in Diverse Oceanoic Ecosystems

海洋蓝藻原绿球藻和聚藻球菌是世界开放海洋中主要的初级生产者。这两个属在不同海域的空间和季节动态具有明显的特点，往往表现为时间和空间上的交替优势。越来越多的证据表明，在每一个属中都存在着不同的“生态型”——在生理和遗传上彼此不同的密切相关的菌株——它们的光收集能力不同，因此在不同的光照条件下适应最佳的生长。本研究将检验它们在其他重要性状上可能存在差异的假设，如氮偏好和同化效率、黑暗生存和对波动光强度的耐受性。已知在原绿球藻中，生态型之间的生理差异与16S核糖体RNA基因（16S rDNA）构建的分子系统发育的差异相对应。这开启了利用分子探针研究野外种群生态型动态的可能性，并研究它们的相对丰度如何随着光照、养分和其他环境变量的变化而变化。为此，该项目将需要进行一系列的实验室和实地研究：培养生态型的遗传多样性：研究人员将对培养中的原绿球藻和聚球菌分离物的23S rDNA基因进行测序，以确定与已知和假设的生理生态型相对应的密切相关的基因型簇。这些序列将使他们能够开发出属于这些细胞簇的特异性探针，用于研究野外种群中生态型的分布和相对丰度。培养生态型的生理多样性：研究人员将利用分批培养和维持在强光和弱光下的n限制环形培养，研究营养有效性是否会影响原绿球藻和聚球藻之间的竞争优势，以及每个属中适应强光和弱光的生态型之间的竞争优势。他们还将研究这些属和生态型是否对波动的光线和长时间的黑暗暴露有不同的反应，这将有助于更好地了解它们在深层混合层中的相对丰度。野外种群生态类型的季节和空间动态：研究人员选择了三个地点进行野外研究——夏威夷海洋时间序列（HOT）、百慕大大西洋时间序列（BATS）站和红海亚喀巴湾——在这些地点原绿球藻和聚藻球菌表现出明显不同的季节模式和深度分布。在每个站点收集的样本中，他们将首先通过克隆PCR产物和使用RFLP分析和部分测序分析克隆来定性描述23S rDNA序列的分子多样性。这将使他们看到我们培养的分离株对该领域存在的基因型有多大的代表性。然后，利用开发的生态型特异性探针和克隆研究中发现的任何独特序列，他们将使用定量和原位杂交来分析研究地点不同生态型的季节和空间动态。他们将使用在我们收集样本时每个地点可用的辅助物理和化学数据，以及我们从实验室培养中进行的生理研究，来揭示导致该领域生态类型相对丰度变化的强迫功能。假设原绿球藻和聚球菌种群中不同“生态型”的存在在决定这两个种群之间的动态方面起着关键作用，并有助于这些种群在世界海洋中的集体稳定。在一个给定的环境中，多种生态型的存在使得原绿球藻和聚藻球菌能够在更广泛的环境中茁壮成长，而不是在生理和遗传上同质的种群中。这些研究的结果不仅将提供关于是什么调节了海洋中这些种群的动态的见解，而且还将告知对一般理解微生物多样性至关重要的问题。

ChisholmThe marine cyanobacteria Prochlorococcus and Synechococcus are dominant primary producers in the world's open oceans. The spatial and seasonal dynamics of the two genera have distinct features in different oceans,-often characterized by alternating dominance in time and space. There is growing evidence that there exists within each of these genera distinct "ecotypes"-closely related strains that are physiologically and genetically distinct from one another-which differ in light harvesting ability and are thus adapted for optimal growth under different light regimes. This study will examine the hypothesis that they might differ in other significant traits such as nitrogen preferences and assimilation efficiencies, dark survival, and tolerance of fluctuating light intensities. It is known that in Prochlorococcus the established physiological differences between ecotypes correspond with differences in molecular phylogenies constructed with the 16S ribosomal RNA gene (16S rDNA). This opens the possibility of studying the dynamics of ecotypes in field populations using molecular probes, and studying how their relative abundances change in response to changing availability of light, nutrients, and other environmental variables. To this end, this project will entail a series of laboratory and field studies:Genetic Diversity in Cultured Ecotypes: Researchers will sequence the 23S rDNA gene of the Prochlorococcus and Synechococcus isolates they have in culture, to identify closely related clusters of genotypes which correspond to known and hypothesized physiological ecotypes. These sequences will allow them to develop probes specific for cells belonging to these clusters for use in studying the distributions and relative abundance of ecotypes in field populations. Physiological Diversity in Cultured Ecotypes: Using batch cultures and N-limited cyclostat cultures maintained at high and low light intensities, researchers will study whether or not nutrient availability influences the competitive advantages between Prochlorococcus and Synechococcus and between the high- and low-light adapted ecotypes within each genus. They will also examine whether the genera and ecotypes respond differently to fluctuating light and prolonged dark exposure, which will help to better understand their relative abundance in deep mixed layers. Seasonal and Spatial Dvnamics of Ecotypes in Field Populations: The researchers have chosen three sites for the field studies-the Hawaii Ocean Time-series (HOT), the Bermuda Atlantic Time Series (BATS) station, and the Gulf of Aqaba in the Red Sea-where Prochlorococcus and Synechococcus display distinctly different seasonal patterns and depth distributions. In samples collected from each of these sites they will first qualitatively describe the molecular diversity of 23S rDNA sequences by cloning PCR products and analyzing the clones using RFLP analysis and partial sequencing. This will allow them to see how representative our cultured isolates are of the genotypes present in the field. Then, using the ecotype-specific probes developed and any unique sequences found in the cloning studies, they will use quantitative and in situ hybridization to analyze the seasonal and spatial dynamics of the different ecotypes at the study sites. They will use the ancillary physical and chemical data that will be available for each of these sites at the time of our sample collection, along with our physiological studies from laboratory cultures, to unravel the forcing functions responsible for the changing relative abundances of the ecotypes in the field. The hypothesis is that the presence of different "ecotypes " within the Prochlorococcus and Synechococcus populations play a critical role in determining the dynamics between the two groups, and contribute to the collective stability of these populations in the world's oceans. The presence of multiple ecotypes in a given environment allows Prochlorococcus and Synechococcus to thrive over a much broader range of environments than would be possible for a physiologically and genetically homogeneous population. The results of these studies will not only provide insights into what regulates the dynamics of these populations in the oceans, but will also inform issues that are critica1 to understanding microbial diversity in general.