Paleoecological Analysis of Oceanic N2 Fixing Cyanobacteria Using a Molecular Biological Approach

Capone 9982721目前的证据表明，N2固定海洋浮游蓝藻可能是一个关键因素控制海洋生产力的变化，因此，在古生态时间尺度上的CO2封存。然而，目前缺乏直接评估N2固定是否或如何在这样的时间尺度上与海洋生产力协变的方法。 迄今为止，我们对古生态学趋势的了解，大部分来自对上覆沃茨中的浮游生物群沉积到海底的物质进行的地球化学分析。 从水柱中脱落的细胞中的DNA可以在地质学上重要的时间尺度（1 K-100 K年）内保存在沉积物中，因此可以提供水柱种群及其代谢潜力的身份的更直接记录。固氮酶（N2固定）酶系统的基因已被广泛的原核生物的特点。研究人员开发了从表层海洋沉积物中有效提取和扩增DNA的方法。蓝藻DNA可以从目前的水生沉积物和nifH序列分离，鉴定，并从其他生理类型的N2 fixers.The PI的nifH序列区分回收将探索使用这种方法来分析和重建N2固定蓝藻的古生态学趋势的能力，通过提取DNA从更深的沉积物层的潜在地区已知的港口N2固定蓝藻在水柱。预计在这些层位中不会有活的蓝藻，它们应该代表沉积物中较早形成的物质。作为这一命题的测试，作者将检查沉积物从3个站点，其中已知的固氮蓝藻已经增殖，并已记录在沉积物中，通过他们的色素签名。这些包括加拿大实验湖区的湖泊系统，波罗的海的哥特兰盆地和地中海腐泥沉积。关键的初步挑战将是：1）确定蓝藻DNA随沉积物深度增加而保存的程度，因此，时间和2）能够提供层位之间基因发生的某种程度的相对定量。如果成功，PI将把这种方法应用到海洋系统的陆架沉积物中，在这些沉积物中，间冰期的时间尺度已经推断，如阿拉伯海-从而提供了重要的直接了解微生物种群动态，可能直接影响气候趋势。此外，这些努力将提供一个模型系统，用于分析其他功能酶的古生态时间scale.The项目的目标是开发和采用分子方法来描述古微生物群落的生物地球化学方面的生物地球化学相关性。具体的目的是研究蓝藻种群的发展，将反映在地质时间尺度上的N2固定条件的存在和不存在。这种方法将提供关于微生物在历史背景下的功能作用的独特数据，从而将提供关于地球上N2固定历史的新信息。

Capone 9982721Current evidence suggests that N2 fixation by marine planktonic cyanobacteria may be a key factor controlling variations in oceanic productivity and, therefore, of C02 sequestration over paleoecological time scales. However, methods are currently lacking to evaluate directly whether or how N2 fixation has covaried with oceanic productivity over such time scales. Much of our knowledge of paleoecological trends to date derives from the geochemical analysis of material sedimented to the sea floor from planktonic populations in overlying waters. DNA in cells falling out of the water column can be preserved in sedimentary deposits over geologically significant (I K- I OOK years) time scales and may therefore provide a more direct record of the identity of water column populations and their metabolic potentials. The genes of the nitrogenase (N2 fixing) enzyme system have been well characterized for a wide variety of prokaryotes. The investigator has developed methods to efficiently extract and amplify DNA from surficial marine sediments. Cyanobacterial DNA can be recovered from current aquatic sediments and nifH sequences isolated, identified, and distinguished from the nifH sequences of other physiological types of N2 fixers.The PI will explore the ability to use this approach to analyze and reconstruct paleoecological trends in N2 fixing cyanobacteria by extracting DNA from deeper sediment horizons underlying areas known to harbor N2 fixing cyanobacteria in the water column. Living cyanobacteria would not be expected in these horizons and should represent material earlier laid down in the sediments. As a test of this proposition, the author will examine sediments from 3 sites where planktonic N2 fixing cyanobacteria are known to have proliferated and have been recorded in the sediments through their pigment signatures. These include a lake system in the Experimental Lake Region of Canada, the Goteland basin of the Baltic Sea, and in Mediterranean sapropel deposits. Key preliminary challenges will be 1) to determine the extent of preservation of cyanobacterial DNA with increasing sediment depth and, therefore, time and 2) to be able to provide some level of relative quantitation of gene occurrence among horizons.If successful, the PI would be to apply this method to shelf sediments of marine systems where strong trends in water column N2 fixation over glacial/ interglacial time scales have been inferred such as the Arabian Sea - thereby providing important direct insights on microbial populations dynamics which may directly affect climatological trends. Furthermore, these efforts would provide a model system for the analysis of other functional enzymes of biogeochemically relevance on paleoecological time scales.The objective of this project is to develop and employ a molecular approach for describing biogeochemical aspects of ancient microbial communities. The specific aim is to examine the development of cyanobacterial populations that would reflect the presence and absence of N2 fixing conditions over geological time scales. This approach would provide unique data on the functional role of microorganisms in a historical context, and thus will provide new information on the history of N2 fixation on Earth.