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

卡彭9982721目前的证据表明，海洋浮游蓝藻对氮气的固定可能是控制海洋生产力变化的关键因素，因此，二氧化碳在古生态时间尺度上的固定可能是一个关键因素。然而，目前缺乏直接评估氮气固定是否或如何与海洋生产力在这样的时间尺度上发生协同变化的方法。到目前为止，我们对古生态趋势的大部分知识来自对上覆水域浮游生物种群沉积到海底的物质的地球化学分析。从水柱中掉出的细胞中的DNA可以保存在具有重大地质意义(k K-1OOK年)的沉积沉积物中，因此可以更直接地记录水柱种群的身份及其代谢潜力。固氮酶(氮气固定)酶系统的基因已经在各种原核生物中得到了很好的表征。这位研究人员已经开发出从海洋表层沉积物中高效提取和扩增DNA的方法。蓝藻DNA可以从目前的水生沉积物和分离、鉴定并区别于其他生理类型的氮气固定物的nifH序列中恢复。PI将探索使用这种方法分析和重建固氮蓝藻的古生态趋势的能力，方法是从水柱中存在固氮蓝藻的深层沉积物中提取DNA。在这些地层中不会出现活的蓝藻，它们应该代表了更早在沉积物中沉积的物质。作为对这一命题的检验，作者将研究3个地点的沉积物，这些地点的浮游氮固定蓝藻已经繁殖，并通过它们的色素特征被记录在沉积物中。其中包括加拿大实验湖地区的一个湖泊系统，波罗的海的戈特兰盆地，以及地中海腐泥沉积。关键的初步挑战将是：1)随着沉积物深度的增加，确定蓝藻DNA的保存程度，从而确定时间；2)能够提供水平间基因出现的某种程度的相对量化。如果成功，PI将应用于海洋系统的陆架沉积物，在这些系统中，已经推断出在冰川/间冰期尺度上水柱固定氮的强烈趋势，如阿拉伯海--从而提供关于微生物种群动态的重要的直接见解，这可能直接影响气候趋势。此外，这些努力将为分析古生态时间尺度上具有生物地球化学相关性的其他功能酶提供一个模型系统。该项目的目标是开发和使用一种分子方法来描述古代微生物群落的生物地球化学方面。其具体目的是检查蓝藻种群的发展，以反映地质时间尺度上氮气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固定氮气的历史的新信息。

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.