IRFP: Constraining the role of photosynthetic organisms in deposition of Banded Iron Formations (BIF) on early Earth

国际研究奖学金计划使美国科学家和工程师能够在国外进行9至24个月的研究。该计划的奖项提供了联合研究的机会，以及使用国外独特或互补的设施，专业知识和实验条件。该奖项将支持由伊丽莎白博士24个月的研究奖学金。Swanner将与德国Eberhard Karls Universität Tübingen的Andreas Kappler教授博士合作。该项目解决了关于地球生物和地球化学共同进化的两个基本问题。第一个假设提出，O2-生产蓝藻的进化和地球大气的不可逆氧化（大氧化事件，GOE）之间的滞后导致最早的蓝藻，减少其初始生长和O2生产的生理限制。蓝藻的生长和O2的生产将在一系列的物理和化学条件下进行评估，可能在太古代海洋之前的GOE（温度，营养物质，微量金属和光供应），以确定他们是否受到生理约束。第二个假设提出，增加了丰富的蓝细菌的适应占主导地位的海洋条件下，解释了消失的交替Fe-Si微带在Fe（III）含带状铁的形成（BIF）后GOE沉积。之前的GOE，铁（III）轴承BIF沉积是由于活动的Fe（II）氧化光合细菌（photorefrorotrophs），产生交替的Fe-Si层时，温育下的波动的温度下，预测太古代海洋。如果蓝细菌和光养铁细菌之间存在营养和光的竞争，因为蓝细菌适应了当时的条件，光养铁细菌将被边缘化到海洋中生产力较低的深度。在这种情况下，主要的铁氧化和沉积机制将是氧化蓝藻产生的O2，而不是Fe-Si微带。为了评估这一假设，蓝细菌和光铁营养菌在共培养的生长和活动将被跟踪，沉积的铁矿物将被比较，由每个单独生活的生物体所形成的。这些实验将有助于我们了解生物圈的发展如何记录在地质记录中，以及早期海洋的地球化学如何影响微生物的进化。该项目将把地球化学技术与生理测量相结合，特别是通过使用伏安微电极来获取实时的水溶液Fe、O2和金属形态和浓度数据，以及基于同步加速器的X射线吸收光谱法来绘制沉淀的铁氧化物中细胞和金属的分布和浓度。此外，该项目将促进博士后与主办实验室的各级科学家和学生以及欧洲合作者之间的国际合作和思想交流。最后，该项目的成果将用于为中小学生编写书面宣传材料。

The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twenty-four-month research fellowship by Dr. Elizabeth D. Swanner to work with Prof. Dr. Andreas Kappler at Eberhard Karls Universität Tübingen, Germany. This project addresses two fundamental questions about the co-evolution of Earth's bio- and geochemistry. The first hypothesis proposes that the lag between the evolution of O2-producing cyanobacteria and the irreversible oxidation of the Earth's atmosphere (the Great Oxidation Event, GOE) resulted from physiological limitations of the earliest cyanobacteria that curtailed their initial growth and O2 production. Cyanobacterial growth and O2 production will be assessed under the range of physical and chemical conditions possible in the Archean ocean prior to the GOE (temperature, nutrient, trace metal and light supply) to determine whether they were physiologically constrained. The second hypothesis proposes that an increase in the abundance of cyanobacteria following their adaptation to prevailing ocean conditions explains the disappearance of alternating Fe-Si microbands in Fe(III)-containing banded iron formations (BIF) deposited after the GOE. Prior to the GOE, Fe(III)-bearing BIF deposition is attributed to the activity of Fe(II)-oxidizing photosynthetic bacteria (photoferrotrophs), which generate alternating Fe-Si layers when incubated under the fluctuating temperatures that are predicted for the Archean ocean. If competition for nutrients and light existed between cyanobacteria and photoferrotrophs, as cyanobacteria adapted to prevailing conditions the photoferrotrophs would have been marginalized to less productive depths in the ocean. In that case the primary Fe-oxidation and deposition mechanism would be oxidation by cyanobacterially-produced O2 and not Fe-Si microbands. To evaluate this hypothesis, the growth and activity of cyanobacteria and photoferrotrophs in co-culture will be tracked, and the deposited Fe minerals will be compared to those formed by each organism living alone. These experiments will contribute to our understanding of how the development the biosphere is recorded in the geologic record, and also how the geochemistry of the early oceans influenced microbial evolution. This project will integrate geochemical techniques with physiological measurements, specifically through the use of voltammetric microelectrodes to acquire real-time aqueous Fe, O2 and metal speciation and concentration data, and synchrotron-based X-ray absorption spectroscopy to map the distribution and concentration of cells and metals in precipitated Fe-oxides. In addition, the project will facilitate international collaboration and exchange of ideas between the postdoc and scientists and students of all levels in the host laboratory, as well as with collaborators in Europe. Finally, the results of the project will be used to create written outreach material for primary and secondary students.