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到24个月的研究。该项目的奖项提供了联合研究的机会，并提供了使用国外独特或互补的设施、专业知识和实验条件的机会。该奖项将资助伊丽莎白·D·斯万纳博士与德国埃伯哈德·卡尔斯图宾根大学的安德烈亚斯·卡普尔教授合作的为期24个月的研究奖学金。这个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。第一种假说认为，产氧蓝藻的进化与地球大气不可逆氧化(大氧化事件，GOE)之间的滞后是由于最早的蓝藻的生理限制，限制了它们的初始生长和氧气的产生。蓝藻的生长和产氧量将在GOE(温度、营养、微量金属和光照供应)之前在太古代海洋可能的物理和化学条件范围内进行评估，以确定它们是否受到生理上的限制。第二种假说认为，蓝藻在适应当时的海洋条件后，其丰度的增加解释了在GOE之后沉积的含Fe(III)的带状铁建造(BIF)中交替的Fe-Si微带的消失。在GOE之前，含Fe(III)的BIF沉积归因于Fe(II)氧化光合细菌(光铁营养细菌)的活动，当它们在太古代海洋预测的温度波动下孵化时，会产生交替的Fe-Si层。如果蓝藻和光养铁细菌之间存在对营养物质和光的竞争，随着蓝藻适应当时的条件，光养铁细菌将被边缘化到海洋中生产力较低的深处。在这种情况下，主要的铁氧化和沉积机制将是蓝藻产生的O2而不是Fe-Si微带的氧化。为了评估这一假设，我们将跟踪蓝藻和光养铁细菌在共培养过程中的生长和活动，并将沉积的铁矿物质与每个单独生活的生物体形成的铁矿物质进行比较。这些实验将有助于我们理解生物圈的发展是如何记录在地质记录中的，以及早期海洋的地球化学如何影响微生物进化。该项目将把地球化学技术与生理测量结合起来，特别是通过使用伏安微电极实时获取水中Fe、O2和金属的形态和浓度数据，以及使用同步辐射X射线吸收光谱仪绘制细胞和金属在沉淀铁氧化物中的分布和浓度图。此外，该项目将促进博士后与东道国实验室各级科学家和学生以及与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.