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

IRFP：限制光合生物在早期地球带状铁形成（BIF）沉积中的作用

• 批准号: 1064391
• 负责人: Elizabeth Swanner
• 金额: $ 15.43万
• 依托单位: Swanner Elizabeth D
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-10-01 至 2015-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1064391&HistoricalAwards=false
• 关键词: IRFP; Constraining; role; photosynthetic; organisms

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.

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九到二十四个月的研究。该项目的奖项提供了联合研究以及使用国外独特或互补的设施、专业知识和实验条件的机会。该奖项将支持 Elizabeth D. Swanner 博士与德国蒂宾根埃伯哈德·卡尔斯大学的 Andreas Kappler 教授合作提供为期 24 个月的研究奖学金。该项目解决了有关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，产生氧气的蓝藻的进化与地球大气的不可逆氧化（大氧化事件，GOE）之间的滞后是由最早的蓝藻的生理限制造成的，这些限制限制了它们的初始生长和氧气的产生。在GOE（温度、营养物、微量金属和光照供应）之前，将在太古代海洋中可能存在的物理和化学条件范围内评估蓝藻的生长和氧气的产生，以确定它们是否受到生理限制。第二个假设提出，蓝藻适应当时海洋条件后丰度的增加解释了GOE之后沉积的含Fe(III)带状铁地层(BIF)中交替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（光铁营养菌）的活性，这些细菌在太古代海洋预测的波动温度下孵育时会产生交替的 Fe-Si 层。如果蓝藻和光铁营养生物之间存在对营养和光的竞争，那么随着蓝细菌适应普遍条件，光铁营养生物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蓝藻产生的 O2 氧化，而不是铁硅微带的氧化。为了评估这一假设，将跟踪共培养中蓝藻和光铁营养菌的生长和活性，并将沉积的铁矿物质与单独生活的每个生物体形成的铁矿物质进行比较。这些实验将有助于我们了解地质记录中如何记录生物圈的发展，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水相铁、氧和金属形态和浓度数据，并使用基于同步加速器的X射线吸收光谱来绘制沉淀铁氧化物中细胞和金属的分布和浓度。此外，该项目还将促进博士后与主办实验室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，该项目的结果将用于为中小学生制作书面宣传材料。