Tracing redox cycles during microbe-clay interactions using stable iron isotopes

使用稳定铁同位素追踪微生物与粘土相互作用过程中的氧化还原循环

• 批准号: RGPIN-2014-05453
• 负责人: Wu, Lingling
• 金额: $ 0.49万
• 依托单位: University of Waterloo
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=634049
• 关键词: Tracing; redox; cycles; during; microbe

Redox reactions involving iron-bearing clay minerals are responsible for many changes in the physical and chemical properties of soils and sediments, and thus influence the fate of contaminants. The development of iron isotope research over the last decade has demonstrated that stable iron isotope geochemistry is a valuable tool to study biogeochemical cycling of iron. Stable iron isotope fractionations during microbial reduction of iron-bearing clay minerals will be examined with increasing complexity in three systems. System 1 will use simple batch reactors with model iron reducing bacteria. Abiological experiments for interaction between aqueous ferrous iron and iron-bearing clays will be carried out to provide a baseline of equilibrium fractionation factors for interpreting biological data. The role of biological activities in impacting iron isotope fractionation between reduced and oxidized iron in clay minerals will be investigated by comparing biological and abiological systems. This work will shed light on the electron transfer and atom exchange process that occurs during microbial reduction of structural ferric iron in clay minerals. System 2 will use a fully automated bioreactor system with model clays and model microorganisms to investigate the impact of oscillating redox conditions on iron isotope fractionations during microbe-clay interactions. Redox conditions will be tightly controlled to mimic redox cycles occurring in natural systems such as riparian zones, sediments that experience seasonal groundwater fluctuations, rice paddies which are regularly flooded and drained, and peatlands which experience drought and rain events. Clay suspensions inoculated with model microorganisms will be subjected to repeated reducing and oxidizing half-cycles. Iron speciation, concentration and isotopic compositions for different reactive iron phases will be monitored during each half-cycle. High quality experimental data from well controlled systems will provide a framework for interpretation of isotope data acquired from natural samples. System 3 will involve a more complex system using natural sediments and indigenous microbial communities. The extent of microbial reduction and dissolution has been revealed by previous studies to decrease with increasing number of redox cycles. All these changes will produce distinct iron isotope signatures during multiple redox cycles. When compared to a controlled system, the iron isotope signature produced in a natural soil system has the potential to provide answers to a key question in soil science: how many redox cycles can clay minerals be subject to before they eventually exhaust the reducing power in natural systems? The proposed work will greatly improve our understanding of molecular-scale processes during redox transformations of iron-bearing clay minerals. By applying iron isotopes as tools to trace redox cycles during microbe-clay interactions, this research will make pioneering contributions to the field of metal stable isotope geochemistry. The research findings will also fill the gap in our understanding of the reactivity and stable isotope properties of iron-containing clay minerals, particularly during their interaction with iron reducing bacteria. The improved knowledge on the nature of ferrous iron formed by microbial reduction of clay minerals will aid in predicting their reactivity towards a variety of environmental contaminants (e.g., pesticides and heavy metals). In addition, iron isotope signature from a controlled system under oscillating redox conditions will significantly advance our understanding of the dynamic nature of soil behavior, therefore greatly benefit management strategies that aim at maximizing soil fertility and performance.

含铁粘土矿物参与的氧化还原反应导致土壤和沉积物的许多物理和化学性质的变化，从而影响污染物的命运。近十年来铁同位素研究的发展表明，稳定铁同位素地球化学是研究铁的地球化学循环的重要手段。含铁粘土矿物微生物还原过程中的稳定铁同位素分馏将在三个系统中进行研究。系统1将使用具有模型铁还原菌的简单间歇反应器。通过非生物实验研究了含水亚铁和含铁粘土之间的相互作用，为解释生物数据提供了平衡分馏因子的基线。通过比较生物和非生物系统，研究生物活动在影响粘土矿物中还原铁和氧化铁之间的铁同位素分馏中的作用。这项工作将阐明在微生物还原粘土矿物中的结构三价铁时发生的电子转移和原子交换过程。系统2将使用具有模型粘土和模型微生物的全自动生物反应器系统来研究微生物-粘土相互作用期间振荡氧化还原条件对铁同位素分馏的影响。将严格控制氧化还原条件，以模拟自然系统中发生的氧化还原循环，例如河岸带、经历季节性地下水波动的沉积物、定期被洪水淹没和排水的稻田以及经历干旱和降雨事件的泥炭地。接种有模型微生物的粘土悬浮液将经受重复的还原和氧化半循环。在每个半周期期间，将监测不同活性铁相的铁形态、浓度和同位素组成。来自良好控制系统的高质量实验数据将为解释从天然样品中获得的同位素数据提供一个框架。系统3将涉及一个更复杂的系统，使用天然沉积物和土著微生物群落。微生物还原和溶解的程度已被先前的研究揭示为随着氧化还原循环次数的增加而降低。所有这些变化将在多个氧化还原循环期间产生不同的铁同位素特征。与受控系统相比，天然土壤系统中产生的铁同位素特征有可能为土壤科学中的一个关键问题提供答案：粘土矿物在最终耗尽自然系统中的还原能力之前，可以经历多少次氧化还原循环？这项工作将大大提高我们对含铁粘土矿物氧化还原转化过程中分子尺度过程的理解。利用铁同位素示踪微生物-粘土相互作用过程中的氧化还原循环，为金属稳定同位素地球化学研究做出了开拓性的贡献。研究结果也将填补差距，在我们的理解含铁粘土矿物的反应性和稳定同位素的性质，特别是在他们与铁还原菌的相互作用。关于通过微生物还原粘土矿物形成的亚铁的性质的改进的知识将有助于预测它们对各种环境污染物的反应性（例如，农药和重金属）。此外，振荡氧化还原条件下受控系统的铁同位素特征将显着推进我们对土壤行为动态本质的理解，因此极大地有利于旨在最大限度地提高土壤肥力和性能的管理策略。