盐湖嗜碱菌作用下粘土矿物结构铁的还原过程及其矿物转变机理

Upon microbial reduction of iron-containing minerals, several new or alterated minerals can possibly form. The biogenic minerals usually exhibit different properties from their inorganic phases, such as mineral size, crystallinity and chemistry. Therefore, biogenic minerals are proposed as bio-signatures to infer past microbial activities. In the field of microbe-ferruginous clay mineral interaction, the secondary mineral assemblages have been established on the basis of studies of Fe(III) bioreduction in clay minerals at circumneutral pH values. However, it has been suggested that Precambrian ocean was a "soda ocean" with a high alkalinity and high pH value. Obviously, the present bioreductive transformation model of clay minerals is not suitable for exploring iron reducers in the alkaline environments, such as Archaean seawarter. By contrast to vast studies on neutral iron-reducing microorganisms, our knowledge of the interaction of alkaliphilic iron-reducing bacteria and clay minerals are still limited. Furthermore, the detailed information on mineral transformation assocaited with alkaline Fe(III) respiration are not available, which is a key point for understanding the role of iron-reducing microbe in the past alkaline habitats. In summary, systematical investigations will be conducted on the interaction of alkaliphilic iron-reducing bacteria and clay minerals in typical saline lakes (e.g., Qinghai Lake) by using multiple approaches (bacterial cultivation, mineral and wet chemistry analysis ), aiming at the establishment of the bioreductive transformation model of clay minerals in alkaline environments. This work would be of great significance for providing the basic date for low-temperature clay transformations in sedimentary settings and the implications for assessing the probability of microbial activities in earth history.

在微生物还原Fe(III)矿物的过程中，常伴随着不同类型的次生矿物的生成，这些次生矿物被认为蕴含着微生物代谢活动的信息，可以作为追溯地质历史时期微生物介导铁还原过程的有效标记物。在厌氧微生物还原含铁粘土矿物的前人报道中，已建立的次生矿物组合特征均是基于以中性铁还原菌为研究对象，而对地质历史时期广泛存在的嗜碱铁还原菌有所忽视，进而制约了我们对不同水化学条件下微生物介导的粘土矿物转变的全局性认识。因此本项目试图应用微生物学、矿物学及地球化学的原理和方法，以现代典型碱性盐湖为研究载体，开展嗜碱铁还原菌-含铁粘土矿物的系统野外调查和室内模拟工作，探讨嗜碱菌还原粘土矿物结构铁的反应过程，重点剖析微生物作用下粘土矿物的相变途径，最终建立碱性环境中微生物与粘土矿物相互作用的矿物学标记。这一研究，对于弥补铁还原菌与粘土矿物相互作用的缺失环节、辨识地质时期的微生物活动具有重要意义。

粘土矿物是广布于各类沉积环境中的一类重要含铁硅酸盐矿物。越来越多的证据表明一些厌氧微生物能以粘土矿物结构Fe(III)作为末端电子受体完成铁呼吸反应。在微生物还原含铁粘土矿物的过程中往往会伴生一些次生矿物的生成。这些次生矿物或矿物组合被认为可作为一种辨识地质历史时期铁还原微生物活动痕迹的生物标记物。需要指出的是，当前基于室内模拟实验为核心的微生物-含铁粘土矿物研究基本以pH中性菌为研究对象，而对碱性铁还原菌关注不够。项目组针对目前碱性条件下厌氧微生物与含铁粘土矿物相互作用研究的欠缺，尝试从我国丰富的碱性盐湖和地下深部流体中分离相关菌株继而开展室内模拟研究。经过三年的研究，成功从内蒙古海拉尔盆地盐湖和中国大陆科学钻探地下碱性流体中分离厌氧菌4株并利用这些菌株还原蒙皂石矿物。研究结果表明：已分离的碱性厌氧菌均具备还原蒙皂石结构铁的能力，同时能促进蒙皂石向伊利石及长石转变；成岩过程中升高的压力虽然抑制微生物铁还原能力但能促进富铁蒙皂石（绿脱石）向伊利石转化；天然有机质的类型及含量多寡是制约微生物介导蒙皂石伊利石化反应的关键因素之一。以上结果为评估微生物参与的铁-碳循环和地质历史时期铁还原微生物的活动痕迹提供了科学依据。