微生物侵蚀黄铁矿研究

【作者】 刘伟；

【导师】 张兴亮；

【作者基本信息】 西北大学 ， 地球生物学， 2013， 博士

【摘要】 微生物氧化黄铁矿作用是自然界中存在的一种极为普遍的微生物新陈代谢作用方式,黄铁矿自形成到被氧化的一系列生物地球化学过程可以有效反映沉积环境中氧化还原反应界面的波动。近年来关于微生物氧化黄铁矿的研究已经成为地球生物学研究领域的热点问题,然而绝大多数的研究工作多集中于铁氧化细菌氧化黄铁矿的实验室研究,对自然条件下的微生物氧化黄铁矿的过程及特点知之甚少。本文首次将微生物侵蚀黄铁矿的地质记录研究与微生物氧化黄铁矿的实验研究以及现代深海热液硫化物的微生物氧化研究相结合。通过对比不同氧化条件下黄铁矿表面所形成的坑痕结构以及次生矿物等的差异,揭示微生物氧化黄铁矿的作用过程、作用机制、控制因素等相关信息。这些认识有助于我们更加深刻的理解铁和硫元素的生物地球化学循环,同时也为我们研究早期微生物代谢作用的起源和演化提供一个全新的思路。论文的主要研究内容包括沉积物中的微生物氧化黄铁矿研究和微生物氧化黄铁矿实验研究。沉积物中的微生物氧化黄铁矿研究涉及古代沉积地层中的微生物氧化黄铁矿地质记录以及现代深海热液硫化物的微生物氧化研究两部分内容,其中前者主要包括样品的岩石学分析、黄铁矿晶体表面坑痕结构特征、次生矿物组成以及微生物群落化石等,后者主要包括硫化物成分分析、黄铜矿和黄铁矿晶体表面坑痕结构特征以及黄铁矿表面的微生物群落研究等内容。微生物氧化黄铁矿实验研究主要包括嗜酸性氧化亚铁硫杆菌(A.ferrooxidans)和嗜酸性氧化硫硫杆菌(A.thiooxidans)氧化黄铁矿的作用机制、黄铁矿晶体表面坑痕结构特征、次生矿物、溶液pH值和Fe3+离子浓度的变化等。通过对上述内容的深入研究,取得如下认识：地层中的自形晶黄铁矿形成于埋藏作用过程,并且在成岩作用的最早期阶段受到微生物侵蚀作用的影响。微生物在侵蚀黄铁矿的过程中会在黄铁矿晶体表面形成一系列的特征性的坑痕结构,这些坑痕结构在形态和大小上都与微生物氧化黄铁矿实验所得到的结果相一致。现代深海热液硫化物的主要矿物成分为黄铁矿和黄铜矿,并且在这些金属硫化物晶体表面保存有大量的坑痕结构,其中黄铜矿晶体表面主要为多边形坑痕结构,黄铁矿晶体表面则以圆形-椭圆形坑痕结构为主。嗜酸性氧化亚铁硫杆菌(A.ferrooxidans)在氧化黄铁矿的过程中采取接触间接式作用机制。随着微生物氧化作用的持续进行,溶液中的H+、Fe3+离子浓度明显升高,黄铁矿晶体表面出现大量的圆形-多边形(主要为六边形)坑痕结构,部分坑痕内部甚至保存有菌体结构,并且在坑痕周围有大量的次生矿物沉淀。嗜酸性氧化硫硫杆菌(Athiooxidans)对于嗜酸性氧化亚铁硫杆菌CA. ferrooxidans)氧化黄铁矿具有明显的促进作用。此外,论文章详细描述了样品中的微生物群落,笔者认为这些杆菌状微生物是矿化保存下来的铁氧化细菌。更多还原

【Abstract】 Microbial oxidation of pyrite is one of the most common microbial metabolisms existing in the nature. A series of biogeochemical process from the formation to oxidation of pyrite reflects the fluctuation of the REDOX reaction interface. In recent years, the study of microbial oxidation of pyrite has become a hot issue in the field of geobiology. However, most of the researches are mainly focused on the laboratory studies; the study of microbial oxidation of pyrite in natural conditions is rare.In this paper, we combined the study of geological records of microbial dissolution of pyrite with the microbial oxidation of pyrite experiments in laboratory and the microbial oxidation of sulfide minerals in modern submarine hydrothermal sediments for the first tine. All of the details such as the erosion pitting patterns on the crystal surfaces, the secondary mineral deposits, the oxidation mechanism and process, the influencing factors were described, compared and discussed. This study will help us understand the biogeochemical iron and sulfur cycles impressively. Furthermore, it is also an important clue to trace the origin and evolution of microbial metabolism.The main research contents of this study includes the study of microbial oxidation of pyrite in sediments, which refers to the ancient sedimentary rocks and the modern submarine hydrothermal sediments, and the study of microbial oxidation of pyrite experiments. The study of the ancient sedimentary rocks is focused on the petrology analyses of the samples, the characteristic pitting patterns on the pyrite crystals, the second mineral deposits and the mineralized microbial community. While, the study of the modern submarine hydrothermal sediments includes the analysis of mineral composition of sulfide minerals, the characteristic pitting patterns on the chalcopyrite and pyrite crystals, and the mineralized microbial communities on the pyrite surfaces. The study of microbial oxidation of pyrite experiments refers to the pyrite oxidation mechanism by A. ferrooxidans and A. thiooxidans, the characteristic pitting patterns on the pyrite crystals, the second mineral deposits, the changes of pH and Fe3+concentration.The results are summarized as follows:The euhedral pyrite in the sediments were formed during the burial process, and eroded by microorganisms in the earliest stage of diagenesis. And a variety of pit structures with characteristic shapes and sizes were formed during microbial oxidation of pyrite, which are generally similar to those obtained from the laboratory studies on the oxidative dissolution of pyrite by iron-oxidizing bacteria. The major mineral phases of the modern submarine hydrothermal sediments are pyrite and chalcopyrite. The sulfide minerals were extensively oxidized with characteristic dissolution pits on the surfaces, mainly polygons pits on chalcopyrite surfaces and rounded-elliptic pits on pyrite surfaces.Experiment study indicates that A. ferrooxidans eroded pyrite with the indirect contact mechanism. The concentration of Fe3+and H+were both increased significantly during the oxidation process. Pyrite were extensively oxidized with characteristic pits, which were rounded and geometric (mainly hexagon) in morphologies. The bacteria and the secondary mineral deposits were also observed in or around the pits. It is also indicated that A. thiooxidans can reinforce the bioleaching ability of A. ferrooxidans.Furthermore, bacillus-sized and-shaped microfossils communities were described, which are very likely to be fossilized sheaths produced by iron-oxidizing bacteria during pyrite oxidative process in the samples.更多还原