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题名: 基于热力学原理的元素耦合与微生物铁还原机制研究
作者: 王辛男1
学位类别: 硕士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 朱永官
关键词: 热力学能量,厌氧微生物,元素地球化学循环,铁还原,腐殖质 ; Thermodynamic energy, Anaerobic microorganisms, Geochemicalcycles, Iron reduction, Humic substances
其他题名: Coupling of elements and mechanisms ofmicrobial Fe(III) reductionbased on the principle of thermodynamics
学位专业: 环境科学
中文摘要: 微生物驱动着生物圈很多关键的过程和元素的氧化还原循环,改变着地表化 学环境。微生物在自然生态系统中对物质和能量转化所起的重要作用已引起广泛 关注。而热力学原理为预测反应能否自发,反应是否可能参与到微生物活动中, 物质与环境之间的能量交换以及微生物反应在环境中的分布提供了基本框架,也 成为微生物反应机制研究的理论基础。理解特定环境中微生物主导的过程必须理 解微生物代谢能量。 铁在土壤和沉积环境中都很丰富,主要以二价铁和三价铁的固态铁矿形式存 在。土壤和沉积物中微生物驱动的二价铁和三价铁矿物的氧化还原显著影响很多 其它元素的地球化学循环,与温室效应、有机污染和重金属污染等多种环境问题 密切相关。因此理解微生物驱动的铁循环有极其重要的意义。虽然人们已经对微 生物驱动的铁还原展开深入的研究,但目前微生物铁还原机制和途径仍然存在很 多未知。微生物在中酸性条件下的铁还原机制已有大量报道,但在碱性条件下微 生物铁还原机制还鲜有研究。 本论文从热力学出发,对环境微生物活动中涉及的最主要的几种元素的耦合 反应进行了研究,评估微生物在不同pH 下铁还原的能力,通过细菌培养实验探 究碱性环境中微生物铁还原的主要机制。论文的主要研究内容如下: (1)厌氧环境中厌氧微生物催化各种氧化还原反应,驱动着元素的地球化 学循环。厌氧微生物从催化氧化还原反应捕获能量以维持生长。这些微生物驱动 的氧化还原反应的热力学可行性由基于环境条件的产出能量所控制。不同的氧化 还原反应会按照热力学梯度从高产能到低产能顺序进行。氧化还原反应的热力学 能量影响各种厌氧生态系统中微生物氧化还原反应的分布和元素的循环转化。在 本研究中我们将厌氧微生物驱动的C、N、Fe 和S 之间的耦合反应与它们的热力 学可行性联系到一起。结果表明环境中已证实的微生物氧化还原反应的存在和分 布与它们的热力学可行性较为一致,热力学原理为氧化还原反应的存在和分布提 供了理论依据。因此,利用热力学原理来探究微生物驱动的元素耦合具有重要意 义。 (2)微生物胞外铁氧化物还原在很多生物地球化学循环中起重要作用。近 中性环境中已提出几种微生物铁还原机制,但在碱性条件下微生物铁还原的途径 还鲜有研究。在本研究中我们利用AQDS 作为腐殖质醌基组分的代表物质,探 究腐殖质在碱性条件下对铁还原的潜在作用。基于热力学计算,我们预测,在碱 性条件下三价铁(氢)氧化物的微生物酶还原热力学可行,但十分微弱。在微生物培养实验中,Shewanella oneidensis MR-1 和Geobacter sulfurreducens PCA 以及 水稻土富集菌混合培养具有较弱还原水铁矿的能力,S0 或AQDS 的存在均显著 促进了铁氧化物的还原。在碱性条件下AQDS 作为电子穿梭体促进铁还原的能 力高于元素硫(S0)。这些结果表明碱性条件下三价铁(氢)氧化物的微生物还原 可能是通过电子穿梭体介导的途径进行的。考虑到腐殖质有较强的电子穿梭能力 并且在环境中分布广泛,腐殖质介导的铁还原可能是碱性环境中微生物铁还原的 主导机制。
英文摘要: Microbial activity drives many key processes and the redox cycle of elements in the biosphere, changing the surface chemical environment on earth. The important role of microbial mass and energy transformation in the nature has attracted increasing attention among researchers. The principle of thermodynamics provides a basic frame for predicting whether a reaction is spontaneous, whether the reaction may be involved in microbial activity, the extent of energy exchange between substrates and the environment, and the distribution of microbial processes in the environment and becomes a theoretical foundation for learning the mechanisms of microbial reactions. Learning the microbial energy metabolism is necessary for understanding redox processes dominated by microorganims in a particular environment. Iron (oxyhdr)oxides, mainly in the form of solid ferric and/or ferrous minerals, are abundant in both soil and sedimentary environments. Redox cycles of ferric and ferrous minerals driven by microorganisms in the soils and sediments significantly affect the geochemical cycles of many elements, and are closely linked to many environmental problems, including release of greenhouse gases, contamination of organic pollutants and heavy metals. Therefore, understanding the microbial iron cycle is of dramatic significance. Although many advanced technologies and methods have been developed for the researches about microbial Fe(III) reduction, the mechanisms and pathways for microbial iron reduction are still unclear. A lot of investigations have been made for mechanisms of microbial Fe(III) reduction under near neutral conditions. However, the mechanisms of microbial Fe(III) reduction under alkaline conditions are rarely investigated. In this paper, we investigated the coupling of elements which are importantly involved in microbial activities from the perspective of thermodynamics. We estimated the feasibility of enzymatic iron reduction at different pHs and explored the main mechanism of microbial iron reduction in alkaline environments through batch culture experiments. The main contents of this paper are as follows: (1) Anaerobic microorganisms catalyze diverse redox reactions in anoxic environments and drive elemental biogeochemical cycles on the earth. They capture energy released from these redox reactions to support growth. The thermodynam feasibility of these redox reactions driven by microbes is controlled by their energy yields depending on environmental conditions. Different redox reactions would proceed following a thermodynamic ladder, sequentially from the high energy yields towards the low energy yields. The energy released by redox reactions therefore affects the distribution of microbial redox reactions and transformation of elements in various anaerobic ecosystems. In this study, the distribution of the coupling reactions between C, N, Fe and S, the most important elements in microbially mediated redox reactions, was linked to their thermodynamic feasibility. The results indicate that there is good consistency between the existence and distribution of microbial redox reactions in the environment and their thermodynamic feasibility. The principle of thermodynamics provides a theoretical foundation for the existence and distribution of the redox reactions. Therefore it is important to explore the coupling of elements driven by microorganisms with the principle of thermodynamics. (2) Extracellular Fe(III) reduction plays important roles in a variety of biogeochemical processes. Several mechanisms have been proposed for microbial Fe(III) reduction in pH-neutral environments, but it has rarely been studied in alkaline conditions. AQDS was used as a representative of qinones within humic substances to investigate the potential role of humic substances on mediating microbial Fe(III) reduction in alkaline environments. Based on thermodynamic calculations, we predicted that the enzymatic reduction of Fe(III) (oxyhydr)oxides would be thermodynamically feasible under alkaline conditions although very weak. In our experiments, the reduction of Fe(III) was significantly increased by anaerobic inoculation of Shewanella oneidensis MR-1, Geobacter sulfurreducens PCA or microbes enriched in a paddy soil respectively in the presence of S0 or AQDS. More Fe(III) minerals were reduced with AQDS as a soluble electron shuttle than that of element sulfur (S0) under the alkaline conditions. These results suggested that microbial reduction of Fe(III) (oxyhydr)oxides may proceed via a pathway mediated by electron shuttles under alkaline conditions. Considering the vast distribution of humic substances and its high ability as electron shuttles, we suggest that Fe(III) reduction mediated by humic substances may potentially be the dominant mechanism for Fe(III) reduction in alkaline environments.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38709
Appears in Collections:中澳联合土壤环境研究室_学位论文

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作者单位: 1.中国科学院生态环境研究中心

Recommended Citation:
王辛男. 基于热力学原理的元素耦合与微生物铁还原机制研究[D]. 北京. 中国科学院大学. 2017.
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