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题名: 水稻土阳极呼吸菌的多样性及其对砷运移的影响
作者: 王亚洁
学位类别: 硕士
答辩日期: 2015-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 朱永官
关键词: 水稻土,砷,土壤微生物燃料电池,根表铁膜,阳极呼吸菌,Paddy soils,Arsenic,Soil microbial fuel cells,Iron plaque,Anode-respiring bacteria
其他题名: The diversity of anode-respiring bacteria and its effect on arsenic migration in paddy soil
学位专业: 环境工程
中文摘要:     砷是一种能够致癌的常见环境毒物,它常常在饮水和食物中积累导致人类健康受到威胁。水稻因其生长在长期淹水的环境中,导致它比其他作物更能富集金属砷。水稻是我国主要粮食作物,我国有60%的人以大米为食。但是目前我国水稻田砷污染严重,导致大米砷成为我国人民日常食用砷的主要来源,其对人们的健康造成了威胁。
    在水稻土中存在一类能够进行胞外呼吸的菌,它们可以将电子传递到细胞外电子受体使其还原,并产生能量维持菌自生生长,此类菌能够通过微生物燃料电池(MFC)的阳极进行富集,因此又被成为阳极呼吸菌。研究表明部分阳极呼吸菌对土壤中三价铁的还原和砷的释放起到重要作用。目前的研究主要集中在河水底泥和活性污泥中有机质对阳极呼吸菌的多样性的影响,但是对水稻土中砷对阳极呼吸菌的菌群结构的影响却鲜有报道。水稻根表铁膜是水稻土壤中重要的三价铁来源,土壤中的微生物能够还原铁膜中的三价铁并导致砷的释放,但是阳极呼吸菌在其中的作用并不清楚。
    基于此,本研究利用土壤微生物燃料电池,研究砷污染对土壤阳极呼吸菌的多样性的影响以及典型阳极呼吸菌Shewanella oneidensis MR-1对水稻根表铁膜的还原及其对砷运移的影响,同时寻找能够控制水稻砷污染的新方法。论文主要的研究内容与成果如下:
1. 水稻土壤不同程度砷污染对阳极呼吸菌的多样性的影响分析
    在本实验中,通过构建土壤微生物燃料电池来研究暴露在砷污染下的阳极呼吸菌的菌群演化方向。实验结果显示,在第一次淹水阶段,微生物燃料电池的极化曲线显示低浓度砷会增强阴极的电势,但是高浓度砷则降低阴极的电势。另一方面不论是暴露在低浓度砷还是高浓度砷下,微生物燃料电池的阳极电势都会随着砷浓度的增加而增加。在实验中干湿交替会降低土壤孔隙水中的砷浓度,从而减轻砷对电极微生物的影响。阴极的微生物在土壤干湿交替后,其多样性并不受砷浓度的影响,但是阳极微生物的多样性依然随砷浓度的变化而不同。结果表明,在高砷浓度下,δ-变形菌是阳极微生物的主要菌群。土壤微生物燃料电池的阴极
和阳极的微生物菌群结构会随土壤砷浓度的变化而改变,原因可能是不同微生物具有不一样的砷解毒机制。此研究结果对理解土壤微生物在砷暴露条件下的菌群结构演化具有重要意义。
2. 阳极呼吸菌Shewanella oneidensis MR-1还原水稻根表铁膜及砷释放研究
    实验以吸附砷磷的水铁矿以及野外采集水稻根系为研究对象,分析Shewanella oneidensis MR-1还原铁膜内铁氧化物过程中,铁还原、砷释放和固定速率。研究表明Shewanella oneidensis MR-1可以将水稻根表铁膜中的Fe(III)快速还原为Fe(II)并释放到溶液中。溶液中的砷在48小时内达到最大值18 μmol·L-1,之后逐渐下降,120小时之后,与最大值相比减少了约60%。利用吸附砷的水铁矿模拟铁膜砷释放过程发现,微生物的吸收作用是造成溶液中砷含量下降的主要原因之一。
3. 土壤微生物燃料电池减少水稻吸收土壤重金属的实际应用研究
    本实验通过构建土壤微生物燃料电池,为土壤胞外呼吸菌提供电子受体,减少土壤三价铁氧化物的还原,减低砷的有效性,从而达到减少水稻吸收重金属砷。实验结果表明,在水稻土中增加土壤微生物燃料电池之后,土壤孔隙水中的二价铁含量比空白对照F0降低了约50%。同时II阶段的第6天,F3处理的孔隙水中As、Pb和Cd的含量比F0对照分别减少了约50%,80%,8%。并且在F3电池中种植1周后的水稻根和地上部分的砷含量分别比F0电池的降低了约10%和50%。本研究证实了构建土壤微生物燃料电池可以有效减少水稻根和地上部分吸收砷等重金属。
英文摘要:     Long-term exposure to arsenic (As) from drinking-water and food can cause cancer and other serious health problem. Rice is usually grown in a flooded field, so it accumulates arsenic more easily than other plants. Rice is the main food in China, but severe arsenic contamination poses great threat to the health problems.
    Bacteria able to extracelluar respiration, which could be enriched in the anode of microbial fuel cells (MFCs), play important roles in dissimilatory iron reduction and arsenic (As) desorption in paddy soils. Previous studies on this topic have largely focused on the effect of soil organic matter on ARB communities in activated sludge or sediment. However, the information is scarce on the effect of arsenic on ARB communities in paddy soils. Arsenic (As) is commom in iron (Fe) plaque on rice root. Microorganisms can affect the migration and transformation of As in Fe plaque. However, the role of anode-respiring bacteria is not clear.
    Soil microbial fuel cells were built in this research to study the effect of arsenic contamination on composition of anode-respiring bacterial community during dry-wet cycles in paddy soils and the effect of anode-respiring bacteria on arsenic mobility in rice root iron plaque. At the same time, we will find a new way to control arsenic contamination in rice. The major contents and findings of this thesis are as follows:
1. Effects of arsenic contamination on the diversity of anode-respiring bacteria
    In this study, soil MFCs were employed to investigate the effects of As on anode respiring bacteria (ARB) communities in paddy soils exposed to As stress. In wet 1 phase, polarization curves of MFCs showed cathode potentials were enhanced at low As exposure, but inhibited at high As exposure. In the meantime, anode potentials increased with As levels. The dry-wet alternation reduced As levels in pore water and their impacts on electrodes microorganisms. However, the difference in patterns of anode microbial communities was still found after dry-wet cycles. Deltaproteobacteria dominated in the anode with high As. The dynamic changes of the communities on cathodes and anodes of soil MFCs in paddy soils with different As addition might be explained by their different mechanisms for As detoxification. These results provide new insights into the microbial evolution in As-contaminated paddy soils.
2. Effects of anode-respiring bacteria on arsenic mobility in rice root iron plaque
    The aim of study was to clarify the effect of microbial reduction and absorption on arsenic mobility. Experiments showed that the ferric iron of Fe plaque could be reduced quickly by Shewanella oneidensis MR-1 and released into the solution. In addition, arsenic in Fe plaque also simultaneously released and its concentration reached 18 μmol·L-1 within 48 hours. Finally, the concentrations of As gradually decreased and were reduced by about 60% after 120 hours. By simulating the process of As release from iron plaque using ferrihydrite which absorbed arsenic, it was shown that microbial absorption was one of the main causes of the decline of arsenic in solution. Promoting the growth of rhizosphere microorganisms may reduce the risk of As in the soil environment.
3. Using soil microbial fuel cells to reduce arsenic content in rice
    This experiment reduced soil Fe(III)-oxide reduction, arsenic availability and concentrations of arsenic in rice by building soil microbial fuel cells, which provided electron acceptors for soil extracellular respiratory bacteria. The result showed that the maximum concentration of porewater Fe(II) in F0-SMFC was 10μmol·L-1. And the maximum concentration of porewater Fe(II) in F3-SMFC was reduced by about 50%. Compared with the heavy metals content in F0-SMFC, the heavy metals contents in F3-SMFC were reduced by about 50%, 80% and 8% for porewater As, Pb and Cd, respectively. Furthermore, the As contents in rice of F3-SMFC were reduced by about 10% and 50% for roots and shoots, respectively. This study confirmed that the construction of soil microbial fuel cells could effectively reduce As content in rice roots and shoots.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34441
Appears in Collections:中澳联合土壤环境研究室_学位论文

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Recommended Citation:
王亚洁. 水稻土阳极呼吸菌的多样性及其对砷运移的影响[D]. 北京. 中国科学院研究生院. 2015.
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