Geobacteraceae种群胞外电子传递过程及对沉积物中砷释放的影响机制

The tailing sediments from abandoned mine areas and in particular As contamination of agricultural soils and crops pose serious management issues, because immobile As can be easily transformed into a mobile phase as the result of Fe(III)-reducing microorganisms activities(e.g. family Geobacteraceae) in sediments, bringing about an additional potential environmental hazard as well. However, the mechanisms of extracellular electron transfer in the family Geobacteraceae remain poorly characterized and are topics of intense international debate. In this proposal, Arsenic-containing tailing sediments samples will be collected from abandoned mine areas in Hunan Province, and a microbial fuel cells-based approach will be utilized to investigate extracellular electron transfer. Techniques of microstructure and molecular ecology(e.g. PCR-DGGE,FISH and real-time PCR) are used in combination with aqueous and solid phase speciation analysis of As and Fe. The component and structure of filaments and its function in extracellular electron transfer will be examined. We will study the abundance, distribution, and phylogenetic diversity of members of the Fe(III)-reducing family Geobacteraceae as well as the distribution of filaments in sediment aggregates. The proposed research will explore the mechanisms of the extracellular electron transfer in the family Geobacteraceae and its effect on transformation of arsenic in sediments, providing valuable information and theoretical support for As-contaminated soil and sediments bioremediation.

含砷废弃尾矿沉积物对周边环境而言是一个潜在的污染源，由于Geobacteraceae等铁还原微生物的活动会影响到砷等微量元素的移动及生物有效性，但目前沉积物中Geobacteraceae种群胞外电子传递过程还没有得到清晰的认识。因此拟以我国典型含砷尾矿沉积物为代表采集样品，在沉积物微生物燃料电池的基础上，结合纯培养体系，利用微结构分析技术联合PCR-DGGE、荧光原位杂交(FISH)和real-time PCR等现代分子生物技术，弄清微生物纳米导线pili的组成、结构与功能及在胞外电子传递过程中的作用；明确尾矿沉积物中Geobacteraceae的种群分布及其功能组成与异化铁还原的关系；揭示尾矿沉积物中pili的分布、功能组成对异化铁还原的规律；阐明Geobacteraceae种群胞外电子传递过程对沉积物中砷形态转化的作用机制，为丰富生物地球化学理论和砷污染控制及修复提供理论依据。

砷污染及其危害己逐渐成为一个显著的生态问题。其中微生物驱动的沉积物中砷的迁移转化是关键因素之一，并且与微界面中的微生物-可溶有机物相互作用密切相关。本项目以湖南省石门县雄黄尾矿沉积物作为研究对象，通过胞外电子穿梭体——蒽醌-2,6-磺酸钠(anthraquinone-2, 6-disulfonate，AQDS)和有机碳系统地开展Geobacteraceae胞外电子传递过程来调控沉积物中砷/铁的释放。主要获得以下结论：AQDS是一种重要的醌类模型化合物，但不同浓度的AQDS对沉积物中As(V)/Fe(III)的生物还原过程及微生物群落结构的影响差异显著。低浓度的AQDS (0.05 mM和0.10 mM)能显著地促进As(V)/Fe(III)的还原释放，而高浓度的AQDS (1.00 mM)处理后则表现出抑制现象。这主要是因为低浓度的AQDS对微生物群落中的金属还原菌(如Bacillus，Lactococcus，Pseudomonas及Geobacter等)丰度有促进作用，而高浓度的AQDS处理后，沉积物中金属氧化菌(如Alicyclobacillus，Burkholderia和Bradyrhizobium等)的丰度较高，不利于As(V)/Fe(III)的还原释放。另外，AQDS还将潜在地改变了沉积物中DOM的变化，尤其是腐殖性DOM会促进As(III)-Fe(II)-humic DOM络合物的形成。本研究结果对今后充分发挥DOM在厌氧土壤环境中可将微生物得到的电子优先传递给污染物以实现环境污染物的原位修复有重要的指导意义。