内蒙古锡林郭勒盟高氟地区土壤中矿物分解菌的分布及其对土壤氟迁移转化行为的影响研究

Fluorine rich minerals are the primary source of the fluorine in soil and shallow ground water. Kinetics of the fluorine release from the fluorine rich minerals is one of the important factors that determine the concentration of bioavailable or leachable forms of soil fluorine. Physico-chemical mechanisms of the release of fluorine from the minerals have been well characterized. However role of microorganisms in this process is poorly understood. There are plenty of mineral-weathering bacterial in soil and mineral surface. Those microorganisms play an important role in mineral weathering and soil formation process. The weathering mechanisms include oxidoreduction reactions and production of weathering agents, such as organic acids and chelating molecules. Some mineral-weathering bacteria use high valence metal elements instead of oxygen as the terminal electron acceptors for their energetic and metabolic needs. The metal elements in the mineral matrix become unstable and readily soluble after reduced by the microbes. Some microbes weather minerals for nutrient acquisition. Those microbes usually solubilize nutrient elements from minerals by secreting mineral-weathering metabolites. When mineral-weathering bacteria actively solubilize some elements from minerals, co-existing elements in the mineral matrix can also be released. And if those bacteria interact with toxic-element-bearing minerals, there could be a risk of environmental pollution. . Bacterial dissolution of fluorine rich minerals has been reported by several groups. However these studies only concentrated on the release of major elements, releasing character of fluorine was not addressed. How do the mineral-weathering bacteria affect the release of fluorine from different minerals? What are the critical factors that control the biogeochemical cycling of fluorine? What effects do the mineral-weathering bacteria have on the migration and transformation of fluorine in the soils of high fluorine area? The present project is planed to answer these questions. Soil samples will be collected from XiangHuangQi of Xilingol League, a typical high fluorine area in Inner Mongolia. Mineral-weathering bacteria will be isolated from the soil samples and mineral-weathering ability of the isolated bacteria will be tested. Concentration of fluorine and other elements will be monitor during bacteria dissolution of frequently occurring fluorine rich minerals and the interdependence of the released element will be analyzed. Bacteria metabolites will be analyzed for elucidating the mechanism of bioweathering. Isolated mineral-weathering bacteria will be inoculated in the fluorine-rich soils and incubated at constant temperature. Change of fluorine speciation with the incubation time will be analyzed to clarify the effect of mineral-weathering bacteria on the release and transformation of fluorine in the soil matrix. Distribution of mineral-weathering bacteria in soils of the high fluorine area in XiangHuangQi will be accessed and their potential roles in the migration and transformation of fluorine will be evaluated. Present project will make important contribution to the understanding of microbiological roles in migration and transformation of fluorine in soils. The present project is also expected to provide theoretical basis for the development of effective strategies to manage fluorine pollution.

高氟区土壤中的富氟矿物被认为是土壤和浅层地下水氟的重要来源。目前关于氟从富氟矿物中溶出和转化的物理化学机制的研究较为深入。然而对其中的微生物因素却了解不多。土壤和矿物表面存在众多矿物分解菌。这些微生物能够加快元素的溶出和转化速率，促进矿物风化和成土过程。矿物分解菌如何影响氟离子的溶出速率和溶出量，受哪些关键因素的控制，矿物分解菌对高氟区土壤氟的迁移转化行为有何影响。本课题拟针对这些问题展开系统性研究。课题组拟从内蒙古锡林郭勒盟镶黄旗高氟区土壤中分离矿物分解菌，研究这些菌种与富氟矿物的作用过程中氟离子的释放和转化特征，阐述其作用机理和控制因素，并根据矿物分解菌在高氟区不同土壤中的分布，结合土壤理化性质，评价矿物分解菌在高氟地区土壤氟的迁移转化过程中的作用。本研究有助于了解高氟区土壤中氟离子的溶出和转化过程中的微生物因素，有望为土壤和地下水氟污染的控制提供新的思路。

微生物在土壤地球化学元素的迁移转化中起着重要的作用。本课题旨在揭示土壤矿物分解菌对高氟区土壤水溶性氟含量的影响。应用平板涂布法从内蒙古镶黄旗土壤中分离出了225株细菌，测定了这些菌株16S rRNA基因全长序列。根据16S rRNA基因序列，以97%的相似度为阈值，将分离出的225株土壤菌分成了10个操作分类单元（operational taxonomic units，OTUs），从每个操作分类单元内随机选取1株菌作为代表，研究这些菌株的矿物分解潜力。矿物溶解实验结果表明，10株代表性菌均能显著增加黑云母和正长石等常见土壤矿物的溶解性。除此之外，这10株菌在钙沉淀菌选择性培养基（B4培养基）中均表现出了钙沉淀菌的特性，即显著降低培养液中的钙离子浓度，并增加体系pH。将这10株代表性菌接种到土壤中，培养两周后发现，与无菌对照相比，土壤水溶性钾、硅和铝含量无显著性增加。说明这些菌在土壤介质中，对土壤矿物溶解的促进作用不明显。相反，在微生物接种的土壤中钙浓度均有显著降低，其中4株土壤菌还能显著增加土壤pH。与之伴随的是大部分（10株中的8株）代表性土壤菌都显著增加了土壤水溶性氟含量。由于钙离子浓度和pH是影响土壤和地下水中氟离子浓度的重要因素，我们认为相比于微生物的矿物分解作用，该地区土壤微生物的潜在钙沉淀作用可能在土壤氟的释放中起着更为重要的作用。对镶黄旗7个不同采样点的土壤样品进行了16S rRNA基因宏基因组分析。结果表明，这10株代表性菌在该地区有着广泛的分布。这一结果表明微生物在该地区土壤水溶性氟含量的升高中有重要的贡献。该研究为揭示该地区高氟水形成机制提供了新的思路和新的参考，具有重要的科学意义。

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