| 啤酒酵母和拟棘壳孢属菌与铀的相互作用机理研究 | |
| Alternative Title | Interaction Mechanisms of Uranium(VI) with Saccharomyces cerevisiae and Pyrenochaetopsis sp. |
| 沈扬皓 | |
| Subtype | 博士 |
| Thesis Advisor | 王铁山 |
| 2021-05-21 | |
| Degree Grantor | 兰州大学 |
| Place of Conferral | 兰州 |
| Degree Name | 理学博士 |
| Degree Discipline | 粒子物理与原子核物理 |
| Keyword | 铀 啤酒酵母Saccharomyces cerevisiae 拟棘壳孢属Pyrenochaetopsis sp. 生物吸附 生物矿化 生物富集 |
| Abstract | 随着核能的和平利用，核工业生产环节产生的大量含铀废水在近地表和地下大量排放，造成了严重的放射性污染，危害公众安全。因此，了解铀的的形态分布、迁移、转化等复杂的生物地球化学反应对放射性废物地质处置的安全评估、放射性元素的回收以及放射性污染环境的生物修复都具有深远的意义。真菌广泛分布于自然界中，也是生物链中参与能量代谢和元素循环的重要组成部分，能够通过吸附、累积、矿化等行为影响铀的行为。因此，本论文针对广泛存在于自然界中的子囊门真菌Saccharomyces cerevisiae，以及放射性污染场地分离出的拟棘壳孢属真菌Pyrenochaetopsis sp.和放射性核素铀相互作用进行了系统的研究。主要结果如下： 甲醛修饰啤酒酵母S. cerevisiae对铀的吸附行为研究 1. 甲醛修饰S. cerevisiae对铀酰离子具有显著的去除作用，并能有效地回收低浓度废水中的铀离子，在较低铀浓度条件下（1 mg/L）时，甲醛修饰S. cerevisiae对U(VI)的吸附能力甚至能达到活细胞的6倍。吸附动力学研究表明铀酰离子的吸附是一个快速的过程，大约90 min可以达到吸附动态平衡，吸附过程存在着电子共用和转移。吸附的最佳pH位于5.8附近，该值可能与细胞表面的离子状配体、氨基酸等电点以及铀酰离子的水解相关。Langmuir和Freundlich等温模型的拟合结果表明，甲醛修饰S. cerevisiae对铀酰离子的吸附是一种单分子层吸附。 2. 介观研究和光谱分析等表征手段表明，甲醛修饰改变了S. cerevisiae细胞的表面形貌，使蛋白结构发生了变化，氨基甲基化生成了羟甲基衍生物，在吸附铀酰之后，细胞表面覆盖了一层鳞片状的铀沉淀，铀的沉淀与络合物形式复杂，主要与-OH，-PO43-,-COO，C=O等基团进行相互作用，铀酰与羧酸根主要络合为双齿配位化合物。甲醛修饰S. cerevisiae与铀酰离子的相互作用还可能存在着络合、沉淀以及静电吸附等多种机理。X射线衍射光谱显示，甲醛修饰S. cerevisiae细胞无法将无定形态的U(VI)转化为晶体。 二、啤酒酵母S. cerevisiae对铀的矿化过程 1. U(VI)对S. cerevisiae细胞的毒性实验表明，约90%以上的S. cerevisiae细胞能在寡营养的水中维持活性达8 d以上，而在不同U浓度的溶液中，细胞则呈现出不同的生存曲线，以60%的活细胞计，在100 mg/L的U(VI)溶液中，S. cerevisiae至少能存活4 d以上。 2. 随着U(VI)快速地吸附到细胞表面，溶液中的U(VI)浓度迅速下降，Pi浓度以及溶液的pH值逐渐升高，体系的pH值最终稳定在~7.0，S. cerevisiae在U溶液中暴露1 d后，体系处于过饱和状态。当细胞在100 mg/L U(VI)中暴露不超过2 d时，表面沉积的U(VI)仍处于非晶态，随后出现的衍射峰证明非晶态的U被转化成四方晶体H2(UO2PO4)2·8H2O。介观研究表明在细胞与U相互作用的初期，U(VI)以不规则片状沉淀方式嵌入细胞表面，随着时间的延长，S. cerevisiae细胞表面无定形的沉淀逐渐消失，转化为稳定的结晶状的沉淀，该沉淀的主要成分是铀酰磷酸盐。晶体学信息表明，所形成的H2(UO2PO4)2·8H2O厚度为由最初的近百纳米逐渐演化到几十纳米，随着结晶时间的延长，S. cerevisiae细胞甚至能将UO22+调节生长成为近乎完美的晶体。 3. S. cerevisiae对U的生物矿化过程分为表面吸附、非晶沉淀以及结晶三个阶段。 三、拟棘壳孢属Pyrenochaetopsis sp.与铀的相互作用 1. 真菌Pyrenochaetopsis sp.在固体培养基上的生长受梯度U浓度影响，真菌的生长速率在0.01 mM的U中最大，在0.1 mM的U中最小，当培养基中U浓度>0.1 mM时，真菌停止生长。低浓度的U（<0.01 mM）能有效地促进真菌地生长。当液体培养基中添加0.01和0.1 mM U时，真菌Pyrenochaetopsis sp.对U的富集呈现出完全不同的趋势：在0.1 mM U中10 d后达到吸附平衡，并使溶液中U的水平维持在一个相对稳定的区间，而在0.01 mM U中，达到吸附平衡后发生U(VI)的解吸。 2. 真菌在固相或者液相生长过程中，细胞均通过菌丝将营养物质与污染物（U）从周围环境中富集到自身上，甚至能使真菌上积累的U浓度达到周围环境的10倍，通过XANES和XAFS光谱可知，浮游生长和固相生长的Pyrenochaetopsis sp.真菌在与U的络合方式上完全相同。在30天的时间尺度下， Pyrenochaetopsis sp.无法在好氧条件下利用电子供体，介导U(VI)的生物还原，而是利用自身的磷酸盐库，在磷酸酶作用下水解磷酸盐，并形成溶解度较低的类钙铀云母矿物。 3. Na+浓度对铀酰磷酸盐的物种分布几乎没有影响。Fe3+在浓度过高时可能析出次生铁矿的沉淀物，使U(VI)沉淀在其表面并阻碍U-P的络合。Pi对U(VI)的沉积具有显著的浓度效应，仅当Pi摩尔浓度数倍于U(VI)时，才可能形成磷酸铀酰类络合物或矿物。 以上结果增进了我们关于环境真菌对铀转化机理的认识，为后续将真菌应用到回收废水中的铀，以及大规模开展微生物对放射性污染土壤及地下水修复提供了理论依据。 |
| Other Abstract | With the peaceful utilization of nuclear energy, considerable uranium-containing wastewater originated from the nuclear industry was discharged into sub- or near- surface and groundwater, resulting in serious radioactive pollution and threatening public safety. Hereby, understanding the complex biogeochemical reactions of uranium, including its speciation, migration and transformation has profound significance for the safety assessment of the geological disposal of radioactive waste, recycling of radioactive elements and the bioremediation of radioactively contaminated environments. Fungi are widely distributed in nature and are also an important part of biological chain that participates in energy metabolism and element cycle. It has been proved that fungi affect the behavior of uranium via multiple pathways, such as biosorption, bioaccumulation, and biomineralization. Therefore, this dissertation systematically evaluate the interaction between uranium and the ascomycete fungus Saccharomyces cerevisiae, whom is widely existed in nature, as well as the fungus Pyrenochaetopsis sp., whom is isolated from radioactive contaminated sites. The main results are as follows: Part I: Adsorption behavior of uranium on methanal modified S. cerevisiae 1. Methanal modification drastically improve the U(VI) adsorption capacity of S. cerevisiae cells, which is even 6 times than that of living cells under the same condition (1 mg/L U). The kinetic study suggests that the biosorption of uranyl ions is a rapid process, which equilibrated within ~90 minutes, and there is electron sharing and transfer in the adsorption process. The optimal pH for adsorption is 5.8, which might be related to the ionic ligands on the cell surface, the pI values of amino acids, and the hydrolysis of uranyl ions. The Langmuir and Freundlich isotherm models fitting results shows that the adsorption of uranyl ions by methanal modified S. cerevisiae is homogeneous (mono-layer coverage only). 2. Scanning electron microscopy(SEM) and Fourier transform infrared spectroscopy(FTIR) showed that methanal modification change the surface morphology of S. cerevisiae cells and protein structure. Aminomethylation lead the hydroxymethyl derivatives. A layer of scale-like uranium precipitation is attached on the cell surface after uranyl adsorption. Uranium associates with -OH, -PO43-, -COO, C=O and other functional groups, where U(VI) complexes -COO into bidentate ligand. The interaction mechanisms between methanal modified S. cerevisiae and uranyl ions might be including complexation, precipitation and electrostatic interaction. X-ray diffraction spectroscopy(XRD) shows that methanal modified S. cerevisiae cells unable to transform amorphous U(VI) into crystals. Part II: The mineralization process of uranium by S. cerevisiae 1. The U(VI) toxicity experiments on S. cerevisiae cells show that more than 90% of S. cerevisiae cells stay alive in oligotrophic water for more than 8 days, while in different U concentration solutions, the cells show totally different survival curves, who survive at least 4 days in a 100 mg/L U(VI) solution based on 60% of the living cells. 2. With the rapid adsorption of U(VI) on cell surface, the U(VI) concentration in the solution drops rapidly, however the Pi concentration and the pH value of the solution gradually increase, and the pH value of solution finally stabilize at ~7.0, After exposure for 1 d, the solution was over-saturated with respect to Chernikovite. As cells expose to 100 mg/L U less than 2 days, the U(VI) on the cell surface keeps in an amorphous state, while the diffraction peaks appears over time, which proved that the amorphous U was transformed into tetragonal Chernikovite. Mesoscopic studies have confirmed that in the initial stage of the interaction, U(VI) is embedded in the cell surface as irregular scale-like precipitations, these irregular precipitations on the cell surface of S. cerevisiae gradually disappears, yet the crystalline precipitations (uranyl phosphate) appear over time. The crystallographic information indicates that the thickness of newly formed Chernikovite is gradually thinning from nearly a hundred nanometers to tens of nanometers, and the S. cerevisiae cells even mediating UO22+ into a nearly perfect crystal. 3. The biomineralization process of U(VI) by S. cerevisiae including three stages: (1) surface adsorption, (2) amorphous precipitation, and (3) crystallization. Part III: The interaction between Pyrenochaetopsis sp. and uranium 1. The growth of the Pyrenochaetopsis sp. on agar is affected by the gradient U concentrations. The maxium growth rate of the fungus is in 0.01 mM-U amended agar and the lowest is in 0.1 mM U counterpart. When U concentration exceeds 0.1 mM, the fungus stops growing. Low concentration of U (<0.01 mM) can effectively promote the growth of fungi. When 0.01 and 0.1 mM U are amended to the liquid medium, the Pyrenochaetopsis sp. showed a totally different trend in the enrichment of U: the adsorption equilibrium reachs after 10 d in 0.1 mM U, and the U level in the solution remains unchange, while in 0.01 mM U, U(VI) desorption occurs after the adsorption equilibrium reached. 2. During the growth of fungi in solid or liquid phase, the cells enrich both nutrients and pollutants (U) from the surrounding environment to themselves through the hyphae, which even accumulate 10-times of U(VI) than surrounding environment. According to XANES and XAFS spectrum, Pyrenochaetopsis sp. grows in both planktonic and solid-phase exhibit the same complexation form with respect to U(VI). Within 30 days timescales, Pyrenochaetopsis sp. is unable to use electron donors and mediate the bioreduction of U(VI) in aerobic environment, yet hydrolyze phosphate from its own phosphate pool under the function of phosphatase, enventually form the low solubility meta-autunite. 3. The concentration of Na+ barely affects the species of uranyl phosphate. High concentration Fe3+ may form the secondary iron minerals, thus making U(VI) precipitate on its surface and hindering the complexation of U-P. Pi has a significant concentration effect on the precipitation of U(VI). Only when the molar concentration of Pi is several times than that of U(VI), can uranyl phosphate complexes or minerals be formed. The above results enhance our understanding of the mechanism of uranium transformation by environmental fungi, which provide a fundamental theory for future application of fungi to the recovery of uranium in wastewater bioremediation of radioactive contaminated soil and groundwater at pilot- or field-scales. |
| Pages | 124 |
| URL | 查看原文 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | https://ir.lzu.edu.cn/handle/262010/459382 |
| Collection | 核科学与技术学院 |
| Affiliation | 核科学与技术学院 |
| First Author Affilication | School of Nuclear Science and Technology |
| Recommended Citation GB/T 7714 | 沈扬皓. 啤酒酵母和拟棘壳孢属菌与铀的相互作用机理研究[D]. 兰州. 兰州大学,2021. |
| Files in This Item: | There are no files associated with this item. | ||||
