黑曲霉产生的胞外多聚物促进污染土壤中重金属异养微生物沥浸去除的作用及机理

Heterotrophic bioleaching process using Aspergillus niger has been shown to be an effective means in removing contaminating metals from soils. A large quantity of extra-cellular polymers (ECP), which are mainly composed of polysaccharides, proteins, uronic acids, nucleic acids and lipids, are commonly found in the A. niger-mediated soil leaching process. Although ECP are well-known for their metal binding potential due to the presence of negatively charged functional groups (e.g., carboxyl, phosphoric, amine and hydroxyl groups), the role of the ECP secreted from A. niger in soil-borne heavy metals bioleaching still remains unclear. The purposes of the current study are to (1) determine the secreting characteristics of ECP (e.g., its concentration, spatial distribution, chemical composition and molecular structure); (2) examine the influence of the complexation of ECP for heavy metal on soil-borne metal solubilization efficiency, including differentiate the various performance of dissolved ECP (D-ECP), loosely bound ECP (LB-ECP), tightly bound ECP (TB-ECP) and total ECP (T-ECP) ; (3) identify the ECP active constituents and reveal the relationship between the ECP structure and their potential functions; (4) analyze the effect of the changing biochemical properties of the secreted ECP on these potential roles. The expected outcome from this work will expand our knowledge of the importance of microbial BEP to metal-laden soil bioleaching treatment and provide information useful for the development of highly efficient bioremediation strategies for toxic metal-contaminated soils.

在弄清黑曲霉产生的胞外多聚物（ECP）的数量、分布、化学组成与分子结构等性质特征的基础上，探讨ECP影响黑曲霉生物沥浸去除污染土壤中重金属的规律及机理。特别是揭示ECP与重金属的络合作用促进重金属生物沥浸去除的途径与强度（包括定量区分溶解态ECP、松散结合态ECP、紧密结合态ECP等三类分层的ECP的不同贡献）；鉴定ECP中起作用的关键组分、并查明其结构与功效的关系；以及阐明黑曲霉ECP性质特征的演化对其作用机理的影响。项目研究成果为丰富和深化人们对微生物胞外多聚物在重金属污染土壤生物沥浸中重要性的认知，为研究调控重金属生物浸除的对策，并最终推动重金属污染土壤异养微生物沥浸技术迈向实际应用提供理论依据。

本项目通过解析土壤重金属异养微生物沥浸过程中黑曲霉（Aspergillus niger）胞外多聚物（ECP）的分泌规律、组成和结构及其与重金属的络合效能与作用原理，阐释ECP促进土壤重金属生物脱除的微观作用机制。研究表明：A. niger分泌的粘性的具有分支网状结构的ECP对Zn(Ⅱ)、Cd(Ⅱ)和Pb(Ⅱ)等重金属有较强的络合能力；准二级动力学模型和Langmuir等温吸附模型可较好的描述这一络合作用。经鉴定，ECP中起络合作用的关键活性成分是多聚糖；该活性多聚糖由两类同多糖A1（鼠李糖）和A2（甘露糖）构成，A1的分子结构主要为[→4)-α-Rhap(1→]和[→4)-β-Rhap(1→]的直链构型，A2分子结构主要为[→2)-α-Manp(1→]的直链构型。发现了与ECP络合的有机大分子重金属配合物ECP-Men+在土壤中的吸持量比自由态重金属离子Men+大幅减少，该现象可能是土壤重金属生物沥浸的功效优于化学沥浸的重要原因。通过岭回归统计分析，建立了A. niger产酸特征与土壤重金属生物沥浸效能之间的关系。柠檬酸产量对Zn和Pb的去除有较大影响，草酸和葡萄糖酸对Cd去除影响较大。结合泥浆反应器的运行，初步检验了A. niger利用土豆皮和秸秆等有机废弃物作为能源底物（替代蔗糖）来进行土壤重金属生物沥浸处理的可行性。项目研究成果对于完善土壤重金属异养微生物沥浸处理的作用机制，推动该技术迈向工程实践提供科学依据和技术支撑。