矿区复合污染土壤真菌多样性及其对稀土-重金属离子的吸附特征

Fungal community structure in mining soil and its adsorption kinetics of rare earth-heavy metal ions

大量的稀土-重金属通过尾矿坝的浮尘、地表径流和渗滤液排放到周边土壤中,影响了土壤中的微生物群落结构。【目的】分析稀土和重金属复合污染土壤真菌群落结构并分离具有同时吸附稀土和重金属的菌株。【方法】本研究基于ITS基因,采用Illumina-Hiseq测序技术分析了包头稀土尾矿坝周边5份稀土-重金属污染土壤样品和距尾矿区20 km的1份相对未受污染的土壤样品的真菌群落特征,同时采用富集培养法从污染样品中筛选出金属耐性真菌,并对其进行吸附稀土-重金属的特性分析。【结果】群落结构为:在门水平,除了未分类门真菌(unclassified Fungi)外,子囊菌门(Ascomycota)真菌在所有土壤中占比较大(13.5%–90.5%);在纲水平上,除了未分类纲真菌外,粪壳菌纲(Sordariomycetes)真菌在B2 (73.1%)、B3 (28.4%)和B4 (20.8%)的丰度显著高于对照样点C (7.4%),而座囊菌纲(Dothideomycetes)在B5 (11.8%)的丰度明显高于B1 (3.5%);在属水平,除了未分类属,足孢子虫属(Podospora)是C(0.9%)和B3(23.6%)样点的优势种。曲霉属(Aspergillus)、未分类的格孢腔菌目(unclassified Pleosporales)和未分类的戴维迪科(unclassified Davidiellaceae)分别为B1 (3.0%)、B4 (10.5%)和B5(5.8%)的优势种,而蜡蚧属(Lecanicillium)真菌只在B2样点土壤存在且占优(51.6%)。Zn污染对真菌群落结构的影响大于稀土元素污染,且其浓度与优势的未分类真菌相对丰度呈负相关。从污染样品中共分离出6株真菌,它们分属于曲霉属(Aspergillus)(5株)和镰刀霉菌属(Fusarium)(1株)。所有分离菌株对镧(La^3+)的吸附率均显著高于锌(Zn^2+),其中Aspergillus sp. B6-3对La^3+和锌Zn^2+的吸附率最高,分别为19.7%和3.9%。【结论】该研究为利用真菌去除稀土和重金属以优化生物吸附过程导向的环境生物修复和保护策略提供了机制基础。

A large number of contaminants from rare earth-mines are discharged into the surrounding soil through the floating dust, surface runoff and leachate of the tailings dam, and affect particular fungal communities. [Objective] To investigate the adaption of fungal community structure to the long-term pollution stress by both rare earth and heavy metals, and to characterize the adsorption kinetics of rare earth and heavy metal by fungi isolates. [Methods] Based on the internal transcribed spacer(ITS) gene, Illumina-Hiseq sequencing technique was used to analyze the fungal community structure in five soils from B1 to B5 with increasingly higher contents of rare earth-heavy metal around Baotou rare earth tailings dam, in addition to an uncontaminated control soil about 20 km away from tailings area(sample C). Meanwhile, a total of 6 fungal isolates were obtained by culture-dependent technique, and their absorption kinetics of both rare earth and heavy metals were analyzed. [Results] At the phylum level, Ascomycota was abundant in fungal communities in all samples(13.5%–90.5%). At the class level, Sordariomycetes was apparently higher in B2(73.1%), B3(28.4%) and B4(20.8%) than control C samples(7.4%);and the relative abundance of Dothideomycetes was lower in the B1(3.5%) than B5(11.8%). At the genus level, Podospora showed strong adaption to contaminant stress, from the low relative abundance of 0.9% in control soil, to 23.6% in B3. Meanwhile, Aspergillus, unclassified Pleosporales, and unclassified Davidiellaceae were also detected with high relative abundances in B1(3.0%), B4(10.5%) and B5(5.8%), respectively. Intriguingly, Lecanicillium was detected only from the B2 sample and dominated(51.6%). The effect of Zn pollutant on fungal communities was greater than that of rare earth elements, and negative correlation was observed between soil Zn content the relative abundance of dominant unclassified fungi. Six fungal isolates were obtained from contaminated soil, and could be assigned to genera Aspergillus(five isolates) and Fusarium(one isolate). All fungal isolates showed significantly higher adsorption capacity of La^3+ than that of Zn^2+, and the Aspergillus sp. B6-3 had the highest adsorption rates for La^3+(19.7%) and Zn^2+(3.9%). [Conclusion] This study provided a mechanistic basis for the use of fungi to remove rare earths and heavy metals towards the optimization of biosorption process-oriented strategy for environmental bioremediation and protection.