黔中白云岩风化壳稀土层可培养放线菌多样性及吸附La(Ⅲ)特性研究

Diversity of culturable actinomycetes and adsorption characteristics of La(Ⅲ) in rare earth layer of dolomite weathering crust in central Guizhou

微生物在风化壳稀土元素迁移、富集过程中一直扮演着重要角色.前期研究采用宏基因组技术分析黔中地区白云岩风化壳稀土富集层微生物多样性时,发现放线菌门为主要优势类群之一.本实验采用纯培养技术研究贵州喀斯特稀土层可培养放线菌生物多样性,并初步研究了放线菌对稀土La^(3+)的吸附过程,以阐明微生物与稀土离子的相互作用机制,完善稀土元素的生物地球化学循环过程.实验采用选择性培养技术共获得190株纯培养物,分别归属于放线菌门19个属,其中,优势菌属有链霉菌属(Streptomyces)、诺卡氏菌属(Nocardia)和小单孢菌属(Micromonospora),分别占总分离菌株的62.1%、12.6%和11.1%.稀土耐受性能较好的菌株Micromonospora aurantiaca KLBMP9018、Streptomyces mirabilis KLBMP8969和Nocardia sp.KLBMP9014在La^(3+)浓度为20 mg·L^(-1)的20 mL溶液中最大吸附量(干重,m/m)分别达到24.32、25.37和20.74 mg·g^(-1).动力学方程拟合结果显示,3株放线菌对La^(3+)的生物吸附过程均遵循拟二级动力学方程,表明吸附过程是一个物理和化学共同作用的结果.同时,Langmuir等温吸附平衡模型能更好地拟合3种放线菌对La^(3+)的吸附过程,表明菌体细胞表面为单分子层吸附.XPS结果显示,吸附在菌体细胞表面的是La^(3+),没有发生还原反应.而FRIR分析表明,菌体细胞壁的氨基、羟基和羧基官能团参与了La^(3+)的吸附过程.这些结果进一步证实黔中地区白云岩风化壳稀土富集层中栖息着丰富多样的放线菌类群,且这些放线菌的生长代谢活动对稀土元素La的地球化学循环过程具有重要作用.

Microorganisms play an important role in the biogeochemical cycle of rare earth elements in weathering crust.In the previous metagenomic analyses of the microbial diversity in dolomite weathering crusts from central Guizhou,the phylum Actinobacteria was found to be a dominant taxon in rare earth-rich layers.In this study,the culturable actinomycetes from the layer of karstic weathering crust in Guizhou were isolated and identified,and their adsorption processes of lanthanum(Ⅲ)were also studied to elucidate the mechanism of microbial adsorption of rare earth elements.A total of 190actinobacterial strains belonging to 19 genera were isolated from the karstic weathering crust in Guizhou by using selective isolation media.Genera Streptomyces,Nocardia and Micromonospora were the dominant groups of culturable actinomycetes,accounting for 62.11%,12.63% and 11.05%,respectively.The maximum adsorption(dry weight,m/m)of the better rare earth tolerant strains Micromonospora aurantiaca KLBMP9018,Streptomyces mirabilis KLBMP8969 and Nocardia sp.KLBMP9014 in a 20 mL solution with La^(3+)concentration of 20 mg·L^(-1)were 24.32 mg·g^(-1),25.37mg·g^(-1)and 20.74 mg·g^(-1),respectively.Kinetic equations were fitted to the experimental data,showed that the process of La^(3+)biosorption by the three actinomycetes belonged to the pseudo second-order equation.The isothermal adsorption model was also plotted,and the Langmuir isothermal equilibrium model could better fit the adsorption process of La^(3+)by the three actinomycetes than the Freundlich isothermal equilibrium model,indicated that the cell surface is adsorbed as a single molecular layer.XPS results showed that the adsorbed La on the cell surface of the bacterium was in the trivalent state and no reduction reaction occurred.The FRIR analysis revealed to the amino,hydroxyl and carboxyl functional groups of the cell wall of the bacterium were involved in the adsorption process of La^(3+).The results validated that diverse actinomycetes inhabit the layer of dolomite weathering crust in central Guizhou,and their metabolic activities have an important role in the geochemical cycling process of La element.