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

Abstract:

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 La³⁺ than that of Zn²⁺, and the Aspergillus sp. B6-3 had the highest adsorption rates for La³⁺ (19.7%) and Zn²⁺ (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.

Key words:rare earth element;heavy metal;molecular survey;fungi community structure;culture-dependent technique;biosorption process