The Variations of Bacterial Community Structures in Tailing Soils Suffering from Heavy Metal Contaminations

Investigations of the impact of heavy metals on microbial community structure are crucial for bioremediation of the contaminated sites. To this end, high-throughput 16S rRNA sequencing was performed to assess the variations of bacterial communities in 6 heavy metal-contaminated soils sampled from Liujiaping (LJP) and Shanping (SP) lead-zinc tailings situated in northwestern China. Compared with those of the farmland soil (NT), the heavy metal levels and chemical properties of the tailing soils were significantly different. Consistently, the bacterial community structures have been changed, displaying as the bacterial richness and diversity in the tailing soils were either increased or decreased, i.e., trending as SP > NT > LJP. The relative abundances of certain bacterial phyla mainly including Actinobacteriota, Acidobacteriota, Cyanobacteria, Gemmatimonadota, and Bacteroidota were significantly increased in certain SP and/or LJP soils. Further, the relative abundances of Actinobacteriota and Bacteroidota were positively correlated with Cd, TP, TK, SOM, TN, and pH. The abundance of Cyanobacteria was significantly upregulated by Cu, Zn, and TP. Acidobacteriota was notably positively correlated with Cr, Pb, and NO3-_N. On the contrary, the relative abundance of Chloroflexi was negatively correlated with all the environmental parameters, especially with Cd, NO3-_N, TP, SOM, and TN. Together, our results implied that the heavy metals and chemical properties were both driving forces of the variations of the bacterial community structures in the tailing soils. Overall, we have successfully identified certain bacterial species such as s__unclassified_g__Sulfurifustis, s__unclassified_f__Rhodanobacteraceae, s__unclassified_g__Conexibacter, s__unclassified_g__norank_f__norank_o__Gaiellales, and s__unclassified_g__Blastococcus which were probably heavy metal-tolerant in these specific tailing soils, and this will provide a theoretical support for further bioremediations.

Automated summary

Investigations into the impact of heavy metals on microbial community structure revealed that heavy metals and chemical properties are the main driving forces behind changes in bacterial diversity and community structure in contaminated soils. The relative abundances of specific bacterial phyla were found to be correlated with the levels of heavy metals and certain chemical properties in the soils. Certain bacterial species identified in these specific tailing soils may have potential tolerance to heavy metals, providing theoretical support for future bioremediation efforts.