Assessment of Soil Bacterial Community Compositions by Structural–Functional Genomics and Soil Edaphic Factors Largely Explain the Impact of Coal Mining

The consequences of coal mining on soil ecosystems are becoming more apparent and worrisome, as these areas are prone to contamination of heavy metal(loid)s. The 16S rRNA gene-based metagenomics analysis was used to investigate the structural and functional variation of the soil bacterial community in coal mine spoils from 4-, 12-, and 15-year-old sites. The variation in soil properties in reference to undisturbed forest soil and the ecological risk analysis of heavy metal(loid)s were also determined. The results suggested that the 12- and 15-year-old coal mine spoils were under ecological risk, as indicated by Hakanson's Risk assessment index. Accordingly, the structure of the bacterial community in the spoil soils were also differentially altered. It was also evident that soil physicochemical parameters and concentration of heavy metal(loid)s have influenced the structure of the bacterial community. The bacteria that predominated in mine spoils under ecological risk were Firmicutes, Actinobacteria, and Archaea. The predicted functional analysis suggests that the coal mine spoils from 12- and 15-year-old site contain abundant genes involved in genetic information processing and metabolism that might have assisted them in tolerating heavy metal(loid)s toxicity and surviving there. The co-occurrence pattern indicated association between the diverse metabolic pathways. Overall, we found changes in the key taxa of bacterial communities and the soil physicochemical properties of different-aged coal mine spoils and unpolluted forest soil. These findings suggest that soil bacterial communities could be used as bioindicators to monitor the condition of coal mining sites, which further helps in designing an appropriate strategy to restore those areas.