Response of soil microbial community composition and function to prolonged heavy metal exposure

Understanding the effects of heavy metals on microbial community composition and function is crucial for environmental restoration. In this paper, soil samples with low, medium, and high levels of potential ecological risk (RI) associated with heavy metals were collected from a gold mining area in northern Laizhou, Shandong Province, Eastern China. The impact of heavy metals on soil microbial communities was assessed through Illumina high-throughput sequencing of 16S rRNA gene amplicons. The results demonstrated that while microbial community evenness remained relatively stable across varying RI levels, significant differences were observed in microbial community richness and composition. Canonical correlation analysis (CCA) revealed that nutrients were the primary factors shaping microbial communities under low RI levels, whereas pH and heavy metals played dominant roles under high RI levels. At the genus level, several taxa, including Acinetobacter, Paracoccus, Marinobacter, Halomonas, Streptococcus, Lactobacillus, Sulfobacillus, Sulfurifustis, Bacillus, and Pseudomonas, were identified as particularly tolerant to heavy metal stress. Co-occurrence network analysis showed that microbial networks were more complex and stable under low contamination, while increased cooperative interactions were observed under high contamination. At the phylum level, Proteobacteria, Firmicutes, and Bacteroidetes emerged as the key taxa in high RI soils. Functional predictions indicated that microbial processes related to replication and repair, extracellular polymeric substance (EPS) biosynthesis, membrane transport, and heavy metal resistance were significantly enhanced in high-risk environments. Keystone taxa employed various survival strategies, including extracellular polymerization, nutrient uptake, intracellular sequestration, active efflux systems, and collaboration with plants, to resist heavy metal stress. These findings provide new insights into the mechanisms of microbial adaptation and remediation in heavy metal-contaminated soils.