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

Understanding the effect of heavy metals on the microbial function and community composition is crucial for environmental restoration. In this paper, three representative sets of samples with Low (L), medium (M) and high (H) levels of combined heavy metals contamination around a gold mining area were selected to assess the effects of heavy metal pollution levels on the soil microbial function and community composition by means of Illumina high-throughput sequencing of 16S rRNA gene amplicon. The results showed that soil microbial community diversity varied little under different concentrations of combine heavy metal, while clear discrepancies exhibited in microbial community richness and composition. The Canonical correlation analysis (CCA) results revealed that TOC, pH, Zn, Cu, Cd, Pb, and Cr were the most important factors in sharping the microbial community structure. At genus level, some bacterial taxa such as Paracoccus , Marinobacter , Halomonas , Streptococcus , Lactobacillus and Pseudomonas with heavy metal tolerance were worth noting. The results of co-occurrence network analysis revealed that Proteobacteria, Bacteroidetes and Firmicutes were the top three keystone taxa in soils with high concentrations of combined heavy metal. In addition, the results of function predictions showed that microbial community functions related biosynthesis of extracellular polymeric substance (EPS), membrane transport, DNA replication, damage repair and recombination significantly enhanced in soil with high concentrations of combined heavy metal were significantly enhanced to resist heavy metal stress. These results provided new insights into the mechanisms of microbial adaptation and remediation in heavy metal contaminated soil environment.