Distinction between Cr and other heavy–metal–resistant bacteria involved in C/N cycling in contaminated soils of copper producing sites

Highlights: • The 90 % of Cu producing sites throughout China were heavily polluted by multimetals. • Catalase/urease were significantly (+) correlated with $C_f^i$/ $E_{\text{r}}^i$ for multimetals except Cr. • There were significantly positive correlation between EPS–WAEP/GRSP and $C_f^i$/ $E_{\text{r}}^i$ for Cr. • Cr was (+) correlated with EPS–producing bacteria which were involved in C/N cycles. • Other metals were (+) correlated with ureolytic bacteria induced $C{O}_3^{2-}$ precipitation. For typical copper producing provinces of Heilongjiang, Henan, Inner Mongolia, Jiangxi, Shandong, Tibet, and Yunnan in China, 90 % of sampling sites were heavily polluted with multiple heavy metals. Soil heterogeneity and mutual interference of multimetals are obstacles to explore bacterial resistance pathways in contaminated field soils. Through analyses of contamination indices and bioindicators, combined with multivariate statistical models, the antioxidant enzyme activity, urease–induced precipitation of heavy metals, excretion of extracellular polymeric substances (EPS) were attributed to different types of heavy metals. Furthermore, through redundancy analysis combined with phylogenetic analysis of metal–resistant bacteria, we identified that Verrucomicrobia, Acidobacteria, and Planctomycetes secreted EPS–polysaccharides and EPS–proteins to detoxify Cr, a metal with lower concentrations and lower ecological risk as compared to other metals. The pathway was innovatively differentiated from the multimetal resistance pathways in urease and/or catalase–producing bacteria such as Proteobacteria, Firmicutes, BRC1, Bacteroidetes, Dadabacteria, Entotheonellaeota, Nitrospirae, and Gemmatimonadetes using field studies and high–throughput sequencing. Moreover, these metal–resistant bacteria were linked to C/N cycling processes of urea hydrolysis, nitrification, denitrification, EPS production, and calcite precipitation. It will provide new insight into soil bacterial resistance to multimetals in field studies.