Detoxification pathways of multiple metals from intensive copper production by indigenous ureolytic microbes coupled with soil nitrogen transformation

Abstract

The ubiquitous ureolytic microbes were potential to clean up toxic heavy metals from environment. Their responses and detoxification mechanisms are largely unknown for multiple metals in field soils. In this study, high-throughput sequencing of the urease-encoding genes and deep learning from bioinformatic analysis were conducted for identifying ureolytic prokaryote-related processes throughout China. The passive adsorption of heavy metals onto cell walls or cell surfaces was mainly performed by G+ ureolytic bacteria in soils located in the large-scale smelting areas with slightly high Hg and low Cu/Zn/Ni contents. For the large-scale smelting areas with the highest Cr and lowest Cu/As contents, the Cr(VI) was reduced to Cr(III) by G– ureolytic bacteria and then accumulated in their periplasmic spaces or cell surfaces. The G– ureolytic bacteria detoxified high contents of multiple metals by intracellular antioxidant defense mechanisms and extracellular urease-induced (co)precipitation in the medium-scale smelting areas, consistent with high urease activities and ureolytic microbial diversity. In addition, this large-scale field work verified that toxic metals stimulated the bacterial hydrolysis of urea as soil nitrogen fertilizers and depressed the bacterial fixation of nitrogen from air. Simultaneously, the heavy metals used nitrate-N and nitrite-N as alternative electron acceptors, driving the soil denitrification processes.