Biologically safe restoration of heavy metal-contaminated soils through plant-microbe synergy

Abandoned mines have created extensive idle areas contaminated with heavy metals (HMs). Conventional remediation methods are often costly, environmentally disruptive, and pose risks to human health. As a sustainable alternative, a biological approach utilizing metal-tolerant plant growth-promoting bacteria (mPGPBs) was employed to remediate HM-contaminated soils and assess their biological safety. Five mPGPB strains-Pseudarthrobacter sp., Pseudomonas sp., and Agrobacterium sp.-were isolated from contaminated mine soils and screened for metal tolerance and plant growth-promoting capabilities. Inoculation of Solanum nigrum L. with Agrobacterium sp. NIBRBAC000502774 proved most effective for phytoremediation, significantly increasing total dry biomass by 139% (from 0.158 ± 0.039 g to 0.378 ± 0.059 g/plant) and showing the highest HM bioconcentration (1.4- to 13.2-fold) compared to uninoculated controls. In subsequent in vivo biosafety assays, soil remediated with Pseudarthrobacter sp. NIBRBAC000502770 was the most effective at attenuating HM-induced hepatotoxicity in mice, as evidenced by normalized liver enzyme levels and reduced apoptosis. Furthermore, mPGPB treatment shifted from HM-tolerant taxa toward a dominance of Proteobacteria and Actinobacteria, and functional predictions indicated enhanced biosynthesis of secondary metabolites. Our findings suggest that specific mPGPBs offer a promising biological approach for restoring idle areas by enhancing the growth and HM uptake of hyperaccumulator plants, thereby reducing environmental HM toxicity and associated health risk. This method also demonstrates biological safety, making it a valuable alternative to conventional remediation techniques for environmental restoration, with the potential to reduce the incidence of diseases associated with HM exposure.