HM-018

The effective strategies for soil remediation in lead (Pb) and cadmium (Cd) co-contaminated areas are critical for environmental restoration. This study aimed to develop a microbial-plant remediation approach by combining a Pb–Cd mobilizing bacterium with the heavy metal-accumulating plant Brassica juncea , elucidating the underlying mechanisms of microbial-assisted phytoremediation. A Pb–Cd mobilizing bacterial strain, HM-18, was isolated from mine tailings and had been identified as Microbacterium foliorum . Soil microcosm experiments with four treatments were conducted to evaluate its remediation efficiency, including control (CK), only HM-18 inoculation (B), Pb/Cd contamination (HM), and combined HM-18 inoculation with Pb/Cd contamination (HM+B). We found that the HM+B treatment significantly reduced soil pH by 2.81%, while increasing soil enzyme activities, including catalase (12.16%), alkaline phosphatase (3.20%), and sucrase (21.46%). Also, inoculation with HM-18 alleviated heavy metal stress in B. juncea significantly by enhancing biomass, photosynthetic efficiency, and antioxidant enzyme activities, thereby mitigating oxidative damage. Furthermore, the expression of key metal transporter genes was increased with HM-18 inoculation, while HMA3 was decreased, which promotes the translocation of Pb and Cd from roots to shoots. The accumulation of Pb and Cd in shoots increased by 72.38% and 27.61%, respectively, with root accumulation rising by 76.46% (Pb) and 56.14% (Cd). This work confirmed that this synergistic system enhanced heavy metal removal through multiple pathways, including increased metal bioavailability, improved root morphology, enhanced photosynthetic capacity, strengthened stress resistance, and regulated transporter activity. These findings offer valuable microbial resources and a theoretical basis for the development of sustainable soil bioremediation strategies.

This work advances the development of sustainable solutions for remediating soils contaminated with harmful heavy metals like lead (Pb) and cadmium (Cd), which pose significant risks to environmental and human health. By developing a microbial-plant remediation strategy that leverages the synergistic effects of a mobilizing bacterium and a metal-accumulating plant, this research improves our ability to effectively detoxify contaminated soils. The insights gained into the underlying mechanisms provide a valuable foundation for designing efficient, environmentally friendly bioremediation strategies. Generally, this investigation contributes to safeguarding ecosystems, promoting soil restoration, and supporting sustainable land use in areas affected by heavy metal pollution.