A novel BC-HMRPGPB-plant system for remediation of low concentration Cd in soil: The process of metal migration and microbial community evolution

HMs are bioaccumulative and non-biodegradable toxicants and can generate serious health risks to living organisms. The threat of low concentrations of HMs in soils is often overlooked. The BC-HMRPGPB-Plant association can provide a feasible green approach for remediation of HM-contaminated sites with low concentrations. In this study, strain AP-3 showed a high tolerance to several metals and exhibited the excellent biosorption for Cd. Then, the strain AP-3 was successfully immobilized on BC by physical adsorption method and functional groups (hydroxyl and carbonyl groups) between BC and AP-3 surface. We discover that encapsulation of BCS with sodium alginate helped microorganisms to resist interference from external HMs. SABCS can effectively improve soil properties, which further facilitated the plant growth and accumulation of HMs in plant roots. The treatment of SABCS reduced the accumulation of metals in edible tissues by 25% compared to the control, which greatly reduced the risk of consumption. The migration of HMs by the BC-HMRPGPB-Plant system was bottom-up process. The activities of S-CAT, S-DHA, S-UE and S-PPO were significantly increased after the bioremediation, which further promoted the biosorption of HMs by plants. Furthermore, BC-HMRPGPB-Plant system alleviated the toxicity of HMs to rhizobacteria and facilitated the accumulation of HMs in the roots. Ultimately, the strain was successfully colonized in the rhizosphere and soil microbial community was not significantly altered after bioremediation. Our study provided that a feasible pathway for the BC-HMRPGPB-Plant system to remediate HM-contaminated sites.