Synergistic Consortia with Bacillus megaterium A14 Enhance Cadmium Immobilization in the Arachis hypogaea Rhizosphere

The microbial immobilization of cadmium bioavailability in peanut-growing soils is crucial for food safety. This study investigated the effects of exogenously applied Bacillus megaterium A14 on the indigenous rhizosphere microbiome of peanut plants and its role in modulating cadmium uptake and bioavailability. Shake-flask experiments revealed that co-culture of A14 with two native rhizosphere strains, Microbacterium S3 and Paenibacillus S22, synergistically enhanced cadmium immobilization. Non-invasive micro-test technology (NMT) further demonstrated that A14 promoted the Cd²⁺ uptake capacity of S22 in co-inoculation. Pot experiments showed that inoculation with the three-strain consortium SD6 (A14, S3, and S22) reduced cadmium (Cd) content in peanut stems and roots by 51.34% and 29.14%, respectively. Additionally, the consortium altered Cd speciation in rhizosphere soil, decreasing the exchangeable fraction from 41% to 23% while increasing the residual fraction from 10% to 30%. B. megaterium A14 attracted cooperative strains S3 and S22 via metabolic secretions, and their close biofilm-based association facilitated metabolite exchange and functional synergy. The consortium immobilized Cd²⁺ through intracellular uptake and extracellular adsorption, thereby reducing soil Cd bioavailability and alleviating Cd-induced oxidative stress in plants. This study proposes an ecological strategy using synergistic microbial consortia to mitigate cadmium bioavailability and uptake in crops, providing new insights into rhizosphere microbial interactions and a theoretical basis for developing composite microbial inoculants in sustainable agriculture.