Using Bacillus sp. TR2 to form nano-BioMnOx to improve 4-chlorophenol rhizoremediation

Aquatic plants and their rhizosphere microorganisms play crucial roles in the remediation of polluted water bodies. However, refractory and toxic organic contaminants often suppress plant and microbial activity, thereby limiting remediation efficiency. The introduction of Mn(II)-oxidizing bacteria (MnOB) enables the in situ formation of nano-biogenic manganese oxides (nano-BioMnOx), which detoxify pollutants and enhance bioactivity. Nevertheless, the feasibility, underlying mechanisms, and synergistic interactions of nano-BioMnOx with plants and microbes remain unclear. In this study, the MnOB Bacillus sp. TR2 successfully colonized the roots of Iris pseudacorus, forming a stable Mn plaque enriched in Mn(III/IV) by 39.10%. The generated nano-BioMnOx catalyzed the oxidative meta-ring cleavage of 4-chlorophenol (4-CP), yielding non-toxic intermediates that facilitated microbial enzymatic degradation. Consequently, 58.49% of 4-CP was removed within 60 h, representing a 1.36-fold increase over the plant-only control and a 97.17% reduction in biotoxicity. Nano-BioMnOx significantly enhanced rhizosphere functionality, as evidenced by a 15.30-fold enrichment of MnOB and a strong correlation (R² = 0.95) between Mn oxidation genes and 4-CP degradation pathways. Moreover, improved rhizosphere conditions promoted plant growth, with leaf length, root length, and chlorophyll content increasing by 16.11%, 36.52%, and 74.67%, respectively. These findings indicate that nano-BioMnOx accelerates pollutant oxidation, stimulates microbial metabolism, and promotes plant growth. These combined processes establish a self-sustaining MnOB-plant system for efficient remediation of polluted aquatic environments.