Integrating pharmacologically important flora into phytoremediation: The role of bacillus strains in mitigating chromium toxicity and enhancing rhizostabilization

Abstract

Plant Growth Promoting Rhizobacteria (PGPR) offer a cost-effective, eco-friendly solution for Cr(VI) bioremediation. This study evaluates the medicinal plants Justicia adhatoda and Solanum trilobatum as novel candidates for Cr(VI) bioremediation. We investigated the ameliorative effects of two PGPR, Bacillus altitudinis M1 (BaM1) and Bacillus flexus M2 (BfM2), isolated from tannery effluent contaminated soil. Both strains significantly improved plants’ biomass in soil containing 300 mg/kg Cr(VI). Inoculation of the PGPR markedly mitigated physiological stress, significantly lowering concentrations of proline, hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) compared to Cr(VI)-only treatments by enhancing the plants phytostabilization potential.While Cr(VI) stress initially triggered a robust antioxidant response, PGPR application attenuated the oxidative pressure, where superoxide dismutase (SOD) and catalase (CAT) activities decreased by up to 66.74% in S. trilobatum and 56.97% in J. adhatoda, respectively. PGPR application significantly reduced Cr(VI) translocation to aerial tissues of both medicinal species, shifting the plants’ strategy toward superior rhizostabilization. This minimizes metal mobility and supports the long-term bioremediation capacity of the medicinal plant–microbe consortium. Our findings establish this approach as a highly efficient, sustainable, and novel strategy for the restoration of Cr(VI) contaminated industrial environments.