Bioremediation of Brilliant Red Azo Dye Toxicity in Vigna radiata Using Encapsulated Bacillus subtilis SC9

The discharge of azo dye-containing wastewater threatens soil microbial activity, plant growth, and ecosystem health because of the persistence and toxicity of synthetic dyes. However, the potential of immobilized siderophore-producing bacteria for simultaneous dye decolorization and mitigation of dye-associated phytotoxicity remains unexplored. This study highlights the decolorization and bioremediation potential of viable free cells and calcium-alginate immobilized Bacillus subtilis SC 9 against brilliant red (BR) dye. Among ten previously identified siderophore producing bacteria (SPB), B. subtilis SC 9 exhibited the highest decolorization efficiency (88.5%). Under optimized conditions, free and immobilized cells achieved 88.5% and 94.86% decolorization, respectively, within 9 days. FTIR and GC-MS analyses confirmed structural transformation of BR dye into simpler degradation intermediates, indicating biodegradation rather than adsorption. Greenhouse studies demonstrated that immobilized B. subtilis SC9 alleviated BR dye phytotoxicity by increasing root length (142.16%), shoot length (160.91%), soil dehydrogenase activity (192.37 µg TPF g^{- 1} soil), FDA hydrolysis (33.71 µg fluorescein g^{- 1} soil), alkaline phosphatase activity (852.20 µg pNP g^{- 1} soil), and siderophore production (331.53%) compared with untreated dye stress. Overall, calcium-alginate immobilized B. subtilis SC 9 is a promising eco-friendly bioinoculant for azo dye bioremediation. Future studies should validate its performance under pilot-scale and field conditions.