International Journal of Plant & Soil Science

Industrial soil contamination by chromium (Cr) is an important environmental and public health concern because hexavalent chromium [Cr(VI)] is toxic, mobile, and carcinogenic. This study investigated the mechanisms involved in reducing toxic Cr(VI) to the less toxic Cr(III) form using an indigenous bacterial consortium isolated from chromium-contaminated industrial soils in Raipur, Chhattisgarh, India. Surface-soil samples from the Urla Industrial Area, Siltara Growth Centre, and Birgaon Industrial Estate contained 567.4 ± 26.35, 893.6 ± 31.72, and 347.2 ± 18.40 mg kg⁻¹ total chromium, respectively. Of 124 bacterial isolates, 18 exhibited Cr(VI)-reducing ability. Under optimised conditions (pH 7.0, 32 °C, and 2% glucose), a consortium comprising Bacillus cereus RC-7, Pseudomonas putida RC-11, and Lysinibacillus sphaericus RC-14 achieved 97.4 ± 1.2% reduction of 100 mg L⁻¹ Cr(VI) within 96 h. Enzyme assays showed increased chromate reductase activity and associated electron-transfer responses during Cr(VI) reduction. Biosorption data fitted the Langmuir (R² = 0.981) and Freundlich (R² = 0.954) models, indicating effective surface interactions. SEM-EDX and FTIR analyses indicated Cr(III) precipitation and chromium binding on bacterial cell surfaces, whereas RT-qPCR showed upregulation of the chrR and nfsA genes under chromium stress. These findings clarify the biochemical, molecular, and surface-interaction mechanisms associated with Cr(VI) detoxification and support further evaluation of the consortium for chromium-contaminated soils and wastewater.