Mechanistic insights into the biodegradation of the cobalt-complex azo dye Acid Red 182 by a defined bacterial consortium

Introduction Metal-complex azo dyes are persistent pollutants that resist conventional treatment. Acid Red 182 (AR182), a 1:2 cobalt-complex monoazo dye, has primarily been treated using physicochemical methods. This study investigated its biological transformation by a defined bacterial consortium. Methods Consortium-G comprised Exiguobacterium mexicanum RA-19, Alcaligenes faecalis RA-26, and Bacillus licheniformis RA-39. Decolorization conditions were evaluated using one-variable-at-a-time screening, a Plackett–Burman design, and a central composite design. Cobalt removal, oxidoreductase activities, and changes in dye structure and metabolite profiles were examined using spectroscopic, chromatographic, and mass-spectrometric techniques. Results Fructose and yeast extract were selected as the principal nutrient supplements. Under the reported optimized conditions, Consortium-G achieved 98.0% ± 0.75% decolorization of 500 mg L − ¹ AR182 within 48 h, compared with 45.46% under unoptimized conditions at 72 h. Cobalt removal exceeded 90%, and the consortium remained viable at dye concentrations up to 7,000 mg L − ¹. Azoreductase activity reached 63.86 U L − ¹ at 48 h. Changes in oxidoreductase activities and analytical profiles were consistent with reductive and oxidative dye transformation. Tentative metabolite annotations informed a proposed degradation pathway. Discussion Consortium-G shows potential for the simultaneous decolorization of AR182 and removal of cobalt from synthetic dye solutions. Metabolite annotations remain tentative, and the proposed pathway requires further validation. Complete mineralization, cobalt speciation, and detoxification were not established; validation using real textile effluents is required.