Bioremediation of Reactive Red 111 by mangrove-derived microbial consortium

The textile dyeing industry generates hypersaline, alkaline effluents enriched with recalcitrant azo dyes, posing a major challenge to conventional treatment systems. In this study, a haloalkaliphilic microbial consortium isolated from the Bhadeli mangrove ecosystem was evaluated for its ability to decolorize Reactive Red 111 under conditions mimicking industrial wastewater. The consortium exhibited significant decolorization of 96.58% within 8 h under static conditions and maintained >95% efficiency across dye concentrations ranging from 100 to 1000 mg/L under pH 7.5–8 and NaCl 10 g/L. Under haloalkaliphilic conditions, optimal activity was observed at pH 9–10, 5% NaCl, and 300 mg/L dye, with removal rates exceeding 10 mg/L/h, while significant tolerance was retained even at extreme salinity (100 g/L NaCl) and alkalinity (pH 11). Nutritional optimization revealed that BH medium supplemented with 0.2% peptone + 0.2% Bengal gram flour enhanced degradation kinetics, achieving 95.77 ± 0.81% decolorization in 24 h. 16S rRNA amplicon sequencing identified a community dominated by Vibrio spp. (60.71%), Vibrio azureus (8.18%) and Alkaliphilus oremlandii (13.45%), highlighting the role of Gammaproteobacteria and Firmicutes in driving degradation under haloalkaliphilic conditions. Mechanistic insights from LC–MS and FTIR analyses revealed a stepwise pathway for the degradation of Reactive Red 111. This process involves azo bond cleavage, partial deconjugation, desulfonation, decarboxylation, dehydration, and terminal deamination, leading to the degradation of Reactive Red 111 via enzymes, as identified through shotgun metagenomic analysis. Phytotoxicity analysis indicated significant removal of toxicity after the treatment process. Collectively, these findings prove the consortium is a highly effective, eco-friendly option for treating saline-alkaline textile wastewater.