Dual dye degradation of methylene blue and orange II by a wetland-derived Acinetobacter species: RSM optimization, GC–MS pathway elucidation, and phytotoxicity assessment

Abstract

Synthetic dyes such as Methylene Blue (MB) and Orange II (O-II) cause serious environmental and phytotoxic risks due to their chemical stability and presence in aquatic systems. Although microbial dye degradation has been widely studied, most reports focus on single dyes and lack comprehensive validation of detoxification, particularly using wetland-derived bacterial strains. In this study, Acinetobacter sp. SC2 was isolated from the Surinsar wetland (Jammu and Kashmir) and evaluated for its ability to independently degrade two structurally different dyes under optimized conditions. Using response surface methodology (RSM), optimal conditions (pH 7.5–10, 40–45 °C, 24 h) resulted in 90.99% degradation of MB and 95.96% degradation of O-II. Fourier transform infrared spectroscopy (FTIR) analysis confirmed dye degradation through the disappearance and shifting of characteristic azo and thiazine functional group peaks, while gas chromatography- mass spectrophotometry (GC–MS) analysis revealed the formation of low-molecular-weight, less toxic metabolites, indicating structural breakdown of the parent dyes. Phytotoxicity studies using Vigna radiata demonstrated severe toxicity of untreated dyes, with significant reductions in seed germination and root growth. In contrast, bacterially degraded dye products showed near-normal germination and growth, confirming effective detoxification. This study provides an integrated evaluation of a wetland derived Acinetobacter sp. SC2 for dual-dye degradation by combining RSM optimization, metabolite analysis, and phytotoxicity assessment. Future studies should focus on enzyme level characterization, mixed-dye systems, and scale-up applications for wastewater treatment.