Decolorization,degradation and detoxification of carcinogenic sulfonated azo dye methyl orange by newly developed biofilm consortia

Metabolites of azo dyes are often carcinogenic, teratogenic, mutagenic and recalcitrant in nature. In this study, four biofilm consortia such as C1 (Vitreoscilla sp. ENSG301, Acinetobacter lwoffii ENSG302, Klebsiella pneumoniae ENSG303 and Pseudomonas fluorescens ENSG304), C2 (Escherichia coli ENSD101, Enterobacter asburiae ENSD102 and E. ludwigii ENSH201), C3 (E. asburiae ENSD102, Vitreoscilla sp. ENSG301 and Bacillus thuringiensis ENSW401), and C4 (E. coli ENSD101, E. ludwigii ENSH201 and B. thuringiensis ENSW401) were applied to degrade and detoxify methyl orange (MO), a carcinogenic, sulfonated mono azo dye, used in textile dyeing industry worldwide. The consortia of C1, C2, C3 and C4 showed 97.30, 98.75, 99.51 and 99.29% decolorization, respectively in yeast extract peptone (YEP) broth containing 200 mg L⁻¹ MO within 60 h of incubation in static condition. The optimum pH and temperature for decolorization was 7.0 and 28 °C, respectively. Some divalent metal ions including Mg²⁺, Ca²⁺, Zn²⁺ and Mn²⁺ could stimulate MO decolorization. UV–Vis spectral analysis showed that the absorption peak at 465 nm originated from the azo (N N) bond was completely disappeared within 60 h of incubation. Fourier transform infrared spectroscopy (FTIR) results also revealed that several major peaks including azo bond peak at 1602.6 cm⁻¹ are completely or partly vanished, deformed or shifted. Activities of azoreductase, NADH-DCIP reductase and laccase were significantly increased in the bacterial cells within 60 h of incubation in comparison to that of control (0 h). The chemical oxygen demand was incredibly reduced by 85.37 to 91.44% by these consortia. Accordingly, plant (wheat seed germination) and microbial (growth of the plant probiotic bacteria such as Pseudomonas cedrina ESR12 and Bacillus cereus ESD3 on biodegraded products) toxicity studies showed that biodegraded products of MO are non-toxic. Thus, all these consortia can be utilized in bioremediation of MO from wastewater for safe disposal into environment. To our knowledge, this is the first report on degradation and detoxification of MO from wastewater by bacterial biofilm consortia.