Optimization of complete RB-5 azo dye decolorization using novel cold-adapted and mesophilic bacterial consortia

Azo dyes are an important group of recalcitrant xenobiotics, which are difficult to degrade and deteriorate in cold environments. In this study, two microbial consortia consisting of cold-adapted and mesophilic bacteria were developed for effective decolorization of Reactive Black-5 azo dye. These bacteria were isolated from textile wastewater and soil of a cold region. Identification of bacterial isolates using 16s rRNA gene analysis revealed that they belong to genus Pseudoarthrobacter, Gordonia, Stenotrophomonas, and Sphingomonas. Decolorization assay was performed for every strain at dye concentrations of 25, 50 and 100 mg/L and the consortia PsGo consisting of mesophilic bacteria and StSp consisting of cold-adapted bacteria were constructed accordingly. Results showed that the consortia PsGo and StSp were able to decolorize 54 and 34 percent of RB-5 (50 mg/L) during 7 days. To improve the dye removal efficiency of the consortia, several parameters including temperature, pH, carbon and nitrogen sources were optimized. Over longer periods, StSp consortium managed to completely decolorize RB-5 (50 mg/L) at optimized conditions of 25-30 °C, pH 9, and using glucose and NH₄H₂PO₄ as carbon and nitrogen source respectively, whereas PsGo consortium decolorized RB-5 (50 mg/mL) completely at 37 °C, pH 11, and with lactose and NH₄H₂PO₄ used as carbon and nitrogen sources. Kinetic of reactions for StSp and PsGo consortia were found to be 0.05 and 0.13 day^-1 respectively, but became 0.71 and 0.9 day^-1 after optimization. In general, cold ecosystems are good sources for the isolation of novel bacterial strains with a potential application, especially when used as consortia, in environmental biotechnology such as decolorization of RB-5.