Characterization and optimization of azo dyes degrading microbes isolated from textile effluent

Azo dyes are highly recalcitrant, persistent, and toxic compounds, extensively used in the textile industry. The untreated discharge of dye effluents from the textile industry poses severe environmental and health risks. This research aimed to isolate and identify bacterial strains from textile wastewater that can decolorize azo dyes. After the subsequent screening of 89 isolates, 4 novel strains were identified utilizing the 16S rRNA gene sequencing technique that could effectively decolorize and degrade azo dyes, methyl red, direct yellow 12, and acid black 210. A thorough assessment of physicochemical parameters was conducted to optimize for maximum decolorization for all four strains. At pH 7, 37° C, and 50 mg/L dye concentration, the maximum decolorization for methyl red, direct yellow 12, and acid black 210 was 79.09% > 72.20% > 64.76%; 84.45% > 62.59% > 54.29%; 83.12% > 70.22% > 61.42%; and 92.71% > 83.02% > 69.84%, for isolate 1, isolate 2, isolate 3, and isolate 4, respectively. The novel strains belonged to the Sphingomonas, Pseudomonas, Shewanella, and Priestia species. The unique sequences of these bacterial strains have been submitted to the GenBank database under the accession numbers "OQ202071", "PP708911", "PP708909", and "PP086977," respectively. Further, an enzyme study and statistical optimization of Priestia flexa species was performed. A Central Composite Design and Response Surface Methodology has been applied for synergistic effects of process parameters namely pH (5-9), initial dye concentration (100-250 mg/L), and temperature (25°-45° C) on the decolorization of the model dyes. The regression analysis indicated a strong correlation between the experimental data and the second-order polynomial supported by a high coefficient of determination (R²). For all three dyes analyzed, the difference between the experimental and predicted values was found to be less than 10%. Fourier Transform Infrared spectroscopy was further employed to analyze and confirm the degradation of the three dyes.