Biological Decolorization of Sulfonated Azo Dye C.I. Acid Blue 193 by Bacillus cereus KTSMD-03 and Its Azoreductase Characterization

Abstract

Wastewater effluents from textile and other dyestuff industries contain significant amounts of synthetic dyes, which adversely affect water resources, soil fertility, aquatic organisms, and ecosystem integrity. Thus, prior treatment is required to prevent groundwater contamination. Among the multitudinal dyes, azo dyes are the predominant class of colorants that are characterized by one or more azo bonds, used in tattooing, cosmetics, foods, and consumer products. In this study, bacteria were subjected to acclimatization with C.I. Acid Blue 193 (AB 193) in minimal basal medium. The most promising bacterial isolate was used for further dye degradation studies. The 16S rRNA gene sequencing and biochemical characteristics revealed the isolated organism as Bacillus cereus KTSMD-03. Optimization of parameters for dye decolorization was studied under static anoxic condition. The optimum pH and temperature for the decolorization was 7.0 and 35 °C, respectively, at static conditions. Additional carbon and nitrogen sources namely, glucose, sucrose, starch, peptone, and yeast extract were added in different combinations to enhance the percentage of decolorization. Of these, peptone with glucose and sucrose showed the maximum decolorization of 91.07 %. In bacteria, the dyes are mainly metabolized by azoreductase that catalyzes an NADH-dependent reduction. Hence in this investigation, kinetic study was carried out for purified enzymes from B. cereus KTSMD-03. Biodegradation of dye was monitored by UV–VIS spectrophotometer and HPLC. Facile conditions and high decolorization potential of the bacterial strain showed it to be as an effective tool for biological treatment of dyeing effluents.