Biodegradation of Reactive Red 198 by textile effluent adapted microbial strains

A sustainable technology to eliminate the persistent reactive dyes from the textile effluents discharged indiscriminately in the environment is highly desirous given the explosive growth of textile industries. The present study investigated the potential of two different bacterial strains, Bacillus cereus SKB12 and Enterobacter hormaechei SKB16 isolated from the dye house effluent sludge in the biotransformation of Reactive Red 198 (RR 198). Process variables such as temperature, pH, shaking conditions and contact time were optimized for the successful decolourization of RR 198. Maximum decolourization of 80% and 85% of RR 198 was achieved at pH 6 and 7, and 40 °C in microaerophilic conditions on treatment with B. cereus and E. hormaechei, respectively. High-Performance Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC-MS) analyses conducted further affirmed that the decolourization of RR 198 was rather due to biodegradation than biosorption through shift in wavenumbers, retention time variations and the appearance of lesser molecular weight peaks. Degradative pathway for RR 198 predicted based on the enzyme assay data and dye degraded metabolite peaks acquired through GC-MS analysis highlighted the significance of azoreductase and laccase in the degradation of RR 198 into smaller non-toxic compounds. In addition, toxicity assessment through zootoxicological and phytotoxicological experiments using brine shrimp and Vigna radiata validated the detoxified status of the metabolites thus proving the promising potentials of the bacterial strains in the remediation of azo dyes.