Decolorization and degradation of azo dye – Reactive Violet 5R by an acclimatized indigenous bacterial mixed cultures-SB4 isolated from anthropogenic dye contaminated soil

► Mixed cultures SB4 decolorized and degraded 1500ppm of RV5 under static condition. ► It decolorized wide array of azo dyes in presence of high salt concentration. ► Mixed cultures consisted of six bacterial strains. ► Four intermediatory compounds were identified during RV5 degradation by NMR and GC–MS. Azo dyes an important group of synthetic compounds are recalcitrant xenobiotics. Conventional technologies are unsuccessful to efficiently remove these compounds from contaminated environment. However, consorted metabolic functioning of innate microbial communities is a promising approach for bioremediation of polluted environment. Bacterial mixed cultures SB4 proficient in complete decolorization of azo dye – Reactive Violet 5R was developed through culture enrichment technique. Bacterial community composition based on 16S rRNA gene analysis revealed that mixed cultures SB4 composed of six bacterial strains namely Bacillus sp. V1DMK, Lysinibacillus sp. V3DMK, Bacillus sp. V5DMK, Bacillus sp. V7DMK, Ochrobacterium sp. V10DMK, Bacillus sp. V12DMK. SB4 grew well in minimal medium containing low amount of glucose and yeast extract (YE) (1g/L) and decolorized 200mg/L of RV5 within 18h under static condition. Mixed cultures SB4 decolorized wide range of azo dyes and maximum rate of decolorization was observed at 37°C and pH 7.0. Decolorization efficiency was found to be unaltered under high RV5 and salt concentration where 1500mg/L of RV5 was decolorized in presence of 20g/L NaCl. We propose the asymmetric cleavage of RV5 and Fourier transformed infrared (FTIR), NMR and gas chromatography–mass spectrometry (GC–MS) confirmed the formation of four intermediatory compounds 1-diazo-2-naphthol, 4-hydroxybenzenesulphonic acid, 2-naphthol and benzenesulphonic acid.