Enhanced decolorization of sulfonated azo dye methyl orange by single and mixed bacterial strains AK1, AK2 and VKY1

Methyl orange, a sulfonated azo dye having various industrial applications was decolorized by three bacteria Bacillus sp. strain AK1, Lysinibacillus sp. strain AK2 and Kerstersia sp. strain VKY1. The effect of various factors such as dye concentration, pH, temperature and NaCl concentration on decolorization was investigated. At 200 mg/L methyl orange concentration, the strains AK1, AK2 and VKY1 exhibited maximum decolorizing potential of 93, 95 and 96%, respectively, at temperature 35 °C and pH 7.0 within 18 h of incubation. These strains decolorized the dye over a wide range of pH (5–10), temperature (15–55 °C), and NaCl concentration (5–20 g/L). Further, these strains decolorize up to 800 mg/L concentrations of methyl orange within 24 h. The dye decolorization efficiency was further increased by using different consortia of these three strains which could decolorize the dye completely within 12 h of incubation. The cell-free extracts of the strains AK1, AK2 and VKY1 grown on methyl orange exhibited the azoreductase activity of 0.4794, 1.56 and 1.01 µM/min/mg protein, respectively. HPLC and FTIR analysis of the dye decolorized sample indicated the formation of 4-aminobenzenesulfonic acid and N,N-dimethyl-p-phenylenediamine as breakdown products of azo bond. The high decolorization potential of these bacterial strains individually and in consortia has potential application in remediation of dye effluent.