Decolourisation of toxic azo dye Fast Red E by three bacterial strains: process optimisation and toxicity assessment

Removal of toxic azo dyes from the industrial effluents has been posing a big challenge since many years. Degradation of azo dyes by bacteria is emerging as an eco-friendly method for the treatment of effluents from dyeing industries. This study presents the decolourisation of azo dye, Fast Red E, by three bacterial strains Bacillus sp. strain AK1, Lysinibacillus sp. strain AK2 and Kerstersia sp. strain VKY1. The bacterial consortium of all the three strains decolourised 93% of the 200 mg/L dye within 18 h. The strains decolourised up to 800 mg/L of the dye. The decolourisation process was optimised under different pH (5–11), temperature (25–55°C) and salt (10–30 g/L) levels. The cell-free extracts of the strains AK1, AK2 and VKY1 grown on Fast Red E revealed the azoreductase activity of 4.0430, 3.0086 and 4.1919 µM/min/mg protein, respectively. The breakdown products of azo bond, 5-Amino-6-hydroxynaphthalene-2-sulphonic acid and 4-Aminonaphthalene-1-sulphonic acid were identified by UV-Vis and HPLC analysis. Phytotoxicity assessment indicated a significant fall in the toxicity of the decolourised medium. Hence, it could be concluded that these strains can be used effectively in the removal of azo dyes from the contaminated sites.