Aims: To evaluate the potential of Brevibacillus laterosporus MTCC 2298 for the decolourization of different textile azo dyes including methyl red, mechanism of biotransformation and the toxicity of products.
Methods and Results: Brevibacillus laterosporus showed decolourization of thirteen different azo dyes including methyl red. Decolourization of methyl red was faster (93% within 12 h) under static condition at the concentration 0·2 g l−1. Induction in the activities of lignin peroxidase, laccase, aminopyrine N‐demethylase, NADH‐DCIP reductase and malachite green reductase was observed in the cells obtained after decolourization. Fourier transform infra‐red spectral analysis of products indicated conversion of methyl red into secondary aryl amines and nitrosamines, which further transformed into the aromatic nitro compounds. Gas chromatography–mass spectroscopy analysis suggested conversion of methyl red into high molecular weight complex derivatives. The heterocyclic substituted aryl amine (m/z 281), p‐(N,N di formyl)‐substituted para‐di amino benzene derivative (m/z 355) and p‐di‐amino benzene derivative (m/z 282) are the mainly elected biotransformation products. Microbial and phytotoxicity studies suggested nontoxic nature of the biotransformation products.
Conclusions: Brevibacillus laterosporus has potential for the decolourization of different textile azo dyes.
Significance and Impact of the Study: Brevibacillus laterosporus decolourized different azo dyes including methyl red and can be utilized for textile dye decolourization.
Brevibacillus laterosporus MTCC 2298 was screened for the decolorization of eight triphenylmethane dyes. Decolorization of malachite green was found to be fastest (87% within 3 hours, at the concentration 0.1 g/L) among the screened dyes. Various triphenylmethane dyes showed differential induction patterns of the dye-degrading enzymes. The activities of the laccase, nicotinamide adenine dinucleotidedichlorophenolindophenol reductase (NADH-DCIP reductase), malachite green reductase, and aminopyrine N-demethylase were increased in the cell-free extract obtained after decolorization of malachite green. Fourier transform infrared spectral analysis indicated formation of N-demethylated products, including primary and secondary aryl amines. High-performance liquid chromatography analysis confirmed the transformation of malachite green into new metabolites rather than its reduced form, leucomalachite green. Gas chromatography-mass spectroscopy analysis detected new degradation products, such as reduced tetradesmethyl leucomalachite green (m/z 283) and [4-(1-cyclohexyl)-(1'-phenyl)-methyl]-2, 4-hexenoic acid (m/z 282). Complete decolorization of malachite green also was observed by the partially purified laccase from B. laterosporus. Water Environ. Res., 81, 2329Res., 81, (2009.
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