Efficient metabolism of the azo dye methyl orange by Aeromonas sp. strain DH-6: Characteristics and partial mechanism

We investigated biodegradation of the azo dye methyl orange (MO) by Aeromonas sp. DH-6. Nearly 100% decolorization of MO (100 mg l −1 ) by the strain was observed at pH 3.0–7.0 and a broad temperature range (5–45 °C) after incubation for 12 h. Most of the tested carbon and nitrogen sources could significantly enhance MO decolorization, but of the metal ions , only Mg 2+ , Mn 2+ , and 1.5 mM of Ca 2+ could increase the decolorization. The strain still showed a high capacity for decolorizing MO even at a concentration of up to 1000 mg l −1 . Based on the gas chromatography-mass spectrometry analysis (GC-MS) and high performance liquid chromatography analysis (HPLC) data, N,N-dimethyl- p -phenylenediamine and 4-aminobenzenesulfonic acid were identified as the main intermediates of MO biodegradation, and a possible degradation pathway was proposed. Moreover, results of enzyme analysis indicated that laccase, NADH-DCIP reductase, and azo reductase were responsible for the degradation. Overall, high biodegradation efficiency at a broad range of temperatures and dye concentrations suggested that strain DH-6 would have high potential in the bioremediation of azo dyes.