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

• The indigenous Aeromonas sp. DH-6 showed an excellent methyl orange (MO) decolorizing ability.
• The strain still decolorizes MO efficiently at a wide temperature and dye concentration range.
• A possible pathway of MO degradation by the strain DH-6 was proposed.

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 Mg2+, Mn2+, and 1.5 mM of Ca2+ 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.