Decolorization and biodegradation of methyl red by acetobacter liquefaciens

Decolorization and biodegradation of the azo dye methyl red (2′‐carboxy‐4‐N,N‐dimethylamino‐azobenzene) in shaking and static cultures of the strict aerobe Acetobacter liquefaciens S‐1 were demonstrated by the disappearance of the brownish orange color of the methyl red containing medium (pH 7.5), by the decrease in absorption maximum of methyl red, and by the identification of two compounds 2‐aminobenzoic acid (anthranilic acid) and N,N′‐dimethyl‐p‐phenylene diamine (4‐N,N‐dimethylamino‐aniline) formed by reductive cleavage of methyl red in parallel with incubation time. Decolorization of methyl red was essentially completed within 17 h of incubation in both shaking and static cultures, which contained 1 g/L of (NH4)2SO4 as nitrogen source, 1% ethanol as carbon source, and up to 400 ppm of methyl red. Cells of A. liquefaciens S‐1 were able to metabolize methyl red as sole nitrogen source for growth, although the time required to achieve high decolorization efficiency (98%) of methyl red was considerably longer (72 h) under this condition.