Decolorization of synthetic dyes by Citrobacter amalonaticus Y19

Newly isolated Citrobacter amalonaticus Y19 could decolorize various synthetic dyes containing different chromogenic groups including azo bond (Crocein Orange G, New Coccine, Chromotrope FB, Congo Red, Remazol Black B), anthraquinone (Reactive blue 2) and indigo (Indigo Carmine). Y19's specific degradation of Black B, due to its industrial importance and high decolorization activity, was studied in detail. Y19's decolorization rate, under anaerobic conditions and with glucose as the carbon source, was enhanced as the temperature was increased from 25 to 40 °C or as the initial dye concentration was increased from 25 to 2000 mg/L. The highest decolorization rate was estimated to be 171 mg dye/g cell h for an initial dye concentration of 2000 mg/L. High-performance liquid chromatograph (HPLC) and mass spectrum analyses indicated that Black B was degraded by reductive cleavage of the azo bond. However, one of the degradation products exhibited spontaneous oxidation under the aerobic conditions, and this resulted in an approximately 10% re-development of Black B's original color intensity. This is the first report of newly isolated C. amalonaticus Y19's efficiency as an azo dye-degrading microbe.