Decolorization of anthraquinone-type dye by bilirubin oxidase-producing nonligninolytic fungus Myrothecium sp. IMER1

The decolorization of an anthraquinone dye, Remazol Brilliant Blue R (RBBR), was carried out using a new isolated nonligninolytic fungus, strain Myrothecium sp. IMER1. In potato dextrose broth (PDB) containing RBBR, this strain was able to grow and decolorize the dye efficiently at pHs ranging from 4.0 to 9.0, and the optimal pH and temperature were pH 7.0 and 28°C. A decolorization efficiency of approximately 90% was achieved by cultivation for 7 d at an initial dye concentration of 80 mg l−1. The adsorption of the dye by cells was observed at the beginning of the decolorization, then the color became faint and finally disappeared when bilirubin oxidase (BOX) was released by the strain. Additionally, the visual observation and ultraviolet- visible (UV-VIS) spectral analysis demonstrated that decolorization involved biosorption and biodegradation. Native polyacrylamide gel electrophoresis of crude enzyme and purified BOX confirmed that BOX, which is an important extracellular oxidoreductase, played a major role in decolorization. Furthermore, purified BOX was demonstrated to degrade RBBR and other dyes by in vitro enzymatic experiments. Our results suggest that both the strain and its extracellular BOX have promising applications in dye effluent decolorization.