Decolorization of recalcitrant dyes by a multicopper oxidase produced by Iodidimonas sp Q-1 with iodide as a novel inorganic natural redox mediator

A multicopper oxidase (IOX) produced by Iodidimonas sp. Q-1 has high catalytic efficiency for iodide (I-) oxidation to form molecular iodine (I-2). In this study, the potential capacity of IOX for decolorization of recalcitrant dyes was determined. Although IOX did not decolorize any dyes in the absence of redox mediator, significant decolorization of Orange G, Indigo Carmine, Amido Black, and Remazol Brilliant Blue R (RBBR) was observed in the presence of iodide. Addition of 0.1 mM iodide was sufficient to decolorize a total of 3 mM Indigo Carmine, suggesting that iodide functions as a mediator. Such mediator-like function of iodide was not observed in commercially available fungal laccases. The IOX-iodide decolorization system showed much alkaline pH optima of 5.5-6.5 and stronger salt tolerance than fungal laccases did. In addition, actual wastewater discharged from a dyeing factory could be decolorized more than 50% by the system. Since iodide is naturally occurring, non-toxic, and cheaper than common synthetic mediators, the IOX-iodide system is potentially more advantageous than fungal laccase-mediator systems for decolorization of recalcitrant dyes.