Abstract
A multicopper oxidase (IOX) produced by Iodidimonas sp. Q-1 has high catalytic efficiency for iodide (I−) oxidation to form molecular iodine (I2). 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.
Highlights
A 10 mU mL−1 each of iodide-oxidizing enzyme (IOX) and fungal laccases was incubated with 0.3 mM Orange G, an azo dye, for 4 h in the presence or absence of potential redox mediators
In the case of IOX, no significant decolorization occurred in the presence of ABTS (Fig. 1c)
Since Wong and Yu23 first reported decolorization of synthetic dyes by Trametes versicolor laccase (TvL), a large number of white rot fungi and their laccases have been studied for their capacity for decolorization[17]
Summary
Suzuki et al.[3] found that the catalytic efficiency of IOX for iodide was 2–5 orders higher than that for the fungal laccases Based on this unique characteristic and on the fact that molecular iodine has a broad antimicrobial spectrum against a wide variety of microorganisms, Yuliana et al.[11] recently prepared a novel enzyme-based antimicrobial system consisting of IOX and iodide, and determined its antimicrobial activity. To remove synthetic dyes from industrial effluents, various physicochemical methods such as adsorption on sorbents, oxidation by chemicals and photo-degradation, filtration, and ion exchange are used[16] These methods are sometimes uneconomical, and generate by-products or concentrated sludge. The decolorization activity of IOX was routinely compared to that of commercially available fungal laccases, i.e. Trametes versicolor laccase (TvL) and Pleurotus ostreatus laccase (PoL)
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