Effects of glucose on the decolorization of Reactive Black 5 by yeast isolates

The cometabolic roles of glucose were investigated in decolorization of an azo dye, Reactive Black 5, by yeast isolates, Debaryomyces polymorphus and Candida tropicalis. The results indicated that the dye degradation by the two yeasts was highly associated with the yeast growth process and glucose presence in the medium. Color removal of 200 mg dye/L was increased from 76.4% to 92.7% within 60 h to 100% within 18-24 h with the increase of glucose from 5 to 10 g/L, although the activity of manganese dependent peroxidase (MnP) decreased by 2-8 times in this case. Hydrogen peroxide of 233.3 mu g/L was detected in 6 h in D. polymorphus culture. The cometabolic functions of glucose and hydrogen peroxide could be also confirmed by the further color removals of 95.8% or 78.9% in the second cycle of decolorization tests in which 7 g glucose/L or 250 mu g H2O2/L was superadded respectively together with 200 mg dye/L.