The synergistic action of ligninolytic enzymes (MnP and Laccase) and Fe3+-reducing activity from white-rot fungi for degradation of Azure B

The knowledge of the oxidative mechanisms displayed by white-rot fungi for lignin biodegradation is important to assess the complete potential application of their lignin-degrading metabolites, as the biodegradation of several pollutants by these fungi has been directly correlated to their capability to degrade lignin. In this context, to obtain better knowledge of their oxidative systems, we studied the synergistic action between Fe3+-reducing activity (FeRA) and the lignin-degrading enzymes MnP and laccase for degradation of the nonphenolic dye Azure B. Degradation of the dye was studied using low molecular weight fractions (<5 kDa) with FeRA (LMWFFRA) and high molecular weight fractions (>5 kDa) with MnP (HMWFMnP) and laccase (HMWFLac) activities isolated from white-rot fungi cultures. Significant Azure B degradation was only observed when it was previously treated with LMWFFRA in the presence of Fenton's reagent (iron and hydrogen peroxide) followed by treatment with HMWFLac or HMWFMnP. OH was evidenced as the main radical oxygen specie formed in the reaction mixtures and showed to be crucial for dye decolorization. In addition, the synergistic action between FeRA/Fe3+/H2O2 (as Fenton-based OH-producing reactions) and the lignin-degrading enzymes MnP and laccase, and also the relevance of this synergism as an oxidative pathway for lignin biodegradation by white-rot fungi and for bioremediation processes are discussed.