Biodecolorization and biotransformation of methylene blue using mixed cultures of brown-rot fungus Daedalea dickinsii and filamentous fungus Aspergillus oryzae: identification of metabolites and degradation pathway

Abstract

This study aimed to examine biodecolorization and biotransformation of methylene blue (MB) using mixed cultures of brown-rot fungus Daedalea dickinsii and filamentous fungus Aspergillus oryzae. In addition, the ratio of D. dickinsii and A. oryzae in mixed cultures was 1 : 1, and the sample was incubated at 30 °C for 7 days in liquid medium potato dextrose broth (PDB). The results showed that the sample had the ability to remove and transform 95.24 mg L^-1 MB. In this study, mixed cultures had the highest removal percentage of 64.77%, while values of 5.94% and 36.82% were obtained for single cultures of D. dickinsii and A. oryzae, respectively. LC-TOF/MS analysis results showed that peak intensity of MB compound (m/z 284) in each treatment chromatogram decreased compared to the control. The metabolites of decolorization by D. dickinsii were C₁₅H₁₆N₃S, C₁₆H₁₉N₃SO, and C₁₆H₂₁N₃SO, while C₃₁H₄₈N₃S⁺ was obtained using A. oryzae. For mixed cultures, the metabolites obtained included C₂₆H₃₇N₂O₃S, C₉H₈N₂O₃S, C₂₈H₃₈NO₂S, and C₂₇H₂₇N₅S₂. Based on the results, mixed cultures of D. dickinsii and A. oryzae had a high MB decolorization and could be used in the textile industry.