Decolorization of the polymeric dye Poly R-478 by wood-inhabiting fungi

Abstract

Decolorization of the polymeric dye Poly R-478, an indicator of phenoloxidase activity, was examined as a potential method for separating white- and brown-rot fungi taxonomically and for screening for ligninolytic capability. In plate tests, decolorization proceeded more slowly than radial growth, which indicates that decolorizing enzymes are associated with growing and developed hyphae. Strains of the same species differed in decolorizing ability, but as expected, there were no differences between monokaryons and dikaryons of the same species. Raising the temperature from 20 to 40 °C usually increased the decolorization rate, but less than it increased the growth rate. Most brown-rot, soft-rot, or xylophilous fungi did not decolorize the dye, but 16 of 47 brown-rot fungi weakly decolorized the dye at 20 or 30 °C. Aspergillus niger and one Henningsomyces sp. also decolorized the dye. Studies with the brown-rot fungi Gloeophyllum trabeum and Fomitopsis pinicola on liquid media revealed no lignin peroxidase or manganese-dependent peroxidase activity, although nonspecific peroxidase activity was detected. Poly R-478 proved useful for selecting most white-rot fungi; however, some brown-rot fungi also reacted positively in these tests. Further studies on the pathways and mechanisms of dye decolorization by brown-rot fungi are recommended. Key words: brown rot, white rot, polymeric dyes, lignin peroxidase, manganese peroxidase.