Iron-reducing capacity of low-molecular-weight compounds produced in wood by fungi

Birch and pine wood specimens were colonized by individual isolates of 12 brown-rot, 26 white-rot, six soft-rot and four blue (sap)-stain fungi. Homogenized wood was subsequently extracted in 75% ethyl acetate and centrifuged. The filtered extracts were analyzed for their iron-reducing capabilities using a ferrozine-based assay. Agar fungal cultures were also examined directly using a spot test for iron reduction. Extracts from wood colonized by brown-rot fungi showed significantly greater iron-reducing capability than extracts from wood colonized by white-rot or non-decay fungi. Results of the spot test ratings were highly variable, but in general the greatest color responses were associated with the brown-rot cultures. The ability of brown-rot fungi to produce compounds and/or modify the wood components that reduce iron is of relevance to the chelator-mediated Fenton mechanism that has been advanced as a theory for the nonenzymatic degradation of wood by brown-rot fungi.