Inhibition of decay fungi using cotton cellulose hydrolysis as a model for wood decay

Abstract

Environmental pressures to replace chromium and arsenic in fixed waterborne preservatives have been increasing. Potential inhibitors of brown-, white- and soft-rot fungi need to be evaluated as alternative preservatives by screening and testing in, in vitro, model systems. This paper reports the inhibition of cellulose depolymerization and weight loss of selected decay fungi by 11 chemical compounds. The ability to depolymerize carbohydrate polymers is analogous to strength loss of wood which can occur independently of utilization (weight loss). Cotton cellulose was pretreated with 1% solutions of compounds selected for their unique ability to stain wood components, dye cellulose or to act as a scavenger of active oxygen species. Cotton cellulose was exposed to three brown-rot fungi ( Gloeophyllum trabeum MAD-617; Postia placenta MAD-698 and Tyromyces palustris TYP-6137) and the white-rot fungus Trametes versicolor MAD-697. After 12 weeks exposure to the fungi in modified soil-block tests, cotton samples were removed and tested for weight loss, reduction in degree of polymerization (DP) and elemental analysis by inductive coupled plasma (ICP) spectroscopy. Only two compounds tested (NHA and ruthenium red) inhibited weight loss for all fungi tested. The remaining compounds were selective in their ability to prevent weight loss or inhibit reduction in DP. In general, antioxidants were only effective against brown-rot fungi. Independent mechanisms of cellulose hydrolysis by brown- and white-rot fungi demonstrates one problem inherent in development of target specific wood preservatives not evident in preservatives containing broad-spectrum biocides, i.e. different mechanisms require different inhibitors.