Resistance of Trichoderma harzianum to the biocide tebuconazol – Proposed biodegradation pathways

Abstract Wood preservatives are moving from metal-based to totally organic chemical systems. A major problem with organic biocides is biodegradation by wood-inhabiting but non-decaying microorganisms during the long service expected from treated wood. While data for triazoles suggest good efficacy against a wide range of basidiomycete fungi, this class of preservatives are less effective against the ascomycetes (soft-rot fungi, molds, and stains). The objective of this study was to examine the biotransformation of tebuconazol as one of the triazoles by the mold Trichoderma harzianum . After inoculation for 21 days, 68% of the tebuconazol was degraded in vitro. MS and IR analysis of isolated metabolites indicated that the major pathway is cleavage of the triazole ring on tebuconazol. Additionally, oxidation reactions occurred on the tert- butyl moiety. The oxidation products are subsequently metabolized by acetylation. Biotransformation resulting in non-toxic degradates is one of the mechanisms employed by this fungus in tolerating tebuconazol.