Doctor of Philosophy (PhD)
Renewable Natural Resources
Wood products are treated with biocides to prevent biodegradation by bacteria, fungi, and insects. Much attention is being directed towards testing of metal-free organic preservative systems. The major disadvantage of organics is that they are biotransformed by micro-organisms in soil and wood. This study explored the biotransformation of the fungicide tebuconazole by a bacteria species (Pseudomonas fluorescens), the mold (Trichoderma harzianum), the white rot fungus (Phanerochaete chrysosporium) and the brown rot (Meruliporia incrassata). After incubation of cultures spiked with tebuconazole, samples were analyzed for chemical remaining and metabolites. M. incrassata, T. harzianum, and the bacterium all cleaved the 1, 2, 4 triazole ring on tebuconazole and performed oxidation reactions forming the alcohol and carboxylic acid oxidation products of the tert butyl moiety on tebuconazole. P. chrysosporium which exhibited the lowest minimum inhibitory concentration (highest tebuconazole efficacy), did not degrade tebuconazole to measurable amounts. T. harzianum, with the highest MIC (lowest efficacy), degraded tebuconazole to the largest extent and tolerated it at concentrations below 200ppm. These suggested that the ability of a fungus to degrade a biocide contributes to the efficacy. The oxidation of tebuconazole was reduced when P450 inhibitors were added to the cultures leading to the conclusion that enzymes involved in the oxidation are cytochrome P450 dependent. Furthermore, the microsomal extract from T. harzianum exhibited a maximum peak at 440-460nm when CO was bubbled into Na2S2O4 treated samples. Testing metal chelators EDTA and TEMED as synergistic additives to tebuconazole showed that EDTA reduced the magnitude of oxidation most likely by binding ions important in the enzymatic system. TEMED had no significant effect while the P450 inhibitors PB and ABT gave the best performance in terms of reducing tebuconazole depletion. T. harzianum was able to germinate and grow in the presence of tebuconazole and all additives used leading to the conclusion that in addition to biotransformation, there are other mechanisms which this species uses to tolerate tebuconazole. While molds and bacteria species are not responsible for decay, they may metabolize a biocide into a less potent derivative making the environment more suitable to wood degrading basidiomycetes and insects.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Obanda, Diana Nasirumbi, "Biotransformation of organic wood preservatives by micro-organisms" (2008). LSU Doctoral Dissertations. 3883.
Todd F. Shupe