Weihong Qi

Date of Award

12-2001

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Advisor

Jody Jellison

Second Committee Member

Barry Goodell

Third Committee Member

Seanna Annis

Abstract

Biodegradation of wood by brown rot fungi is dependent upon a non-enzymatic system involving Fenton chemistry. Iron biochelators with molecular weights lower than 1kD are important components in this process. Phenolate biochelators drive a hydroxyl radical generating Fenton reaction by reducing ferric iron. Biochelators may be mineralized or alternately, in some cases oxidized biochelators may be regenerated via a quinone redox cycle. Electron donors for this postulated regeneration have not been identified. Extracellular cellobiose dehydrogenase has also been found to drive the Fenton reaction by generating ferrous iron and hydrogen peroxide. This research compared the production of biochelators and the cellobiose dehydrogenase in white rot, brown rot and non-decay fungi to elucidate the brown rot mechanisms. The transplasma membrane redox system and intracellular quinone reductases were also characterized in the brown rot fungus GloeophyIIum trabeum. All the tested fungi produced iron chelating compounds and cellobiose dehydrogenase. The chemical characteristics and iron-reducing abilities of the biochelators produced varied, with the brown rot fungi producing biochelators showing significant higher iron reducing ability. The brown rot fungus Fomitopsis pinicola produced biochelators with the greatest iron reducing activity. Gloeophyllum trabeum mycelia showed 1,4-benzoquinone reducing ability. The transplasma membrane redox system was characterized based on its ferricyanide reduction kinetics. The fungus also produced constitutive intracellular NAD(P)H dependent 1,4-benzoquinone reductases. Reduction of 1,4-benzoquinone by intact mycelia and the intracellular enzymes showed different characteristics. An intracellular NADH dependent flavin mononucleotide containing 1,4-benzoquinone reductase was purified from G. trabeum. The phy.sica1 and catalytical properties of the purified enzyme were characterized. The enzyme was highly inducible by 2,6-dimethoxy-1,4- benzoquinone and had a high turn over number for multiple quinones, which indicated it functioned efficiently in quinone metabolism. Quinone reductases can play an important role in pH regulation, protecting hyphae against free radicals, and may in some cases act as one type of electron carrier potentially capable of transporting electrons from the intracellular NADH pool to the extracellular Fenton reaction. The research described here contributes to the understanding of brown rot degradative mechanisms and to an enhanced understanding of the biochemistry and physiology of the brown rot fungus G. trabeum.

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