| Several white-rot fungi were investigated for their ability to remove lignin, as well as low molecular weight aromatics, from Coastal Bermuda grass (CBG) cell walls to improve the digestibility of lignocellulosic materials by rumen microorganisms. Results from analyses of these fungal-treated CBG residues concerning their aromatic constituents, biodegradation by rumen microorganisms and production of volatile fatty acids (VFAs) indicated that Ceriporiopsis subvermispora and Cyathus stercoreus selectively delignified CBG cell walls and considerably improved their biodegradation by rumen microorganisms. The ester-linked phenolic acids in grass cell walls appeared to be partially susceptible to removal by the fungi. Pre-treatment of lignocelluloses from various plants with C. subvermispora and C. stercoreus showed specific plant-fungus associations, often resulting in a selective delignification and improved biodegradability by rumen microorganisms.; C. subvermispora produced an array of plant cell wall degrading enzymes in defined culture media. However, the enzyme patterns were very much dependent on the substrates used. In general, C. subvermispora showed low cellulase, but high hemicellulase and ligninolytic, activities. A preference for utilization of soluble substrates, i.e., glucose and cellobiose, over insoluble polysaccharides was also demonstrated. No exo-1,4-{dollar}beta{dollar}-glucanase activity was detected in any of the C. subvermispora cultures, and the poor growth of C. subvermispora on highly crystalline cellulosic substrates was most likely due to the lack of a complete cellulose transforming system.; Production of ligninolytic enzymes and its relationship to the rate of mineralization of {dollar}sp{lcub}14{rcub}{dollar}C-ring-labeled dehydrogenative polymerizates (DHPs) was monitored in static cultures of C. stercoreus. An inverse correlation was observed between the rates of DHP mineralization and laccase and manganese peroxidase (MnP) production with varying levels of nitrogen and glucose. No lignin peroxidase (LiP) activity was detected under any of the culture conditions used. External addition of LiP and veratryl alcohol did not influence on the rates of DHP mineralization. An increase in pH-levels occurred in high nitrogen cultures and was associated with low rates of DHP mineralization.; Several aromatic monomers were tested for their effect on growth, as well as laccase and MnP production, by C. subvermispora and C. stercoreus. Benzaldehyde compounds were more toxic to both fungi than the corresponding benzoic and cinnamic acid derivatives. Growth response and enzyme production in the presence of the aromatic compounds were generally not related and seemed to be specific for the individual compounds.; A laccase from C. stercoreus was purified and characterized. The enzyme was glycosylated and had a molecular weight of 70 kDa. Its pI, pH optimum, thermal stability, substrate specificity, and inhibitor studies indicated that the enzyme was similar to laccases from other typical basidiomycetes. Further, the N-terminal amino acid sequence showed close homology to laccases from other wood-degrading fungi. The apparent K{dollar}rmsb{lcub}m{rcub}{dollar} and V{dollar}rmsb{lcub}max{rcub}{dollar} for guaiacol of the laccases purified from fermentor- and static-cultures were 473 {dollar}mu{dollar}M and 0.17 {dollar}mu{dollar}M/min, and 1735 {dollar}mu{dollar}M and 0.39 {dollar}mu{dollar}M/min, respectively. (Abstract shortened by UMI.)... |
