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Title: Fungal delignification of lignocelluloses : physiological aspects and enhancement of rumen fermentation
Author: Asiegbu, Frederick Obioma
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 1991
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This project was primarily concerned with clarifying the extent to which fungal delignification in solid substrate fermentations could be optimised and applied to enhancing the nutritional value of high-fibre lignocellulosic ruminant feeds. Ten fungi were assessed for their ability to grow on media containing cell-wall related phenolic compounds and polysaccharides. Five strains were selected as being particularly active in secreting enzymes depolymerising native insoluble crystalline celluloses and lignins. The key cell wall phenolic ferulic acid was shown to exhibit differential patterns of inhibition of saccharification of cell wall carbohydrates with differential effects on cellulose depolymerisation, endoglucanase and B-glucosidase production. Two strains were shown to secrete phenol oxidases, which were presumed to be laccases, and three produced lignin oxidases, assayed as ability to decolourise polymeric dyes in surface agar culture. Solid substrate fermentation of hay and b arley straw with lignocellulose-degrading fungi (Pleurotus sajo-caju, Chaetomium cellulolyticum and Trichoderma harzianum) gave increases in acid detergent lignin except with Coriolus versicolor or Phanerochaete chrysosporium. P. sajo-caju,C. versicolor and P. chrysosporium reduced the lignin content of spruce and birch sawdust but had no marked effect on that of rice bran. All the five fungi reduced polysaccharide contents of lignocelluloses, but depletion was not at a rate directly related to period of fermentation. Fermentations with mixed cultures of three lignolytic fungi (C. versicolor, P. sajo-caju and P. chrysosporium) led to greater reduction in lignin content than did with monocultures. Although synergistic attack was observed on total insoluble polysaccharides and hemicelluloses, this was not found with depolymerisation of celluloses. Accumulation of total solubles, both carbohydrates and phenolics, was also markedly higher with mixed than with monocultures. Five lignocelluloses were evaluated as feeds in a simulated rumen model system (RUSITEC). The lignocelluloses were supplied prior to and following fungal delignifications. Fungal pretreatment of spruce sawdust enhanced feed digestibility and daily carbon dioxide production; with untreated sawdust production of total gas and volatile acids, and bacterial population decreased with incubation in the rumen. Addition of chitin and D(+) glucosamine, major components of fungal cell walls, had no adverse effect on digestibility, production of acetate or fermentation gases except when concentrations reached >30% chitin and >1% glucosamine. The influence of cell-wall related phenolic compounds and a toxic fungal metabolite, aflatoxin, on fibre digestion and the output of rumen fermentation end products was studied. Addition of the phenolics or fungal metabolite led to varied effects on bacterial populations, volatile acid and gas (CH₄ & CO₂) evolution.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available