Microbial transformation of lignin

dc.contributor.authorKadam, Kiran L.en
dc.contributor.departmentChemical Engineeringen
dc.description.abstractPetroleum reserves are forecast to dwindle during the next century. The imminent shortage of chemicals derived from fossil fuels has given an impetus to research on utilization of renewable resources throuqh microbial treatment. This work looks at the concept of lignin bioprocessing from the vantage point of a biochemical engineer. Coriolus versicolor, Phanerochaete chrysosporium and Sporotrichum pulverulentum, which being white-rot fungi are traditional lignin degraders, were found to be much less efficient in lignin metabolism than Aspergillus fumigatus, a soft-rot fungus isolated in our laboratory. Lignin fermentations with white-rot fungi failed to show any net accumulation of low molecular weight products derived from lignin. Genetic manipulation is necessary to contrive the accumulation of desired intermediates during lignin fermentations. Though recalcitrant carbohydrates and low initial glucose concentrations supported higher lignolytic activities than easily metabolized carbohydrates and high initial glucose concentrations, respectively, glucose catabolite repression was not evident during lignin metabolism by C. versicolor. It was surmised that the effect of carbohydrates on lignin metabolism may depend on the history of the organism. Through the concretion of above observations and the absolute requirement for carbohydrates during lignin metabolism, the existence of upper and lower critical glucose concentrations in lignin metabolism was postulated. Lignin metabolism relative to carbohydrate metabolism was studied by monitoring the ratio of lignin derived CO₂/total CO₂ during A. fumigatus and C. versicolor fermentations. The variability of the above ratio during lignin fennentations suggested that lignin metabolism may not be stoichiometrically linked with carbohydrate metabolism. The rate of ¹⁴CO₂ evolution from ¹⁴C-labeled kraft lignin and the ratio of lignin derived CO₂/total CO₂ during A. fumigatus fermentation were concordant and each showed a maximum with respect to time. Two new parameters, lignolytic efficiency and normalized lignolytic efficiency, were defined to evaluate the performance of large-scale lignin fermentations. During a deep-tank fermentation with A. fumigatus, lignolytic efficiency correlated well with biomass whereas normalized lignolytic efficiency decreased continually. Analyses of degraded lignins divulged that A. fumigatus brought about corporeal changes in the lignin macromolecule whereas C. versicolor was responsible for only cursory changes. Data obtained from degraded lignins such as OCH₃ loss, OH loss and yield of monomers and dimers upon permanganate oxidation were consonant with ¹⁴CO₂ evolution data from ¹⁴C-labeled lignin. The effect of nitrogen concentration and C/N ratio on lignin metabolism by A. fumigatus could not be adequately studied since the organism lost its once prodigious lignolytic capacity. C. versicolor fermentations were grossly insensitive to variations in nitrogen concentration and C/N ratio. A kinetic model was developed on the premise that cell-lignin contact is imperative for lignin metabolism. The model is, in general, concordant with real observations. Though particular mixed and successive fermentations with Poria placenta and C. versicolor were not successful, the idea of such fermentations involving brown-rot, whiterot and other lignin-degrading fungi is worth investigating.en
dc.description.degreePh. D.en
dc.format.extentxiii, 199 leavesen
dc.publisherVirginia Polytechnic Institute and State Universityen
dc.relation.isformatofOCLC# 39973968en
dc.rightsIn Copyrighten
dc.subject.lccLD5655.V856 1979.K34en
dc.titleMicrobial transformation of ligninen
thesis.degree.disciplineChemical Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.namePh. D.en


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