Date of Award
Master of Science (MS)
Lignin, a heterogeneous three-dimensional biopolymer, is one of the building blocks of lignocellulosic biomass. Due to its limited chemical reactivity, lignin is currently processed as a low value by-product in pulp and paper mills. Therefore, valorization of lignin holds great potential as this would provide a readily available source of aromatic compounds for various industrial applications. In this study, indulin AT biodegradation was assessed by comparing the effects of basidiomycetous fungi (Coriolus versicolor and Trametes gallica) and actinobacteria (Mycobacterium sp. and Streptomyces sp.) to those of two commercial laccases, those from T. versicolor (≥ 10 U/mg) and C. versicolor (≥ 0.3 U/mg) while using a suite of chemical analysis methods.
The research results showed that after 54 days of cultivation, microbial (especially fungal) lignin biodegradation is significantly greater than that caused by commercial laccases, reaching a maximum of 20 wt. % degradation for C. versicolor by gravimetric analysis. The extent of microbial degradation was further confirmed by thermal carbon analysis (TCA), as all treatments led to changes of the thermal carbon elution profile in the supernatants. However, laccase treatments resulted in only minor changes with increases occurring in the 850 Â°C and char fractions, thus evidencing the formation of cross-linked polymers. The fungally treated lignin showed a similar change in the thermal carbon elution profile, along with a gradual decrease of the total carbon in the supernatant,
indicating significant lignin mineralization. Bacterial treatment, on the other hand, mainly led to carbon solubilization instead of mineralization.
Chemical characterization of lignin degradation products performed by Thermal Desorption-Pyrolysis-Gas Chromatography-Mass Spectrometry (TD-Pyrolysis-GC-MS) corroborated the carbon fractionation obtained by TCA. The laccase treatments yielded more phenol-based compounds and aromatic hydrocarbons eluting only at higher pyrolytic temperatures, i.e., 700 Â°C at the expense of monomers eluting at lower temperatures, thus confirming extensive lignin polymerization. The fungal treatments led to similar changes, with a significant consumption of low molecular weight phenolics whereas the bacterial treatments, conversely, facilitated the production of phenolic monomers eluting at low temperatures. Thus, fungi appear to mostly cause significant lignin mineralization combined with polymerization whereas bacteria instead tend to produce phenolic monomers without their further catabolism.
Asina, Fnu, "Biodegradation Of Lignin By Fungi, Bacteria And Laccases" (2016). Theses and Dissertations. 1864.