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Lignin degradation with oxidative enzymes and crude extracts obtained from submerged cultivation of white-rot fungi

After cellulose, lignin is the second most abundant renewable biopolymer. It is the one of major component of lignocellulosic biomass. This complex aromatic heteropolymer is tightly cross-linked with other cell walls components, covalently bound to hemicellulose. Lignin consists of three phenylpropane monomer units also known as monolignols: sinapyl, coniferyl and p-coumaryl alcohol. The compact structure that is insoluble in water and other common solvents make lignin biodegradation a challenge. Biological lignin degradation, caused by oxidative enzymes and/or small molecular weight mediators or factors such as radical, is unspecific. Fungi produce a variety of extracellular enzymes involved in the conversion and degradation of lignin aromatic compounds. These enzymes are required to degrade large aromatic compounds to smaller subunits. In our experiment the crude extracts from white-rot fungi (Trichoderma reesei and Phanerochaete chrysosporium) and oxidative enzymes (CDH, GDH, GOx, laccase) were used for direct treatment of lignin solution with the aim to degrade lignin. Firstly, we dissolved lignin in 50mM NaOH by applying ultrasound. Initially, the pH of lignin solution was adjusted to 5.0 by 100mM H3PO4 and then inoculated with crude extracts and oxidative enzymes with (or without) inducers (FeCl2, MnCl2) and incubated for 48 hours. As a control we added H2O instead of enzymes. The resulting degradation was confirmed by UV/VIS spectrometric and size-exclusion chromatography (SEC) measurements on incubated and control samples. The increase in the absorbance of lignin after incubation with crude extracts and enzymes has been considered as a criterion for the extent of lignin biodegradation.

lignocellulosic biomass ; lignin degradation ; white-rot fungi ; oxidative enzymes

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