Screening of fungi capable of degradation of β-aryl ether bond from lignin model compounds by using highly fluorescent-emitting detection

Lignin is an aromatic polymer and composed of phenylpropane units polymerized by dehydrogenases in cell walls. Lignin has a complex chemical structure with C-C and C-O-C bonds, and it is difficult to decompose lignin structure by microorganisms in natural conditions. For the microbial degradation of lignin structure, wood decay fungi can non-specifically degrade the lignin polymeric structure by oxidases. Moreover, soil bacteria have unique enzymes such as β-etherases for the degradation of lignin structure in the natural environment. In contrast, there are few studies on degrading enzymes of lignin that can specifically cleave the main lignin structure with fungi. To examine enzymes that can selectively cleave the β-aryl ether (β-O-4) bond, which accounts for 40-60% of the chemical bonds in lignin structure, this study used some lignin model compounds (e.g., guaiacylglycerol-β-O-4-methylumbelliferone, α-O-methylumbelliferyl-β-hydroxyl-propiovanillone, and O-benzyl-guaiacylglycerol-β-O-4-methylumbelliferone) with a highly sensitive fluorescence detection. Fluorescence activity was evaluated by visual observation for the presence of fluorescence and by quantifying the intensity of fluorescence. Two candidates were selected from 1407 samples in the fluorescence analysis. Based on the screening system with fluorescence and identification based on sequencing of the ITS4 and ITS5 region, Fusarium sp. and Cunninghamella sp. were classified as zygomycete, and have high fluorescent activity.