Variations in lignin monomer contents and stable hydrogen isotope ratios in methoxy groups during the biodegradation of garden biomass

Abstract Lignin is the most difficult aromatic substance to degrade. Selective biodegradation under mild conditions is a promising method, but the dynamic variations in lignin monomers during the biodegradation of lignocellulose are not fully understood. In this study, we examined degradation of lignin monomers and changes in stable hydrogen isotope ratios (δ2HLM) in methoxy groups to test the potential of Pseudomonas mandelii, Aspergillus fumigatus, and their co-culture. The degradation weight loss and net degradation loss of lignocellulosic biomass during biodegradation improved dramatically with fungal inoculation. Syringyl monolignol (S-lignin), which contains two methoxy groups, was more difficult to degrade than guaiacyl (G-lignin), which contains only one methoxy group. The δ2HLM values generally remained stable during the depolymerization of lignin. The fluctuation of δ2HLM values during the initial phase of biodegradation may be related to the loss of pectic polysaccharides (another methoxy donor) from the leaves. Our statistical analysis showed that δ2HLM values did not differ among the microbial cultures or change over time despite decreasing G/S ratios. Our results suggest that lignin monomer ratios can be used to monitor differences in microbial metabolism during lignocellulose biodegradation, whereas δ2HLM signatures cannot be used.