A comparative study on microbial and enzymatic degradation of lignin

This study focused on using microbial and in vitro laccase treatment to degrade lignin and characterize the degraded products using Thermal Carbon Analysis (TCA) and TD-Pyr-GC-MS. A comparative study was conducted on the degradative effect of basidiomycetous fungi (Coriolus versicolor and Trametes gallica), actinobacteria (Mycobacterium sp. and Streptomyces sp.) and two commercial laccases from T. versicolor (≥ 10 U/mg) and C. versicolor (≥ 0.3 U/mg), with Indulin AT as a substrate. Results showed that microbial (especially fungal) degradation is more efficient in lignin degradation compared to laccase treatment. TCA results indicated significant changes in thermal carbon elution profile in the supernatant of microbial treated samples whereas only minor changes occurred after laccase treatment. In addition, laccase treatment led to an increase in the 850 °C and char fractions indicating the formation of cross-linked polymers. Fungal treatment led to a significant mineralization of lignin while bacterial treatment resulted in carbon solubilization. Chemical characterization of lignin degraded products by TD-Pyr-GC-MS corroborated the carbon fractionation obtained by TCA. The laccase treatment led to more phenol-based compounds and aromatic hydrocarbons eluting only at the highest pyrolytic temperatures at the expense of monomers eluting at lower temperatures, indicating lignin polymerization. Fungi treated samples had similar elution profile to laccase treated samples. Bacterial treatment, on the other hand, facilitated the production of low molecular phenolics eluting at low temperatures. Therefore, fungi had a combined effect of mineralization and polymerization on Indulin AT whereas bacteria facilitated carbon solubilization and production of phenolic monomers after 54 days of treatment.