Characterization of lignin degrading enzymes from fungi and bacteria

Abstract

Fossil fuels serve as a source of raw materials and energy worldwide but their continued use is unsustainable due to rapidly depleting sources and the harm their use causes to the environment. Lignocellulosic biomass is a renewable and sustainable source that can contribute to the generation of fuels and raw materials which fossil fuels, a non-renewable resource currently provides. Lignin degrading enzymes are very important for the full break down of biomass as lignin content is closely linked with biomass recalcitrance. In this project, a fungal enzyme, identified as a laccase from Panus rudis was cloned and expressed using the Pichia pastoris expression system. It showed an ability to degrade several lignin model compounds. Several techniques including scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and Fourier-transform ion cyclotron resonance (FTICR) spectrometry were used to investigate the effect of this laccase on Kraft lignin in the presence of several mediators. Two bacterial lignin degrading enzymes from Pseudomonas putida and Bacillus subtilis were also investigated. Using X-ray crystallography, structural data for both enzymes was obtained and the active site residues identified. These studies have enabled a better understanding of lignin degrading enzymes and the lignin breakdown process.