Enhancing the enzymatic degradation of lignocellulosic biomass

Fossil fuels are the major source of energy and carbon-based chemicals the world over but their use is unsustainable. A 'greener' alternative source for both the generation of fuel and raw materials is lignocellulosic biomass. The disruption of this biomass to access cellulose and hemi-cellulose for biofuels results in lignin waste of little value that constitutes 15-30% of the initial plant biomass but lignin, the 'woody' part of plants, is also a renewable substrate and a potential source of aromatic monomers. In the natural environment, microorganisms using enzymes such as laccases and peroxidases break down the lignin in biomass1. This project will study the enzymatic process of lignin degradation by such enzymes using model and waste lignins, aiming to enhance and industrialise the process. Analysis of the lignin structure remains essential if progress is to be made in deriving value from this abundant and sustainable carbon feedstock. For example, at present molecular weight determination, which is typically done by gel permeation chromatography using polystyrene standards, is proving inadequate. There is a need to improve analysis, especially when performed alongside degradation experiments as planned here. The PhD student selected will use techniques such as SEM, FT-IR and FT-ICR MS to build on our detailed analysis of readily available lignin waste products, Organosolv and Kraft lignins. Expertise from St Andrews in the use of advanced NMR methods will also contribute to this study. One important transformation of lignin that has been validated as a route for its selective depolymerisation to aromatic monomers involves selective oxidation of the benzylic hydroxyl group in the most common b-O-4 linkage. Studies by us2 and others have shown that this oxidation can be achieved using chemical approaches but this oxidation can also be carried out enzymatically. In order to study this, the student will prepare suitable lignin model compounds3 in the Westwood Lab (St Andrews) and use these models to assess the ability of lignin processing enzymes (including laccases, manganese peroxidases and lignin peroxidases that will be produced in the Horsfall lab) to carry out this oxidation. Once the methods have been optimised on lignin model compounds the student will apply these approaches to lignin itself including a newly generated highly water soluble b-O-4 rich lignin available in the Westwood lab.