Tracing fungal wood decay processes with advanced infrared spectroscopic methods and multivariate data analysis

Background: The main structural wood constituents - cellulose, hemicelluloses, and lignin - are the most abundant biopolymers in Earth`s carbon cycle. It is well known that mainly wood rotting fungi perform the conversion of this lignocellulosic material in nature and that most of these species belong to the basidiomycetes. The impact of fungal action on wood, however, is far from being completely understood. Hypothesis: During fungal decay, the structural polymers of wood are chemically modified and degraded. The degradation mechanisms of basidiomycetes are diverse and thus have different effects on the well-ordered wood ultrastructure in which, besides covalent bonds, also weaker intra- and intermolecular interactions, particularly hydrogen bonds (H-bonds) are involved. Furthermore it is expected that due to pore-formation the accessibility of cell wall layers to small molecules including water will increase. All these alterations in the cell wall start taking place at incipient decay stages, at which most methods fail to detect them. The most valuable tools to analyse interactions between polymers are found among advanced infrared (IR) spectroscopic techniques. Aims and methods: The project aims at connecting the knowledge about wood ultrastructure and wood chemistry and that about microbiology and biochemistry of fungal wood degradation. For that purpose, fungal action shall be traced by investigating the interactions between the biopolymers employing recently developed IR methods. Various stages of brown rot, white rot, and selective white rot of spruce wood will be analysed in the mid infrared (MIR) and near infrared (NIR) region of the electromagnetic spectrum, starting from incipient decay, at which fungal action can hardly be traced with other methods. Using dynamic Fourier transform (FT)-MIR the viscoelastic behaviour of a wood sample can be attributed to a chemical environment and to H-bonds affected by the applied strain, both expected to be altered by fungi already at incipient degradation stages. Furthermore IR spectroscopy in combination with deuterium exchange during solute diffusion and moisture equilibration offers elegant methods to elucidate the accessibility of the increasingly porous material. Thus, the newly formed pores can be attributed to a chemical environment within the wood cell wall. Data will be analysed using multivariate statistical methods and two-dimensional correlation spectroscopy (2DCOS). Despite its comparably low lateral resolution, we aim at employing IR microscopy for "semi-localising" the investigated changes within degraded samples or at distinct sites of wood cell walls. Innovation and relevancy: The mostly non-destructive IR methods, which have not yet been applied in the context of fungal wood degradation, will substantially contribute to the following topics still under investigation and discussion: The accessibility of the cell wall polymers to low-molecular-mass substances putatively involved into brown-rot and (selective) white-rot degradation in different degradation stages starting from incipient ones; the influence of different fungi on the viscoelastic behaviour of their substrate wood, and on the molecular interactions within the wood cell wall and the sequence of the degradation processes caused by different fungi starting from very early degradation stages. The ambitious aims of the project can only be fulfilled by an interdisciplinary approach, which includes microbiology, biochemistry, wood chemistry, and advanced data analysis. My co-authors and I can contribute to all these fields.