Use of electron microscopy for aiding our understanding of wood biodegradation

The use of electron microscopy (EM) has proved to be an invaluable tool for studying structural aspects of lignocellulose degradation by fungi and bacteria and therefore improving our understanding of wood biodegradation. The present review details the application of conventional (SEM, TEM, STEM), analytical (EM X-ray microanalysis, (EDXA)), and immunogold cytochemical EM procedures in the field and gives specific examples of its use for each of the known important types of microbial wood decay including bacterial (tunnelling and erosion), soft rot (cavity and erosion), brown rot and white rot (simultaneous decay and preferential lignin degraders), and discusses important advances made by adopting the techniques. The more recent use of immunogold cytochemistry for studying microbe and fungal enzyme-wood cell wall interactions and its application for localization of specific wood-degrading (laccase, Mn(II) and lignin peroxidases, and cellulases) and H2O2 producing (pyranose oxidase) enzymes in situ during white rot decay are also reviewed, as is the application of EM for studying non-enzymatic wood decay. Methods for labelling and detecting wood components (lignin, hemi- and cellulose) in situ by EDXA and enzyme immunogold cytochemistry are also outlined. The use of EM in wood biodegradation research is rapidly expanding and is seen as an important compliment to biochemical and chemical approaches. The future should see even greater advances in our understanding of wood decay as more advanced and recently developed EM techniques are also exploited.