Fourier Transform Infrared (FTIR) Microscopy and Imaging of Fungi
This chapter will begin with the basic principles of Fourier transform infrared (FTIR) spectroscopy, microscopy and imaging followed by highlighted examples of applications. FTIR imaging is an excellent tool to directly study the spatially resolved chemical composition of fungal material without requiring labels. Areas or band heights of selected spectral ranges can be calculated and colour-coded for each image pixel to visualise the spatial distribution of the corresponding chemical substance within samples. Although the size of single hyphae is close to the wavelength-dependent resolution limit, modern FTIR microscopes are capable of spatially resolved chemical imaging of single hyphae. Multivariate statistics can be used to reveal pattern differences of spectra within the sample or between various samples. The main spectral differences can be identified and their chemical nature concluded from the wavelength/wavenumber of absorption without prior knowledge of their chemical basis. Thus, it is possible, for example, to image the distribution of fungal mycelium within growth substrates such as wood. FTIR analysis, by comparing spectral pattern differences, enables discrimination of fungi at various taxonomic levels . Discriminating a limited number of fungi with distinct spectral features is very simple, but distinguishing many taxa having spectral similarity requires more sophisticated statistical discrimination models. In addition to imaging fungal material and discriminating fungal taxa, it is also possible to detect changes in chemical composition due to biotic interactions . Good examples examine the effect of wood-degrading fungi on lignin and cellulose/polysaccharide distribution within wood or the interactions of fungi and living organisms. Finally, the future potential of FTIR microscopy is discussed.