Microorganisms synthesize over 200 different fatty acids. The presence of specific acids and their relative amounts are constant for a particular species. Since the 1960s, bacteria and fungi are identified by gas chromatographic analysis of fatty acids, which were previously derivatized to methyl esters. The technique has also been used to identify wood-decay fungi like Phanerochaete chrysosporium, P. sordaria, Trametes versicolor, T. hirsuta, and T. pubescens (Diehl et al. 2003).
The technique of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was developed in the 1980s, and was used in many fields for peptide, protein, and nucleic acid analyses Otirgens 2004; Welker et al. 2004). The method was suitable to differentiate and identify viruses, bacteria, and fungi (yeasts and Deuteromycetes) (e.g., Fenselau and Demirev 2001). In MALDI-TOF MS, biomolecules and even whole cells are embedded in a crystal of matrix molecules, which absorb the energy of a laser. The sample is ionized by means of the matrix, and both the matrix and the analyte are transferred to the gas phase. The ions are accelerated in an electric field, and their time of flight is determined in a detector. After calibration of the instrument with molecules of known mass, the flight time of the analyte ions is converted to mass-to-charge ratios (m/z). Organism-specific signal patterns ("fingerprints") in the mass range 2,000-20,000 Da were obtained. Figure 2.24 shows the first MALDI-TOF MS fingerprints of Basidiomycetes, namely the closely related sister taxa Serpula lacrymans, S. himantioides and Coniophora puteana, C. marmorata (Schmidt and Kallow 2005). The obtained spectra may be used for subsequent diagnosis of unknown fungal samples by comparison.
Fatty acid profiles and MALDI-TOF mass spectrometry
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