Combining sterol and fatty acid profiles for the characterization of fungi

Forty two strains of fungi belonging to 16 species and 11 genera within Phycomycetes, Ascomycetes and Basidiomycetes were cultivated on agar plates and analysed for their fatty acids by a slightly modified method commonly used in the investigation of bacteria. Several fungal sterols were also detected in the fatty acid extracts following an extended gas chromatographic separation. Differences between fatty acid profiles and combined fatty acid+sterol profiles of the fungi were evaluated by multivariate discriminant analysis. Not all genera could be separated on the basis of their fatty acid profiles alone. Considerable improvement was achieved when the sterol profiles were included in the statistical analysis. This enabled even the differentiation of two sibling species of Heterobasidion annosum (type S and P). The ergosterol and ergosta-7,22-dien-3-ol content proved to be especially valuable for grouping of these fungi. Compared to untreated mycelia, better recovery of sterols was obtained when fungal mycelial samples were frozen in liquid nitrogen and homogenized in a ball mill prior to extraction. Small temperature deviations (±3 °C) during cultivation of fungi may affect fungal identification using this method. There are no earlier reports on the fatty acid composition of four genera ( Ascocoryne, Gremmeniella, Neobulgaria and Amylostereum ) investigated.