Secondary Metabolites of Some Non-Lichenized Ascomycetes
Many secondary metabolites offer potential supplementary taxonomic criteria for ascomycete fungi, in that they are all derived from a few key intermediates of primary metabolism. They are therefore closely linked to some of the most fundamental enzymes of living processes. It is not yet clear whether all enzymes of so-called secondary metabolic pathways are unique to that role or are primary enzymes with multiple functions, but some secondary metabolites derived from several diverse precursors (e.g. indole-isoprenoids, prenylated diketopiperazines, benzodiazepines) may involve more DNA sequences than pathways leading to pigments. Specific end-products of secondary metabolic pathways are probably not good taxonomic criteria for dichotomous differentiation at the genus level, and even pathways predictably involving at least several enzymes may be too widely distributed to augment current taxonomic boundaries. For example, ochratoxin A, first found in Aspergillus ochraceus, is more consistently produced by Penicillium verrucosum. Taking a wider perspective, non-lichenized ascomycetes may elaborate a vast array of chemical structures but may only express these biosyntheses when the fungi are unrecognisable as having ascomycete sexuality. Elaboration of complex secondary metabolites, often of no perceived function for the organism, is usually incompatible with the metabolic demands of sexual fructification. Nevertheless, some secondary metabolites may have a role in rationalising taxonomic boundaries at the level of species as has been shown in recent detailed study of Penicillium aurantiogriseum and closely related species.
KeywordsSecondary Metabolite Gibberellic Acid Secondary Metabolism Ergot Alkaloid ANTHRANILIC Acid
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