Metabolomic Studies on the Chemical Ecology of the Xylariaceae (Ascomycota)

Abstract

Fruiting bodies collected in the field during the vegetation period in different developmental stages and mycelial cultures of 50 representatives of xylariaceous fungi were tested for antimicrobial and nematicidal activities, and 50 of their characteristic metabolites were studied for comparison. Furthermore, analytical HPLC profiling using diode array and electrospray mass spectrometric detection was performed to identify and quantify the major constituents, revealing that up to 10% of the dry fruiting body biomass may be composed of secondary metabolites. In several species, significant antimicrobial effects were noted upon incubation of the fruiting bodies in an agar diffusion assay, i.e., without any need for extraction and concentration of active constituents. These results suggest that most of the characteristic constituents of subfamily Hypoxyloideae (i.e. Hypoxylon and related genera) are involved in non-specific defense reactions that underwent specific permutations in the course of evolutionary processes, resulting in a broad diversity of unique polyketides and other secondary metabolites. In contrast, the fruiting bodies of representative species of Biscogniauxia and subfamily Xylarioideae generally contained no significant activities. Only cultures of most Xylarioideae exhibited antimicrobial effects, due to the presence of cytochalasins and other toxins, while extracts from cultures of Hypoxyloideae, except for Daldinia and Entonaema, were only weakly active. Cytochalasins and other yet unidentified compounds that do not constitute pigments are responsible for enhanced biological activity in maturing stromata of H. howeanum, H. rubiginosum, and H. fuscum from Alnus, whereas in H. fuscum from Corylus and further species of Hypoxylon and Annulohypoxylon, merely the concentrations of major metabolites varied during the vegetation period. Usually, the highest yields of secondary metabolites and the strongest activities were observed in the growing stromata of Hypoxyloideae, prior to or concurrent with the production of the sexual stage. These results are discussed with regard to current hypotheses on the evolution and phylogeny of the Xylariaceae.