Bioactive natural compounds from the widely distributed, diverse root endophytic fungal genus Darksidea.

The endophytic fungal genus Darksidea, one of the most abundant members of root-associated fungal communities in Eurasian and North American grasslands, was investigated for its specialized metabolites. Molecular phylogenetic analysis of 51 Darksidea isolates revealed 15 well-supported clades, including eight potentially novel species. Following a metabolite screening of the in vitro-cultivated fungal isolates, 18 characteristic metabolites of the genus were identified and isolated. Their chemical structures were elucidated by high-performance liquid chromatography coupled with high-resolution tandem mass spectrometry (HPLC-HR-MS/MS), which revealed structure-specific fragmentation patterns. The structures were subsequently confirmed by nuclear magnetic resonance (NMR) spectroscopy. These analyses also led to the identification of four previously undescribed compounds: two eremophilane-type sesquiterpenes, 1-dehydroisopetasol and 3-petason, and two polyketides, mannuronyl-epicoccamide A and mannuronyl-epicoccamide D. Plant bioassay with Lemna minor showed that ten of the 18 compounds inhibited plant growth. In addition, the polyketide quinone ascomycone A exhibited mild antibacterial activity against both methicillin-resistant and methicillin-susceptible Staphylococcus aureus strains.