Mycology and Chemical Investigations of Fungal Endophytes from Medicinal Herbs (Milk Thistle and Goldenseal)

Our ongoing studies of medicinal herbs such as milk thistle [Silybum marianum (L.) Gaertn.] and goldenseal (Hydrastis canadensis L.) led us to examine the fungal endophytes (fungi that occur asymptomatically in healthy tissues) inhabiting these plants. These herbs have not been previously studied for their chemical mycology. In this study, fungal endophytes isolated from leaves, stem, roots and seeds of milk thistle and goldenseal were investigated to determine: 1) if host taxonomy effects the phylogenetic diversity and species composition of fungi, and 2) if chemistry of endophytic fungi influences the chemistry (and perhaps, biological activity) of these medicinal herbs. Approximately 100 fungal isolates were identified, of which 30 were isolated from milk thistle and 70 from goldenseal, all belonging to the Ascomycota, which is one of the most diverse phyla of the kingdom fungi. The crude extracts were tested for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and cytotoxicity in the brine shrimp test. Chemical separation of these organic extracts led to the isolation of a variety of compounds representing diverse classes of secondary metabolites. The structures of the known compounds were identified using various NMR and mass spectrometry techniques.