Bioactive natural products from North Atlantic algal endophytes

Research into the natural products chemistry of marine endophytic fungi is an area where few studies have been undertaken. The discovery that terrestrial endophytes can be an important source of bioactive compounds coupled with the constant stresses imposed on algae by the marine environment, suggests that algal endophytic microorganisms could represent an important source of biologically active secondary metabolites. Fungal endophytes were isolated from nine algal species (four brown, three red and two green), collected from the Shetland Islands, United Kingdom in October 2010. Endophyte isolates were identified both morphologically and through DNA sequencing resulting in 64 distinct endophyte isolates covering 47 species being isolated from the nine algal host species. Extracts of the endophytes were screened in common laboratory bioassays with 16 fungi showing cytotoxicity, 25 fungi showing antibacterial activity and 24 fungi showing antifungal activity. An extract from a Penicillium species was subjected to bioassay-guided fractionation resulting in the isolation of (±)-patulin (IC₅₀ 42µg/mL Staphylococcus aureus, 139µg/mL Pseudomonas aeruginosa) as the major bioactive constituent and three biosynthetically related compounds that exhibited weak bioactivity.