Biological activities of ophiobolin K and 6-epi-ophiobolin K produced by the endophytic fungus <i>Aspergillus calidoustus</i>

<div><p>Endophytic fungi represent ubiquitous microbial organisms able to live in the tissues of different plants around the world and represent a prolific source of bioactive metabolites. In the present study, the endophytic fungus <i>Aspergillus calidoustus</i> was isolated from the medicinal plant <i>Acanthospermum australe</i> (<i>Asteraceae</i>), and identified using molecular, physiological and morphological methods. A methylene chloride crude extract of <i>A. calidoustus</i> has been produced and subjected to antifungal bioassay-directed fractionation which resulted in the isolation of the two bioactive compounds: ophiobolin K and 6-epi-ophiobolin K. These pure compounds displayed antifungal activity against fungal plant pathogens, protozoal activity against <i>Trypanosoma cruzi</i>, and cytotoxic activity against human tumoral cell lines. The results show that <i>A. calidoustus</i> was able to produce the antifungal and cytotoxic metabolites ophiobolin K and 6-epi-ophiobolin K, which may help the fungus to colonise and occupy the substratum as well as survive in natural environments.</p></div