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

Abstract

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 Aspergillus calidoustus was isolated from the medicinal plant Acanthospermum australe (Asteraceae), and identified using molecular, physiological and morphological methods. A methylene chloride crude extract of A. calidoustus 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 Trypanosoma cruzi, and cytotoxic activity against human tumoral cell lines. The results show that A. calidoustus 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.

Keywords:

• cancer
• endophytic fungi
• Chagas' disease
• secondary metabolites

Acknowledgements

We are grateful for the financial support from CAPES, CNPq and FAPEMIG. We thank Ms J.L. Robertson, Ms R. Pace, Mrs Amber Reichley and Mr Solomon Green III for their technical support. The target species of Colletotrichum used for the antifungal assay were obtained from Dr Barbara J. Smith, U.S. Department of Agriculture, Agricultural Research Service, Poplarville, MS, USA. We also thank Dr N. Tabanca, B.J. Smith and the anonymous reviewers for important suggestions in the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the CAPES [23038.003478/2013-92]; CNPq [471721/2013-1]; and FAPEMIG [0050-13].