Production of an antimicrobial cytochalasan by an endophytic Chaetomium globosum HYML55 from Hypericum mysorense and its RNA secondary structure analysis

Abstract

The mutualistic benefits and disadvantages of non-clavicipitaceous endophytes for their hosts are not well studied and are postulated as being distinct from free-living or pathogenic counterparts. The defensive metabolites and antioxidants produced by endophytes are postulated to be the benefits offered for the hosts. Therefore, the antimicrobial and free-radical-scavenging activities of a foliar endophyte Chaetomium globosum HYML55 isolated from Hypericum mysorense of Western Ghats, India were studied. RNA secondary structure analysis refuted the unique biotope postulation because strain HYML55 was more similar to a coprophilous strain than to endophytic strains. Ethyl acetate extract of the fungus inhibited bacteria and fungi. The extract also quenched 98.65% 1,1-diphenyl- 2-picrylhydrazyl radicals with total antioxidant capacity of 13.62 mg ascorbic acid equivalent/g. A yellow amorphous antimicrobial compound purified from the extract was identified as chaetoglobosin F, which had a minimum inhibitory concentration of 7.8–15.6 μg/mL, except against Pseudomonas aeruginosa. This is the first report on the antimicrobial activity of chaetoglobosin F and other bioactivities of any endophytes from H. mysorense. The study emphasises the inter-habitat cycling of endophytes and possible benefits of C. globosum for the host. Chaetoglobosin F is an anti-inflammatory and anti-neoplastic compound, and C. globosum HYML55 could be exploited for the industrial production of this compound.

Keywords:

• antimicrobial activity
• antioxidant activity
• mycotoxin
• free radical
• endophyte

Acknowledgements

Authors acknowledge Indian Council of Medical Research, Government of India for the funding in the form of senior research fellowship (Award no. 45/70/2012/BMS/TRM dated 12.09.2012) to carry out this work. The authors are grateful to Dr K. R. Prabhu, Senior Scientific Officer, Department of Organic Chemistry, Indian Institute of Science, Bangalore for his help during the study.