Evaluation of in vitro alpha-glucosidase inhibitory, antimicrobial, and cytotoxic activities of secondary metabolites from the endophytic fungus, Nigrospora sphaerica, isolated from Helianthus annuus

Purpose This study aimed to evaluate alpha-glucosidase inhibition and antimicrobial activity as well as cytotoxic activity of extracts from the endophytic fungus, Nigrospora sp., isolated from leaves of Helianthus annuus, which is widely cultivated for food and used as a medicinal plant. Methods The fungus (TSU-CS003) was identified based on internal transcribed spacer ribosomal DNA sequences and fungal biomass, and fermentation broth was subjected to extraction by solvents (hexane and ethyl acetate). All extracts were tested for their antimicrobial activity, alpha-glucosidase inhibition, and cytotoxicity activity. In addition, the active extract was analyzed by using gas chromatography mass spectrometry (GC-MS) Results TSU-CS003 was identified as Nigrospora sphaerica. The fermentation broth extract (BE) showed strong antimicrobial activity against Staphylococcus aureus and methicillin-resistant S. aureus (Gram-positive bacteria) with minimum inhibitory concentration (MIC) values in the range of 16-32 mu g/mL and a few yeasts with MIC values ranging from 64 to 128 mu g/mL, especially Talaromyces marneffei with an MIC value of 4 mu g/mL. The effects of BE were observed by SEM. The results showed that this extract affected the cell morphology of T. marneffei. The half-maximal inhibitory concentration (IC50) of BE from alpha-glucosidase inhibition was recorded as 17.25 mu g/mL and also showed significant cytotoxicity against A549 human cancer cell lines with an IC50 value of 22.41 mu g/mL. Furthermore, BE was analyzed by using GC-MS and divided into three main compounds, including 5-pentyldihydrofuran-2(3H)-one, (Z)-methyl 4-(isobutyryloxy)but-3-enoate, and 2-phenylacetic acid. Conclusion This was the first report of the endophytic fungus N. sphaerica from H. annuus. It is a potential source of active metabolites, which gave the strong antifungal activity, antioxidant activity, and cytotoxicity to A549 cancer cell lines.