The Cytotoxicity and Antioxidant Potentials of the Endophytic Fungus Xylaria sp. KET18 Associated with Keteleeria evelyniana Mast.

Fungal endophytes colonizing plant tissues are considered a reservoir of secondary metabolites that exhibit diverse bioactivities applicable in biomedicine. This study aims to reveal for the first time endophytic fungi associated with Keteleeria evelyniana as a potential source of bioactive compounds. A total of 24 fungal endophytes were successfully isolated from K. evelyniana and classified into 10 genera: Aspergillus, Penicillium, Fusarium, Xylaria, Talaromyces, Nodulisporium, Apiospora, Neopestalotiopsis, Diaporthe, and Hypoxylon. Screening for antimicrobial activity revealed that 8 out of 24 ethyl acetate extracts inhibited antimicrobial activity against at least one tested pathogen. Among them, Xylaria sp. KET18 showed the most potent antimicrobial activity with inhibition diameters ranging from 16.5 to 21.5 mm. In addition, the KET18 extract showed the most significant cytotoxic effects against A549 (IC50 = 18.8 ± 3.1 µg/mL) and MCF7 cell lines (IC50 = 24.1 ± 2.5 µg/mL). The KET18 extract showed moderate antioxidant activity against hydroxyl and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. The chemical characterization and structural elucidation indicated the presence of four bioactive compounds that have not been found in fungi, including methyl pyroglutamate, prunetin, macrolactin A, and macrolactin F. These findings demonstrated that K. evelyniana is a host of endophytic fungi with antimicrobial, anticancer, and antioxidant potential.