Bioactivity and biosynthetic insights into Penicillium brefeldianum BPSRJ7, an endophyte associated with the ethnomedicinal orchid Dendrobium chrysotoxum lindl.

Endophytic fungi are recognized as prolific sources of bioactive secondary metabolites with therapeutic potential, often complementing the pharmacological properties of their host plants. Dendrobium chrysotoxum, an ethnomedicinal orchid, has long been used in traditional healthcare practices for treating fever, infections, and general weakness; however, the contribution of their endophytic microbiota to these bioactivities remains largely unexplored. In this study, thirty endophytic fungal isolates were obtained from roots, stems, and leaves of D. chrysotoxum, representing seven morphologically distinct taxa. Comprehensive phytochemical profiling revealed the presence of alkaloids, phenolics, flavonoids, tannins, and terpenoids, with Penicillium brefeldianum BPSRJ7 consistently exhibiting the highest metabolite abundance across the tested isolates. Functional assays demonstrated that P. brefeldianum BPSRJ7 possessed strong antioxidant capacity, broad-spectrum antimicrobial activity, and selective cytotoxicity against MCF-7 and A549 cancer cells, while sparing non-malignant HEK-293 cells. FTIR and GC-MS analyses indicated the chemical complexity of P. brefeldianum BPSRJ7 metabolites, suggesting the presence of aromatic acids, phenolic derivatives, terpenoids, and lipophilic compounds. Biosynthetic gene analysis targeting the ketosynthase domain of Type I polyketide synthase (pks) genes predicted clusters associated with naphthopyrones, mitorubrinol, brefeldin A, and 1,3,6,8-tetrahydroxynaphthalene, underscoring its genetic potential for producing pharmacologically significant polyketides. Cell membrane disruption, evidenced by leakage of nucleic acids, proteins, and LDH in treated cells, suggested a preliminary mechanism underlying the antimicrobial and cytotoxic activities. This study highlights P. brefeldianum BPSRJ7 as a promising candidate for natural product discovery and underscores the importance of endophytic fungi in the pharmacological potential of traditional medicinal plants.