An Endophytic Colletotrichum sp. Closely Related to C. siamense from Enhydra fluctuans : Molecular Characterization, LC-MS-based Metabolite Profiling, and Bioactivity Evaluation

The study aimed to isolate and identify endophytic fungi from Enhydra fluctuans leaves and evaluate their secondary metabolites and biological activities. A fungal isolate EF-1 was cultivated on rice medium and extracted separately with ethyl acetate (EA), methanol, and n-hexane. All extracts were subjected to phytochemical screening and biological activity assays. The EA extract demonstrated the strongest antioxidant activity, with the lowest IC 50 value (52.34 µg/mL). The EA and n-hexane extracts also exhibited strong antibacterial activity against Staphylococcus aureus and Escherichia coli , producing inhibition zones of up to 19.067 ± 0.076 mm and 19.883 ± 0.388 mm, respectively, with minimum inhibitory concentration values of 0.5 mg/mL against both pathogens. Molecular identification based on internal transcribed spacer sequencing indicated that isolate EF-1 was Colletotrichum sp., closely related to Colletotrichum siamense , and its sequence was deposited in GenBank with accession number PQ409585. A diverse range of bioactive compounds was putatively identified in the EA extract by liquid chromatography-mass spectrometry, comprising flavonoids, steroids, phenols, and terpenoids. The isolation, chemical profiling, and bioactivities of the Colletotrichum sp. closely related to C. siamense from E. fluctuans are reported here for the first time. These findings support further investigation of fungal-derived bioactive compounds for potential use in pharmaceutical, nutraceutical, and food industries.