Diversity of Endophytic Fungi Isolated from Thai Medicinal Plants (Casearia grewiifolia) in Khon Kaen, Thailand, and Their Bioactive Compounds

Endophytic fungi were isolated from Casearia grewiifolia and evaluated for antimicrobial activity. Seven different fungal taxa, including Aspergillus candidus, Neosartorya fischeri, N. tatenoi, Paecilomyces herbarum, Phomopsis sp., Xylaria berteri, and X. feejeensis were the dominant endophytes recovered in this study. They all grouped into the species belonging to Ascomycota with limited morphological and molecular data. Phomopsis sp. had the highest colonization frequency found in the plant. Colonization was greater during summer season in samples taken from leaves. The similarity indices between leaf and twig were 0.571 for Jaccard's and 0.727 for the Sorenson index, respectively. Neosartorya spp. showed antimicrobial activity against several pathogenic microorganisms. Among endophytic fungi, N. fischeri KK-KP-P2 produced the most effective extra-cellular metabolite, which had broad spectrum activity against 10 different species of tested pathogens. Interestingly, this fungal isolate inhibited the growth of Fusarium oxysporum f. sp. lycopersici, well with 56.92% of radial growth inhibition in dual culture test. The major bioactive compound from N. fischeri KK-KP-P2 was isolated by chromatographic techniques and identified by spectroscopic methods as a sesquiterpenoid. This compound had the great antimicrobial activity against many pathogens and clearly affected on bacterial cell morphology when observed by scanning electron microscopy. Our study infers that Thai medicinal plants are able to provide a wide variety of endophytes that might be a potential source of novel bioactive compounds.