Endophyte-Derived Metabolites From the Bark of Xylocarpus mekongensis: Source of Antioxidant, Antimicrobial, and Antidiabetic Agents.

Endophytic fungi have emerged as promising reservoirs of pharmacologically potent metabolites, garnering increasing scientific interest over the past three decades. Their ability to enhance host resilience against diverse biotic and abiotic stresses further underscores their biotechnological value. This study explores the hypothesis that endophytes from mangrove ecosystems, specifically the bark of Xylocarpus mekongensis, thrive under extreme conditions such as high salinity, humidity, temperature, and variable soil composition and may therefore produce unique bioactive compounds. The endophytic fungi were initially cultured in potato dextrose broth (PDB). The crude fungal extract was then obtained by solvent extraction, where the broth was first extracted with n-hexane to remove nonpolar compounds, followed by extraction with ethyl acetate, which yielded the crude extract containing secondary metabolites. This procedure led to the successful isolation of three distinct culturable fungal endophytes, designated as X2, X4, and X7, and assessed for antimicrobial, antioxidant, and α-glucosidase inhibitory properties through solvent fractionation. Among the isolates, X4 exhibited the most compelling pharmacological profile. Crude extracts of X4 demonstrated notable antioxidant activity in DPPH free radical scavenging activity (IC50: 94.179 μg/mL), supported by high total phenolic content (TPC: 66.542 mg GAE/g), total flavonoid content (TFC: 173.770 mg QE/g), and total tannin content (TTC: 42.717 mg GAE/g), although still less potent than standard ascorbic acid (IC50: 15.987 μg/mL). All crude and fractionated extracts exhibited measurable antibacterial activity, with X4 crude extract showing the strongest inhibition zones against Escherichia coli and Bacillus subtilis (21 mm). No antifungal effects were observed. Minimum inhibitory concentrations ranged from 31.5 to 250 μg/mL. Additionally, the X4 isolate and its fractions displayed significant α-glucosidase inhibition, with the crude extract showing the lowest IC50 (0.416 mg/mL), outperforming its ethyl acetate (0.824 mg/mL) and dichloromethane (1.032 mg/mL) fractions. These findings affirm that X. mekongensis bark harbors potent endophytic fungi capable of producing bioactive metabolites with strong therapeutic potential.