Antioxidant Metabolite Production from Endophytic Fungi of Mezzetia parviflora Becc.: A Potential Natural Source of Antioxidants

Background: Ongkea (Mezzetia parviflora Becc.) is a plant species employed as the traditional medicine by the Buton district people in Southeast Sulawesi, Indonesia. This traditional use suggests the plant's potential pharmacological activity, which may be associated with its endophytic fungi. Endophytic fungi, living symbiotically within plant tissues, are known to produce bioactive compounds that often mirror or enhance the host plant's therapeutic potential. In this study, we investigated the in vitro antioxidant activities of endophytic fungi, optimized the fermentation conditions for maximum production of bioactive metabolites, and compared the intracellular and extracellular antioxidant activities of the metabolites to gain a comprehensive understanding of their potential applications. Methods: The related genera of endophytic fungi were determined by morphological and molecular analyses of the 18S rRNA gene. The antioxidant potential was assessed using methods involving DPPH free radical scavenging, hydrogen peroxide scavenging, and reducing power assays. Metabolite production was optimized by varying carbon and nitrogen sources. Results: Based on the phylogenetic tree, the strain of endophytic fungi was assigned to Botryosphaeria sp. FUHM17, being closely related to Botryosphaeria sp. P483 KT213569. The most effective synthesis of antioxidant metabolites was demonstrated when glucose and yeast extract were employed as the respective carbon and nitrogen sources. The optimal production of antioxidant metabolites was observed when glucose and yeast extract were employed as a carbon source of 10 g/L glucose and a nitrogen source of 10 g/L yeast extract, respectively. Intracellular metabolites from selective fungi exhibited 26.67% DPPH scavenging activity after 10 days of culture. In addition, the intracellular and extracellular metabolite extracts had IC50 values of 208.07 μg/mL and 832.22 μg/mL, respectively. Compared to ascorbic acid (IC50: 5-10 μg/mL), the metabolites exhibited moderate antioxidant activity. Conclusion: In the present study, the antioxidant metabolite of endophytic fungi was obtained from culture filtrate and biomass extract and confirmed by HPLC analysis. The findings indicated that the metabolites generated by endophytic fungi obtained from Ongkea hold promise as a prospective reservoir of unique natural antioxidants.