Endophytic fungal diversity and bioactive potentials: investigating antimicrobial and antioxidant activities

This study investigates the colonization of endophytic fungi in nettle leaf tissues and evaluates their antibacterial and antioxidant activities. Using an inverted optical microscope, extensive fungal colonization was observed in all leaf parts, with hyphae prevalent in epidermal cells, parenchyma cells, and vascular tissues. 144 endophytic fungal isolates were isolated from 800 leaf fragments, indicating an 18% retention rate. ANOVA analysis revealed significant differences (p < 0. 001) in colonization frequencies among 20 subjects, with subject 3 showing the highest frequency (40%) and subject 11 the lowest (2. 5%). Ethyl acetate extracts of the three most abundant endophytic fungi demonstrated notable antibacterial activity against both Gram-positive and Gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Inhibition zones ranged from 9. 5 to 15. 16 mm, with minimum inhibitory concentrations (MICs) between 0. 19 to 25 mg/mL. Alternaria sp. exhibited the highest antimicrobial activity against MRSA. Antioxidant activity was assessed using the DPPH radical scavenging test and FRAP method. All extracts showed substantial free radical scavenging properties, with IC50 values close to those of standards like BHT. Alternaria sp. had the highest antioxidant activity, followed by Epicocum sp. and Ulocladium sp. The FRAP method confirmed high reducing potential, with Alternaria sp. again exhibiting the highest activity. These findings highlight the potential of endophytic fungi in nettle leaves as sources of antimicrobial and antioxidant agents, with significant implications for pharmaceutical and biotechnological applications.