Vol. 9, Special Issue 6, Part D (2025)

Microbial communities associated with seaweed, particularly endophytic fungi, are recognized as highly diverse and abundant sources of bioactive compounds with broad-spectrum antimicrobial activities such as antibacterial, antifungal, antiviral, and antioxidant effects. This research focused on evaluating the antimicrobial properties of fungal extracts from seaweed against human and fish pathogens, as well as assessing their antioxidant potential. The endophytic fungi were isolated from green seaweed Chaetomorpha sp. using Potato Dextrose Agar (PDA) and identified as Aspergillus fumigatus isolate V2 (AFV2; Accession No. MK490926) based on morphological and molecular analyses. The isolated fungi were cultured in potato dextrose broth (PDB) at 25 °C for 2-3 weeks, after which crude compounds were extracted from the broth and mycelium using ethyl acetate. The extracted crude compounds were tested against human and fish pathogens using the well diffusion method, while their antioxidant potential was analyzed through nitric oxide radical scavenging assay (NORSA) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The broth extract of AFV2 demonstrated the highest inhibition zone (15.5±1 mm) against Candida albicans, whereas the lowest inhibition (6.5±2 mm) was observed against Enterococcus faecalis, with no inhibition noted against Pseudomonas aeruginosa. The mycelium crude extract exhibited inhibition against all pathogens tested, with the highest zone against Candida albicans (15.6±0.94 mm) and the lowest against Staphylococcus aureus (8±0.81 mm) and Pseudomonas aeruginosa (8±0.81 mm). In the antioxidant assays, the broth extract showed maximum DPPH free radical scavenging activity at 500 µg (94.11±0.004%) and minimum at 100 µg (82.67±0.002%). Nitric oxide radical scavenging activity was observed as 63.30±0.003% for 100 µg and 73.44±0.012% for 500 µg.