Antimicrobial and Antioxidant Potential of Marine Endophytic Fungus Penicillium javanicum Ul1 Associated with Ulva lactuca

Abstract

Marine seaweeds are known to host diverse microbial communities, including endophytic fungi that are important sources of bioactive secondary metabolites with significant pharmacological potential. The present study investigated the antimicrobial and antioxidant activities of an endophytic fungal isolate obtained from the green seaweed Ulva lactuca. The isolate was cultured on Potato Dextrose Agar (PDA) and identified through morphological and molecular characterization as Penicillium javanicum isolate UL1 (GenBank Accession No. MN559951). The fungal isolate was cultivated in Potato Dextrose Broth (PDB) for 2–3 weeks, and crude metabolites were extracted from the mycelium and culture broth separately using ethyl acetate. The antimicrobial potential of the extracts was evaluated against six human pathogens and four fish pathogens. The culture broth extract exhibited inhibitory activity against all tested human pathogens except Enterococcus faecalis. The highest antibacterial activity was observed against Pseudomonas aeruginosa (17 ± 2 mm), while the lowest inhibition was recorded against Staphylococcus aureus (13.6 ± 1.52 mm). Among fish pathogens, the strongest inhibition was detected against Edwardsiella tarda (18 ± 2.64 mm), whereas the lowest activity was observed against Vibrio vulnificus (15 ± 1.73 mm). In comparison, the mycelial extract showed limited activity, inhibiting three human pathogens (S. aureus, E. faecalis, and P. aeruginosa) and one fish pathogen, Aeromonas hydrophila, with a zone of inhibition of 11.3 ± 1.24 mm. Antioxidant activity was determined through DPPH and nitric oxide radical scavenging assays. The extract demonstrated a maximum DPPH radical scavenging activity (64.12 ± 0.009 %) and nitric oxide scavenging activity (62.26 ± 0.011 %) at a concentration of 500µg. The lowest activity was observed at 100µg in both the assays. Additionally, the total antioxidant activity and total phenolic content were found to be 55.38 ± 1.00 µg/ml and 40.38 ± 2.00 µg/ml, respectively. These results suggest that the endophytic fungus Penicillium javanicum associated with U. lactuca represents a promising source of antimicrobial and antioxidant compounds with potential biomedical and aquaculture applications.