Lichen-associated Fungi Inhabiting from a Mangrove Ecosystem in Sri Lanka: A Novel Source of Antibacterial Agents

Abstract

The global threat of antimicrobial resistance has spurred interest in discovering innovative antimicrobial agents from diverse sources. Amid the rise of new diseases, the quest for novel drug leads has intensified. This study explores the antibacterial potential of lichen-associated fungi in mangrove ecosystems, using NARA Regional Research Centre in Kalpitiya, Sri Lanka as the study site. Lichen-associated fungi were isolated from collected lichens and the antibacterial activities of the isolates were tested using two gram-positive bacteria: Staphylococcus aureus (ATCC 25923) and Bacillus cereus (ATCC 11778) and two gram-negative bacteria: Pseudomonas aeruginosa (ATCC 25853) and Escherichia coli (ATCC 25922). Putative fungal isolates were primarily screened using agar plug diffusion assay and ethyl acetate extracts of fungal isolates with marked activity were secondarily screened using the well diffusion assay in triplicate. Isolate LIF 0803 identified as Trichosporon faecale showed the most outstanding antibacterial activities as 2.58, 3.43, 4.2, 4.5 cm of zone diameter at 100 mg/mL, and 1.95, 3.08, 3.7, 4.3 cm of zone diameter at 50 mg/mL against P. aeruginosa, S. aureus, B. cereus, and E. coli respectively. All nine fungal isolates showed promising antibacterial activity against both gram-positive and negative bacteria. Therefore, this study showed that lichen-associated fungi in mangrove ecosystems have potent antibacterial activities. Hence, bioassay-guided fractionation of active compounds from lichen-associated fungi and structure elucidation are warranted.