Predominance of Colletotrichum species among endophytic fungi from Lumnitzera racemosa and their bioactive potential

Endophytic fungi are microorganisms that reside within healthy plant tissues without causing harm and are well known for their ability to produce diverse bioactive compounds. Mangrove ecosystems, with their high salinity, tidal stress, and nutrient-poor conditions, offer a unique ecological niche that fosters the evolution of metabolically versatile and stress-tolerant endophytic fungi with significant biotechnological potential. This study aimed to isolate and characterize endophytic fungi from the black mangrove Lumnitzera racemosa , collected from the Aayiramthengu mangrove forest, Kollam, Kerala. Ten healthy leaf samples from ten plant samples were processed, and fungal endophytes were cultured on potato dextrose agar. Morphological and molecular identification was performed using ITS and β-tubulin gene sequencing. Antibacterial activity was assessed by the Kirby-Bauer disk diffusion method, and qualitative enzymatic screening was conducted. A total of 174 fungal isolates, all belonging to the phylum Ascomycota, were obtained, with an isolation frequency of 58 %. Seventy-one percentage of the isolates belonged to the class Sordariomycetes, 26 % Dothideomycetes, and 3 % Eurotiomycetes. Colletotrichum siamense was the dominant species (31 %), followed by Phyllosticta capitalensis (20 %) and C. fructicola (16 %). P. capitalensis strains EF 52 and EF 187 exhibited notable antibacterial activity, against Bacillus cereus , Vibrio proteolyticus , A. hydrophila , and E. tarda . Aspergillus aculeatus EF 98 showed remarkable activity against various Vibrio species. The endophytic fungal isolates showed maximum activity against Vibrio proteolyticus (14.85 ± 4.5 mm) followed by Vibrio parahaemolyticus (13.25 ± 2.38 mm), Bacillus cereus (13.0 ± 6.8 mm) and Aeromonas hydrophila (13.0 ± 2.8 mm) indicating their antibacterial potential. Over 90 % of the isolates produced amylase, protease, and lipase and considerable proportion of the isolates exhibited asparaginase, glutaminase, ligninase, and laccase activity. These results highlight mangrove-derived endophytes as a rich source of antimicrobial compounds for application in human medicine and aquaculture. Also their importance as source of various commercially important enzymes for further exploration and industrial applications are discussed. • Isolation frequency of endophytic fungi from the mangrove Lumnitzera racemosa was 58 % • Colletotrichum (47 %) is the most prevalent genus, followed by Phyllosticta (20 %) and Escovopsis (14 %) • Colletotrichum siamense was the dominant species, followed by Phyllosticta capitalensis and Colletotrichum fructicola . • Colonization frequency was highest for Colletotrichum siamense (18 %) • Their bioactive potential indicates their suitability for commercial exploitation.