Antibacterial potential of indigenous red mangrove (Rhizophora racemosa) fungal endophytes and bioactive compounds identification

The antibacterial activity of indigenous red mangrove leaves- endophytic fungi against marine pathogenic bacteria and bioactive compounds identification and quantification were carried out. Healthy leaves of red mangrove (Rhizophora racemosa) were collected from Eagle Island mangrove forest in Port Harcourt, Nigeria. The endophytic fungi were isolated with acidified Potato dextrose agar plates after incubation at 28°C for 5 days. Isolated colonies were identified based on their colonial and microscopic morphology. The ethyl acetate and methanolic extracts of the mangrove leaves-endophytic fungal isolates were screened against marine pathogenic bacteria (Staphylococcus aureus, Salmonella sp., Shigella sp., Vibrio cholerae and Vibrio parahaemolyticus) using agar well diffusion assay at different concentrations. An isolate which was active against all the pathogens was further identified molecularly and the bioactive compounds in its methanolic extract identified and quantified using Gas chromatography – Mass spectrometry analysis. Six endophytic fungi of the genera Rhizopus, Pestalotiopsis, Aspergillus, Penicillium, Geotrichum and Phomopsis were isolated. Methanolic extract of Aspergillus sp., identified molecularly as Aspergillus niger KU350621.1, was active against all the tested pathogens. Eleven bioactive compounds were identified in its methanolic extract with 9, 12-Octadecadienoic acid (Z, Z) methyl ester (C19H34O2) as the major compound at 39.896% peak area. These results reveal that red mangrove leaves- endophytic fungi have antibacterial effect against marine pathogenic bacteria. The identified bioactive compounds can be used for drug development. Published by the International journal of Microbiology and Mycology (IJMM