Extraction, Gc-Ms analysis and bioactivity test of secondary metabolites from the cultures of mangrove endophytic fungi

Abstract

Mangrove plants and their associated micro fauna have been a rich source of bioactive molecules, but only a limited antimicrobial screening of this chemo-diversity source has been reported. The unique adaptation of mangroves towards their extreme environment is largely aided by endophytic fungi. Endophytic fungi are underexplored group of microorganisms since only a few plants have been studied with regards to this community. Endophytic fungi live inside the tissues of other organisms, such as mangrove plants and provide protection to them. In return, endophytic fungi support their hosts by fighting off pathogens through the production of antimicrobial compounds. These bioactive compounds are the secondary metabolites which are often produced as waste- or by-products. In this study, the leaves, barks and roots of red, black and white mangroves found along the Ayensu estuary and the Muni lagoon in Winneba were screened for their endophytic fungi in a malt-glucose culture media containing 3%(w/w) malt extract and 6%(w/w) glucose. Five fungi from BBMAV, BWMS, LBMS, RBMAV and BBMS were obtained and cultured in malt-glucose media containing 3%(w/w) malt extract and 6%(w/w) glucose for 8 weeks for their secondary metabolites. The TLC studies and GC-MS analysis of the crude extracts from culture media of the fungal isolates reveal that fungi produced several secondary metabolites. A bioassay on the crude extracts was carried out using human pathogenic microbes Methicillin resistant Staphylococcus aureus (NCTC 12493), Staphylococcus aureus (NCTC 12973), E. coli (NCTC 12241), S. mutants (ATCC 700610), P. aeroginosa (ATCC 4853), S. typhi (ATCC 14028), K. pneumonia (NCTC 13440) and Candida albicans (ATCC 90028) and two fungi that infest cocoa (Phytophthora palmivora and Phytophthora megakarya). The bioassay results indicated that the crude extracts were active against all the test organisms. The crude extracts were tested for antioxidant activity using ABTS and DPPH as scavenging agents. The results indicate that the crude extracts of all the fungal isolates exhibited high antioxidant activity.