Screening of mangrove endophytic fungi for bioactive compounds

Endophytic fungi are an underexplored group of microorganisms as only a few plants have been studied with regards to this community. They live inside the tissues of other organisms, such as mangrove plants that provide protection to them and in return endophytic fungi support their hosts by fighting off pathogens through the production of antimicrobial compounds. These bioactive compounds are secondary metabolites which are often produced as waste- or by-products. Besides, endophytic fungi also help the host plant in adapting to (extreme) environments, for example by removing harmful heavy metals. In Malaysia, mangrove forests continue to be threatened by heavy metal pollution, resulting from industrial waste water pollution and urbanization.The presence of heavy metals can lead to severe damage as they are bioaccumulative and toxic. In the present study, endophytic fungi isolated frommangrove plants were characterized and assessed for their antimicrobial, cytotoxicity activity and heavy metal biosorption potential. Twelve endophytic fungi were isolated and identified (using molecular methods) to belong to 7 families: Penicillium, Curvularia, Diaporthe, Aspergillus, Guignardia, Neosartorya and Eupenicillium. Antimicrobial activities of these 12 fungal endophytes were tested against gram positive bacteria (Bacillus subtilis and Staphylococcus aureus among others), gram negative bacteria (Escherichia coli among others), yeast (Saccharomyces cerevisiae) and fungi (Candida albicans and Aspergillus niger). Two strains; Isolate 7 and Isolate 13 (related to Guignardia sp. and Neosartoya sp., respectively) showed strong antimicrobial (and antifungal) activity which was indicated by the formation of clear zone of inhibition, whereas the rest showed no activity. Compounds were isolated from the extracts of both isolates and screened using HPLC. Whereas for cytotoxicity assay, two strains; Isolate 3 and Isolate 9 (related to Diaporthe sp. and Eupenicillium sp., respectively) displayed toxicity against the matured brine shrimps at concentrations of 500 ppm after 24 hours incubation. For heavy metal biosorption, Isolate 2, which is closely related to Curvularia sp., is the most efficient in removing Cu, up to 25mg Cu/g biomass (using dead biomass). On the other hand, Isolate 8 and Isolate 13 (both related to Neosartorya sp.) are the most efficient in removing zinc (also using dead biomass), with a removal of up to 24 mg Zn/g biomass.The findings clearly indicate the potential of mangrove endophytic fungi to be used for drug development and also in wastewater bioremediation.