Chemical and Biological Investigations of four Mangrove Medicinal Plants of Bangladesh and their associated Endophytic Fungi

In the present study, four mangrove medicinal plants (Pandanus foetidus Roxb., Sonneratia apetala (Buch). Ham., Sarcolobus globosus Wall. and Derris trifoliate Lour.) were investigated for their bioactivities, isolation and structure elucidation of secondary metabolites and isolation of endophytic fungi producing antimicrobial, cytotoxic and antioxidant metabolites. From the plants P. foetidus Roxb. and S. globosus Wall. 6 secondary metabolites were identified, of which 1 was proposed as novel metabolite and 4 were reported first time from their respective plant species. The structures were determined by spectroscopic analysis and comparison of spectral data with published literature. From this study, fifteen endophytic fungi were isolated of which four fungal strains were taxonomically identified upto the genus level (SGBE-1 as Nigrospora sp. and strains SGBE-2, SGBE-4 and SGBE-5 as Fusarium sps.). Chemical screening of these fungi exhibited that they contain potentially beneficial compounds like isocoumarin/coumarin, flavonoid, anthaquinone and terpenoid. Both crude extracts and fractions of plants and their associated endophytic fungi were assayed for inhibition of bacterial and fungal pathogens by disc diffusion, cytotoxicity against the matured brine shrimps and free-radical scavenging activity with DPPH. The crude plant extracts of S. apetala barks and leaves exhibited mild to good activity against most of the test bacteria and fungal extracts of SGBE-4, SGBE-5, SABE-1 and SABE-2 showed significant antimicrobial activities. In brine shrimp cytotoxicity assay probable LC₅₀ were found from crude plant extract of D. trifoliate (12.7 µg/mL), column fraction of P. foetidus leaf (3.6 µg/mL) and fungal strains SGBE-3 (2 µg/mL), SABE-2 (6 µg/mL) & SALE-1 (8 µg/mL). SGLE-1 and SGBE-5 exhibited free radical scavenging activity with IC₅₀ values 65.13 and 146.55 μg/mL respectively. The extract exhibited prominent bioactivities merit further pharmacological evaluation. This proved the enormous biosynthetic potential of the mangrove medicinal plants of Bangladesh and their associated endophytic fungi in the production of bioactive metabolites. This study could be a good source of reference in the scientific world due to its findings and would contribute for the discovery of potential bioactive compounds or leads for drug development. 

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