Secondary metabolites of mangrove-derived endophytic fungus, Pseudopestalotiopsis species investigated for antimicrobial and antioxidant activities

Abstract

Attention is being diverted toward the bioprospecting of newer bioactive compounds from marine endophytic fungi. This is because marine fungi have shown a large chemo-diversity of untapped important secondary metabolites needed for drug development. In the present study, the secondary metabolites of a mangrove-derived endophytic fungus Pseudopestalotiopsis species isolated from the root of Rhizophora racemosa were investigated for antimicrobial and antioxidant activities. The fungal isolation, taxonomic identification, fermentation, extraction, and isolation of the fungal secondary metabolites were carried out using standard techniques. The fermentation product was subjected to fractionation. The crude extract and its fractions were screened for antimicrobial and antioxidant assays. The active extracts and fractions exhibited good antimicrobial activities against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas oleaginous, and Candida albicans with MIC values that ranged between 0.06 to 1 mg/mL. The Gram negatives were the most susceptible bacteria while C. albicans was the most susceptible fungi. Moderately low antioxidant activities were recorded in the DPPH and FRAP assays. The chromatographic separation and HPLC analysis of the fungal secondary metabolites yielded compounds: Palitantin (A), Cytosporin D (B), Cytosporin K (C), and Fusarielin (D). These compounds have been previously reported to possess varying pharmacological activities which include antimicrobial and antioxidant activities. Thus, The results of this study show that these compounds may, in part, account for the anti-microbial and antioxidant effect of the root of Rhizophora racemosa ethno medically.