Discovery of pharmaceutical compounds in endophytic fungi from mangrove trees

Abstract

Mangrove forest is a unique wetland ecosystem that is highly productive and provides an environment for a variety of microorganisms. Endophytic fungi derived from mangrove plants provide the plants with protection from adverse environmental conditions, while also allowing the fungi to produce valuable bioactive compounds. The present study sampled 11 mangrove trees and isolated, screened, and identified the potent endophytic fungi and their bioactive substances showing anti-pathogenic, anti-mutagenic and antioxidant activities, while the endophytes were investigated for their enzymatic potential. In total, 47 endophytic fungi were isolated from the leaves (36) and stems (11) of the host plants and all isolates were tested for antagonistic activities against selected plant pathogens. Based on the results, isolates BgS-04 and BcL-05 had the highest anti-pathogenic activities against Curvularia sp., Fusarium sp., and Colletotrichum sp. Therefore, the ethyl acetate crude extracts from these two fungi were further investigated for their antioxidant and anti-mutagenic activities and their phenolic compound contents, based on phytochemical analysis. Based on the results, the crude extracts of BgS-04 and BcL-05 contained 5.24 and 4.8 mg gallic acid equivalent/g of total phenolic compounds, respectively, and had antioxidant activity (half maximal inhibitory concentration) levels of 7.4 and 4.26 mg/mL, respectively. The preliminary qualitative phytochemical analysis of the fungal crude extracts identified tannins and coumarins. The anti-mutagenic activity levels of BgS-04 and BcL-05 against the mutagenic compounds, Trp-P-1 and DMBA, were determined using the Ames test, which revealed that the crude extracts of BgS-04 and BcL-05 had moderate-to-high antimutagenic potential against TA98 and TA100.

All 47 endophytic isolates were assessed for their potential role in producing extracellular enzyme; they were capable of producing protease (53%), pectinase (28%), amylase (26%) and cellulase (19%) but none of them produced lipase. Among the isolates, RmL-01 derived from the leaves of Rhizophora mucronata had the significantly highest amylase production. Maximum amylase production (141.2 U/mL) was observed at 30 °C, pH 7.0 and 120 h of incubation time. Molecular identification of the isolates BgS-04, BcL-05 and RmL-01 using nuclear ribosomal DNA internal transcribed spacer sequences revealed that they were Pestalotiopsis parva, Collectotrichum perseae, and Aspergillus oryzae, respectively, with high bootstrap support. It was concluded that the distinct groups of mangrove endophytes were potential sources of novel and valuable bio-based compounds with impressive anti-plant pathogen, anti-mutagenic, and antioxidant activities and capable of producing multi-industrial enzyme cocktails that might be important and useful for biotechnological applications.