Biological potential and chemical composition of bioactive compounds from endophytic fungi associated with thai mangrove plants

Abstract

Plant endophytic microorganisms, which live symbiotically within their plant host, are a novel resource of active secondary metabolites. The current study was carried out to isolate fungal endophytes from 11 mangrove plants, to investigate their antifungal activity against phytopathogenic fungi and to assess their enzyme production. The ethyl acetate crude extracts of selected endophytic fungi were determined for their antioxidant and anti-mutagenic activities and the active compounds present in the extracts were identified. Of the 37 isolates of endophytic fungi, 30 were isolated from leaves and 7 from stems. For anti-pathogenic activity, all endophytes were tested against 5 plant pathogens. The results revealed that AmL-02 and CtL-06 had the highest growth inhibition of Curvularia sp. and Fusarium sp. respectively and they were chosen for phytochemical analysis and to explore further their anti-mutagenic activities. A preliminary qualitative phytochemical analysis of the fungal crude extracts revealed the presence of constituents such as alkaloids, tannins and coumarins. Gas chromatography-mass spectrometry analysis of the ethyl acetate extract of AmL-02 revealed the presence of various chemical compounds with the highest amount present being 1,3-butanediol (11.37%), while the highest amount of compound present in CtL-06 was kojic acid (95.6%). The antimutagenic activities were determined of AmL-02 and CtL-06 against the mutagenic substances 3-amino-1-methyl-gamma-carboline (Trp-P-2) and 7,12-dimethylbenzo[a]anthracene (DMBA) based on an Ames test using the Salmonella Typhimurium strains TA98 and TA100 which revealed that the extracts of AmL-02 and CtL-06 had strong antimutagenic activity against both mutagens. All the endophytic isolates were assessed for their potential role in producing extracellular enzymes on solid media. The results showed that the endophytic isolates had the capability of producing lipase (78%) cellulase (30%) protease (22%) and pectinase (19%), but none could produce amylase. One of the endophytic isolates (XmL-02) isolated from leaves had significant maximum lipase enzyme activity based on extracellular enzyme production ratio values (3.56 mm). Isolate XmL-02 had the highest lipase activity (82.22 U/ml) in the culture media for 72 hours at 30°C and pH 3. Hence, the three isolates, AmL-02, CtL-06 and XmL-02, were identified based on a combination of their morphological characteristics and internal transcribed spacer (ITS) sequences. The results revealed that CtL-06, AmL-02 and XmL-02 were as Aspergillus luchuensis, Xylaria feejeensis and Colletotrichum gloeosporioides, respectively. These results indicated that the mangrove plants at this location harbored rich sources of fungal endophytes with different types of bioactivity.