Secondary metabolites of endophytic fungi isolated from Casuarina equisetifolia and their bioactivities

Objective  To isolate and identify endophytic fungi from branches and fruits of Casuarina equisetifolia Forst., and screen active endophytic fungi with antibacterial and antioxidant activities.

Method  Endophytic fungi from branches and fruits of C. equisetifolia were isolated by the tissue block separation method, and identified by combining colony observation with molecular biology. The antibacterial activities of secondary metabolites produced by endophytic fungi against different bacteria were determined using TLC-bioautography and their antioxidant activities were determined using the multi-orifice plate-DPPH coloration method.

Result  Twelve strains were isolated and identified from branches and fruits of C. equisetifolia. There were significant difference between endophytic fungi isolated from branches and fruits. There were only two same endophytic fungus strains in branches and fruits, namely Cef-1 (Pseudofusicoccum sp.) and Cef-7 (Pestalotiopsis sp.). All endophytic fungi were mainly distributed in nine different genera, including Pseudofusicoccum, Botryosphaeria, Pestalotiopsis, Trichoderma, Aspergillus, Rhytidhysteron, Phomopsis, Fusarium and Colletotrichum. Among them, Botryosphaeria had the most species and was the dominant species, followed by Pestalotiopsis. Cef-2 (Botryosphaeria sp.) showed the strongest inhibitory activity and the diameters of antibacterial spots were more than 10 mm, which were stronger than that of the positive control streptomycin sulfate. Cef-1 and Cef-9 (Fusarium sp.) showed well inhibition on Ralstonia solanacearum. Cef-2 displayed the best antioxidant activity and the IC₅₀ value was 0.80 mg/mL.

Conclusion  There are endophytic fungi in branches and fruits of Casuarina equisetifolia, and Botryosphaeria is the dominant species. There are significant differences of fungi species between branches and fruits. Endophytic fungus Cef-2 exhibits the strongest antibacterial and antioxidant activities, which can be used as a candidate strain for further isolation and identification of active component.