Purification of four strains of endophytic fungi from Astragalus and their optimized liquid fermentations

This study was designed to isolate endophytic fungi from A. mongholicus (growing in northeast China) to determine whether they can produce bioactive metabolites. Four strains of endophytic fungi (strains 16, 17, 23 and 75) were successfully isolated from A. mongholicus using the surface disinfection method. According to ITS-rDNA sequences analysis, strains 16 and 75 were identified as Fusarium oxysporum, and strains 17 and 23 were identified as Bionectria ochroleuca. We applied the Box-Behnken design (BBD) to optimize the liquid fermentation conditions and obtain the maximum cell dry weight (CDW) yield. Optimal parameters were obtained under the following experimental conditions: temperature of 28°C, potato dextrose agar (PDA) liquid medium of 80 mL and rotation speed of 150 rpm. The four isolated endophytic fungi did not produce astragalosides I–IV, flavonoids or polysaccharides. Isolation of additional species of endophytic fungi from A. mongholicus and determination of their capacity to produce biologically active substances are subjects in need of further research.