Antimicrobial activity of saponins produced by two novel endophytic fungi from Panax notoginseng

Endophytes in plants may be co-producer of the bioactive compounds of their hosts. We conducted a study to bioprospect for saponin-producing endophytic fungi from Panax notoginseng and evaluate the antimicrobial activity of saponins. Two novel fungal endophytes, Fusarium sp. PN8 and Aspergillus sp. PN17, were isolated from traditional Chinese medicinal herb P. notoginseng. After eight days of fermentation, the total saponins produced in the culture broth of PN8 and PN17 were 1.061 and 0.583 mg mL-1, respectively. The saponin extracts exhibited moderate to high (inhibition zone diameter 15.7-28.4 mm, MIC 1.6-12.5 mg mL-1) antimicrobial activity against pathogens tested. Further analysis showed that triterpenoid saponins produced by Fusarium PN8 were Rb1, Rd and 20(S)-Rg3, while Aspergillus PN17 had the ability to synthesise ginsenoside Re, Rd and 20(S)-Rg3. The isolated endophytes may be used as potential sources for microbial production of plant secondary metabolites and for antimicrobial agents.