Study on Isolation of Endophytes from the Medicinal Plant Tripterygium Wilfordii and Screening of Its Antibacterial Activity

OBJECTIVE To study the isolation and antibacterial activity of endophytic fungi from medicinal plant Tripterygium wilfordii and predict the types of secondary metabolites, provide the basis for further screening of natural antibacterial substances produced by endophytic fungi of Tripterygium wilfordii. METHODS The methods of tissue block and repeated line were used to isolate and purify the endophyte from T. wilfordii. The activity of the liquid fermentation broth of endophyte against the tested strains of S. aureus, C. albicans and P. aeruginosa was detected through the filter paper method, and the minimum inhibitory concentration(MIC) of active strains was detected by microdilution method. The fermentation broth of strains with antibacterial function was analyzed by UPLC/Q-TOF-MS method, and the total ion chromatogram of each sample was obtained. Combined with relevant databases and software, mass spectrometry network analysis was carried out on its components to predict the types of microbial secondary metabolites. RESULTS There were 20 strains of endophytic fungi obtained from T. wilfordii. The fermentation broth of 5 endophytic fungi had significant antibacterial activity against S. aureus. Among them, LGT-15 had high antibacterial activity against S. aureus, P. aeruginosa and C. albicans with the inhibition zones diameters 38.0, 34.0, 13.1 mm, and the MICs 0.49, 0.61, 1.46 μg·mL^-1, respectively. According to the results of mass spectrometry data analysis, LGT-3 and LGT-15 metabolites were more numerous in number and types, and both contained azaspiroketones, while LGT-15 also contained novel quinazoline alkaloids. CONCLUSION Five active strains are identified by colony morphology and molecular biology. LGT-15 is identified aspergillus fumigatus. The secondary metabolites of LGT-15 should further be explored according the mass spectrometry data.