Abstract: 【Objective】The objectives of this experiment are to screen bioactive endophytic actinomycete from Berberis thunbergii, a traditional Chinese medicinal plant, study the taxonomic status and antimicrobial activity of the active strain, investigate the chemical structures and antimicrobial activity of active ingredients in the fermentation, and to provide a basis for the development of agricultural fungicide.【Method】 The endophytic actinomycete was isolated from the leaf of B. thunbergii by using selective culture techniques, and the obtained strain was identified by using 16S rDNA sequencing. The antibacterial and antifungal activities of the fermentation broth against seven species of tested bacteria (such as Ralstonia solanacearum) and plant pathogenic fungi (such as Botrytis cinerea) were tested by cylinder-plate method and mycelial growth method, respectively. The active ingredients were obtained by the techniques of macroporous resin adsorption, silica gel column chromatography and preparative reverse phase high performance liquid chromatography. Structures of the obtained compounds were elucidated by NMR and ESI-MS techniques. Minimum inhibitory concentrations (MICs) of active ingredients against tested bacteria were determined by micro-broth dilution method. Antifungal activity of H2101 against B. cinerea was tested by the methods of mycelial growth and spore germination, respectively.【Result】Strain H21, an active species, was isolated from the plant, and it was identified as Streptomyces sp. by the method of 16S rDNA sequencing. Except Pseudomonas aeruginosa, the fermentation broth of H21 showed strong antibacterial against the tested bacteria, such as R. solanacearum, P. syringae pv. actinidiae, Bacillus subtilis, B. cereus, Staphylococcus aureus and Escherichia coli. However, the fermentation broth could only inhibit the mecelial growth of B. cinerea. No inhibitory effect was observed against other tested fungi. Holomycin, a member of the pyrrothine class of antibiotics, as well as N-acetyl-2-(4-hydroxyphenyl)-ethylamine and cyclo (L-Leu-L-Arg), was isolated from the broth of strain H21. Holomycin exhibited broad antimicrobial activity, and the MIC values against R. solanacearum, P. syringae pv. actinidiae, B. cereus, B. subtilis, E. coli and S. aureus were 0.156, 0.313, 0.078, 0.313, 0.156 and 0.313 µg·mL^-1, respectively. Meanwhile, holomycin had strong antifungal activity against B. cinerea, and its IC₅₀ values against mycelial growth and spore germination were 13.56 and 7.89 µg·mL^-1, respectively.【Conclusion】Streptomyces sp. is a newly discovered producer of holomycin, and it has the antibacterial holomycin against R. solanacearum and P. syringae pv. actinidiae, two species of plant pathogenic bacteria. In general, holomycin is a valuable lead compound for the development of agricultural fungicides with those acts on bacteria.

Key words: Berberis thunbergii, endophytic actinomycete, holomycin, antimicrobial activity