[Screening, identification and characterization of a broadspectrum antagonistic strain in banyan rhizosphere soil]

Rhizosphere soil samples were collected from an ancient banyan tree grown in the Wanli period of Ming Dynasty in Ji'an City, Jiangxi Province. Twenty-three kinds of indicator bacteria were used to screen soil actinomycetes by cylinder-plate method and mycelium growth rate method. A broad-spectrum antagonistic strain AHF-20 with stable passage was obtained. According to the morphological observation, physiological and biochemical tests, and molecular biological identification, the antagonistic strain was identified as Streptomyces. We examined the antibacterial active substance of the strain. The results showed that the fermentation products of Streptomyces AHF-20 had antagonistic effects on all the 23 test indicator bacteria. The antibacterial ability was stable, tolerant to temperature, light, ultraviolet, acid and alkali. Antibacterial activity still existed after heating at 121 ℃ for 20 min. The fermentation product was extracted with n-butanol according to the polarity of the active substance. The obtained crude n-butanol extract was diluted to 1 μg·mL^-1, which still had inhibitory effect for Escherichia coli. The results indicated that it has well utilization potential for biocontrol and developing new microbial drug.