Preliminary Studies On The Screening And The Metabolite Of Antagonistic Actinomycete In Soil

In this study, 174 strains of actmomycetes were isolated and purified from soil samples which collected from various areas in the north region of Shaanxi. All the actmomycetes were identified by the classical classified method. The result showed that they could be classified into 8 genera, Streptomyces, Nocardia, Micromonospora, Actinomyces, Actinoplanes, Mycobacterium, Dermatophilus and Streptosporangium. Streptomyces was the main genus, followed by Nocardia and Micromonospora.10 strains of actinomycetes with antagonism were screened from the isolated actinomycetes by the method of fermentation filtrate diffusion. The atifungal activity of the NW136 strain was better than other antagonistic actinomycetes. Its fermentation filtrate inhibited multi-pathogentic fungi intensively. The results of mycelium growth rate showed that the values of EC50 against Bipolaris sorokiniana, Botrytis cintrea, Fusarium graminearum, Alternaria longipes and Exserohilum turcicum were 1.81mL/L 12.93mL/L 8.16mL/L 3.96mL/L 3.92mL/L respectively. The results of the antagonistic function test proved that NW136 strain not only could produce antibiotics outside of the cell but also had competitive effect.In order to increase the production of the fungicidal substance, the liquid media composition was optimized and the fermentation condition was primarily studied. The optimum fermentation medium of the NW136 Strain was composed of corn powder 2.0%, glucose 1.5%, starch 1.5%, K₂HPO₄ 0.05% , CaCO₃ 0.5%. The optimum fermentation condition was the initial pH of medium 7.5, fermentation temperature 28℃, inoculum size 8%, liquid volume 50 ml (in 250ml flask) , 210r/min for 108h.The stability of the antibiotic productivity of the NW136 strain was not changed by serial subculture. The fungicidal substance produced by the NW136 strain was heat-resistant and acid-resistant, but it could not sustain the ultraviolet irradiation and the basic condition.The results of the potted plant experiment showed that the fermentation filtrate of the NW136 strain had a certain degree protective and therapeutic effect on Botrytis cintrea, and the protective effect was better than the therapeutic effect. Thecontrol effect were above 70% at the concentration of 200mL/L. The results of the field plot experiment indicated that the control effect on the diseased blades and fruits of tomato plant could be 69.82% and 72.74% at the concentration of 300ml/L respectively.By the classical classified method, the NW136 strain was primarily identified as Albosporus group of Streptomyces, which is similar to Streptomyces albidus.