STUDIES ON THE IDENTIFICATION OF THE STRAIN OF Bl 1 AND CHARACTERISTICS OF ANTIMICROBIAL SUBSTANCE PRODUCED BY IT

An antagonistic bacterial strain Bn isolated from the soils, produced large amount of antimicrobial substance, strongly inhibits the growth of Fusarium oxysporum f.sp.niveum. On the basis of observation of colong and cell morphology, biochemical test, Grain stain reaction and the 16s rDNA sequence analysis, the strain of Bll was identified as Bacillus subtil is. Yield of antimicrobial substance produced by Bll was affected by medium, culturing temperature, pH and culturing times. The optimum conditions for producing antimicrobial substance by the strain of Bll were in YDCmedium, initial pH 7.0-8.0 and at 40"C after culturing 12d.The antimicrobial substance was purified by ammonium sulphate at 50% saturation and has the best inhibitory activity against Fusarium oxysporum f.sp.niveum. Thissubstance is thermostable(125 30min) and resists to Ultraviolet rays, Proteinase K and RNase. But it is partially sensitive to pepsin, Trypsin and chloroform. Its active pH is6.0-8.0oThe antimicrobial substance has inhibitory activity against many plant pathogenic fungi and bacteria, such as Thanatephorus cucumeris, Sclerotinia sclerotiorwn, Pyricularia grisea, Phytophthora nicotianae, Botrytis sp. and Ralstonia solanacearum et.. But it has no inhibitory activity against Pythium aphanidermatumand Xanthomonas oryiae pv. Oryzae. The mechanism of the antimicrobial substance against the growth of F. oxysporum f.sp. niveum was mainly to make hypha abnormal, cytoplasm condensation and the spores germinate abnormally.