Isolation And Identification Of Strain A And Characteristics Of Its Antifungal Substance

Antagonistic bacteria showed strong antagonistic activities against Bipolaris maydis were isolated from the diseased leaves of corn. The bacteria, designated as strain A, have inhibitory activity to many plant pathogenic fungi in vitro, such as Bipolaris maydis, Magnaporthe grisea, Fusarium graminearum, Fusarium oxysporum f.sp.Vasinfectum, Colletotrichum capsici, phytophora capsici, Colletotrichum lagenarium, Sclerotinia allii, Verticillium dahliae and Alternaria alternate.On the basis of observation of colony and cell morphology, biochemical test, Grain stain reaction and the 16S rDNA sequence analysis, the strain A was identified as Bacillus subtilis.The antimicrobial substance from the strain A cell-free culture was purified by ammonium sulphate at 60 % saturation and has the best inhibitory activity against Bipolaris maydis . This substance is thermostable (100℃,10 min) and partially sensitive to Ultraviolet rays, Trypsin. But it is sensitive to Proteinase K and chloroform. Its active pH is 6.0-8.0. The mechanism of the antimicrobial substance against the growth of Bipolaris maydis was mainly to make hypha abnormal, cytoplasm condensation and the spores germinate abnormally.The antimicrobial substance deposited by ammonium sulphate at 60 % saturation was purified by DE-52 cellulose column and Sephadex G-200 column. The fraction contained antifungal activity exhibited two bands with SDS-PAGE. The aim of this research is to obtain the purified antimicrobial peptide and analyze its amino acid sequence. However, the purification of antimicrobial peptides have not yet been finished, it will be carried on in our laboratory in the future.