Identification And Characterization Of Antibiotics With Strong Antifungal Activity From Bacillus Amyloliquefacies Q-12

Plant disease can cause serious crop losses, and chemical control of disease is costly both to the environment and to the farmer. In order to screen antifungal bacteria for use in biological control, 200 compost samples were taken from different regions in China. Strain Q-12 with clear antifungal activity was isolated from the composts, which strongly inhibits the growth of many plant pathogenic fungi such as Fusarium Oxysporum, Rhizoctonia solan, Fusarium graminearium, Curvularia lunata, Exsero turcicum, Bipolaris maydis, Coniothyrium diplodiella, Sclerotinia sclerotiorum and Colletotrichum lindemuthianum.According to the characteristics of morphology, physiology and biochemistry tests and the comparison of 16S rDNA sequence, it is found that the strain Q-12 was similar to B. subtil is and B. amyloliquefaciens. Some specific genes yyaR, yyaO and tetB were analysed to clarify further the classification of Q-12. From the analysis of fingerprints obtained with the designed primers, strain Q-12 and B. amyloliquefaciens showed identical genomic fingerprints, indicating their closely genetic relationship, and the strain Q-12 was identified as B. amyloliquefaciens.In the investigation of the culture condition, growth was carried out in a basal medium and gradually supplemented with the various ingredients to be investigated. The strain is easy to cultivate, and the optimal antibiotic production condition is growth in a medium (5 g/L glucose, 1 g/L NH4CI, 0.8 g/L beef extract, 5 g/L NaCl2, pH 6.0) at 33℃ for 30 h. The antimicrobial substance produced by Q-12 was heat-stable, not sensitive to pH, inactivated by proteolytic enzymes, and strongly inhibit many plant pathogenic fungi and was affected on the spore formation of Fusarium oxysporum.Four fractions with high antifungal activity were isolated from the fermentation of Q-12 through ammonium sulfate precipitation and anion exchange chromatography. One of the fractions QA I was further purified by gel filtration and semi-RP HPLC separation, and whose chemical structure was elucidated by ultraviolet, infrared, 1H nuclear magnetic resonance and electrospray ionization mass spectrometry. The results showed that molocular weight of QA I was 1017.8 Da and it was different to polysaccharide and protein.