Study On An Antagonistic Bacterium And Its Antagonistic Substance With Antifungal Activity Against Rice Sheath Blight

The endophytic bacterial strain 223 was screened from rice leaves in Fuyang, Zhejiang Province, China. Based on the analysis of phenotypic characteristics,16S rDNA and gyrB gene sequences,223 was found both highly similar to Bacillus pumilus and Bacillus safensis, so it is worthwhile to do more study for the identification of strain 223.In this work, a novel protein produced by a Bacillus strain 223 with high inhibitory activity against Rhizoctonia solani was purified. The purification procedure consisted of ammonium sulfate precipitation, dialyzation, gel filtration chromatography on Sephadex G-100 column and lyophilize on a cryosublimation trap. After the final step, one protein named ZJU223 with antifungal activity was obtained, and its concentration was 47.78μg ml-1. The molecular mass of this protein was determined as 10.7～14.4 kDa by Tricine-SDS-PAGE. Two amino acid sequences were obtained by N-terminal sequencing, and they both showed low identity to other antimicrobial protein/peptides from bacteria. Partial characterization study indicated ZJU223 was a thermal unstable protein, its optimum temperature for the antifungal activities was about 30～45℃, and it could be destroyed by protease K and protease E, but not by pepsin. Besides, the antifungal activity of ZJU223 was relatively stable in a wide range of pH (2-12). Several species of fungal including Fusarium graminearum could be inhibited by ZJU223 in vitro, and the minimal inhibitory concentration to Rhizoctonia solani was 0.32μg ml-1. ZJU223 also exhibited favorable antifungal activity to R. solani in vivo, and the control effects were not second to Jinggangmycin.The results of this research showed the potential of Bacillus strain 223 and its antagonistic substance for the control of rice sheath blight. It provided the experimental basis for the study of its structure and function, and the development of a kind of new biological pesticides against rice sheath blight at last. In the next, further research on this strain and its antagonistic substances will be taken, and we expect that we can develop a new kind of biological pesticide by using this strain in the future.