Studies On Screening, Identification, And Antibiotic Physicochemical Property Of Antagonistic Streptomyces Against Bacterial Canker Of Tomato

Bacterial canker of tomato caused by Clavibacter michiganensis subsp. michiganensis (Cmm) is a worldwide bacterial disease. It caused huge economic losses in tomato production. Safety and effectiveness bactericides for canker control have not been found yet. In this research, Streptomyces were used to screen biological control agents against Cmm, and the antagonistic strain was identified at the meanwhile. Besides that, the physicochemical property of the antibiotic substance was analysed. What we have done will lay the groundwork for biocontrol of the disease in the future.One hundred and seventy strains of Streptomyces were isolated from tomato rhizosphere in this study, twenty four strains of Streptomyces that were kept in our lab were tested for antibiotic Streptomyces against Cmm. On double-layer agar sixty seven isolates showed an antibiosis activity with a diameter of an inhibition zone ranging from 1.0~6.5 cm. Fourteen Streptomyces strains had a strong antibiosis activity against Cmm with a diameter of the inhibition zone above 4.0 cm in double-layer agar. Especially, the strain named Z-L-22 showed the strongest antibiosis activity among them with 6.5 cm of zone inhibition. The fermentation filtrate showed a high inhibition activity against Gram-positive bacteria such as Streptomyces scabies, Staphylococcus aureus, Bacillus subtilis. Morphological, physiological and biochemical tests and 16S rDNA sequence analysis were made to identify the strain Z-L-22. Characteristics of the Z-L-22 are similar to those of Streptomyces setonii, and the 16S rDNA sequence showed 99.4% homology to S. setonii. Based on the polyphase taxonomical views, Z-L-22 was identified as S. setonii.The optimum fermentation conditions were determined that 25 mL liquid soybean cake medium were added in 250 mL flask and were cultured at (30±2)℃, 200 r/min for 72 hours.The antibiotic substance produced by Z-L-22 showed a stable antibiotic activity to heat and pH. This substance not only existed in the fermentation liquid but also in the mycelium, it was soluble both in organic phase and in aqueous phase. The antibiotic substance was isolated and purified primary using the methods of solvent extraction and Thin Layer Chromatography (TLC). The results showed that the antibiotic substance contained four components, and the component Ⅰ and Ⅱ had bioactivity against Cmm. The extraction had three absorbance peaks respectively at 253 nm, 424 nm and 443 nm in...