Isolation And Identification Of Myxobacteria From Soils In Bayannaoer Area And Preliminary Study On Their Antibiotic Activities Against Phytophthora Infestans

Myxobacteria are gliding gram-negative bacteria with complicated multicellular behaviors and morphogenesis. They can synthesize a large number of biologically active secondary metabolites. Myxobacterial metabolites exhibit many unique structural features as well as rare or novel modes of action, many of which are antibacterial, antiviral, and antitumor compounds. Therefore, the research on myxobacteria has received more and more attention.In this study,45 soil samples were collected from Bayannaoer city and physical and chemical indicators of these soil samples were tested.249 myxobacteria strains were isolated from the 45 soil samples by rabbit dung inducing method, filter inducing method, E. coli inducing method and 147 of them were purified. The purified strains were primarily identified by their colony and fruting body morphology. Then,16 representative strains were identified by 16S rDNA sequencing method. The results showed that those strains which could be identified belonged to 9 species of myxobacteria, including Myxococcus xanthus, Myxococcus virescens, Myxococcus stipitatus, Myxococcus fulvus, Corallococcus macrosporus, Corallococcus exiguous, Corallococcus coralloides, Pyxidicoccusfallax, Cystobacter violaceus.The antagonistic strains against Phytophthora infestans were screened by plate confrontation assay and the strain YR-7 and YR-35 exhibited the strangest antagonistic activity among these strains, an inhibition rate of 96.67% to Phytophthora infestans. They were futher identified by their vegetative cell and myxospore morphology, physiological and biochemical characteristics, and their 16S rDNA gene sequence. It was indicated that the YR-7 strain was identified as Myxococcus xanthus and the YR-35 strain was identified as Myxococcus virescens.The strain YR-7 was further studied on its antibiotic activity. Its antibiotic substances could tolerate high temperature well. Its activity could be maintained from 30℃ to 50℃ (inhibition rate of 50.90%) and decreased when the temperature exceeded 50℃. Its activity still remained an inhibition rate of 25.45% after treated at 90℃ for 1h. The concentrated fermentation supernatant was stable from pH 4.0 to 9.0 and its inhibition rate was more than 40.21%. Its activity significantly decreased when the pH value was less than 4.0 or greater than 9.0. The active substances could not be degraded by protease and their activity was not affected by UV and natural light exposure. The relative lesion area of potato leaves declined from 68.19% to 0.35% when the concentrated fermentation supernatant was sprayed on the leaves before the spore suspension of Phytophthora infestans was inoculated. The antibiotic substances have good stability and could effectively inhibit Phytophthora infestans from infecting potato leaves, which have the potential value for developing biological pesticides resistant to potato late blight.