Isolation and Identification of Myxobacterial Strain X6-II-1 Resistant to Phytophthora infestans and Its Antibiotic Activity and Optimal Fermentation Condition
Abstract：Abstract Potato late bright is the most serious disease of Solanum tuberosum, and its pathogen is Phytophthora infestans. In order to screen culturable myxobacteria resistant to the pathogen of potato late blight from soil samples, myxobacteria were isolated from the soil sample by Escherichia coli inducing method in this study. The strains resistant to the pathogen of potato late blight were screened by plate confrontation assay and identified by morphological observation, physiological and biochemical characteristics, and the 16S rRNA sequence analysis. Then, the antimicrobial activities of the strain were determined by plate confrontation method. Then, the growth curve of the target strain was determined by the weighing method and the distribution of antibiotic substances was measured by filter paper disc method. The fermentation parameters were studied by the combination of univariate analysis and orthogonal optimization. Five strains were isolated in this experiment and 3 of them presented antagonistic activity against Phytophthora infestans. The activity of strain X6-II-1 was the strongest among them and the shortest distance from the edge of mycelia of Phytophthora infestans to the edge of colony of strain X6-II-1 was 5 mm. The identification results showed that this strain belonged to Myxococcus stipitatus. The strain could kill and dissolve E. coli and inhibit the growth of Bacillus subtilis. The antibiotic substances against Phytophthora infestans were mainly present in the extracellular matrix. The optimal fermentation conditions of strain X6-II-1 were as follows: Inoculum size 10%, shaking speed 180 r/min, incubation temperature 30 ℃, incubation time 7 d. The strain X6-II-1 can produce antibiotic substances against the pathogen of potato late blight, which has the potential value for developing biological pesticides resistant to potato late blight. These findings may lay a foundation for isolation and identification of the antibiotic substances and the development of new pesticides resistant to potato late blight.
