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Impact of Valinomycin, a novel antibiotic produced by Streptomyces sp. S8 in Large patch

Chang Wook Jeon: Gyeongsang National University

<div>Large patch disease, caused by <em>Rhizoctonia solani</em> AG2-2, is a fungal disease commonly found on Zoysiagrass, it poses a significant threat to golf courses and turfgrass field. In order to rectify such issues, <em>Streptomyces </em>sp. S8 was selected based pyrosequencing and microbial-ecology studies. S8 is known to possess exceptional antagonistic actions against the large patch pathogen found at grass plantations. This study aimed to demonstrate the feasibility of using the strain as a biological agent through a series of root colonization assays and addition to elucidate the microorganisms’ antifungal mechanism. The S8 strain root colonization ability was found to be outstanding with over 6 log cfu/g of rhizosphere soil by the fourth week of plantation. Subsequent to treatment the S8 strain suppressed densities of the pathogen, the <em>R. solani</em> AG2-2 population density was 0.7 cfu/toothpick on the first week, which rose marginally to 1.2 cfu/toothpick on the fourth week and it was also excellent in terms of controlling the large patch disease. As the result, genome of the S8 strain was sequenced and existence of valinomycin biosynthesis gene was confirmed. The valinomycin biosynthesis gene was composed of the <em>vlm1</em> and <em>vlm2</em> genes, which were known to produce substances that have outstanding antifungal activity in previous studies. In order to verify the finding, a deletion mutant was created by CRISPR/Cas9 system in the valinomycin biosynthesis gene, <em>vlm2</em>. The deletion strain showed significantly reduced antifungal activity against the large patch pathogen. Therefore, it is anticipated that eco-friendly microorganism preparations derived from the S8 strain can be utilized to control the large patch disease in turfgrass.</p> <p></div>