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Biofilm formation of Bacillus subtilis on tomato roots enhances biocontrol efficacy against tomato bacterial wilt disease caused by Ralstonia solanacearum.
Y. CHEN (1), F. Yan (1), H. Liu (1), Y. Chai (2), J. Guo (1). (1) Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Nanjing, Peoples Republic of China; (2) Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA, U.S.A.

The soil-living bacterium <i>Bacillus subtilis</i> is able to form architecturally complex cell communities, known as biofilms. <i>B. subtilis</i> has long been used in the field of agriculture as a biocontrol reagent to protect plants against soil-borne plant pathogens. The exact mechanisms for plant biocontrol have not been clearly addressed. In this study, we established <i>B. subtilis</i>-tomato interaction system to explore the biocontrol mechanisms. We isolated many <i>B. subtilis</i> strains form various natural environments in China, and obtained 6 wild stains demonstrated above 50% biocontrol efficacy against the <i>R. solanacearum</i> under greenhouse conditions. They also showed robust biofilm formation both in biofilm-inducing media and on tomato plant roots, and exhibited strong antagonistic activities again various plant pathogens <i>in vitro</i>. We knocked out 7 key genes related to <i>B. subtilis</i> biofilm formation by transformation and evaluated the biocontrol efficacy of these mutants. Results indicated the biofilm formation ability of<i> B. subtilis</i> is positively correlated to biocontrol efficiency against tomato bacterail wilt disease. Meanwhile, the antimicrobial capability is also necessary to inhibit <i>R. solanacearum</i>, especially surfactin. The surfactin mutant strains seriously decreased biocontrol efficacy. Finally, we suggested <i>B. subtilis</i> biofilm formation and production of antimicrobial agents may act synergistically to enhance biocontrol efficacy during the plant diseases management. <p><p>Keywords: Bacteria-Phytoplasma-Spiroplasma-Fastidious Prokaryote, Vegetables, Tomato

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