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Elucidation of the mechanisms employed by Bacillus mycoides BM02 in controlling tomato Fusarium wilt

Je-Jia Wu: Ph.D. Program in Microbial Genomics, National Chung Hsing University and Academia Sinica

<div><em>Bacillus mycoides </em>in the <em>B. cereus </em>group forms rhizoidal colonies on solid medium, and the strain BM02 isolated from tomato rhizoplane in Taiwan has proven to have promising biocontrol activity. The <em>de novo </em>assembled complete genome of BM02 (5,782,184 bp) is composed of one chromosomal DNA and four plasmids, and subsequent genome mining revealed several gene clusters for synthesizing secondary metabolites might be involved in biocontrol activity. Application of formulated BM02 reduced the disease severity of tomato Fusarium wilt, and activated defense-related genes in SA (<em>PR1a</em>) and ET (<em>LeACO5</em>) signaling pathways in tomato roots that were co-inoculated with BM02 and <em>Fusarium oxysporum </em>f. sp.<em> lycopersici</em> Fol-04. Microscopic observation revealed that BM02 was able to interfere with the infection of GFP-tagged Fol-04 by reducing conidia germination, inducing abnormal hyphae, and inhibiting the formation of appressorium-like structure on tomato roots. The crude extracts of siderophores with iron chelating activity from the culture filtrate of BM02 were found to inhibit conidia germination and stimulate abnormal hyphae formation of Fol-04 <em>in vitro</em>; further analysis, including the chemical structure of the bioactive compound(s), are in progress to determine the biological activities of BM02. Altogether, BM02 has the capacities of activating plant defense responses and producing antifungal metabolites that were collectively involved in controlling tomato Fusarium wilt disease.</div>