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• Genetic marker development and LC-MS analysis rapidly detected antimicrobial compounds in 47 Bacillus strains. • Only 19 Bacillus strains possessed antimicrobial compounds among the screened strains. • Bacillus strains and their methanolic extracts showed suppression of Sclerotinia sclerotiorum during in vitro assays. Bacillus strains are well studied for antagonistic effect against fungal pathogens, but the selection of potential antifungal strains is laborious and time-consuming process. Newly developed genetic markers and LC-MS based detection was undertaken simultaneously to detect eight antimicrobial compounds viz., surfactin, bacillomycin, iturin, fengycin/plipastatin, bacilysin, bacillaene, bacillibactin and plantazolicin in forty-seven Bacillus strains. Out of these strains, 19 were positive for the presence of marker genes encoding antimicrobial compounds. Bacillus strains FZB42, EZ1509, EZ1507, VM10, GBAC46, VM49 and LLCG43 possessed genes for maximum number of antimicrobial compounds. LC-MS analysis of antimicrobial compounds showed corresponding results except OKB105 and 168. Contrary to marker-based detection of genes, LC-MS analysis revealed that OKB105 can produce surfactin but unable to synthesize fengycin, while 168 was deficit in both compounds. To assay antifungal potential, 19 Bacillus strains and their methanolic extracts were tested in vitro to inhibit mycelial growth of S. sclerotiorum. Results revealed that EZ1509, VM10, GBAC46, VM49 and FZB42 showed highest inhibitory activity. A bioassay on detached rapeseed leaves demonstrated that strains VM10, EZ1509, FZB42 and GBAC46 were excellent in reducing lesion diameter, while, OKB105 and 168 were completely ineffective to control S. sclerotiorum. Interestingly, antifungal activity of Bacillus strains was positively co-related to the number of antimicrobial genes, indicating their role in antifungal activity of Bacillus strains. Our findings suggest that combining genetic markers and LC-MS analysis can rapidly screen Potential Bacillus strains with antifungal attributes and this screening method can serve as foundation for the development of new biopesticides. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria (PGPR) are beneficial soil microorganisms that colonize plant roots for nutritional purposes and benefit plants by increasing plant growth or reducing plant disease. To clarify the complex mechanisms underlying plant-PGPR interactions, transcriptomic analyses of the response of rice ( Oryza sativa ) 9311 to Bacillus amyloliquefaciens FZB42 were carried out using RNA-Seq technology. This resulted in the identification of 379 differentially expressed genes in rice roots and 719 in rice leaves following FZB42 interaction that are likely to be related to plant-PGPR interactions, plant stress-resistance, pathogen-resistance, growth and development and basic and energy metabolism. We focused on plant disease-resistance mechanisms induced by FZB42. Variations in the expression of crucial genes COI1 , MEKK1 , WRKY, and PR that are involved in signal transduction following plant-pathogen interaction at different interaction time points were examined. Significantly up-regulated expression of PR , LOX, and ERF genes involved in the salicylic acid, jasmonic acid, and ethylene signal transduction pathways, respectively, were detected, suggest that defense reactions in rice were induced following interaction with FZB42. Phytoalexin changes in rice induced by FZB42 were examined and momilactone A, phytocassane A, phytocassane D, phytocassane E levels were low at 12 h, rose between 24 and 48 h, suggesting a PGPR-mediated mechanism of plant pathogen resistance. The study indicated that plant responses to PGPR in multi-metabolism pathways, which includes improving plant pathogen-resistance by mediating multi-signal transduction that regulates the expression of PRs and other defense genes, as well as influencing fundamental metabolic pathways to enhance the plant’s physical condition. [ABSTRACT FROM AUTHOR]

Root colonization is important for the application of Plant Growth-Promoting Rhizobacteria (PGPR). Previously, chemotaxis was believed to be the major trait for colonization. However, because chemotaxis defective mutants are usually swarming impaired at the same time, in this study we clarified the roles played by swarming motility and chemotaxis in tomato root colonization by Bacillus subtilis SWR01. Tomato seeds were treated with B. subtilis SWR01 or mutants before being sown in Simons’ gnotobiotic system, and the colonization efficacy at root tips were observed after 2 weeks. Both microscopy and plate counts showed that the colonization efficacy of swarming defective and chemotaxis proficient mutants ( ΔswrA , ΔminJ and ΔsrfAC ) was about 5%–15% that of the parental strain SWR01, while the colonization efficacy of the swarming normal and chemotaxis impaired mutant ΔcheV was 78.9% that of the wild-type bacteria. These results demonstrate that while both chemotaxis and swarming motility are important in root colonization, and the role played by swarming is greater than that of chemotaxis. In addition, non-flagellated mutants ( Δhag ) showed 0.47% colonization efficacy relative to that of B. subtilis SWR01, suggesting more than 99% root colonization requires the presence of flagella. This study indicates new ways to enhance PGPR rhizoplane colonization, which is useful in agricultural applications. [ABSTRACT FROM AUTHOR]