title: Plant methyl salicylate induces defense responses in the rhizobacterium Bacillus subtilis.
abstract: Bacillus subtilis is a rhizobacterium that promotes plant growth and health. Cultivation of B. subtilis with an uprooted weed on solid medium produced pleat-like architectures on colonies near the plant. To test whether plants emit signals that affect B. subtilis colony morphology, we examined the effect of plant-related compounds on colony morphology. Bacillus subtilis formed mucoid colonies specifically in response to methyl salicylate, which is a plant-defense signal released in response to pathogen infection. Methyl salicylate induced mucoid colony formation by stimulating poly-γ-glutamic acid biosynthesis, which formed enclosing capsules that protected the cells from exposure to antimicrobial compounds. Poly-γ-glutamic acid synthesis depended on the DegS-DegU two-component regulatory system, which activated DegSU-dependent gene transcription in response to methyl salicylate. Bacillus subtilis did not induce plant methyl salicylate production, indicating that the most probable source of methyl salicylate in the rhizosphere is pathogen-infected plants. Methyl salicylate induced B. subtilis biosynthesis of the antibiotics bacilysin and fengycin, the latter of which exhibited inhibitory activity against the plant pathogenic fungus Fusarium oxysporum. We propose that B. subtilis may sense plants under pathogen attack via methyl salicylate, and express defense responses that protect both B. subtilis and host plants in the rhizosphere.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science & Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kobayashi
mesh_terms: D000900:Anti-Bacterial Agents / Q000096:biosynthesis; D001412:Bacillus subtilis / Q000276:immunology* / Q000378:metabolism; D005670:Fusarium / Q000502:physiology; D010935:Plant Diseases / Q000276:immunology / Q000382:microbiology; D010944:Plants / Q000276:immunology* / Q000382:microbiology; D011099:Polyglutamic Acid / Q000031:analogs & derivatives / Q000096:biosynthesis; D058441:Rhizosphere; D012459:Salicylates / Q000276:immunology*
chemical_list: D000900:Anti-Bacterial Agents; D012459:Salicylates; C511775:poly(gamma-glutamic acid); D011099:Polyglutamic Acid; C033069:methyl salicylate