Identification of an ISR-related metabolite produced by rhizobacterium Klebsiella oxytoca C1036 active against soft-rot disease pathogen in tobacco.

Background: Klebsiella oxytoca C1036 (C1036) causes induced systemic resistance (ISR) activity against the soft-rot pathogen Pectobacterium carotovorum subsp. carotovorum SCC1 (SCC1). However, microbial metabolites from C1036 involved in ISR activity remain unknown. The present study was performed to identify an ISR-related metabolite produced by C1036.

Results: The supernatants of C1036 cultures grown on Luria-Bertani medium were subjected to solvent extraction, repeated column chromatography and preparative liquid chromatography for isolation of an ISR-related metabolite. High-resolution mass spectrometer analysis of the isolated metabolite indicated a C9H15O3N compound with a mass of 185.11. Low-resolution mass spectrometer analysis of the metabolite showed a molecular ion peak at 185 and its fragment ions at 84 and 56. Nuclear magnetic resonance spectrometer analyses characterised all protons and carbons of the isolated metabolite. Based on the data, the isolated metabolite was determined to be butyl 2-pyrrolidone-5-carboxylate (BPC). BPC at 12 mM significantly suppressed the disease symptoms in ISR bioassays against SCC1.

Conclusion: This is the first report identifying BPC as an ISR-related metabolite produced by C1036. C1036 may play a role in promoting plant growth because it produces ISR-related metabolites against the plant pathogen SCC1.