Xenocoumacin 1 from Xenorhabdus nematophila CB6-T2: Antibacterial Spectrum and Multi-Target Mode of Action against Ralstonia solanacearum K60-1

Abstract Xenocoumacin 1 (Xcn1), a dihydroisocoumarin-derived antimicrobial natural product from Xenorhabdus nematophila CB6-T2, exhibits broad-spectrum antifungal activity, yet its antibacterial mechanism remains unknown. This study evaluated the antibacterial spectrum of Xcn1 against 13 bacterial strains, with Ralstonia solanacearum K60-1 showing the highest susceptibility (MIC90 = 0.780 μg/mL). In pot experiments, Xcn1 provided >66.0% efficacy against bacterial wilt, comparable to zhongshengmycin. Phenotypic assays revealed antibacterial effects characterized by membrane disruption, together with antivirulence effects, including inhibition of biofilm formation (90.3%) and suppression of swimming and twitching motilities (>61.0%). Integrated transcriptomic and proteomic analyses identified 934 differentially expressed genes and 356 differentially expressed proteins, highlighting oxidative phosphorylation as the most enriched pathway and ubiB and glmU as key downregulated hub genes. These findings reveal a multi-target antibacterial mechanism involving membrane disruption, energy metabolism collapse, and virulence attenuation, positioning Xcn1 as a promising green antibacterial candidate for the management of bacterial wilt. Future studies should focus on formulation optimization, field-scale efficacy and long-term resistance monitoring, and further confirmation of its direct molecular targets.