Multitargeted antibacterial mechanisms of Iturin A derived from Bacillus amyloliquefaciens against tomato bacterial wilt

Abstract

Tomato bacterial wilt is a devastating disease caused by Ralstonia solanacearum . This study aimed to evaluate the antibacterial activity of Iturin A, a cyclic lipopeptide produced by Bacillus amyloliquefaciens strain Cas02, against R. solanacearum and investigate its mechanisms of action. The results indicated that Iturin A effectively inhibited the growth of R. solanacearum with an MIC and IC 50 of 25.00 and 15.79 μg/mL, respectively. In pot experiments, Iturin A significantly reduced disease incidence with a control efficacy of 74.27%. Microscopy observations revealed that Iturin A induced severe morphological damage, including membrane disruption and cytoplasmic leakage, and inhibited biofilm formation. Additionally, Iturin A caused the accumulation of intracellular reactive oxygen species, a decrease in succinate dehydrogenase activity, reductions in NAD + and NADH content, and alterations in cytochrome c oxidase staining, indicating disruption of the electron transport chain and energy metabolism. Transcriptome analysis further indicated the downregulation of genes related to the membrane structure and type III secretion system. Overall, these findings suggest that Iturin A may exert antibacterial effects through multiple pathways, including impairment on cell integrity, biofilm formation, energy metabolism, and virulence-associated functions. This study provides a basis for further exploration of Iturin A as a potential antibacterial agent for managing tomato bacterial wilt.