Bacterial wilt caused by Ralstonia solanacearum is a highly destructive soil-borne disease. Lipopeptides produced by Bacillus species are promising biocontrol agents. However, whether lipopeptides can exert biocontrol effects by attenuating the pathogenicity of R. solanacearum remains unclear. This study aims to investigate the mechanism by which lipopeptides target and reduce the pathogenicity of R. solanacearum, and to provide a theoretical basis for developing novel biocontrol agents based on pathogenicity regulation.

The minimum inhibitory concentration (MIC) of lipopeptides was determined using the broth dilution method. The control efficacy of lipopeptides against bacterial wilt was evaluated through pot experiments. Defense-related enzyme activities including superoxide dismutase (SOD), catalase (CAT), polyphenol oxidase (PPO), and peroxidase (POD), as well as the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in tomato plants were determined using commercial assay kits. Combined with scanning electron microscopy, semi-solid plate motility test, and transcriptome sequencing, the effects of lipopeptides on the morphology, motility, and gene expression of R. solanacearum were systematically analyzed.

The MIC of lipopeptides from Bacillus sp. FJAT-2349 was 0.1875 mg·mL^-1. At a sub-inhibitory concentration (0.075 mg·mL^-1), the incidence of tomato bacterial wilt decreased by 29.2% compared to the R. solanacearum control group. No significant changes were observed in the activities of SOD, CAT, PPO, POD, or the contents of MDA and H₂O₂ in tomato leaves, indicating that this concentration of lipopeptides failed to induce systemic resistance in tomato plants. SEM analysis showed that lipopeptide-treated R. solanacearum cells exhibited an elongated rod-shaped morphology with a length approximately three times that of normal cells, suggesting impaired cell division. Motility assays showed that bacterial movement was reduced by approximately 36%. Transcriptomic analysis revealed significant down-regulation of genes associated with cell division (ZapE), type Ⅲ secretion system (T3SS) regulation (hrpB1, hrpB2), flagellar transcriptional regulator (flhC) and genes encoding virulence effector proteins. The gene expressions of cell division-related enzyme (ftsK), flagellin (fliC), histidine utilization-related enzyme (hipO), and RNA polymerase β' subunit (rpoC) were up-regulated. KEGG enrichment analysis indicated that differentially expressed genes were significantly enriched in pathways related to metabolism (energy metabolism, amino acid metabolism, and biosynthesis of secondary metabolites), genetic information processing (translation and RNA processing and metabolism), and environmental information processing (ABC protein transport), suggesting that lipopeptide treatment interferes with energy metabolism and substance transport, disrupts protein synthesis and turnover, reprograms the metabolic activity of R. solanacearum, and thereby inhibits its growth and reproduction.

Bacillus sp. FJAT-2349 lipopeptides at sub-inhibitory concentration exert their biocontrol effect primarily through a dual-core mechanism: blocking cell division progression and suppressing T3SS virulence, which synergistically interfere with pathogen energy metabolism and substance transport, disrupt protein synthesis and turnover, and reduce pathogen motility, thereby attenuating the pathogenicity of R. solanacearum.