An in-depth study of the growth inhibition of Vibrio parahaemolyticus by Surfactin and its effects on cell membranes, ROS levels and gene transcription.

Acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio parahaemolyticus (Vp) poses a significant challenge to the shrimp farming industry. Although lipopeptides produced by Bacillus subtilis have been shown to exert strong inhibitory effects against Vibrio parahaemolyticus, the underlying mechanisms remain largely unexplored. This study reveals that the lipopeptide surfactin, produced by Bacillus subtilis, significantly inhibits the Vp strain JSHY-1669 through multiple mechanisms. Using antagonistic assays and transcriptomic analysis, this paper investigates the molecular mechanisms of surfactin's inhibitory action on Vp strain JSHY-1669. The minimum inhibitory concentration (MIC) of surfactin against JSHY-1669 was determined to be 0.125 mg/mL, with a cumulative inhibitory effect. Exposure to surfactin caused significant structural damage to the bacterial cells, markedly inhibiting their growth and virulence gene expression. Transcriptomic analysis identified 64 genes with significant differential expression, including upregulation of genes involved in key metabolic pathways such as carbohydrate transport, and downregulation of non-essential pathways like amino acid and sulfur metabolism. Surfactin affects JSHY-1669 by disrupting key physiological processes. Specifically, it increases cell membrane depolarization, reactive oxygen species (ROS) production, and malondialdehyde (MDA) levels. These changes collectively lead to the loss of membrane integrity, which ultimately inhibits bacterial growth. Additionally, the study found downregulation of slyA, a key regulatory factor related to DNA-binding transcription, virulence regulation, and carbohydrate metabolism. Surfactin may expand its inhibitory range by affecting the slyA regulatory network, providing a basis for surfactin's broader antibacterial targets. These findings elucidate the inhibitory mechanisms of surfactin on Vp strain JSHY-1669, laying a foundation for its potential applications.