Broad-Spectrum Antibacterial Action of Lipopeptides Derived from Bacillus smithii by Targeting Quorum Sensing

Foodborne pathogenic microorganisms and the escalating crisis of antibiotic resistance present significant threats to global public health and food safety. This necessitates the urgent development of sustainable, green, and safe antibiotic alternatives. Lipopeptides, a class of emerging natural antimicrobial agents, offer considerable promise due to their low toxicity, broad-spectrum antibacterial activity, and environmental compatibility. Bacillus smithii, a facultative anaerobic thermophilic bacterium, exhibits probiotic properties, including antibacterial and anti-inflammatory effects. However, research on its antimicrobial components, particularly their isolation, purification, and mechanistic understanding, remains limited. This study focused on strains of B. smithii XY1 and B. smithii DSM4216^T. Comparative analysis of their secondary metabolite biosynthetic gene clusters revealed high similarity to the fengycin cluster, suggesting both strains possess the potential for efficient expression of analogous lipopeptide antimicrobials. Lipopeptides were successfully isolated and purified using an ammonium sulfate-ethanol extraction method. In vitro assays demonstrated that these lipopeptides possess broad-spectrum inhibitory activity, effectively suppressing the growth, biofilm formation, and swarming motility of pathogenic bacteria. The minimum inhibitory concentration (MIC) for all pathogenic bacteria tested was less than 62.5 μg/mL. Furthermore, the lipopeptides alleviated bacterial infection in a zebrafish model. Mechanistically, the lipopeptides inhibited the quorum sensing (QS) system of Burkholderia cenocepacia H111, specifically targeting the Burkholderia diffusible signal factor (BDSF) associated signaling pathway. This interference resulted in the suppression of the pathogen's group behaviors and virulence factor expression. This work establishes a theoretical foundation for developing B. smithii-derived lipopeptides as novel natural antimicrobial agents. The strategy of targeting QS inhibition demonstrates significant potential for future antimicrobial interventions.