A chemical bactericide dioctyldiethylenetriamine (Xinjunan) exerts a non-lethal effect by inhibiting RpfG activity to regulate the quorum sensing system

Bacterial diseases pose a major threat to global agriculture and food security. Bactericides are highly effective in disease control due to their direct antibacterial effect. However, it causes “life or death” selection pressure on the target bacteria and can lead to bactericide resistance. Quorum sensing inhibitors exert indirect antibacterial effect that weakens their virulence and combined use of bactericides and quorum sensing inhibitors demonstrated more significant disease control than a single agent. In this study, dioctyldiethylenetriamine, a bactericide that has previously been proven to have a direct antibacterial effect, exhibited an indirect antibacterial effect that weakened bacterial virulence. Using transposon sequencing, we found that the quorum sensing system, which is closely related to virulence in Xanthomonas oryzae pv. oryzae ( Xoo , PXO99A), was significantly affected by dioctyldiethylenetriamine. It was further found that RpfG, which is responsible for transduction of the quorum sensing signal molecules in PXO99A, was significantly inhibited at both transcriptional and translational levels after dioctyldiethylenetriamine treatment, resulting in impaired phosphodiesterase activity, which in turn caused bacterial quorum quenching (QQ). QQ not only weakened the virulence of the bacteria, but also reduced their motility, which could effectively prevent the bacteria from escaping the direct antibacterial effect of dioctyldiethylenetriamine, thus providing a more effective control effect. Finally, we found that the QQ induced by dioctyldiethylenetriamine appeared to be specific, occurring in a subset of bacteria containing RpfG. The interspecific competitiveness within the same ecological niche also appeared to be weakened, which was accompanied with QQ. These findings have enriched our understanding of the antibacterial mechanism of bactericides and provided a theoretical basis for the scientific and rational use of bactericides as well as the development of “RpfG-based” indirect antibacterial agents with both efficient antibacterial activity and ecological safety.