A Quorum Quenching Bacterial Isolate Contains Multiple Substrate-Inducible Genes Conferring Degradation of Diffusible Signal Factor

Quorum quenching, which disrupts quorum sensing (QS) by either degradation of QS signals or interference of signal generation or perception, is a promising strategy for the prevention and control of QS-mediated bacterial infections. Diffusible signal factor (DSF) is widely conserved in many Gram-negative bacterial pathogens. In this study, we developed an efficient method for screening of highly active DSF degradation microorganisms. Among them, Pseudomonas sp. strain HS-18 showed a superior DSF degradation activity. Bioinformatics and genetic analyses showed that at least 4 genes, designated digA to digD, encoding fatty acyl coenzyme A ligase homologues, are responsible for DSF signal degradation. Interestingly, all 4 dig genes were induced by exogenous DSF, with digA being the most significantly induced. Expression of the dig genes in Xanthomonas carnpestris pv. carnpestris markedly reduced the accumulation of endogenous DSF, decreased production of virulence factors, and attenuated bacterial virulence on host plants. Similarly, application of strain HS-18 as a biocontrol agent could substantially reduce the disease severity caused by X. carnpestris pv. carnpestris. These results unveil the molecular basis of a highly efficient DSF degradation bacterial isolate and present useful genes and biocontrol agents for control of the infectious diseases caused by DSF-dependent bacterial pathogens. IMPORTANCE Diffusible signal factor (DSF) represents a family of widely conserved quorum sensing signals involved in the regulation of virulence factor production in many Gram-negative bacterial pathogens. In this study, we developed a novel and efficient method for screening highly active DSF degradation microorganisms. With this method, we identified a bacterial isolate, Pseudomonas sp. strain HS-18, with a superb DSF degradation activity. We further found that strain HS-18 contains 4 genes responsible for DSF signal degradation, and significantly, these were induced by exogenous DSF molecules. These findings unveil the molecular basis of a highly efficient DSF degradation bacterial isolate and present useful methods, genes, and agents for control of the infectious diseases caused by DSF-dependent bacterial pathogens.