RdmB Activates the Quorum Quenching Activity of Pseudomonas nitroreducens HS-18 by Direct Regulating Two Sets of DSF Signal Degradation Enzymes.

Abstract

Many pathogenic bacteria produce diffusible signal factor (DSF) quorum sensing (QS) signals to regulate virulence. Quorum quenching (QQ) frequently interferes with QS via enzymatic signal degradation to alleviate pathogenicity. However, DSF-targeted QQ regulatory mechanisms remain largely vague. Recently, we reported two sets of DSF-degrading genes (digABCD and dmgABCDEFGH) and their repressor RdmA in the non-pathogenic soil QQ bacterium Pseudomonas nitroreducens HS-18. In this study, genetic and genomic analyses led to identify a novel regulator of DSF metabolism (RdmB) activating DSF utilization. RdmB directly bound to the digA and dmgA promoters. In contrast to RdmA binding to the dmg promoter by interacting with the right and left binding motifs, the activator RdmB interacted with only one binding site overlapping the right binding motif of RdmA at the dmg promoter. Along with bacterial growth, rdmA transcript levels decreased, while rdmB increased, a pattern markedly potentiated by DSF. These findings demonstrated that RdmB and RdmA constitute a potent pair of regulators to modulate DSF metabolism in response to environmental changes and physiological need. Such a dual repressor-activator regulatory mechanism would allow QQ agent HS-18 to activate DSF degradation enzymes when necessary, thus keeping its fitness and competitive edges.