| Summary: | Sulfane sulfur, such as inorganic and organic polysulfide (HS<sub>n</sub><sup>−</sup> and RS<sub>n</sub><sup>−</sup>, <i>n</i> > 2), is a common cellular component, produced either from hydrogen sulfide oxidation or cysteine metabolism. In <i>Pseudomonas aeruginosa</i> PAO1, LasR is a quorum sensing master regulator. After binding its autoinducer, LasR binds to its target DNA to activate the transcription of a suite of genes, including virulence factors. Herein, we report that the production of hydrogen sulfide and sulfane sulfur were positively correlated in <i>P. aeruginosa</i> PAO1, and sulfane sulfur was able to modify LasR, which generated Cys<sup>188</sup> persulfide and trisulfide and produced a pentasulfur link between Cys<sup>201</sup> and Cys<sup>203</sup>. The modifications did not affect LasR binding to its target DNA site, but made it several-fold more effective than unmodified LasR in activating transcription in both in vitro and in vivo assays. On the contrary, H<sub>2</sub>O<sub>2</sub> inactivates LasR via producing a disulfide bond between Cys<sup>201</sup> and Cys<sup>203</sup>. <i>P. aeruginosa</i> PAO1 had a high cellular sulfane sulfur and high LasR activity in the mid log phase and early stationary phase, but a low sulfane sulfur and low LasR activity in the declination phase. Thus, sulfane sulfur is a new signaling factor in the bacterium, adding another level of control over LasR-mediated quorum sensing and turning down the activity in old cells.
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