CzcR Is Essential for Swimming Motility in Pseudomonas aeruginosa during Zinc Stress.

Two-component system (TCS) plays a vital role in modulating target gene expression in response to the changing environments. Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen that can survive under diverse stress conditions. The great adaptability of P. aeruginosa relies heavily on the abundant TCSs encoded by its genome. However, most TCSs in P. aeruginosa have not been well-characterized. CzcS/CzcR is a metal responsive TCS which displays multiple regulatory functions associated with metal hemostasis, quorum sensing activity and antibiotic resistance. In this study, we found that swimming motility of P. aeruginosa was completely abolished during zinc (Zn2+) stress when the czcR gene from the TCS CzcS/CzcR was deleted. Noticeably, CzcR was dispensable for swimming without the stress of Zn2+ excess. CzcR was shown to be activated by Zn2+ stress possibly through inducing its expression level and triggering its phosphorylation to positively regulate swimming which was abolished by Zn2+ stress in a CzcR-independent manner. Further TEM analyses and promoter activity examinations revealed that CzcR was required for the expression of genes involved in flagellar biosynthesis during Zn2+ stress. In vitro protein-DNA interaction assay showed that CzcR was capable of specifically recognizing and binding to the promoters of operons flgBCDE, flgFGHIJK, and PA1442/FliMNOPQR/flhB. Together, this study demonstrated a novel function of CzcR in regulating flagellar gene expression and motility in P. aeruginosa when the pathogen encounters Zn2+ stress conditions. IMPORTANCE The fitness of bacterial cells depends largely on their ability to sense and respond quickly to the changing environments. P. aeruginosa expresses a great number of signal sensing and transduction systems that enable the pathogen to grow and survive under diverse stress conditions and cause serious infections at different sites in many hosts. In addition to the previously characterized functions to regulate metal homeostasis, quorum sensing activity, and antibiotic resistance, here we report that CzcR is a novel regulator essential for flagellar gene expression and swimming motility in P. aeruginosa during Zn2+ stress. Since swimming motility is important for the virulence of P. aeruginosa, findings in this study might provide a new target for the treatment of P. aeruginosa infections with Zn2+-based antimicrobial agents in the future.