Sha (also known as Mrp/Mnh/Pha) is a Na؉ /H ؉ antiporter encoded by a cluster of six or seven genes that probably form a multisubunit transport complex. The Sha system is important for the homeostasis of H ؉ , Na ؉ , and other monovalent cations and plays a critical role in various functions, including alkaliphily, sporulation, and symbiosis. Here, we characterized the sha homologue genes from the opportunistic pathogen Pseudomonas aeruginosa, which exist as a cluster of six genes (PA1054 to PA1059). The gene cluster PA1054 to PA1059, but not the cluster with a deletion of PA1054, complemented a growth defect in the presence of 0.2 M NaCl and a defect in Na ؉ /H ؉ antiport activity of the Escherichia coli TO114 mutant lacking the three major Na ؉ /H ؉ antiporters, indicating that genes PA1054 to PA1059 are responsible for Na ؉ /H ؉ antiport activity. We disrupted PA1054 (a shaA homologue gene) and determined its effect on Na ؉ tolerance during growth, Na ؉ efflux, and pathogenicity in mice. Disruption of PA1054 resulted in severe Na ؉ sensitivity during growth and decreased Na ؉ efflux activity. In mice, the deletion mutant of PA1054 also exhibited an attenuated virulence in systemic, pulmonary, and urinary tract infections and also a decrease in colonization of the infected organs. From these results, we conclude that the genes PA1054 to PA1059 encode a Na ؉ /H ؉ antiporter that is largely responsible for Na ؉ extrusion in P. aeruginosa and has a role in the infection of the pathogen. We propose to designate PA1054 to PA1059 as the sha (sodium hydrogen antiporter) genes, shaABCDEFG.

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