A Functional Homolog of Escherichia coli NhaR in Vibrio cholerae

Escherichia coli NhaR controls expression of a sodium/proton (Na+ /H+ ) antiporter, NhaA. TheVibrio cholerae NhaR protein shows over 60% identity to those ofEscherichia coli andSalmonella enteritidis. V. cholerae NhaR complements anE. coli nhaR mutant for growth in 100 mM LiCl–33 mM NaCl, pH 7.6, and enhances the Na+ -dependent induction of anE. coli chromosomalnhaA ::lacZ fusion. These findings indicate functional homology toE. coli NhaR. TwoV. cholerae nhaR mutants were constructed by using kanamycin resistance cartridge insertion at different sites to disrupt the gene. Both mutants showed sensitivity to growth in 120 mM LiCl, pH 9.2, compared with the wild-type strain and could be complemented by the introduction ofV. cholerae nhaR on a low-copy-number plasmid. AnnhaR mutation had no detectable effect on the virulence of theV. cholerae strain in the infant mouse model, suggesting that the antiporter system involved is not required in vivo, at least in this animal model.