A FUNCTIONAL HOMOLOG OF ESCHERICHIA-COLI NHAR IN VIBRIO-CHOLERAE

Escherichia coli NhaR controls expression of a sodium/proton (Na+/H+) antiporter, NhaA. The Vibrio cholerac NhaR protein shows over 60% iden tity to those of Escherichia coli and Salmonella enteritidis. V. chole rae NhaR complements an E. coli nhaR mutant for growth in 100 nM LiCl- 33 mM NaCl pH 7.6, and enhances the Na+-dependent induction of an E. c oli chromosomal nhaA::lacZ fusion, These findings indicate functional homology to E, coli NhaR. Two V. cholerae nhaR mutants were constructe d 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 comp lemented bg the introduction of V, cholerae nhaR on a low-copy-number plasmid, An nhaR mutation had no detectable effect on the virulence of the ir, cholerae strain in the infant mouse model, suggesting that th e antiporter system involved Is not required in vivo, at least in this animal model.