Cloning and characterization of a Na+/H+ antiporter gene of the moderately halophilic bacterium Halobacillus aidingensis AD-6T

A gene encoding a Na+/H+ antiporter was obtained from the genome of Halobacillus aidingensis AD-6(T), which was sequenced and designated as nhaH. The deduced amino acid sequence of the gene was 91% identical to the NhaH of H. dabanensis, and shared 54% identity with the NhaG of Bacillus subtilis. The cloned gene enable the Escherichia coli KNabc cell, which lack all of the major Na+/H+ antiporters, to grow in medium containing 0.2 M NaCl or 10 mM LiCl. The nhaH gene was predicted to encode a 43.5 kDa protein (403 amino acid residues) with 11 putative transmembrane regions. Everted membrane vesicles prepared from E. coli KNabc cells carrying NhaH exhibited Na+/H+ as well as Li+/H+ antiporter activity, which was pH-dependent with the highest activity at pH 8.0, and no K+/H+ antiporter activity was detected. The deletion of hydrophilic C-terminal amino acid residues showed that the short C-terminal tail was vital for Na+/H+ antiporter activity.