A Na+/H+ antiporter gene of the moderately halophilic bacterium Halobacillus dabanensis D-8T: cloning and molecular characterization.

A gene encoding a Na⁺/H⁺ antiporter was cloned from a chromosomal DNA of Halobacillus dabanensis strain D-8^T by functional complementation. Its presence enabled the antiporter-deficient Escherichia coli strain KNabc to survive in the presence of 0.2 M NaCl or 5 mM LiCl. The gene was sequenced and designated as nhaH. The deduced amino-acid sequence of NhaH consists of 403 residues with a calculated molecular mass of 43 481 Da, which was 54% identical and 76% similar to the NhaG Na⁺/H⁺ antiporter of Bacillus subtilis. The hydropathy profile was characteristic of a membrane protein with 12 putative transmembrane domains. Everted membrane vesicles prepared from E. coli cells carrying nhaH exhibited Na⁺/H⁺ as well as Li⁺/H⁺ antiporter activity, which was pH-dependent with highest activities at pH 8.5–9.0 and at pH 8.5, respectively. Moreover, nhaH confers upon E. coli KNabc cells the ability to grow under alkaline conditions. [ABSTRACT FROM AUTHOR]