Bacillus subtilis CPx-type ATPases: characterization of Cd, Zn, Co and Cu efflux systems

Metal ion homeostasis requires the balanced expression of metal ion uptake systems, when metals are limiting, and corresponding efflux or storage systems, when metals are in excess. CPx-type ATPases are a family of membrane-bound transporters that often function to export toxic metals from cells. The Bacillus subtilis genome encodes three CPx-type ATPases: zosA, yvgW and yvgX. We demonstrate that yvgW and yvgX encode CadA and CopA, respectively, and that these genes function in metal ion resistance. A cadA mutant was sensitive to Cd(II), Zn(II) and Co(II), but not copper. Transcription of cadA initiates from a single, sigmaA-type promoter and was induced by Cd(II), Zn(II), and Co(II). The adjacent copZA operon is expressed as a bicistronic transcript from a sigmaA-type promoter and is selectively induced by copper. Mutation of either copZ, encoding a metallochaperone, or copA sensitizes the cells to copper but not to other metal ions.