Zinc(II) tolerance in Escherichia coli K‐12: evidence that the zntA gene (o732) encodes a cation transport ATPase

Abstract

A transposon (Tn10dCam) insertion mutant of Escherichia coli K‐12 was isolated that exhibited hypersensitivity to zinc(II) and cadmium(II) and, to a lesser extent, cobalt(II) and nickel (II). The mutated gene, located between 75.5 and 76.2 min on the chromosome, is named zntA (for Zn(II) transport or tolerance). The metal‐sensitive phenotype was complemented by a genomic DNA clone mapping at 3677.90–3684.60 kb on the physical map. Insertion of a kanamycin resistance (Kn^R) cassette at a Sal I site in a subcloned fragment generated a plasmid that partially complemented the zinc(II)‐sensitive phenotype. DNA sequence analysis revealed that the Kn^R cassette was located within the putative promoter region of an ORF (o732 or yhhO) predicted to encode a protein of 732 amino acids, similar to cation transport P‐type ATPases in the Cpx‐type family. Inverse PCR and sequence analysis revealed that the Tn10dCam element was located within o732 in the genome of the zinc(II)‐sensitive mutant. The zntA mutant had elevated amounts of intracellular and cell surface‐bound Zn(II), consistent with the view that zntA⁺ encodes a zinc(II) efflux protein. Exposure of the zntA mutant to cobalt(II) and cadmium(II) also resulted in elevated levels of intracellular and cell surface‐bound metal ions.