ZINC(II) TOLERANCE IN ESCHERICHIA-COLI K-12 - EVIDENCE THAT THE ZNTA GENE (O732) ENCODES A CATION-TRANSPORT ATPASE

A transposon (Tn 10dCam) 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 (f or Zn(II) transport or tolerance). The metal-sensitive phenotype was c omplemented by a genomic DNA clone mapping at 3677.90-3684.60 kb on th e physical map. Insertion of a kanamycin resistance (Kn(R)) cassette a t a SalI site in a subcloned fragment generated a plasmid that partial ly complemented the zinc(II)-sensitive phenotype. DNA sequence analysi s revealed that the Kn(R) cassette was located within the putative pro moter 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 Cp x-type family. Inverse PCR and sequence analysis revealed that the Tn1 0dCam element was located within o732 in the genome of the zinc(II)-se nsitive mutant. The zntA mutant had elevated amounts of intracellular and cell surface-bound Zn(II), consistent with the view that zntA(+) e ncodes a zinc(II) efflux protein. Exposure of the zntA mutant to cobal t(II) and cadmium(II) also resulted in elevated levels of intracellula r and cell surface-bound metal ions.