COMBINED NICKEL-COBALT-CADMIUM RESISTANCE ENCODED BY THE NCC LOCUS OFALCALIGENES XYLOSOXIDANS 31A

The nickel-cobalt cadmium resistance genes carried by plasmid pTOM9 of Alcaligenes xylosoxidans 31A are located on a 14.5-kb BamHI fragment. By random Tn5 insertion mutagenesis, the fragment was shown to contai n two distinct nickel resistance loci, ncc and nre. The ncc locus caus es a high-level combined nickel, cobalt, and cadmium resistance in str ain AE104, which is a cured derivative of the metal-resistant bacteriu m Alcaligenes eutrophus CH34. ncc is not expressed in Escherichia coli . The nre locus causes low-level nickel resistance in both Alcaligenes and E. coli strains. The nucleotide sequence of the nce locus reveale d seven open reading frames designated nccYXHCBAN. The corresponding p redicted proteins share strong similarities with proteins encoded by t he metal resistance loci cnr (cnrYXHCBA) and etc (czcRCBAD) of A. eutr ophus CH34. When different DNA fragments carrying nce genes were heter ologously expressed under the control of the bacteriophage T7 promoter , five protein bands representing NccA (116 kDa), NccB (40 kDa), NccC (46 kDa), NccN (23.5 kDa), and NccX (16.5 kDa) were detected.