Identification of a gene cluster, czr, involved in cadmium and zinc resistance in Pseudomonas aeruginosa

Pseudomonas aeruginosa CMG103 was isolated from a metal-polluted river in P akistan and displayed a high level of Zn and Cd resistance. An Omega-Km tra nsposon mutant of strain CMG103, which showed a substantial decrease in res istance to Zn and Cd, was obtained. A 12.8 kb region determining Zn and Cd resistance in strain CM103 was cloned by complementing the mutant strain, a nd its nt sequence was determined. Five genes, czrSRCBA, involved in Zn and Cd resistance, were identified. The predicted gene products of czrCBAshow a significant similarity with the proteins encoded by the plasmid borne met al resistant determinants czc, cnr and ncc of Ralstonia strains, which dete rmine a chemiosmotic cation-antiporter efflux system. The predicted CzrS an d CzrR proteins show a significant similarity to the sensor and regulatory protein, respectively, of two component regulatory systems, such as CopS/Co pR and PcoS/PcoR involved in the regulation of plasmid-borne Cu-resistant d eterminants, and CzcS/CzcR involved in the regulation of etc. The cloned cz rregion contained downstream of czrCBA additional ORFs whose predicted gene products are similar to proteins involved in catabolism of aromatic compou nds. DNA-DNA hybridization indicated strong conservation of czr in other en viromental P. aeruginosa isolates and in the P. aeurginosatype strain PAO1, a clinical isolate. This was confirmed by a comparison of the sequence of the CMG103 czr region with the currently available genome sequence of strai n PAO1. A high sequence identity (till 99% at the nt level) and organizator y conservation of the czr region of CMG103 was found in PAO1 as well regard ing coding sequences as intervening sequences between ORFs. The czr locus w as localized between coordinates 2400 and 2550 kb on the physical map of th e chromosome of PAO1. (C) 1999 Elsevier Science B.V. All rights reserved.