Cloning and functional analysis of the pbr lead resistance determinant of Ralstonia metallidurans CH34

The lead resistance operon, pbr, of Ralstonia metallidurans (formerly Alcaligenes eutrophus) strain CH34 is unique, as it combines functions involved in uptake, efflux, and accumulation of Pb(II). The pbr lead resistance locus contains the following structural resistance genes: (i) pbrT, which encodes a Pb(ll) uptake protein; (ii) pbrA, which encodes a P-type Pb(ll) efflux ATPase; (iii) pbrB, which encodes a predicted integral membrane protein of unknown function; and (iv) pbrC, which encodes a predicted prolipoprotein signal peptidase. Downstream of pbrC, the pbrD gene, encoding a Pb(II)-binding protein, was identified in a region of DNA, which was essential for functional lead sequestration. Pb(II)-dependent inducible transcription of pbrABCD from the PpbrA promoter is regulated by PbrR, which belongs to the MerR family of metal ion-sensing regulatory proteins. This is the first report of a mechanism for specific lead resistance in any bacterial genus.