An efflux transporter PbrA and a phosphatase PbrB cooperate in a lead-resistance mechanism in bacteria

The gene cluster pbrTRABCD from Cupriavidus metallidurans CH34 is thought to encode a unique, specific resistance mechanism for lead. However, the exact functions of these genes are unknown. In this study we examine the metal specificity and functions of pbrABCD by expressing these genes in different combinations and comparing their ability to restore Pb2+, Zn2+ and Cd2+ resistance in a metal-sensitive C. metallidurans strain DN440. We show that lead resistance in C. metallidurans is achieved through the cooperation of the Zn/Cd/Pb-translocating ATPase PbrA and the undecaprenyl pyrophosphate phosphatase PbrB. While PbrA non-specifically exported Pb2+, Zn2+ and Cd2+, a specific increase in lead resistance was observed when PbrA and PbrB were coexpressed. As a model of action for PbrA and PbrB we propose a mechanism where Pb2+ is exported from the cytoplasm by PbrA and then sequestered as a phosphate salt with the inorganic phosphate produced by PbrB. Similar operons containing genes for heavy metal translocating ATPases and phosphatases were found in several different bacterial species, suggesting that lead detoxification through active efflux and sequestration is a common lead-resistance mechanism.