The metal-binding GTPases CobW2 and CobW3 are at the crossroads of zinc and cobalt homeostasis in Cupriavidus metallidurans

Abstract

The metal-resistant beta-proteobacterium Cupriavidus metallidurans is also able to survive conditions of metal starvation. We show that zinc-starved cells can substitute some of the required zinc with cobalt but not with nickel ions. The zinc importer ZupT was necessary for this process but was not essential for either zinc or cobalt import. The cellular cobalt content was also influenced by the two COG0523-family proteins, CobW2 and CobW3. Pulse-chase experiments with radioactive and isotope-enriched zinc demonstrated that both proteins interacted with ZupT to control the cellular flow-equilibrium of zinc, a central process of zinc homeostasis. Moreover, an antagonistic interplay of CobW2 and CobW3 in the presence of added cobalt caused a growth defect in mutant cells devoid of the cobalt efflux system DmeF. Full cobalt resistance also required a synergistic interaction of ZupT and DmeF. Thus, the two transporters along with CobW2 and CobW3 interact to control cobalt homeostasis in a process that depends on zinc availability. Because ZupT, CobW2, and CobW3 also direct zinc homeostasis, this process links the control of cobalt and zinc homeostasis, which subsequently protects C. metallidurans against cadmium stress and general metal starvation.