Copper uptake and its compartmentalization in Pseudomonas aeruginosa strains: Chemical nature of cellular metal

Abstract

Copper-sensitive (Cu5) and copper-resistant (Cu1) strains of Pseudomonas aeruginosa were characterized in terms of Cu2+ sensitivity, uptake and its compartmentalization in the possible cell sectors. Minimum inhibitory concentrations (MICs) of Cu2+ for the Cur strain (3.2 mM and 0.12 mM in enriched- and in minimal-medium, respectively) were almost 5-fold higher over that of its sensitive counterpart. While Cu(s) strain accumulated Cu2+ to a maximum of 1.8 μmol mg-1 protein, Cu(r) strain increased it to 2.37 μmol mg-1 protein. Both the strains also demonstrated energy- and pH-dependent Cu2+ uptake through the broad-substrate range divalent cation (Zn2+, Mg2+, Co2+) uptake system as well as through the system specific for Cu2+. Cell-fractionation study revealed that in Cu(r) strain, periplasm and membrane are the main Cu2+ binding sites, whereas, in case of Cu(s) strain, it is the cytoplasm. The overall observations indicate that the Cur strain restricted Cu2+ sequestration exterior to the cytoplasm as the possible strategy for Cu-resistance. The chemical nature of Cu2+ deposition in the respective strains was also ascertained by X-ray powder diffraction analysis.