Defining the surface adsorption and internalization of copper and cadmium in a soil bacterium, Pseudomonas putida

The distribution of cadmium (Cd) and copper (Cu) ions onto and within two soil pseudomonads, Pseudomonas putida strains KT2440 and Corvallis, was investigated using selective extraction procedures and modeled using Langmuir isotherms. Cadmium and Cu associated differently with the surface, periplasm and cytoplasm of the two strains. Both of these pseudomonad cells allowed more Cu to pass into the periplasmic space and to the cytoplasm than Cd. The distribution of Cu among the cellular spaces was solution concentration dependent, with limited amounts of Cu entering the cell at higher exposure concentrations. The Langmuir isotherm with a single binding site fit well to the observed data for Cu cell association. Cadmium was mainly found on the surface of the cells. The capacity of surface exchange sites for Cd increased with solution concentration, possibly indicating a modification of surface functional groups with ion concentration. This surface sorption behavior of Cd was best described using a two-site Langmuir model, whereas all other Cu and Cd associations were described using a one-site model. Although potentiometric titration identified differences in site densities for proton binding to the two strains, these differences were not consistently displayed with Cu and Cd surface interactions.