title: Cd bioaccumulation by a freshwater bacterium, Rhodospirillum rubrum.
abstract: Cd bioaccumulation by Rhodospirillum rubrum, a Gram-negative freshwater bacterium, was studied in a synthetic medium. The free ion (Cd2+) was the best predictor of the Cd internalization fluxes. Representation of the short-term uptake fluxes as a function of [Cd2+] in the medium demonstrated a linear relationship, as would be expected for a rate-limiting, first-order internalization with a single transporter. Nonetheless, several different accumulation profiles were observed, depending on the Cd concentration. Cd uptake was regulated differently for concentrations above and below 10(-6) M (or was regulated only above [Cd2+] = 10(-6) M). Short-and long-term studies revealed that regulation was rapidly initiated for the highest Cd concentrations examined, effectively decreasing both adsorbed and internalized Cd. Anodic stripping voltammetry demonstrated that a Cd complexing ligand was produced within minutes upon exposure to 5 x 10(-6) M Cd2+ and that an extracellular sequestration of Cd was one mechanism regulating Cd uptake. Competition studies with other cations revealed a competitive inhibition of Cd uptake by Zn and an uptake enhancement in the presence of Mn and Cu.
authors.affiliation: Laboratory of Bacteriology and Microbial Ecology, Department of Botany and Plant Biology, University of Geneva (Bastions), 3 Place de l'Université, 1211 Geneva 4, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Smiejan
authors.forename: K J
authors.initials: KJ
authors.lastname: Wilkinson
authors.forename: C
authors.initials: C
authors.lastname: Rossier
mesh_terms: D002104:Cadmium / Q000493:pharmacokinetics*; D007700:Kinetics; D012247:Rhodospirillum rubrum / Q000737:chemistry*; D014873:Water Pollutants / Q000493:pharmacokinetics*
chemical_list: D014873:Water Pollutants; D002104:Cadmium