| Abstract
| - Short-term uptake of cadmium by a wild-type (2137) and acell wall-less strain (CW-2) of Chlamydomonas reinhardtiiwas examined as a function of Cd speciation in a well-defined, aqueous medium. Internalization fluxes weredetermined for free cadmium concentrations ranging from5 × 10-10 M to 5 × 10-4 M in the presence of ligandsforming both labile and inert hydrophilic complexes. A first-order biological internalization, as predicted by the freeion activity model (FIAM), was observed for both strains.The maximum Cd internalization flux, Jmax, for the wild-typestrain was 5-fold higher (1.3 × 10-11 mol cm-2 min-1)than for the CW-2 strain (2.3 × 10-12 mol cm-2 min-1) andwas not influenced by the presence of competitors suchas Ca in the experimental solution. The conditional stabilityconstant for the adsorption of Cd to transport sites ofthe CW-2 strain was 5-fold higher (106.7 M-1) than for the wild-type strain (106 M-1). Competition experiments demonstratedthat Mo, Mn, Cu, Co, Zn, Ni, Ca, and Pb inhibited, atleast partially, Cd uptake, while no inhibition was observedfor similar concentrations of Mg and Fe. The stabilityconstant for the competitive binding of Ca to the Cd transportsite was determined to be 104.5 M-1. Cu and Zn competedwith Cd uptake sites with stability constants of 105.6and 105.2 M-1, respectively. Protons also appeared tocompete with Cd uptake sites as uptake could generallybe predicted quantitatively in their presence. Finally, in thepresence of low concentrations (<20 mg L-1) of SuwanneeRiver fulvic acid, Cd internalization fluxes could bepredicted from [Cd2+], in accordance with the FIAM.
|
