Cadmium Adsorption by Chlamydomonas reinhardtii and its Interaction with the Cell Wall Proteins

Environmental Context. In natural waters, trace metals levels are largely controlled by microbiology; organisms take up, metabolize, store, and detoxify the metals. However, aquatic organisms may regulate their own uptake via dynamic processes that result in a system that is far from equilibrium. By examining the model title alga with a battery of techniques, a more realistic assessment of metal uptake and metal regulatory processes could be gained. Abstract. Cadmium adsorption by a wild type strain of Chlamydomonas reinhardtii and a cell wall-less mutant was quantified as a function of Cd speciation in a well-defined aqueous medium. For both strains, Cd adsorption to the cell surface was not predicted by a single-site (Langmuirian) model. Indeed, no saturation of the cell wall was observed, even for Cd concentrations in excess of 5 × 10−3 M. A continual production of Cd binding sites appeared to be responsible for the observed increase of Cd adsorption with time. SDS-page separations and measurements of the protein content of algal supernatants demonstrated that organic matter was released by the algae, both in the presence and absence of Cd. Both the nature (e.g. polysaccharides, proteins) and the quantity of exudate production was influenced by the physicochemistry of the external medium. Measurements using the permeation liquid membrane (PLM) and anodic stripping voltammetry (ASV) demonstrated that dissolved cadmium was rapidly complexed by the organic exudates produced by the algae.