Characterization of silver biosorption and uptake mechanisms in a green microalga
Résumé
Silver is one of the most eco-toxic metals. Its widespread industrial use leads to environmental contamination and poses a threat to both ecosystems and human health. The characterization of new model organisms with a high capacity for accumulating metals is particularly relevant for the bioremediation of metal-polluted waters and more generally to assess the fate of pollutants into the environment. In this context, we have isolated a unicellular green microalga of the genus Coelastrella that is hypertolerant to uranium and silver and accumulates large quantities of these metals. Hazardous metal bioaccumulation in Coelastrella is a two-step process. First, biosorption is a quick, passive and reversible adsorption of metal ions onto the cell wall. The variety of functional groups on the surface of the cell wall (such as carboxyl, sulfur and amino groups) can indeed act as binding sites for metals. The second step is the active cellular uptake of metals through the plasma membrane via transporters. The aim of this work is to characterize the mechanisms of silver biosorption to the cell wall and its uptake into Coelastrella cells. To thoroughly elucidate these mechanisms, algal cells are subjected to two types of silver stress: an acute, short-term stress and a moderate, long-term stress that may reveal acclimation processes. The biochemical characterization of the cell wall is currently underway. Ongoing physiological and molecular investigations are comparing cellular responses to metal stress in acclimated and non-acclimated cells.