Incorporation of zinc into the frustule of the freshwater diatom Stephanodiscus hantzschii

Zinc incorporation into the frustule (siliceous cell wall) of the freshwater diatom Stephanodiscus hantzschii was studied for Zn2+ concentrations ranging from 25 pmol L-1 to 25 nmol L-1. A sigmoidal dependency was observed between Zn2+ concentrations in the culture medium and the concentration of Zn in the frustule. Concentrations of intracellular Zn were positively correlated with Zn in the frustule, suggesting that Zn in the frustule originated from intracellular pools. The processes leading to Zn incorporation into the cell wall were examined by determining the role(s) of Si and Mn via competition experiments. Results demonstrated that Zn competed with Mn for incorporation into the frustule. Zn/Si values for S. hantzschii were consistent with field data obtained from Lake Geneva (Switzerland). The study suggests that the Zn content of fossil frustules could be a valuable tool to study past levels of bioavailable Zn in freshwaters. (C) 2009 Elsevier B.V. All rights reserved.