Distribution of copper in the diatom Haslea ostrearia simonsen

Abstract

Haslea ostrearia is a pennate diatom important for oysters culture. This species was selected to study experimentally the distribution of copper in algal cells since the phytoplankton exhibits a high capacity for metal accumulation and thus influences metal transfer to consumers. This alga was grown in batch culture and exposed to copper (30 μg/l) added in the medium on the first day of experiment. In order to separate the soluble and insoluble fractions binding copper algal cells were centrifuged after homogenization with Tris NaCl buffer (pH 8.6). A part of the cytosol was heat-denatured and then centrifuged again to separate heat-stable and heat denaturable compounds. Gel filtration Sephadex (G-75SF:10 3−7 × 10 4 Da) was used to determine the molecular weight of soluble compounds binding copper. In controls, insoluble compounds were preponderant (63%) versus soluble compounds whereas in contamined cells, soluble compounds became preponderant (66%). In the cytosol of both controls and contamined cells, copper was mainly associated with thermoresistant compounds (about 80%). In contamined cells, gel filtration have shown that copper binding compounds had low molecular weights less than 3 KDa associated with sulfhydrl groups represented 65% of total cytosolic copper and few minority (8%) compounds binding copper between 3 and 9 KDa. In conclusion, contamination of Haslea ostrearia by copper induces an increase of copper-binding to cytosolic, heat stable, thiol-rich compounds of low molecular weight with characteristics of phytochelatins.