SPECIATION OF COPPER AND RESPONSES OF THE MARINE DIATOM DITYLUM-BRIGHTWELLII UPON INCREASING COPPER CONCENTRATIONS

In continuous culture, cells of the marine diatom Ditylum brightwellii were subjected to increasing Cu concentrations. Cu Speciation due to production of dissolved organic ligands by the diatom and changes in adsorption characteristics of the cell walls were studied. With increasing total dissolved Cu concentrations, four phenomena were observed: (1) the rate of cell division decreased; and (2) the concentration of organic ligands with a conditional stability constant of K' = 10(10) increased; (3) Cu complexed with relatively hydrophobic ligands (K' = 10(9.6)) increased; a positive relationship between the biovolume of the broken cells and the concentration of hydrophobic Cu-complexes was found; and (4) the adsorption capacity of the cell walls increased at high total dissolved Cu concentrations. Calculations showed that the Cu2+ concentration was buffered at 0.2 nM by the production of organic ligands up to a total dissolved Cu concentration of 110 nM. Further addition of Cu, however, could not be compensated, and resulted in the collapse of the culture and large increases in both ligand concentrations and adsorption capacity of the cell walls. The resulting free Cu concentration decreased to 0.08 nM.