ZINC ADSORPTION AND TRANSPORT BY CHLAMYDOMONAS VARUIABILIS AND SCENEDESMUS SUBSPICATUS (CHLOROPHYCEAE) GROWN IN SEMICONTINUOUS CULTURE1

The amount of zinc adsorbed onto the cell surface of the unicellular green algae Scenedesmus subspicatus Hodat and Chlamydomonas variabilis Dangeard was operationally defined by extraction with EDTA; it was a function of the concentration of free ionic zinc remaining in the growth medium, rather than that of the total (free plus complexed) zinc concentration, and could be described by Langmuir isotherms. Conditional adsorption equilibrium constants for zinc were 0.123 and 0.039 L ·μmol^?1 for S. subspicatus and C. variabilis, respectively. A portion of the zinc adsorbed onto C. variabilis was released into solution after 1 h of contact with the metal, providing a possible tolerance mechanism for this alga; the division rate of C. variabilis was not altered by up to 12 μmol Zn²⁺· L^?1, although the cell yield obtained during the stationary phase was significantly decreased. The amount of transported or cellular zinc, for both algal species, was operationally defined as the zinc remaining with the cell after EDTA-extraction; it was a linear function of the free ionic zinc concentration remaining in solution, suggesting that the zinc transported into the cell was not derived from the total adsorbed fraction, although the latter may contain some zinc originating from specific sites leading to zinc transport.