CADMIUM TRANSPORT BY CHLORELLA-PYRENOIDOSA

Chlorella pyrenoidosa, incubated at 31°C in a medium containing CdCl2 concentrations ranging from 0.025 to 0.500 μg/ml, incorporated cadmium in a linear fashion for 60 min. The rate of uptake was dependent upon the exogenous cadmium concentration; 2.98 μM CdCl2 was required to half-saturate the transport system. Cd uptake is reduced by lower temperatures and when cultures are not illuminated. Both manganese and iron inhibited cadmium uptake but zinc and cobalt had no effect. The inhibition of cadmium uptake by manganese could be correlated with the concentration of manganese present; kinetic studies showed manganese to be a competitive inhibitor. Similar kinetic studies revealed that Mn transport is competitively inhibited by cadmium. The ability of C. pyrenoidosa to incorporate cadmium and manganese is determined, in large part, by the composition of the growth medium. Cells, grown in a medium containing low levels of Mn, incorporate both Cd and Mn at a faster rate than cells grown in a medium containing high levels of Mn. The rate of Cd and Mn incorporation is also faster in cells that have been previously exposed to Cd. The data support the conclusion that manganese and cadmium share a common transport system in C. pyrenoidosa. © 1979.