Morphological changes and depressed phagocytic efficiency in Dictyostelium amoebae treated with toxic concentrations...

The morphology and phagocytic efficiency of Dictyostelium discoideum amoebae exposed to cadmium was investigated at two Cd concentrations: a low toxic concentration--7 X 10(-5) M, and a high toxic concentration--2 X 10(-4) M. Both concentrations inhibited growth completely; however, only in the culture containing a high toxic concentration of cadmium were severe ultrastructural anomalies observed, notably, nucleolar changes and autophagic vacuolar formation. Using biological indices we conclude that the high concentration of cadmium was lethal and that morphological changes associated with this dose of cadmium may be secondary to cell death. In contrast, amoebae treated with a low toxic but nonlethal concentration of Cd showed an altered size distribution of cytoplasmic vacuoles and a decreased phagocytic efficiency. Cultures whose growth was completely inhibited with cobalt were also examined, as were untreated control cultures. By 24 hr Cd-treated amoebae showed a 20% decrease in the cytoplasmic mean-vacuolar diameter and a 69% decrease in phagocytic efficiency whereas Co and untreated controls showed no significant decrease in the cytoplasmic mean-vacuolar diameter. Phagocytic efficiency was only slightly diminished by Co. Changes in vacuolar profiles had been shown earlier to be related to membrane utilization in Dictyostelium amoebae. Cd at low toxic concentrations affects membrane function in Dictyostelium amoebae.