Cytoplasmic DNA-containing bodies and the response of amoebae to dimidium bromide.

The growth of Amoeba proteus (T1P) and Amoeba discoides (T1D) in the trypanocidal phenanthridinium, dimidium bromide was examined. At concentrations of drug between 2 and 4 /ig/ ml, A. proteus divided twice before inhibition and death. A. discoides was able to undergo an additional cycle of division before death. At other concentrations there were no differences in their response. Heterotransfers between these strains resembled A. discoides, both dividing three times before death. Examination of clones derived from the micro-injection of small quantities of A. discoides cytoplasm into A. proteus showed that the ability to divide additionally in dimidium bromide could be transferred. Some other strains of A. proteus (nP, T4P) also resembled A. discoides in their response. Cells of all the strains used were treated with acridine orange and observed under the fluorescence microscope for the presence of DNAand RNA-containing cytoplasmic 'bodies'. All strains able to undergo an additional division cycle also possessed cytoplasmic DNAcontaining bodies. The converse was not 100%, but this may be due to a quantitative difference in the number of DNA-containing bodies in the cytoplasm. It is proposed that the difference in response to dimidium bromide observed in A. proteus and A. discoides may be associated with the presence of DNAand RNA-containing bodies in the cytoplasm of A. discoides.