Biochemical and ultrastructural data on Tetrahymena pyriformis treated with copper and cadmium.

The addition of copper (10 micrograms ml-1) or cadmium (5 micrograms ml-1) to the medium is well tolerated by Tetrahymena pyriformis GL. Both metals are accumulated by cells, cadmium to a greater extent than copper. The growth rate is not affected and from the micrographs it is evident that the ultrastructure is not altered by the treatments. After 3 days of culture the macronucleus contains dense masses of chromatin and numerous nucleolar fusion bodies. Granules, cytolysomes and many food vacuoles are present in both control and treated cells. Cadmium induces the formation of a chelating protein; the amino acid analyses and the ultraviolet spectrum indicate that it is similar to the metallothionein isolated by higher organisms. The molecular weight of native protein is about 27,000. After treatment by sulphitolysis or oxidation we obtained a peak of molecular weight at about 6,000. The treatment with copper does not appear to induce metallothioneins or other chelatins. The high tolerance of Tetrahymena towards cadmium is believed to be due to the formation of a Cd-Zn metallothionein. The different chelating proteins induced by copper and cadmium in other groups of Protozoa and the different detoxification mechanisms present in these organisms are discussed.