Differences in the effects of seleno-cystine (CySe)2 and inorganic Se(IV) and Se(VI) compounds on uranium(VI) uptake by yeast cells, Saccharomyces cerevisiae have been studied. The Se, U, Zn and Co levels of the yeast cells were measured by neutron activation analysis. An increase in the concentration of U cells within the first 2 hours of incubation was produced by the presence of SeO2 (2 . 10(-4)-5 . 10(-4)M) and (CySe)2 (1 . 10(-4)M) in the yeast medium. Moreover, the highest SeO2 concentration (5 . 10(-4)M) and (CySe)2 more efficiently enhanced the U content of the cells than SeO2 at the low concentration end (2 . 10(-4)M). However, the effect of SeO2 and (CySe)2 on U uptake diminishes with incubation time (from 2 to 48 hours). Se(VI) [as (NH4)2SeO4] leads to a marked decrease in the content of uranium in Saccharomyces cerevisiae (an antagonistic interaction). As expected, uranium uptake by the yeast influenced the retention of selenium in the cells. Uranium significantly increased the uptake yield of Se by Saccharomyces cerevisiae when the yeast was incubated in the medium containing (CySe)2. Furthermore, during the initial 24 hours of the incubation an increase of the Se content of the cells in the presence of U was observed when Se(VI) was in the culture medium. Selenium and uranium dosages affected the Zn and Co contents of cells.
