At the concentration used in this work (10 ppm), cadmium was efficiently removed from the environment by stationary yeast cells. While exponential phase cells showed low capacity of cadmium absorption, stationary cells removed 97% of the original metal in 24 hours. Total cadmium absorption shown by dry cells was lower than that of fresh ones, although both cells removed 50% of metal during the first hour of treatment. We also verified that only viable cells were capable of absorbing cadmium. Independently of the growth phase, cells showed high tolerance to 10 ppm CdSO4 and about 80% of cells remained viable after 24 hours exposure to cadmium. However, when stationary phase cells were previously dehydrated and then exposed to cadmium, they exhibited poor survival. By using an oxidation-dependent fluorescent probe, we observed that, once absorbed by cells, cadmium increases the intracellular level of oxidation, which may be responsible for its toxic effect. Crude extracts from stationary phase cells exposed to cadmium showed a 10-fold increase in fluorescence, while extracts from cells of exponential phase did not increase in fluorescence. Dry cells treated with the metal showed a high increase in fluorescence, mainly caused by dehydration.
Saccharomyces cerevisiae; cadmium; absorption; intracellular oxidation
