Evidence for the involvement of vacuolar activity in metal(loid) tolerance: vacuolar-lacking and -defective mutants of Saccharomyces cerevisiae display higher sensitivity to chromate, tellurite and selenite.

The responses of Saccharomyces cerevisiae towards the oxyanions tellurite, selenite and chromate were investigated in order to establish the involvement of the yeast vacuole in their detoxification. Three mutants of S. cerevisiae with defective vacuolar morphology and function were used; mutant JSR180 delta 1 is devoid of any vacuolar-like structure while ScVatB and ScVatC are deficient in specific protein subunits of the vacuolar (V)-H(+)-ATPase. All the mutant strains showed increased sensitivity to tellurite and chromate compared to their parental strains. Such sensitivity of the mutants was associated with increased accumulation of tellurium and chromium. These results indicate that accumulation of both tellurium and chromium occurred mainly in the cytosolic compartment of the cell, with detoxification influenced by the presence of a functionally-active vacuole which may play a role in compartmentation as well as regulation of the cytosolic compartment for optimal expression of a detoxification mechanism, e.g. reduction. In contrast, the vacuolar-lacking mutant, JSR180 delta 1, and the defective V-H+ATPase mutant ScVatB displayed lower selenium accumulation than their parental strains. Additionally, the mutant strain ScVatB displayed a higher tolerance to selenite than the parental strain. This result suggests that accumulation of selenium occurs mainly in the vacuolar compartment of the cell with tolerance depending on the ability of the cytosolic component to reduce selenite to elemental selenium, which might, in turn, be related to activity of the V-H(+)-ATPase. These results are discussed in relation to vacuolar compartmentation and the significance of the vacuolar H(+)-ATPase in cytosolic homeostasis of H+ both of which may affect the accumulation, reduction, and tolerance to the tested metal(loids).