Arsenate Tolerance in Saccharomyces cerevisiae is Associated with Efflux Capability

Arsenic is a common contaminant in soils, affecting soil microbiome and all soil organisms. The present study examined arsenate tolerance of two Saccharomyces cerevisiae strains isolated from contami¬nated soil. Their tolerance to sodium arsenate (AsV) was studied in a liquid medium for 24 hours, while the ability of the populations to reduce their intracellular arsenic content was subsequently investigated through kinetic studies of arsenate transport at 33.3, 133.2, and 266.4 μM of AsV. The dependence of tolerance on the efflux system was demonstrated by the use of amiloride hydrochloride, which is known as a suppressor of ion transport through the cell membrane. The maximum concentration tolerated by S. cerevisiae AS09 was found to be about 72.8% lower than that by the tolerant S. cerevisiae AS07. The influx and efflux of arsenate across the cell membranes of both strains were dependent on the concentration of metalloid in the medium and on the anion net balance. Both strains rapidly increased their internal As concentration to a maximum point, although only the tolerant strain was able to decrease it subsequently in all concentrations used. When the highest concentration was applied, the cells of the non-tolerant strain were found to be dead. When amiloride hydrochloride was used it was found that the tolerant cells behaved like sensitive cells, and at 266.4 μM the cells of both strains were found to be dead, because the extrusion of the toxic anion was interrupted. Kinetic differences in arsenate transport through the cell membrane explain the different degrees of tolerance of the studied strains.