Osmoregulation in xerotolerant and not-tolerant yeasts

Osmoregulation in both the xerotolerant yeast S. rouxii (strain YA) and the non-tolerant S. cerevisiae (strain Y41) involves the accumulation of the compatible solute glycerol. The intracellular concentration of glycerol increases in a similar manner in both yeasts in response to decreased a^ of the growth medium, whether this is adjusted with sodium chloride or PEG 200 (polyethylene glycol, average molecular weight 200). However, glycerol accumulation occurs by different means in the two yeasts. The major factor responsible for the increase in the intracellular concentration of glycerol in rouxii is that, as the a^ of the growth medium is lowered, an increased proportion of glycerol is retained in the cell but the total amount of glycerol produced differs only slightly from that when the yeast is grown at a high a^ in basal medium. In contrast, the production of glycerol by cerevisiae increases markedly but there are only very minor changes in its retention.