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Yeast

yeast
Survival of air drying (16 h, 30˚C) of wild type and mutant yeast strains at various stages of growth (left panel) and corresponding intracellular trehalose concentrations (right panel)

Trehalose is thought to be important for desiccation tolerance in a number of organisms, including the yeast Saccharomyces cerevisiae, but there is limited in vivo evidence to support this hypothesis. In wild type yeast, the degree of desiccation tolerance has been shown previously to increase in cultures after diauxic shift and also in exponential phase cultures after exposure to heat stress. Under both these conditions, increased survival of desiccation correlates with elevated intracellular trehalose concentrations.

We have confirmed the above findings but have tested the apparent importance of trehalose using mutant strains with a deleted trehalose-6-phosphate synthase gene (tps1Δ). Although they do not produce trehalose, tps1Δ strains are nevertheless capable of desiccation tolerance (see figure), and the degree of tolerance also increases post-diauxic shift and following heat stress, albeit usually to levels somewhat lower than in the wild type. Conversely, when wild type yeast are subjected to osmotic stress, mid-exponential phase cultures produce high concentrations of intracellular trehalose but show little improvement in desiccation tolerance.

These results show that there is no consistent relationship between intracellular trehalose levels and desiccation tolerance in S. cerevisiae. Trehalose seems to be neither necessary nor sufficient for, although in some strains might quantitatively improve, survival of desiccation, suggesting that other adaptations are more important.

We are now exploring other adaptations that might be involved in yeast desiccation tolerance.


References:

Ratnakumar, S. and Tunnacliffe, A. (2006) Intracellular trehalose is neither necessary nor sufficient for desiccation tolerance in yeast. FEMS Yeast Res. 6: 902-913.