Trehalose lowers membrane phase transitions in dry yeast cells.

Recent work has clearly demonstrated a direct correlation between the amount of trehalose present in the yeast Saccharomyces cerevisiae and its ability to tolerate dehydration, but has failed to elucidate the specific role played by trehalose. By using Fourier transform infrared spectroscopy we measured the transition temperature of phospholipids in both intact S. cerevisiae and isolated plasma membranes dried in the presence and absence of trehalose. Our results show that trehalose lowers the temperature of the dry gel to liquid crystal phase transition in yeast from around 60 degrees C to about 40 degrees C, thus allowing yeast rehydrated above 40 degrees C to avoid the damaging effects of passing through a phase transition. These results explain both the need for trehalose and the observation that yeast must be rehydrated with warm water if they are to remain viable. Only when trehalose is present is the dry transition within a physiologically tolerable range and only when the cells are rehydrated above 40 degrees C will they avoid passing through a phase transition.