Trehalose as cryoprotectant for preservation of yeast strains

Preservation of genetic banks of yeast strains as well as of any kind of eukaryotic cells during dehydration and subsequent rehydration depends upon the maintenance of the integrity of the cell membrane. Trehalose has been successfully used as a non-toxic cryoprotectant for plant cells (Bhandal et al., 1985), as well as for lobster sarcoplasmic vesicles (Rudolph and Crowe, 1985). The hypothesis underlying these observations is that the disaccharide avoids fusion of membranes by replacing water molecules in the bilayer (Crowe et al., 1984). The viability of yeast strains submitted to different drying techniques is reported in this paper. Mutant strains with defects in the regulation of the trehalose-6-phosphate synthase complex were compared. Yeast strains dried in layers at 37°C for 6 h did not lose their viability, however, they died thereafter at 5°C, unless trehalose was used for resuspending the cells before drying. It should be noted that no trehalose accumulation was seen during drying at 37°C under our experimental conditions. In experiments in which cells were frozen at ?120°C, addition of 10% trehalose to the suspending buffer had a significant protective effect. On the other hand, a mutant strain with an extremely high trehalose-6-phosphate synthase activity showed an intrinsic capacity for survival which did not depend upon addition of exogenous trehalose. This raises the question of the location of the internal trehalose pool and whether it could replace the externally added cryoprotectant.