Cold-shock response and adaptation to near-freezing temperature in cold-adapted yeasts

Yeasts, such as Saccharomyces cerevisiae, are exposed in their natural habitat to ambient temperatures. They can form colonies at 4 °C and can grow at 10-18 °C. Therefore, the temperature downshift to 10 °C is a moderate cold stress for yeasts. Thus, there is no dramatic induction of cold-shock proteins (CSPs) upon temperature downshift from 30 to 10 °C. On the other hand, the response observed at near-freezing temperatures is more likely to represent the strong cold-shock response for yeasts. The changes in yeast plasma membrane fluidity are the primary signal triggering the cold-shock response. The responses of the yeast cell to temperature downshift to 10 °C can be categorized into three phases. The early and mid-phases are characterized by the initial up-regulation of a number of genes that are associated with the transcriptional machinery, which is then followed by an up-regulation of the translational machinery in the mid-phase. The third phase is characterized by the transcriptional activation of typical stress-marker genes, for example, the heat-shock protein (HSP) genes, and genes that are involved in the cellular processes of metabolism and signal transduction. On the other hand, it has been shown that the cold-induced accumulation of trehalose, glycerol, and HSPs plays a crucial role in protecting the yeast cells against freeze injury. Each of these three cryoprotectants is discussed in detail, along with the relevance of these studies for biotechnological application of yeasts.