Effect of copper ion on recovery process from freeze-thaw injury in Saccharomyces cerevisiae

In frozen dough baking technology, bakers yeast Saccharomyces cerevisiae encounter freeze-thaw injury. After thawing, dramatically decrease in cell viability and fermentation activity is caused by freeze-thaw injury. The freezing period is critical factor in freeze-thaw injury, thus we focused and investigated time-dependent gene expression profiles in recovery process from freeze injury. First, changes in gene expression profiles in S. cerevisiae in recovery process from freeze-thaw injury were analyzed using a DNA microarray. The results showed the genes which were involved in homeostasis of metal ions were time-dependent up-regulated 2-fold or more in a series. Then we examined whether these genes were related to tolerance in freeze-thaw injury by using deletion strain. The results showed that deletion of MAC1, CTR1, and PCA1 genes which involved in copper ion transport exhibited freeze-thaw sensitivity in compared with wild type. These genes are involved in copper ion uptake to a cell under a copper deficiency condition or in copper ion homeostasis, suggesting that it may be related between freeze-thaw injury and copper ion transport. To determine the effect of supplementation of copper ion on cells after freeze-thaw treatment, cell viability, intracellular superoxide dismutase (SOD) activity, and intracellular levels of reactive oxygen species (ROS) were examined by various copper ion condition medium. The results showed that intracellular SOD activity was increased and intracellular levels of ROS were decreased by supplementation of copper ion, but there was no significant difference in cell viability. These results of the present study may suggest that copper ion concentration in yeast cell after freeze-thaw treatment is important to recovery from freeze-thaw injury due to redox control of intracellular levels of ROS, but copper ion did not directly affect cell viability.

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