Interesting physiological response of the osmophilic yeast Candida krusei to heat shock

The response of cellular physiology of Candida krusei to heat shock was studied in shake flasks and bioreactors. Heat shock treatment increased trehalose content (based on g/g dry cells) and decreased glycerol content of C. krusei cells. The optimal heat shock temperature, period and timing condition was 45 °C for 1 h starting at the 12th h of cultivation. With this heat shock, the cellular trehalose content was 2.0, 2.8 and 3.8-fold that of control at 12.3, 12.6 and 13 h, respectively, while the corresponding glycerol content was 0.8, 0.6 and 0.4-fold that of control. When the temperature was shifted back to a normal one (from 45 °C to 35 °C) after the heat shock, the content of both trehalose and glycerol also returned to a control level. A further study on periodic heat shock treatment (at 45 °C for 1 h each time) was performed at 12, 18 and 24 h of cultivation, respectively. It was confirmed that the trehalose content of heat shocked cells was much higher than that of control at the end of each 1 h heat shock cycle (i.e., at 13, 19 and 25 h of cultivation), while the corresponding glycerol content was much lower than that of control. The dynamic enzyme activities of glycerol-3-phophate dehydrogenase (ctGPD), mitochondrial glycerol-3-phosphate dehydrogenase (mtGPD) and trehalose-6-phosphate synthase (T-6-P synthase) were also investigated during heat shock. Different from ctGPD, both mtGPD and T-6-P synthase showed much higher activities for the heat shocked cells compared to the control. The results suggest that heat shock may alter the metabolic flux by shifting the pathway from glycerol to trehalose synthesis in C. krusei cells.