Small changes in cultivability, big changes in heat treated yeast transcriptome

During the application of thermal treatment, cell survival depends on biological factors (such as growth stage, culture conditions, and the composition of the stress medium) as well as physical factors inherent to the thermal process (including amplitude, duration at the stress temperature, and the rate of temperature increase). In this study, the yeast Saccharomyces cerevisiae BY4742 was exposed to two different thermal treatment kinetics in a nutrient medium after being cultivated in YPD medium at 25 °C for 48 hours (to reach the stationary growth phase). The thermal treatments were applied between 25 °C and 50 °C, followed by a 30-minute hold at 50 °C before returning to 25 °C. The yeast cells were exposed either to a heat shock (heating kinetics: 50 °C/min) or to a gradual temperature increase (heating kinetics: 0.5 °C/min). Generally, it is known that heat shock induces lower survival (30%) compared to the gradual increase (80%). In this study, we demonstrate that despite the small difference in survival rate (less than one logarithmic reduction in both cases), the transcriptomes vary significantly. The use of bioinformatics tools such as WGCNA revealed a correlation between differentially expressed gene clusters and phenotypic traits (measured by spectroscopy, fluorescence microscopy, flow cytometry, among others). Here, we focused on both mRNA and ncRNA (non coding RNA). Yeast were submitted to a heat shock (HS) or a heat ramp (HR) and then imediatly recpvered at 25°C before extracting mRNA and ncRNA. Controls (CTL) corresponded to untreated yeasts (collected before the heat treatment).