ABSTRACT
The thermotolerant yeast Kluyveromyces marxianus displays a potential to be used for ethanol production from both whey and lignocellulosic biomass at elevated temperatures, which is highly alluring to reduce the cost of the bioprocess. Nevertheless, contrary to Saccharomyces cerevisiae, K. marxianus cannot tolerate high ethanol concentrations. We report the transcriptional profile alterations in K. marxianus under ethanol stress in order to gain insights about mechanisms involved with ethanol response. Time-dependent changes have been characterized under the exposure of 6% ethanol and compared with the unstressed cells prior to the ethanol addition. Our results reveal that the metabolic flow through the central metabolic pathways is impaired under the applied ethanol stress. Consistent with these results, we also observe that genes involved with ribosome biogenesis are downregulated and gene-encoding heat shock proteins are upregulated. Remarkably, the expression of some gene-encoding enzymes related to unsaturated fatty acid and ergosterol biosynthesis decreases upon ethanol exposure, and free fatty acid and ergosterol measurements demonstrate that their content in K. marxianus does not change under this stress. These results are in contrast to the increase previously reported with S. cerevisiae subjected to ethanol stress and suggest that the restructuration of K. marxianus membrane composition differs in the two yeasts which gives important clues to understand the low ethanol tolerance of K. marxianus compared to S. cerevisiae.