Very High Thermotolerance of an Adaptive Evolved Saccharomyces cerevisiae in Cellulosic Ethanol Fermentation

Abstract

High thermotolerance is an important property of Saccharomyces cerevisiae for stable and efficient bioethanol production, especially for large-scale bioethanol production with weak heat transfer and the simultaneous saccharification and fermentation (SSF) of lignocellulosic biomass at high temperatures (above 40 °C). Despite extensive studies involving metabolic engineering and chemical mutagenesis, the improvement of thermotolerance in S. cerevisiae under harsh thermal stress (42–45 °C) has been limited. A highly thermotolerant strain, S. cerevisiae Z100, by a 91 days’ laboratory adaptive evolution in wheat straw hydrolysate was applied for cellulosic ethanol fermentation. The results showed that the cell survival ratio of S. cerevisiae Z100 at 50 °C improved by 1.2 times that of the parental strain. The improved thermotolerance of S. cerevisiae Z100 at 50 °C was found to contribute significantly to enhanced cellulosic ethanol fermentability. The ethanol production of S. cerevisiae Z100 increased by 35%, 127%, and 64% when using wheat straw as feedstock after being maintained at 50 °C for 12 h, 24 h, and 48 h, respectively. Transcriptome analyses suggested that the enhanced trehalose and glycogen synthesis, as well as carbon metabolism, potentially contributed to the improved thermotolerance and the ethanol fermentability of S. cerevisiae Z100. This study provides evidence that adaptive evolution is an effective method for increasing the thermotolerance of the S. cerevisiae strain for stable and efficient cellulosic ethanol production.