A Saccharomyces cerevisiae strain with high tolerance: breeding by gradual acclimation and fermentation performance

Abstract:

[Background] Saccharomyces cerevisiae is an important microorganism in the fermentation of glucose to yield ethanol. However, high concentrations of ethanol and sugar, high temperature, low pH, and other highly stressful conditions often occur during the fermentation, which affect the fermentation efficiency of S. cerevisiae. [Objective] To obtain a S. cerevisiae strain with improved tolerance to high concentrations of ethanol and sugar and high temperatures and evaluate the fermentation performance of the domesticated strain in the case of high sugar levels. [Methods] A laboratory-preserved strain (CICC 33068) of S. cerevisiae was gradually acclimated to an environment of highly concentrated ethanol. The domesticated strain was compared with the original strain in terms of the growth curves and fermentation performance under high concentrations of ethanol and sugar, high temperature, and low pH for the evaluation of its tolerance. [Results] Compared with the original strain, the domesticated strain displayed a complete growth cycle and normal morphology in the broth medium with 13% ethanol. The domesticated strain was capable of growing in the presence of 450 g/L glucose and at 45 ℃ and pH 3.5, with the glucose-to-ethanol conversion rate of 79.22%, which was 7.72% higher than that of the original strain. The gene expression levels indicated that the improved tolerance was associated with the up-regulation of intracellular trehalose synthesis pathway. [Conclusion] A S. cerevisiae strain with improved tolerance to high concentrations of ethanol and sugar and high temperatures and low pH was obtained by environmental acclimation to high levels of ethanol. The domesticated strain outperformed the original strain in the fermentation with high glucose for ethanol production. The results demonstrate that adaptive acclimation could enhance the strain tolerance by upregulating intracellular trehalose synthesis. The findings provide fundamental data for subsequent domestication and screening of other strains.

Key words:Saccharomyces cerevisiae;adaptive acclimation;high-stressed conditions;tolerance;glucose-to-ethanol conversion rate