Adaptive evolution and mechanism elucidation for ethanol tolerant Saccharomyces cerevisiae used in starch based biorefinery.

Ethanol tolerant Saccharomyces cerevisiae is compulsory for ethanol production in starch based biorefinery, especially during high-gravity fermentation. In this study, adaptive evolution with increased initial ethanol concentrations as a driving force was harnessed for achieving ethanol tolerant S. cerevisiae. After evolution, an outstanding ethanol tolerant strain was screened, which contributed to significant improvements in glucose consumption and ethanol production in scenarios of 300 g/L initial glucose, high solid loadings (30 wt%, 33 wt%, 35 wt% and 40 wt%) of corn, and high solid loadings (30 wt% and 33 wt%) of cassava, compared with the original strain. Genome re-sequencing was applied for the evolved strain, and 504 sense mutations in 205 genes were detected, among which PAM1 gene was demonstrated related to the elevated ethanol tolerance. In sum, this study provided a practical approach for obtaining ethanol tolerant strain and the identified PAM1 gene enhanced our understanding on ethanol tolerant mechanism, as well as provided a target basis for rational metabolic engineering.