Abstract
We evaluated whether epigenetic changes contributed to improve ethanol tolerance in mutant populations of Saccharomyces cerevisiae (S. cerevisiae). Two ethanol-tolerant variants of S. cerevisiae were used to evaluate the genetic stability in the process of stress-free passage cultures. We found that acquired ethanol tolerance was lost and transcription level of some genes (HSP104, PRO1, TPS1, and SOD1) closely related to ethanol tolerance decreased significantly after the 10th passage in ethanol-free medium. Tri-methylation of lysine 4 on histone H3 (H3K4) enhanced at the promoter of HSP104, PRO1, TPS1 and SOD1 in ethanol-tolerant variants of S. cerevisiae was also diminished after tenth passage in stress-free cultures. The ethanol tolerance was reacquired when exogenous SOD1 transferred in some tolerance-lost strains. This showed that H3K4 methylation is involved in phenotypic variation with regard to ethanol tolerance with respect to classic breeding methods used in yeast.
Highlights
Ethanol is one of the oldest biochemical products known to human civilization
The other ethanol-tolerant population was obtained by chemostat-mediated acclimation of S. cerevisiae F1 to high-ethanol concentrations in a 500 ml fermenter in which the ethanol concentration was slowly increased from 80 mg ml−1 to 150 mg ml−1 over a period of 800 h
The results showed that HSP104, PRO1, TPS1 and SOD1 were high activated in breeding high-yield strains while expressed in a low level after passage culture in ethanol-free medium (Fig. 4)
Summary
Ethanol is one of the oldest biochemical products known to human civilization. It has been widely used for human consumption and as an industrial chemical and fuel. Saccharomyces cerevisiae, the brewers’ (budding) yeast, is the primary microorganism used in the production of ethanol through fermentation. Yeast strains with good tolerance to high concentrations of ethanol are highly desirable. It is still difficult to obtain such strains through modern genetic modification because ethanol tolerance to high concentration of alcohol is a very complex phenotype, involving the expression of many genes. More than 250 genes are believed to be involved in ethanol tolerance (Hu et al, 2007; Auesukaree et al, 2009; Teixeira et al, 2009; Hou, 2010; Mira et al, 2010)
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