Stress-tolerance Mechanism In Saccharomyces Cerevisiae Based On Metabolomics

Environmental stress-tolerance is one of the most important phenotypes in industrial Saccharomyces cerevisiae strains. Breeding of stress-tolerance yeast is an important direction for fermentation indutrial researchers. Hence understanding the stress-tolerance mechanism in S. cerevisiae may provides reference in yeast strain breeding. Research in the environmental stress-tolerance mechanism so far was focused on one of the phenotype, gene, proteins and metabolites. Despite the fact that many genes and cellular protestants were found to play important roles in yeast stress-tolerance, the relationship among the phenotype, gene expression and metabolism is still elusive. The analysis method integrated phenotype, gene expression and metabolism is more favorable to reveal a series of stress response of S. cerevisiae under various environmental stresses.For providing a basis phenotype data for further experiment, the genetic and physiological characteristics of 16 strains yeast were studied. The yeast strains were all identificated to be S. cerevisiae species (belonging Saccharomyces genus) through 26 s rDNA analysis. These strains have been classified into three groups depending on the amount of ethanol production. Moreover, we analyzed and ordered the difference of stresses (heat stress, osmotic stress and ethanol stress) tolerance of 16 yeast strains by growth inhibition. In addition, we estimated the fermentation ability of 16 strains. It was found that 10#,XQ1,GIM2.143,GIM2.71 are thermophilic strains, 6#,10#,2# are osmotic tolerant strains, 7#,5#,GIM2.143 are ethanol tolerant strains. We have been able to establish a correlation between the groups based on fermentative behaviour and resistance to stress conditions by applying statistics analysis to the data obtained in these experiments. Our results indicate a clear relationship between heat and sorbitol stress resistance and fermentative behaviour and this opens up the possibility of using this information as a criterion for the future selection of wine yeasts.In various stress conditions, the changes in metabolites and the possible relationship between stress resistance were analysied by metabolomics. After heat shock, the synthesis of almost all amino acids of most strains were up regulated, illustrating the synthesis of amino acids may be a common yeast response to heat stress. Meanwhile, almost all the amino acids of 9# strain (with the poor stresses-resistance) were reduced, which further validated the synthesis of amino acids help to improve the strains stressed-tolerance. The upregulated amino acids of thermophilic yeast were all non-charged, which suggests that the polar amino acids with no-charge may played a key protection role under the heat shock. Moreover, The gene expression of thermophilic yeast XQ1 after heat shock was analized with DNA array, the result showed that the expression of gene was almost consistent with the concerning metabolites, like inositol, L-valine, L-isoleucine, D-mannose. The metabolism of strain BY4743 showed stronger response in the face of sorbitol and ethanol stresses than the other industrial strains,which have well developed a complete stress reaction and not so sensitive to adverse environment like control strain BY4743.Trehalose and glycerol have been implicated as potential stress protectants that accumulate in yeasts during various stress conditions. We investigated the levels of glycerol and trehalose and the expression profiles of genes involved in their metabolism to determine their involvement in the response of thermophilic yeast XQ1 to thermal, sorbitol and ethanol stresses. The results showed that the genes involved in the synthesis and degradation of trehalose and glycerol were stress induced, and that trehalose and glycerol were synthesized simultaneously during the initial stages (a sensitive response period) of diverse stress treatments. Trehalose accumulated markedly under heat treatment, but not under sorbitol or ethanol stress, whereas glycerol accumulated strikingly under sorbitol stress conditions. Interestingly, extracellular trehalose seemed to be involved in protecting cells from damage under unfavorable conditions. Moreover, our results suggest that the stress-activated futile ATP cycles of trehalose and glycerol turnover are of general importance during cellular stress adaptation.In summary, the means of phenomics, transcriptomics and metabonomics were integrated to analyze the responses of the yeasts under various stresses conditions, which may provide references for the unveiling of yeast thermotolerance mechanism.