## 4 The Behavior of _Saccharomyces cerevisiae_ in Stressors Action  
Once environmental stress acts on microorganisms, it produces changes at a genetic and molecular level. For example, yeast cells produce much higher amounts of trehalose in response to heat stress and the disaccharide acts to stabilize plasma membranes. Also, some genes that have a role in the synthesis of ergosterols are able to exert thermotolerance properties in yeasts [2]. An overview of the yeast adaptive response in osmotic, ethanol, and oxidative stress is presented in Figure 3[62; 70]. Yeast cells adapt to stress by activating or inhibiting the genes responsible for actions against it. An alternative is epigenetic mechanisms by which yeasts quickly adapt to cellular stress. These processes involve an organization of chromatin into histones, DNAmodifications or changes in transcription patterns [13; 71; 72; 73]. Certain responses of yeast cells to environmental stress are shown in Table 2.  
Due to problems with nutrient-poor environments or poor parameters control during fermentation, the conversion of sugar to alcohol is often slowed down. Apart from these causes, there are also certain factors that cause damage during the process of obtaining alcohol. Osmotic stress, ethanol toxicity or certain pH and temperature values can affect the growth of yeast cells, but also their metabolism. For example, an ethanol concentration greater than 10% (\(v/v\)) and a temperature above 35 \({}^{\circ}\)C greatly reduce the viability of microorganisms [2]. Zinc is an important micronutrient in the growth process of _S. cerevisiae_ cells. About 3% of their proteome requires zinc to function properly. In other words, 105 proteins use it as a cofactor, and another 360 need it to maintain structural stability through binding domains where it is a key factor. The trace element also enters into the structure of some proteins called zinc fingers, these being the largest family of proteins that bind nucleic acids and that have an important function in regulating transcription [74]. Table 3 lists some examples and how they act against cellular stress in the yeast _S. cerevisiae_. Different yeasts from the class _Saccharomycescetes_ have been analyzed and it has been observed that each exhibits distinct defense techniques against osmotic and salt stress. For example, _Zygosaccharomycesc rouxii_ and _S. cerevisiae_ can export Na\({}^{+}\) cations out of the cell or into vacuoles. In contrast, _Debaryomyces hausenii_ accumulates Na\({}^{+}\) ions in the cell without suffering intoxication [75]. Table 4 highlights the cation transport systems in several yeast \begin{table}
\begin{tabular}{c c} \hline \hline
**Stress Response** & **Details** \\ \hline Apoptosis & Near the end of life, senescent cells enter apoptosis \\ \hline Genotypic changes & Mutations are common in yeasts subjected to stress during the brewing process \\ \hline Changes in intracellular metal ion homeostasis & Several stressors lead to the loss of key metal ions such as Mg and Zn \\ \hline Blocking the cell division cycle & Stress leads to the blocking of the yeast cell cycle, thus inhibiting growth \\ \hline Induction of stress enzymes & For example, the induction of antioxidant enzymes during the action of oxidative stress \\ \hline Activation of glycerol biosynthesis & Glycerol is produced in excess during osmotic stress \\ \hline Induction of trehalose biosynthesis & Cells produce large amounts of trehalose in response to heat shock and other stressors \\ \hline Structural changes in the cell membrane & Disorders of membrane integrity caused by stressors \\ \hline Induction of heat shock protein synthesis (hot/cold) & Heat shock proteins are induced in response to high temperatures and other factors \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _S. cerevisiae_ stress response [2]. Figure 3: Molecular mechanisms of osmotic, ethanol, and oxidative stress response in yeast [62; 70]. species. For yeast species where a gene is present, a \"+\" was marked in the corresponding box.