# Proteomics Analysis of _Zygosaccharomyces mellis_ in Response to Sugar Stress
## 4 Discussion  
Honey contains a large number of nutrients, including protein, amino acids, enzymes, minerals, vitamins and aromatic compounds except sugar. Honey also has antioxidant and antibacterial activity, which can be used for anti-aging and burn treatments [25]. In addition, honey is also a natural food to make wine using yeast. A few studies have shown that mixed yeast strains show better fermentation characteristics, such as increasing glycerol content and total acidity and producing a variety of volatile phenols, esters, ketones and other special substances [26]. In this study, _Z. mellis_ that was isolated from honey showed high hypertonic tolerance in response to high sugar stress with the potential for food fermentation. Figure 3: The influence of sugar stress on the relative expression of FDH1 gene (**A**), ATP content (**B**) and NADH content (**C**) of BY4741, BY4741\(\triangle\)scFDR11 and BY4717 zmFDR11. a: BY4741, b: BY4741\(\triangle\)scFDR11, c: BY4717 zmFDR11 (one-way analysis of variance (ANOVA) followed by Tukey test). * represents significant difference, \(p\) value < 0.05, and ** represents extremely significant difference between treatment and control, \(p\) value < 0.01. Figure 2: The influence of sugar stress on the growth of BY4741, BY4741\(\triangle\)scFDR11 and BY4717 zmFDR11. (**A**): The OD600 values of BY4741, BY4741\(\triangle\)scFDR11 and BY4717 zmFDR11. (**B**): The intracellular glycerol and trehalose contents of BY4741, BY4741\(\triangle\)scFDR11 and BY4717 zmFDR11 under 60% YPD. (**C**): The enzyme activities of CAT, SOD and POD of BY4741, BY4741\(\triangle\)scFDR11 and BY4717 zmFDR11 under 60% YPD. (**A**): Two-way analysis of variance (ANOVA); (**B,C**): one-way analysis of variance (ANOVA) followed by Tukey test. * represents significant difference, \(p\) value < 0.05, ** represents extremely significant difference between treatment and control, \(p\) value < 0.01, and *** represents extremely significant difference between treatment and control, \(p\) value < 0.001. Hyperosmotic stress stimulates a large variety of adaptive responses in yeast cells that affect many different physiological functions to adapt to the environment. During the fermentation process, because high concentrations of sugar and accumulated ethanol have toxic effects on yeast cells, yeasts have a series of physiological regulatory mechanisms to resist high osmotic stress, leading to growth delays [27; 28; 29]. Previous studies have shown that yeast can produce and retain metabolically compatible osmolytes, including intracellular glycerol and trehalose, to adapt to the hyperosmotic environment [30; 31; 32]. Transcriptomics analysis revealed that some genes involved in the pathway of the high osmolarity glycerol mitogen-activated protein kinase (HOG-MAPK) signal transduction and trehalose synthesis, as well as the oxidative stress response, were upregulated under high-glucose tolerance in _Z. mellis_[6]. In addition, the morphological and structural properties of the cell wall and plasma membrane can also be regulated [33]. In this study, proteome analysis revealed that the proteins involved in the regulation of cell-wall, membrane and envelope biogenesis were all downregulated. Among them, Chitin cross-links with \(\beta\)-glucan to form a cell-wall skeleton and plays a key role in maintaining cell morphology and structure [34; 35]. Ergosterol, an important component of the microbial cell membrane, can stabilize the membrane structure by combining with phospholipids to regulate membrane permeability, membrane fluidity, integrity and cell material transport [36]. Under alcohol treatment, the content of ergosterol in the cell membrane of _S. cerevisiae_ can increase to inhibit membrane damage and maintain normal membrane permeability [36; 37; 38]. However, in this study, due to the growth delay, the proteins involved in cell-wall and ergosterol synthesis were downregulated.