Jinjing Wang

Lager yeast, which is mainly used for lager beer brewing, withstands significant oxidative stress during brewing process, leading to its rapid aging in serial beer brewing. Mitophagy plays a critical role in the antioxidant stress response of yeast. However, the relationship between mitophagy and the antioxidant capacity of yeast is still unclear. Previous studies indicated that ATG gene family in mitophagy significantly affects the antioxidant capacity of yeast cells in beer brewing. Herein, the expression of ATG8, ATG11, ATG32, DNM1, and MMM1 genes was regulated. The results showed that the overexpression of ATG8 and ATG11 significantly reduced the intracellular ROS contents to 52.05% and 22.57% of the initial state, respectively, and helped to maintain a high mitochondrial vitality during serial fermentation. Disruption of ATG8, ATG11 and ATG32 resulted in significant decrease in cell vitality when exposed to H₂O₂ stimulation. Meanwhile, the disruptions of these genes were detrimental to the balance of intracellular ROS. Excess DNM1 activity could affect the cellular energy balance and ATP depletion under prolonged stress conditions. The repression of MMM1 led to lower ATP levels during serial beer fermentation. The ATG8, ATG11, and ATG32 genes might be potential targets for regulating the antioxidant capacity of yeast. The current work provides new insights into improving the antioxidant capacity of yeast through mitophagy regulation.

Food brewing technology is an important technology in the modern worldwide food industry, which uses the specific traits of microorganisms to produce food by traditional or modern engineering techniques

(1) Background: The degradation products of ribonucleic acid (RNA)are widely used in the food and pharmaceutical industry for their flavoring and nutritional enhancement functions. Yeast is the main source for commercial RNA production, and an efficient strain is the key to reducing production costs; (2) Methods: A mutant Saccharomyces pastorianus G03H8 with a high RNA yield was developed via ARTP mutagenesis and fed-batch fermentation was applied to optimize production capacity. Genome sequencing analysis was used to reveal the underlying mechanism of higher RNA production genetic differences in the preferred mutant; (3) Results: Compared with the highest RNA content of the mutant strain, G03H8 increased by 40% compared with the parental strain G03 after response surface model optimization. Meanwhile, in fed-batch fermentation, G03H8′s dry cell weight (DCW) reached 60.58 g/L in 5 L fermenter by molasses flowing and RNA production reached up to 3.58 g/L. Genome sequencing showed that the ribosome biogenesis, yeast meiosis, RNA transport, and longevity regulating pathway were closely related to the metabolism of high RNA production; (4) Conclusion: S. pastorianus G03H8 was developed for RNA production and had the potential to greatly reduce the cost of RNA production and shorten the fermentation cycle. This work lays the foundation for efficient RNA content using S. pastorianus.

Yeast flocculation plays an essential role in industrial application. Appropriate flocculation of yeast cells at the end of fermentation benefits the cell separation in production, which is an important characteristic of lager yeast for beer production. Due to the complex fermentation environment and diverse genetic background of yeast strains, it is difficult to explain the flocculation mechanism and find key genes that affect yeast flocculation during beer brewing. By analyzing the genomic mutation of two natural mutant yeasts with stronger flocculation ability compared to the parental strain, it was found that the mutated genes common in both mutants were enriched in protein processing in endoplasmic reticulum, membrane lipid metabolism and other pathways or biological processes involved in stress responses. Further functional verification of genes revealed that regulation of RIM101 and VPS36 played a role in lager yeast flocculation under the brewing condition. This work provided new clues for improving yeast flocculation in beer brewing.