Effect of mitophagy related genes on the antioxidant properties of Saccharomyces cerevisiae / 生物工程学报

Mitophagy is a process whereby cells selectively remove mitochondria through the mechanism of autophagy, which plays an important role in maintaining cellular homeostasis. In order to explore the effect of mitophagy genes on the antioxidant activities of Saccharomyces cerevisiae, mutants with deletion or overexpression of mitophagy genes ATG8, ATG11 and ATG32 were constructed respectively. The results indicated that overexpression of ATG8 and ATG11 genes significantly reduced the intracellular reactive oxygen species (ROS) content upon H2O2 stress for 6 h, which were 61.23% and 46.35% of the initial state, respectively. Notable, overexpression of ATG8 and ATG11 genes significantly increased the mitochondrial membrane potential (MMP) and ATP content, which were helpful to improve the antioxidant activities of the strains. On the other hand, deletion of ATG8, ATG11 and ATG32 caused mitochondrial damage and significantly decreased cell vitality, and caused the imbalance of intracellular ROS. The intracellular ROS content significantly increased to 174.27%, 128.68%, 200.92% of the initial state, respectively, upon H2O2 stress for 6 h. The results showed that ATG8, ATG11 and ATG32 might be potential targets for regulating the antioxidant properties of yeast, providing a new clue for further research.

Manipulation of isocitrate dehydrogenase genes affects the anti-autolytic ability of lager yeast / 生物工程学报

Yeast autolysis affects the flavor and quality of beer. The regulation of yeast autolysis is a need for industrial beer production. Previous studies on brewer's yeast autolysis showed that the citric acid cycle-related genes had a great influence on yeast autolysis. To explore the contribution of isocitrate dehydrogenase genes in autolysis, the IDP1 and IDP2 genes were destroyed or overexpressed in typical lager yeast Pilsner. The destruction of IDP1 gene improved the anti-autolytic ability of yeast, and the anti-autolytic index after 96 h autolysis was 8.40, 1.5 times higher than that of the original strain. The destruction of IDP1 gene increased the supply of nicotinamide adenine dinucleotide phosphate (NADPH) and the NADPH/NADP+ ratio was 1.94. After fermentation, intracellular ATP level was 1.8 times higher than that of the original strain, while reactive oxygen species (ROS) was reduced by 10%. The destruction of IDP2 gene resulted in rapid autolysis and a decrease in the supply of NADPH. Anti-autolytic index after 96 h autolysis was 4.03 and the NADPH/NADP+ ratio was 0.89. After fermentation, intracellular ATP level was reduced by 8% compared with original strain, ROS was 1.3 times higher than that of the original strain. The results may help understand the regulation mechanism of citric acid cycle-related genes on yeast autolysis and provide a basis for the selection of excellent yeast with controllable anti-autolytic performance.

Effect of RIM21 gene disruption on flocculation of lager yeast / 生物工程学报

Lager yeast is the most popular yeast strain used for beer production in China. The flocculation of yeast plays an important role in cell separation at the end of fermentation. Therefore, appropriately enhancing the flocculation capability of the lager yeast without affecting its fermentation performance would be desirable for beer industry. Our previous study showed that the defect of gene RIM21 might contribute to the enhanced flocculation capability of a lager yeast G03. To further investigate the role of the RIM21 gene in flocculation of strain G03, this study constructed a RIM21-deleted mutant strain G03-RIM21Δ through homologous recombination. Deletion of RIM21 improved the flocculation capability of strain G03 during wort fermentation at 11 °C without changing its fermentation performance significantly. The expression of FLO5, Lg-FLO1 and some other genes involved in cell wall integrity pathway were up-regulated in strain G03-RIM21Δ. In addition, the disruption of RIM21 enhanced resistance of yeast cells to cell wall inhibitors. These results provide a basis for elucidating the flocculation mechanism of lager yeast under low-temperature fermentation conditions.

Regulations of RLM1 gene affect the anti-autolytic ability of lager yeast / 生物工程学报

The autolysis of brewer's yeast seriously affects the quality of beer and the quality of yeast is considered as one of the key factors in beer brewing. Previous studies on brewer's yeast autolysis showed that RLM1 gene, an important transcription factor in cell integrity pathway, is closely related to the autolysis of yeast. In this study, RLM1 was knocked out and overexpressed in a haploid brewer's yeast. RLM1 disruption resulted in poor anti-autolysis performance of yeast, whereas overexpression of RLM1 contributed to the anti-autolytic ability of yeast. In addition, RLM1 gene knockout affected the osmotic stress resistance, cell wall damage resistance, nitrogen starvation resistance and temperature tolerance of yeast strain. The transcriptional level of GAS1 involved in cell wall assembly and DNA damage response was regulated along with the expression of RLM1, whereas other genes in CWI pathway did not show apparent regularity. RLM1 might mainly affect the expression of GAS1 so as to improve the stress resistance of lager yeast in harsh environment. The result from this study help further understand the mechanism of yeast autolysis and lay a foundation for breeding brewer's yeast strain with better anti-autolytic ability.

Progress in brewer's yeast cell wall stress response / 生物工程学报

Yeast cell wall plays an important role in the establishment and maintenance of cell morphology upon the cell wall stress. The cell wall of yeast consists of β-glucans, mannoproteins and chitin. The composition and structure remodel due to cell wall stress. Brewer's yeast cell wall exhibits stress response during long-term acclimation in order to adapt to environmental changes. This paper reviews the composition and structure of yeast cell wall and the molecular mechanisms of cell wall remodeling and signal pathway regulation.

Research progresses in microbial 1,3-1,4-β-glucanase: protein engineering and industrial applications / 生物工程学报

1,3-1,4-β-glucanase (E.C.3.2.1.73) is an important industrial enzyme which cleave β-glucans into oligosaccharides through strictly cutting the β-1,4 glycosidic bonds in 3-O-substituted glucopyranose units. Microbial 1,3-1,4-β-glucanase belongs to retaining glycosyl hydrolases of family 16 with a jellyroll β-sandwich fold structure. The present paper reviews the industrial application and protein engineering of microbial β-glucanases in the last decades and forecasts the research prospects of microbial β-glucanases.

Physiological changes of Saccharomyces cerevisiae during serial re-pitching: a review / 生物工程学报

The morphological structure and physiological indexes of Saccharomyces cerevisiae have changed during serial re-pitching due to the stress conditions in serial handlings and the cells become aging. It is of great significance to study the physiological changes of S. cerevisiae during serial re-pitching to understand the anti-aging effect of S. cerevisiae. In this paper, the changes of the physiological indexes during re-pitching of yeast are summarized, and based on the analysis of the previous works further research directions are proposed.