酵母菌的致孔作用对PVA/CMC水凝胶性能的影响

利用酵母菌发泡制备了聚乙烯醇/羧甲基纤维素多孔水凝胶(D-PC)，采用FTIR对其化学结构进行了表征和Zeta电位分析共同证明了酵母菌和材料之间的相互作用；利用SEM和BET分别对其三维网络结构进行了观察以及比表面积、孔径进行了测定；研究了D-PC在不同条件下对亚甲基蓝(MB)的去除，通过纤维素降解酶实验测试了D-PC的降解性。研究结果表明：酵母菌通过静电作用包覆在D-PC内；随着酵母菌量的增加，D-PC的比表面积增大、平均孔径减小；D-PC对MB的去除机制以化学吸附为主，且吸附动力学符合伪二级动力学方程；去除效率随着酵母菌的增加而增大，随着pH、温度的增加先增大后减小；一定条件下D-PC能降解水凝胶中的聚乙烯醇。     

The Emi2 Protein of Saccharomyces cerevisiae is a Hexokinase Expressed under Glucose Limitation

Hexokinases catalyze glucose phosphorylation at the first step in glycolysis in eukaryotes. In the budding yeast Saccharomyces cerevisiae , three enzymes for glucose phosphorylation have long been known: Hxk1, Hxk2, and Glk1. In this study, we focus on Emi2, a previously uncharacterized hexokinase-like protein of S. cerevisiae . Our data show that the recombinant Emi2 protein (rEmi2), expressed in Escherichia coli , possesses glucose-phosphorylating activity in the presence of ATP and Mg ²⁺ . It was also found that rEmi2 phosphorylates not only glucose but also fructose, mannose and glucosamine in vitro . In addition, we examined changes in the level of endogenous Emi2 protein in S. cerevisiae in the presence or absence of glucose and a non-fermentable carbon source. We found that the expression of Emi2 protein is tightly suppressed during proliferation in high glucose, while it is strongly upregulated in response to glucose limitation and the presence of a non-fermentable carbon source. Our data suggest that the expression of the endogenous Emi2 protein in S. cerevisiae is regulated under the control of Hxk2 in response to glucose availability in the environment.     

Genome-wide effect of tetracycline,doxycycline and 4-epidoxycycline on gene expression in Saccharomyces cerevisiae

Tetracycline (Tet) and derivative chemicals (e.g., doxycycline or Dox) have gained widespread recognition for their antibiotic properties since their introduction in the late 1970s, but recent work with these chemicals in the lab has shifted to include multiple techniques in all genetic model systems for the precise control of gene expression. The most widely used Tet-modulated methodology is the Tet-On/Tet-Off gene expression system. Tet is generally considered to have effects specific to bacteria; therefore, it should have few off-target effects when used in eukaryotic systems, and a previous study in the yeast Saccharomyces cerevisiae found that Dox had no effect on genome-wide gene expression as measured by microarray. In contrast, another study found that the use of Dox in common cell lines and several model organisms led to mitonuclear protein imbalance, suggesting an inhibitory role of Dox in eukaryotic mitochondria. Recently, a new Dox derivative, 4-epidoxycycline (4-ED) was developed that was shown to have less off-target consequences on mitochondrial health. To determine the best tetracycline family chemical to use for gene expression control in S. cerevisiae, we performed RNA sequencing (RNA-seq) on yeast grown on standard medium compared with growth on media supplemented with Tet, Dox or 4-ED. We found each caused dozens of genes to change expression, with Dox eliciting the greatest expression responses, suggesting that the specific tetracycline used in experiments should be tailored to the specific gene(s) of interest when using the Tet-On/Tet-Off system to reduce the consequences of confounding off-target responses.     

A yeast surface display platform for plant hormone receptors: Toward directed evolution of new biosensors

Small-molecule biosensors have major applications in biotechnology and medicine but remain difficult to engineer. Plant hormone receptors represent an attractive platform for engineering such biosensors because their chemically induced dimerization architectures naturally decouple small-molecule sensing and sensor actuation. Rapid biosensor engineering will require quantitative high-throughput screening methods. Here we develop a yeast surface display (YSD) platform for the PYR1/HAB1 abscisic acid sensor of Arabidopsis thaliana. We extensively optimized PYR1 surface display, HAB1 purification, and binding reaction conditions. Our system reproduces previous results with wild-type and engineered receptors, and a mathematical analysis of the PYR1/HAB1 system allows us to infer all binding constants. Critically, we find that a previously engineered PYR1 receptor with altered ligand specificity binds HAB1 with identical affinity, suggesting that substantial reengineering of the PYR1 binding pocket does not compromise sensor actuation. This YSD platform for A. thaliana PYR1/HAB1 will facilitate future biosensor engineering efforts.     

Variation in content of tyramine,histamine, 2-phenylethylamine,tryptamine and their precursor amino acids in a Chardonnay wine by using different commercial active dry yeasts and nitrogen sources

Wine is a fermented beverage that could be affected by high concentrations of biogenic amines, thus altering organoleptic and health properties. In this work, the capacity of different selected yeast strains regarding to affect the content of tyramine, histamine, 2-phenylethylamine, tryptamine and their precursor amino acids (pAA) during fermentation has been described. Overall, biogenic amines (BAs) and pAA contents appeared significantly related both to the strain and to the nutrient supplementation applied. Among BAs, without and (with) nitrogen source addition, the concentrations covered a range between 0.1 and 9.5 (0.1–10.3) mg L⁻¹ for tyramine; 0.1 and 4.4 (0.1–4.6) mg L⁻¹ for histamine; 0.4 and 1.1 (0.4–1.4) mg L⁻¹ for 2-phenylethylamine; and 0.02 and 0.14 (0.01–0.12) mg L⁻¹ for tryptamine, respectively. Considering that also wine yeast species are responsible for BAs formation, the evidence from fermentation trials underlined the relevance of a careful choice of ADY strains and nitrogen sources in the management of alcoholic fermentation in wine.     

Effect of a halophilic aromatic yeast together with Aspergillus oryzae in koji making on the volatile compounds and quality of soy sauce moromi

Koji making is an essential step in the production of high‐quality soy sauce. In this study, we inoculated koji with a halophilic aromatic yeast (Zygosaccharomyces rouxii) and Aspergillus oryzae and investigated the effects on the volatile compounds and quality of soy sauce moromi. Our results suggest that the optimal yeast inoculation was approximately 1.5 × 10⁶ yeast per gram of koji, and excessive yeast greatly decreased A. oryzae enzyme activity. In comparison with the control group, there were no significant changes in the concentrations of amino nitrogen, total titratable acids, total soluble nitrogen and reducing sugar by extending the fermentation time during the first fermentation month, whereas the concentration of glutamate in the yeast‐inoculated sample increased by 46.16% and the arginine concentration decreased by 61.07%. After the second fermentation month, 17, 38 and 38 volatile components were identified by GC–MS in C1, C2 and C5, respectively. Moreover, a large number of volatile components, such as 2‐Methoxy‐4‐vinylphenol, ethyl acetate and 1‐Octen‐3‐ol were found in C2 and C5. And the total contents of volatile compounds in C2 were obviously higher than C5. This work furthers our understanding of the traditional multistrain koji making and provides a new method for enhancing the quality and flavour of soy sauce.