利用基元模式分析酿酒酵母的葡萄糖厌氧发酵过程以提高乙醇产量

Elementary flux mode （EFM） analysis was used in the metabolic analysis of central carbon metabolism in Saccharomyces cerevisiae based on constructed cellular network. Calculated from the metabolic model, the ethanol-producing pathway No. 37 furthest converts the substrate into ethanol among the 78 elementary flux modes. The in silico metabolic phenotypes predicted based on this analysis fit well with the fermentation performance of the engineered strains, KAM3 and KAMll, which confirmed that EFM analysis is valid to direct the construction of Saccharomyces cerevisiae engineered strains, to increase the ethanol yield.     

酒精-沼气双发酵耦联工艺中丙酸对酿酒酵母酒精发酵的影响(英文)

Propanoic acid accumulated in an ethanol-methane coupled fermentation process affects the ethanol fermentation by Saccharomyces cerevisiae. The effects of propanoic acid on ethanol production were examined in cassava mash under different pH conditions. Final ethanol concentrations increased when undissociated propanoic acid was <30.0 mmol·L-1 . Propanoic acid, however, stimulated ethanol production, as much as 7.6% under proper conditions, but ethanol fermentation was completely inhibited when undissociated acid was >53.2 mmol·L-1 . Therefore, the potential inhibitory effect of propanoic acid on ethanol fermentation may be avoided by controlling the undissociated acid concentrations through elevated medium pH. Biomass and glycerol production decreased with propanoic acid in the medium, partly contributing to increased ethanol concentration.     

Improvement of ethanol production in Saccharomyces cerevisiae by hetero‐expression of GAPN and FPS1 deletion

BACKGROUND: During anaerobic bioethanol fermentation of Saccharomyces cerevisiae, the main byproduct glycerol is essential to regulate redox balance (reoxidize NADH to NAD⁺), which is necessary to maintain cell growth and fermentation. Hetero‐expression of a NADP⁺‐dependent glyceraldehydes‐3‐phosphate dehydrogenase (GAPN) [EC.1.2.1.9] in S. cerevisiae could redirect the carbon flux from glycerol to ethanol involving a net oxidation of NADH. The present study investigates whether combination of GAPN hetero‐expression and glycerol exporter Fps1p disruption would result in less glycerol and more ethanol production without affecting growth rate during anaerobic fermentations. RESULTS: The results of anaerobic fermentations showed that the fps1Δ mutant with GAPN (named 4FG) produced 21.47% less glycerol and 9.18% more ethanol compared with a parental strain with a control plasmid, while the rates of growth and fermentation were not changed. Moreover, the engineered strain 4FG yielded less glycerol and acetic acid, and more ethanol than the control, fps1Δ mutant or with GAPN only. CONCLUSIONS: During anaerobic fermentations, hetero‐expression of GAPN restored the reduced grow rate of the fps1Δ mutant, and led to less byproducts and more ethanol production. This combination strategy could be used to modulate glycerol metabolism and optimize the anaerobic fermentation of S. cerevisiae. Copyright © 2011 Society of Chemical Industry     

Production of fructose and ethanol from media with high sucrose concentrations by a mutant of Saccharomyces cerevisiae

The production of enriched fructose syrups and ethanol from a synthetic medium with high sucrose concentrations was studied in a batch process using Saccharomyces cerevisiae ATCC 36858. The results showed that the fructose yield was above 92% of theoretical values in synthetic media with sucrose concentrations between 180 g dm^?3 and 726 g dm^?3. Ethanol yield was about 82% in media with sucrose concentrations up to 451 g dm^?3. A product containing 178 g dm^?3 fructose, which represents 97% of the total sugar content, and 79 g dm^?3 ethanol was obtained using a medium with 360 g dm^?3 sucrose. The fructose fraction in the carbohydrates content in the produced syrups decreased with increases in the initial sucrose concentration. In a medium with initial sucrose concentration of 574 g dm^?3, the fructose content in the produced broth was 59% of the total carbohydrates. Glycerol and fructo‐oligosaccharides were also produced in this process. The produced fructo‐oligosaccharides started to be consumed when the concentration of sucrose in the media was less than 30% of its initial value. Complete hydrolysis of these sugars was noticed in media with sucrose concentrations below 451 g dm^?3. These findings will be useful in the production of ethanol and high fructose syrups using sucrose‐based raw materials with high concentrations of this carbohydrate. © 2001 Society of Chemical Industry     

Characterization of Saccharomyces cerevisiae immobilized onto chrysotile for ethanol production

Saccharomyces cerevisiae (CCT 3174 and commercial baker's yeast) was immobilized by adsorption onto chrysotile. The adsorbed yeast cells were easily washed out, but cells grown in situ were strongly attached by entrapment by chrysotile microfibres. In fermentation experiments with 30% (w/v) glucose solution, the immobilized cells showed a 1·3-fold increase in initial reaction velocity. For immobilized CCT 3174, the final ethanol yield was 26% higher than that with free cells. © 1998 Society of Chemical Industry     

酿酒酵母在硅橡胶膜生物反应器中连续发酵的生长动力学

实验研究了酿酒酵母在硅橡胶膜生物反应器中的细胞生长速率与操作参数之间的关系。在三水平正交实验基础上,用Gauss Newton非线性最小二乘法拟合了细胞比生长率与葡萄糖浓度、乙醇浓度和细胞浓度3变量之间的关系式,得到硅橡胶膜生物反应器乙醇连续发酵的细胞最大比生长率、饱和常数、产物抑制常数和群聚抑制常数等基本动力学参数,表明当细胞浓度达到15g/L或乙醇浓度达到70g/L时细胞生长受到完全抑制。连续发酵实验验证了硅橡胶膜生物反应器中的细胞生长动力学满足拟合模型的规律。     

异源转氢酶NNT对酿酒酵母木糖代谢的影响

表达有毕赤酵母木糖还原酶(XR)和木糖醇脱氢酶(XDH)的重组酿酒酵母,能代谢木糖.但是XR和XDH分别偏好辅酶NADPH和NAD⁺,造成辅酶的不平衡和副产物的积累,所以重组酿酒酵母利用木糖产生乙醇的效率很低.转氢酶可以催化辅酶NADPH和NADH之间的相互转化,因此本实验将黑曲霉的转氢酶基因NNT转入到重组酿酒酵母中,通过实验确定了NNT基因的表达蛋白在酵母细胞内定位于线粒体中,NNT基因分别用pPGK1、pCCW12和pHXT7启动子进行表达,在微好氧的木糖发酵条件下,NNT基因的导入使酿酒酵母甘油产量下降,乙醇产率提高,在由pCCW12和pHXT7表达NNT基因的重组酿酒酵母中,木糖醇产率分别下降86.3%和49.3%,乙醇产率提高16.7%和12.7%,说明转氢酶NNT的存在改善了木糖代谢的辅酶不平衡,提高了乙醇的转化率.     

离子液体1-乙基-3-甲基咪唑醋酸盐对酿酒酵母AY93161的毒性及其酒精发酵过程的影响

为了考察离子液体在由木质纤维原料制备可发酵糖中的残留对后续酒精发酵过程的影响,对离子液体1-乙基-3-甲基咪唑醋酸盐([Emim]Ac)对酿酒酵母AY93161的毒性及其酒精发酵过程的影响进行研究。通过亚甲基蓝染色,利用OLYMPUS CX41显微镜观察不同[Emim]Ac浓度下对数生长期酵母细胞的形态结构,出芽情况及代谢活性,发现在[Emim]Ac浓度高于5 g·L^-1时,酵母细胞的形态结构会发生变化,在[Emim]Ac浓度高于0.1 g·L^-1时,随着[Emim]Ac浓度的增加,酵母的出芽速率及代谢活性降低。通过平板培养和液体悬浮培养测得[Emim]Ac对酵母的半有效浓度EC50和半抑制浓度IC50分别为4.45、7.70 g·L^-1。通过测定不同[Emim]Ac浓度下酵母酒精发酵的过程数据,发现在[Emim]Ac浓度低于0.1 g·L^-1时,对酵母酒精发酵过程几乎无影响,在[Emim]Ac浓度高于0.1 g·L^-1时,对酵母酒精发酵有抑制作用,[Emim]Ac对酵母酒精发酵的抑制作用主要是由其对菌体生长的抑制所致。     

纤维素乙醇生产重组酿酒酵母菌株的构建与优化研究进展

寻找化石能源的替代品以及开发和利用生物能源已引起国内外研究者的广泛关注。提高酿酒酵母利用来源广泛、贮存丰富的农林废弃物等木质纤维素原料生产燃料乙醇的效率是生物能源的重要研究内容,但是,重组酿酒酵母木糖发酵性能低是限制纤维素乙醇经济性的关键问题。本文总结了酿酒酵母中木糖代谢途径的构建和优化以及木糖转运对木糖利用的影响,分析了重组酵母利用纤维素水解液进行乙醇发酵的研究现状,并对进一步提高重组酿酒酵母纤维素乙醇生产效率的研究趋势进行了展望。目前国内外已经构建了可有效利用木糖产乙醇的重组酵母,但对其木糖代谢机制的研究还尚未深入,限制了重组菌株的定向改造。此外,目前缺少在纤维素生物质水解液发酵实际应用过程中对重组菌株的评价。因此,加强重组酵母菌株对木糖利用相关代谢调控机理的分析,注重多种抑制物对菌株发酵性能的影响,结合真实底物纤维素乙醇发酵过程进行重组菌株的构建和优化,从而进一步提高纤维素乙醇生产的经济性,是未来菌株构建的重要研究方向。     

Effects of light wavelength and intensity on the production of ethanol by Saccharomyces cerevisiae in batch cultures

BACKGROUND: Photoreceptors have been identified in Saccharomyces cerevisae, however, the influence of light on the performance of ethanol fermentation of S. cerevisiae is not yet clear. The aims of this study are to elucidate the influence of light wavelength and intensity on the growth and ethanol production of S. cerevisiae and to describe a novel two‐stage LED light process to optimize ethanol fermentation. RESULTS: Experimental results indicated that maximum biomass concentration X_max of the batch under red LED light increased monotonically with light intensity, and the optimal specific product yield Y_p/x was 13.2 g g^?1 at 600 lux. Maximum ethanol concentration P_max of the batch under blue LED light increased monotonically with light intensity, and the optimal Y_p/x was 18.4 g g^?1 at 900 lux. A novel two‐stage LED light process achieved maximum P_max, of 98.7 g dm^?3 resulting in 36% improvement compared with that of the batch in the dark. CONCLUSION: The light wavelength and its intensity significantly affected cell growth and ethanol formation of S. cerevisiae. Red LED light (630 nm) stimulated cell growth but slightly inhibited ethanol formation. In contrast, blue LED light (470 nm) significantly inhibited cell growth but stimulated ethanol formation. A novel two‐stage LED light process has been successfully demonstrated to optimize ethanol fermentation of S. cerevisiae. Copyright © 2009 Society of Chemical Industry     

Continuous ethanol production from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor

The continuous production of ethanol from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor has been investigated. At a substrate concentration of 150 g dm^?3, maximum ethanol productivity of 16 g dm^?3 h^?1 was obtained at D = 0·4 h^?1 with 62·3% of theoretical yield and 83·6% sugars′ utilization. At a dilution rate of 0·1 h^?1, optimal ethanol productivity was achieved in the pH range 3·5–5·5, temperature range 30–35·C and initial sugar concentration of 200 g dm^?3. Maximum ethanol productivity of 24·5 g dm^?3 h^?1 was obtained at D = 0·5 h^?1 with 58·8% of theoretical yield and 85% sugars′ utilization when non-sterilized carob pod extract containing 200 g dm^?3 total sugars was used as feed material. The bioreactor system was operated at a constant dilution rate of 0·5 h^?1 for 30 days without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical) and sugars′ utilization were 25 g dm^?3 h^?1, 58·8% and 85·5%, respectively.     

乙醇发酵过程中酿酒酵母的磷脂组变化

磷脂分子是细胞膜的重要组成,在酵母发酵产乙醇过程中起重要作用。通过液质联用方法对两株酿酒酵母细胞（工业酵母O和实验室酵母S）的磷脂分子进行定性和定量分析,应用主成分分析（PCA）和正交偏最小二乘（OPLS）对O和S不同生长时期的磷脂图谱进行模式识别。结果发现,在乙醇发酵过程中,两株酵母共同的变化规律是：从延滞期进入指数期过程中,饱和短链磷脂分子增加,不饱和长链磷脂分子减少。而两株酵母的差异表现在延滞期时,具有较低生长速率的酵母PE分子含量更高。