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1.
The glucose transport capacity of Saccharomyces cerevisiae CBS 8066 was studied in aerobic glucose-limited chemostat cultures. Two different transport systems were encountered with affinity constants of 1 and 20 mM, respectively. The capacity of these carriers (Vmax) was dependent on the dilution rate and the residual glucose concentration in the culture. From the residual glucose concentration in the fermenter and the kinetic constants of glucose transport, their in situ contribution to glucose consumption was determined. The sum of these calculated in situ transport rates correlated well with the observed rate of glucose consumption of the culture. The growth kinetics of S. cerevisiae CBS 8066 in glucose-limited cultures were rather peculiar. At low dilution rates, at which glucose was completely respired, the glucose concentration in the fermenter was constant at 110 microM, independent of the glucose concentration in the reservoir. At higher dilution rates, characterized by the occurrence of both respiration and alcoholic fermentation, the residual substrate concentration followed Monod kinetics. In this case, however, the overall affinity constant was dependent on the reservoir glucose concentration.  相似文献   

2.
In previous studies it was shown that deletion of the HXK2 gene in Saccharomyces cerevisiae yields a strain that hardly produces ethanol and grows almost exclusively oxidatively in the presence of abundant glucose. This paper reports on physiological studies on the hxk2 deletion strain on mixtures of glucose/sucrose, glucose/galactose, glucose/maltose and glucose/ethanol in aerobic batch cultures. The hxk2 deletion strain co-consumed galactose and sucrose, together with glucose. In addition, co-consumption of glucose and ethanol was observed during the early exponential growth phase. In S.cerevisiae, co-consumption of ethanol and glucose (in the presence of abundant glucose) has never been reported before. The specific respiration rate of the hxk2 deletion strain growing on the glucose/ethanol mixture was 900 micromol.min(-1).(g protein)(-1), which is four to five times higher than that of the hxk2 deletion strain growing oxidatively on glucose, three times higher than its parent growing on ethanol (when respiration is fully derepressed) and is almost 10 times higher than its parent growing on glucose (when respiration is repressed). This indicates that the hxk2 deletion strain has a strongly enhanced oxidative capacity when grown on a mixture of glucose and ethanol.  相似文献   

3.
Recombinant S. cerevisiae strains, with elevated levels of the enzymes of lower glycolysis (glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate mutase, phosphoglycerate kinase, enolase, pyruvate kinase, pyruvate decarboxylase and alcohol dehydrogenase) were physiologically characterized. During growth on glucose the enzyme levels in the recombinant strains (YHM4 and YHM7) were 1.1-3.4-fold higher than in the host strain (CEN.PK.K45). The recombinant strains were grown in aerobic or anaerobic batch cultures on glucose or a mixture of glucose and galactose. The specific ethanol production rates in the recombinant strains were the same as for the host strain and the physiological behaviour of the recombinant strains and the host strain was similar. When the cellular demand for ATP was increased by means of glucose pulses (final concentrations of 3.9 g/l or 2.0 g/l, respectively) to aerobic chemostat cultures maintained at a dilution rate of 0.08/h, the specific carbon dioxide production rate (qCO(2)) of CEN.PK.K45 accelerated at 6x10(-3) mmol/g/min(2) during the first 15 min, whereas during the same time period the qCO(2) of YHM7 accelerated twice as fast at 12x10(-3) mmol/g/min(2), indicating a higher fermentative capacity in the recombinant strain.  相似文献   

4.
Mixed bacterial cultures derived from the rumen were grown in a remen fluid medium in a chemostat at three dilution rates (.02, .06, and .12 per h), each at four growth-limiting glucose concentrations (5.8, 9.9, 12.7, and 25.0 mM). Microscopic observations indicated that a relatively complex mixture of bacterial species was maintained and proportions of fermentations products were similar to those of the rumen except for elevated proportions of methane and acetate. Cell concentration increased linearly with increases in glucose concentration. The range of glucose concentrations had little effect on yields of cells or products produced per mole of glucose fermented. With increases in dilution rates, the amount of butyrate and methane produced per mole of glucose fermented decreased and the amount of propionate increased. Yield glucose (grams cells produced per mole of glucose fermented) increased from 42 at a dilution rate of .02 to 84 at a dilution rate of .12. These large increases are discussed in relationship to the energy requirements for maintenance of bacteria. A theoretical maximum yield glucose of 89.3 and a maintenance requirement of .26 mmol glucose per g cells per h were calculated. Moles of adenosine triphosphate produced per mole of glucose fermented and yield of cells produced per mole of adenosine triphosphate are discussed.  相似文献   

5.
细胞稀释强化硅橡胶膜生物反应器连续乙醇发酵   总被引:1,自引:1,他引:0  
通过原位重力沉降分离酵母和渗透汽化分离乙醇构建了细胞稀释连续乙醇发酵的硅橡胶膜生物反应器。采用酿酒酵母,以0.05/h的细胞稀释率在膜生物反应器中实现了170 h的连续稳定乙醇发酵。重力沉降分离酵母对硅橡胶膜生物反应器产生的细胞稀释作用可以通过反应器内酵母自身生长得到平衡,发酵液细胞浓度稳定在5g/L。渗透汽化原位分离使发酵液内乙醇浓度维持在50 g/L。细胞稀释膜生物反应器连续发酵的乙醇体积产率达到1.63 g/(L.h),相对于同等工艺参数的细胞封闭循环膜生物反应器连续乙醇发酵细胞比产率提高了31%。  相似文献   

6.
考察了D-核糖单级连续发酵的起始时间、稀释率、流加糖浓度对D-核糖单级连续发酵的影响。结果表明,在24 h后以稀释率为0.06 h-1,流加糖浓度为200 g/L时进行单级连续发酵,D-核糖产率达到最大,可达4.0 g/(L.h)以上。  相似文献   

7.
8.
对三株野生型产酒精耐高温马克斯克鲁维酵母(Kluyveromyces marxianus)在不同温度、pH、酒精浓度、糖浓度下的生理耐性进行了研究,并与安琪耐高温酵母进行了比较,得出的结论为:三株野生型耐高温酵母K. marxianus GX-17,K. marxianus HN-79,K.marxianus HN-138高温条件下的生长和产酒精能力明显高于安碘酵母;K marxianus GX-17对pH变化的适应力较安琪酵母强;野生型耐高温酵母的耐糖能力略低于安琪酵母;安琪酵母的耐酒精能力明显高于野生型耐高温酵母.  相似文献   

9.
In tequila production, fermentation is an important step. Fermentation determines the ethanol productivity and organoleptic properties of the beverage. In this study, a yeast isolated from native residual agave must was identified as Kluyveromyces marxianus UMPe-1 by 26S rRNA sequencing. This yeast was compared with the baker's yeast Saccharomyces cerevisiae Pan1. Our findings demonstrate that the UMPe-1 yeast was able to support the sugar content of agave must and glucose up to 22% (w/v) and tolerated 10% (v/v) ethanol concentration in the medium with 50% cells survival. Pilot and industrial fermentation of agave must tests showed that the K. marxianus UMPe-1 yeast produced ethanol with yields of 94% and 96% with respect to fermentable sugar content (glucose and fructose, constituting 98%). The S. cerevisiae Pan1 baker's yeast, however, which is commonly used in some tequila factories, showed 76% and 70% yield. At the industrial level, UMPe-1 yeast shows a maximum velocity of fermentable sugar consumption of 2.27g·L(-1)·h(-1) and ethanol production of 1.38g·L(-1)·h(-1), providing 58.78g ethanol·L(-1) at 72h fermentation, which corresponds to 96% yield. In addition, the major and minor volatile compounds in the tequila beverage obtained from UMPe-1 yeast were increased. Importantly, 29 volatile compounds were identified, while the beverage obtained from Pan1-yeast contained fewer compounds and in lower concentrations. The results suggest that the K. marxianus UMPe-1 is a suitable yeast for agave must fermentation, showing high ethanol productivity and increased volatile compound content comparing with a S. cerevisiae baker's yeast used in tequila production.  相似文献   

10.
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