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1.
The activity and the cofactor specificity of xylose reductase and xylitol dehydrogenase were studied in extracts of yeasts from the genera Candida, Kluyveromyces, Pachysolen, Pichia, and Torulopsis grown under microaerobic conditions. It was found that xylitol dehydrogenase in all of the yeast species studied is specific for NAD+; xylose reductase in the xylitol-producing species C. didensiae, C. intermediae, C. parapsilosis, C. silvanorum, C. tropicalis, Kl. fragilis, Kl. marxianus, P. guillermondii, and T. molishiama is specific for NADPH; and xylose reductase in the ethanol-producing species P. stipitis, C. shehatae, and Pa. tannophilus is specific for both NADPH and NADH. 相似文献
2.
Yablochkova E. N. Bolotnikova O. I. Mikhailova N. P. Nemova N. N. Ginak A. I. 《Microbiology》2004,73(2):129-133
The activities of xylitol dehydrogenase and xylose reductase in the yeasts Candida shehatae, C. didensiae, C. intermediae, C. tropicalis, Kluyveromyces marxianus, Pichia stipitis, P. guillermondii, Pachysolen tannophilus, and Torulopsis molishiama were studied at different oxygen transfer rates (OTRs) to the fermentation medium (0, 5, and 140 mmol O2/(l h)). The activities of these enzymes were maximum in the yeasts P. stipitis and C. shehatae. The xylitol dehydrogenase of all the yeasts was NAD+-dependent, irrespective of the intensity of aeration. The xylose reductase of the yeasts C. didensiae, C. intermediae, C. tropicalis, Kl. marxianus, P. guillermondii, and T. molishiama was NADPH-dependent, whereas the xylose reductase of P. stipitis, C. shehatae, and Pa. tannophilus was specific for both NADPH and NADH. The effect of OTR on the activities of the different forms of xylitol dehydrogenase and xylose reductase in xylose-assimilating yeasts is discussed. 相似文献
3.
The activities of xylitol dehydrogenase and xylose reductase in the yeasts Candida shehatae, C. didensiae, C. intermediae, C. tropicalis, Kluyveromyces marxianus, Pichia stipitis, P. guillermondii, Pachysolen tannophilus, and Torulopsis molishiama were studied at different oxygen transfer rates (OTRs) to the fermentation medium (0, 5, and 140 mmol O2/(1 h)). The activities of these enzymes were maximum in the yeasts P. stipitis and C. shehatae. The xylitol dehydrogenase of all the yeasts was NAD-dependent, irrespective of the intensity of aeration. The xylose reductase of the yeasts C. didensiae, C. intermediae, C. tropicalis, Kl. marxianus, P. guillermondii, and T. molishiama was NADPH-dependent, whereas the xylose reductase of P. stipitis, C. shehatae, and Pa. tannophilus was specific for both NADPH and NADH. The effect of OTR on the activities of the different forms of xylitol dehydrogenase and xylose reductase in the xylose-assimilating yeasts is discussed. 相似文献
4.
Background
Ethanolic fermentation of lignocellulosic biomass is a sustainable option for the production of bioethanol. This process would greatly benefit from recombinant Saccharomyces cerevisiae strains also able to ferment, besides the hexose sugar fraction, the pentose sugars, arabinose and xylose. Different pathways can be introduced in S. cerevisiae to provide arabinose and xylose utilisation. In this study, the bacterial arabinose isomerase pathway was combined with two different xylose utilisation pathways: the xylose reductase/xylitol dehydrogenase and xylose isomerase pathways, respectively, in genetically identical strains. The strains were compared with respect to aerobic growth in arabinose and xylose batch culture and in anaerobic batch fermentation of a mixture of glucose, arabinose and xylose.Results
The specific aerobic arabinose growth rate was identical, 0.03 h-1, for the xylose reductase/xylitol dehydrogenase and xylose isomerase strain. The xylose reductase/xylitol dehydrogenase strain displayed higher aerobic growth rate on xylose, 0.14 h-1, and higher specific xylose consumption rate in anaerobic batch fermentation, 0.09 g (g cells)-1 h-1 than the xylose isomerase strain, which only reached 0.03 h-1 and 0.02 g (g cells)-1h-1, respectively. Whereas the xylose reductase/xylitol dehydrogenase strain produced higher ethanol yield on total sugars, 0.23 g g-1 compared with 0.18 g g-1 for the xylose isomerase strain, the xylose isomerase strain achieved higher ethanol yield on consumed sugars, 0.41 g g-1 compared with 0.32 g g-1 for the xylose reductase/xylitol dehydrogenase strain. Anaerobic fermentation of a mixture of glucose, arabinose and xylose resulted in higher final ethanol concentration, 14.7 g l-1 for the xylose reductase/xylitol dehydrogenase strain compared with 11.8 g l-1 for the xylose isomerase strain, and in higher specific ethanol productivity, 0.024 g (g cells)-1 h-1 compared with 0.01 g (g cells)-1 h-1 for the xylose reductase/xylitol dehydrogenase strain and the xylose isomerase strain, respectively.Conclusion
The combination of the xylose reductase/xylitol dehydrogenase pathway and the bacterial arabinose isomerase pathway resulted in both higher pentose sugar uptake and higher overall ethanol production than the combination of the xylose isomerase pathway and the bacterial arabinose isomerase pathway. Moreover, the flux through the bacterial arabinose pathway did not increase when combined with the xylose isomerase pathway. This suggests that the low activity of the bacterial arabinose pathway cannot be ascribed to arabitol formation via the xylose reductase enzyme. 相似文献5.
Oskar Bengtsson Bärbel Hahn-Hägerdal Marie F Gorwa-Grauslund 《Biotechnology for biofuels》2009,2(1):9-10
Background
Xylose reductase (XR) and xylitol dehydrogenase (XDH) from Pichia stipitis are the two enzymes most commonly used in recombinant Saccharomyces cerevisiae strains engineered for xylose utilization. The availability of NAD+ for XDH is limited during anaerobic xylose fermentation because of the preference of XR for NADPH. This in turn results in xylitol formation and reduced ethanol yield. The coenzyme preference of P. stipitis XR was changed by site-directed mutagenesis with the aim to engineer it towards NADH-preference. 相似文献6.
In order to better understand the differences in xylose metabolism between natural xylose-utilizing Pichia stipitis and metabolically engineered Saccharomyces cerevisiae, we constructed a series of recombinant S. cerevisiae strains with different xylose reductase/xylitol dehydrogenase/xylulokinase activity ratios by integrating xylitol dehydrogenase gene (XYL2) into the chromosome with variable copies and heterogeneously expressing xylose reductase gene (XYL1) and endogenous xylulokinase gene (XKS1). The strain with the highest specific xylose uptake rate and ethanol productivity on pure xylose fermentation was selected to compare to P. stipitis under oxygen-limited condition. Physiological and enzymatic comparison showed that they have different patterns of xylose metabolism and NADPH generation. 相似文献
7.
Metabolic engineering for improved fermentation of pentoses by yeasts 总被引:23,自引:0,他引:23
The fermentation of xylose is essential for the bioconversion of lignocellulose to fuels and chemicals, but wild-type strains of Saccharomyces cerevisiae do not metabolize xylose, so researchers have engineered xylose metabolism in this yeast. Glucose transporters mediate xylose uptake, but no transporter specific for xylose has yet been identified. Over-expressing genes for aldose (xylose) reductase, xylitol dehydrogenase and moderate levels of xylulokinase enable xylose assimilation and fermentation, but a balanced supply of NAD(P) and NAD(P)H must be maintained to avoid xylitol production. Reducing production of NADPH by blocking the oxidative pentose phosphate cycle can reduce xylitol formation, but this occurs at the expense of xylose assimilation. Respiration is critical for growth on xylose by both native xylose-fermenting yeasts and recombinant S, cerevisiae. Anaerobic growth by recombinant mutants has been reported. Reducing the respiration capacity of xylose-metabolizing yeasts increases ethanol production. Recently, two routes for arabinose metabolism have been engineered in S. cerevisiae and adapted strains of Pichia stipitis have been shown to ferment hydrolysates with ethanol yields of 0.45 g g–1 sugar consumed, so commercialization seems feasible for some applications. 相似文献
8.
Aloke K. Bera Nancy W. Y. Ho Aftab Khan Miroslav Sedlak 《Journal of industrial microbiology & biotechnology》2011,38(5):617-626
Robust microorganisms are necessary for economical bioethanol production. However, such organisms must be able to effectively
ferment both hexose and pentose sugars present in lignocellulosic hydrolysate to ethanol. Wild type Saccharomyces cerevisiae can rapidly ferment hexose, but cannot ferment pentose sugars. Considerable efforts were made to genetically engineer S. cerevisiae to ferment xylose. Our genetically engineered S cerevisiae yeast, 424A(LNH-ST), expresses NADPH/NADH xylose reductase (XR) that prefer NADPH and NAD+-dependent xylitol dehydrogenase (XD) from Pichia stipitis, and overexpresses endogenous xylulokinase (XK). This strain is able to ferment glucose and xylose, as well as other hexose
sugars, to ethanol. However, the preference for different cofactors by XR and XD might lead to redox imbalance, xylitol excretion,
and thus might reduce ethanol yield and productivity. In the present study, genes responsible for the conversion of xylose
to xylulose with different cofactor specificity (1) XR from N. crassa (NADPH-dependent) and C. parapsilosis (NADH-dependent), and (2) mutant XD from P. stipitis (containing three mutations D207A/I208R/F209S) were overexpressed in wild type yeast. To increase the NADPH pool, the fungal
GAPDH enzyme from Kluyveromyces lactis was overexpressed in the 424A(LNH-ST) strain. Four pentose phosphate pathway (PPP) genes, TKL1, TAL1, RKI1 and RPE1 from S. cerevisiae, were also overexpressed in 424A(LNH-ST). Overexpression of GAPDH lowered xylitol production by more than 40%. However, other
strains carrying different combinations of XR and XD, as well as new strains containing the overexpressed PPP genes, did not
yield any significant improvement in xylose fermentation. 相似文献
9.
Reduced Oxidative Pentose Phosphate Pathway Flux in Recombinant Xylose-Utilizing Saccharomyces cerevisiae Strains Improves the Ethanol Yield from Xylose 总被引:1,自引:0,他引:1
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Marie Jeppsson Bjrn Johansson Brbel Hahn-Hgerdal Marie F. Gorwa-Grauslund 《Applied microbiology》2002,68(4):1604-1609
In recombinant, xylose-fermenting Saccharomyces cerevisiae, about 30% of the consumed xylose is converted to xylitol. Xylitol production results from a cofactor imbalance, since xylose reductase uses both NADPH and NADH, while xylitol dehydrogenase uses only NAD+. In this study we increased the ethanol yield and decreased the xylitol yield by lowering the flux through the NADPH-producing pentose phosphate pathway. The pentose phosphate pathway was blocked either by disruption of the GND1 gene, one of the isogenes of 6-phosphogluconate dehydrogenase, or by disruption of the ZWF1 gene, which encodes glucose 6-phosphate dehydrogenase. Decreasing the phosphoglucose isomerase activity by 90% also lowered the pentose phosphate pathway flux. These modifications all resulted in lower xylitol yield and higher ethanol yield than in the control strains. TMB3255, carrying a disruption of ZWF1, gave the highest ethanol yield (0.41 g g−1) and the lowest xylitol yield (0.05 g g−1) reported for a xylose-fermenting recombinant S. cerevisiae strain, but also an 84% lower xylose consumption rate. The low xylose fermentation rate is probably due to limited NADPH-mediated xylose reduction. Metabolic flux modeling of TMB3255 confirmed that the NADPH-producing pentose phosphate pathway was blocked and that xylose reduction was mediated only by NADH, leading to a lower rate of xylose consumption. These results indicate that xylitol production is strongly connected to the flux through the oxidative part of the pentose phosphate pathway. 相似文献
10.
Peter M. Bruinenberg Peter H. M. de Bot Johannes P. van Dijken W. Alexander Scheffers 《Applied microbiology and biotechnology》1984,19(4):256-260
Summary The kinetics and enzymology of d-xylose utilization were studied in aerobic and anaerobic batch cultures of the facultatively fermentative yeasts Candida utilis, Pachysolen tannophilus, and Pichia stipitis. These yeasts did not produce ethanol under aerobic conditions. When shifted to anaerobiosis cultures of C. utilis did not show fermentation of xylose; in Pa. tannophilus a very low rate of ethanol formation was apparent, whereas with Pi. stipitis rapid fermentation of xylose occurred. The different behaviour of these yeasts ist most probably explained by differences in the nature of the initial steps of xylose metabolism: in C. utilis xylose is metabolized via an NADPH-dependent xylose reductase and an NAD+-linked xylitol dehydrogenase. As a consequence, conversion of xylose to ethanol by C. utilis leads to an overproduction of NADH which blocks metabolic activity in the absence of oxygen. In Pa. tannophilus and Pi. stipitis, however, apart from an NADPH-linked xylose reductase also an NADH-linked xylose reductase was present. Apparently xylose metabolism via the NADH-dependent reductase circumvents the imbalance of the NAD+/NADH redox system, thus allowing fermentation of xylose to ethanol under anaerobic conditions. The finding that the rate of xylose fermentation in Pa. tannophilus and Pi. stipitis corresponds with the activity of the NADH-linked xylose reductase activity is in line with this hypothesis. Furthermore, a comparative study with various xylose-assimilating yeasts showed that significant alcoholic fermentation of xylose only occurred in those organisms which possessed NADH-linked aldose reductase. 相似文献
11.
The thermophilic mouldMalbranchea pulchella var.sulfurea TMD-8 produced extracellular xylanases in wheat straw hemicellulose as well as wheat straw. This mould utilized xylose less efficiently than glucose. Mycelial extracts contained xylose isomerase, xylose reductase, and xylitol dehydrogenase. Xylose isomerase was less thermostable than that from other microorganisms. However, xylitol dehydrogenase and xylose reductase were relatively more thermostable in comparison with these enzymes from other microorganisms. The affinity of xylose isomerase for xylose was very high (Km 10mM), while that of xylose reductase was low (Km 23.5mM). The xylitol dehydrogenase exhibited relatively high affinity for xylitol (Km 0.02mM). The activity of this enzyme, however, declined steeply, in the alkaline range. This is the first report on the occurrence of three intracellular enzymes, xylose isomerase, xylose reductase, and xylitol dehydrogenase in a thermophilic mould, which play an important role in xylose metabolism. 相似文献
12.
Metabolic engineering of Saccharomyces cerevisiae for xylose fermentation has often relied on insertion of a heterologous pathway consisting of nicotinamide adenine dinucleotide (phosphate) NAD(P)H-dependent xylose reductase (XR) and NAD+-dependent xylitol dehydrogenase (XDH). Low ethanol yield, formation of xylitol and other fermentation by-products are seen for many of the S. cerevisiae strains constructed in this way. This has been ascribed to incomplete coenzyme recycling in the steps catalyzed by XR and XDH. Despite various protein-engineering efforts to alter the coenzyme specificity of XR and XDH individually, a pair of enzymes displaying matched utilization of NAD(H) and NADP(H) was not previously reported. We have introduced multiple site-directed mutations in the coenzyme-binding pocket of Galactocandida mastotermitis XDH to enable activity with NADP+, which is lacking in the wild-type enzyme. We describe four enzyme variants showing activity for xylitol oxidation by NADP+ and NAD+. One of the XDH variants utilized NADP+ about 4 times more efficiently than NAD+. This is close to the preference for NADPH compared with NADH in mutants of Candida tenuis XR. Compared to an S. cerevisiae-reference strain expressing the genes for the wild-type enzymes, the strains comprising the gene encoding the mutated XDH in combination a matched XR mutant gene showed up to 50% decreased glycerol yield without increase in ethanol during xylose fermentation. 相似文献
13.
Background
Metabolic engineering of Saccharomyces cerevisiae for xylose fermentation into fuel ethanol has oftentimes relied on insertion of a heterologous pathway that consists of xylose reductase (XR) and xylitol dehydrogenase (XDH) and brings about isomerization of xylose into xylulose via xylitol. Incomplete recycling of redox cosubstrates in the catalytic steps of the NADPH-preferring XR and the NAD+-dependent XDH results in formation of xylitol by-product and hence in lowering of the overall yield of ethanol on xylose. Structure-guided site-directed mutagenesis was previously employed to change the coenzyme preference of Candida tenuis XR about 170-fold from NADPH in the wild-type to NADH in a Lys274→Arg Asn276→Asp double mutant which in spite of the structural modifications introduced had retained the original catalytic efficiency for reduction of xylose by NADH. This work was carried out to assess physiological consequences in xylose-fermenting S. cerevisiae resulting from a well defined alteration of XR cosubstrate specificity. 相似文献14.
The effect of oxygen limitation on xylose fermentation by Pichia stipitis (CBS 6054) was investigated in continuous culture. The maximum specific ethanol productivity (0.20 g of ethanol g dry weight−1 h−1) and ethanol yield (0.48 g/g) was reached at an oxygen transfer rate below 1 mmol/liter per h. In the studied range of oxygenation, the xylose reductase (EC 1.1.1.21) and xylitol dehydrogenase (EC 1.1.1.9) activities were constant as well as the ratio between the NADPH and NADH activities of xylose reductase. No xylitol production was found. The pyruvate decarboxylase (EC 4.1.1.1) activity increased and the malate dehydrogenase (EC 1.1.1.37) activity decreased with decreasing oxygenation. With decreasing oxygenation, the intracellular intermediary metabolites sedoheptulose 7-phosphate, glucose 6-phosphate, fructose 1,6-diphosphate, and malate accumulated slightly while pyruvate decreased. The ratio of the xylose uptake rate under aerobic conditions, in contrast to that under anaerobic assay conditions, increased with increasing oxygenation in the culture. The results are discussed in relation to the energy level in the cell, the redox balance, and the mitochondrial function. 相似文献
15.
Xylitol is a five-carbon sugar alcohol that has a variety of uses in the food and pharmaceutical industries. In xylose assimilating yeasts, NAD(P)H-dependent xylose reductase (XR) catalyzes the reduction of xylose to xylitol. In the present study, XR with varying cofactor specificities was overexpressed in Saccharomyces cerevisiae to screen for efficient xylitol production. Xylose consumption and xylitol yields were higher when NADPH-dependent enzymes (Candida tropicalis XR and S. cerevisiae Gre3p aldose reductase) were expressed, indicating that heterologous enzymes can utilize the intracellular NADPH pool more efficiently than the NADH pool, where they may face competition from native enzymes. This was confirmed by overexpression of a NADH-preferring C. tropicalis XR mutant, which led to decreased xylose consumption and lower xylitol yield. To increase intracellular NADPH availability for xylitol production, the promoter of the ZWF1 gene, coding for the first enzyme of the NADPH-generating pentose phosphate pathway, was replaced with the constitutive GPD promoter in a strain expressing C. tropicalis XR. This change led to a ~12% increase in xylitol yield. Deletion of XYL2 and SOR1, whose gene products can use xylitol as substrate, did not further increase xylitol yield. Using wheat stalk hydrolysate as source of xylose, the constructed strain efficiently produced xylitol, demonstrating practical relevance of this approach. 相似文献
16.
《Journal of Fermentation and Bioengineering》1993,75(2):83-88
The xylose reductase gene originating from Pichia stipitis was subcloned on an expression vector with the enolase promoter and terminator from Saccharomyces cerevisiae. The transformants of S. cerevisiae harboring the resultant plasmids produced xylose reductase constitutively at a rate about 3 times higher than P. stipitis, but could not assimilate xylose due to the deficient conversion of xylitol to xylulose. The xylitol dehydrogenase gene was also isolated from the gene library of P. stipitis by plaque hybridization using a probe specific for its N-terminal amino acid sequence. The gene transferred into S. cerevisiae was well expressed. Furthermore, high expressions of the xylose reductase and xylitol dehydrogenase genes in S. cerevisiae were achieved by introducing both genes on the same or coexisting plasmids. The transformants could grow on a medium containing xylose as the sole carbon source, but ethanol production from xylose was less than that by P. stipitis and a significant amount of xylitol was excreted into the culture broth. 相似文献
17.
在导入表达毕赤酵母(Pichia stipitis)木糖还原酶(xylose reductase,XR)和木糖醇脱氢酶(xylitol dehydrogenase,XDH)基因的重组酿酒酵母中,木糖还原酶活性主要依赖辅酶NADPH,木糖醇脱氢酶活性依赖辅酶 NAD+,两者的辅助因子不同导致细胞内电子氧化还原的不平衡,是造成木糖醇积累,影响木糖代谢和乙醇产量的主要原因之一.将经过基因工程改造获得的NADH高亲和力的木糖还原酶突变基因m1,与毕赤酵母木糖醇脱氢酶(PsXDH)基因xyl2共转染酿酒酵母AH109,以转染毕赤酵母木糖还原酶(PsXR)基因xyl1和xyl2重组质粒的酵母细胞为对照菌株,在SC/-Leu/-Trp营养缺陷型培养基中进行筛选,获得的阳性转化子分别命名为AH-M-XDH和AH-XR-XDH.重组酵母在限制氧通气条件下对木糖和葡萄糖进行共发酵摇瓶培养,HPLC检测发酵底物的消耗和代谢产物的产出情况.结果显示,与对照菌株AH-XR-XDH相比,AH-M-XDH的木糖利用率明显提高,乙醇得率增加了16%,木糖醇产生下降了41.4%.结果证实,通过基因工程改造的木糖代谢关键酶,可用于酿酒酵母发酵木糖生产乙醇,其能通过改善酿酒酵母细胞内氧化还原失衡的问题,提高木糖利用率和乙醇产率. 相似文献
18.
Affinity Purifications of Aldose Reductase and Xylitol Dehydrogenase from the Xylose-Fermenting Yeast Pachysolen tannophilus
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Although xylose is a major product of hydrolysis of lignocellulosic materials, few yeasts are able to convert it to ethanol. In Pachysolen tannophilus, one of the few xylose-fermenting yeasts found, aldose reductase and xylitol dehydrogenase were found to be key enzymes in the metabolic pathway for xylose fermentation. This paper presents a method for the rapid and simultaneous purification of both aldose reductase and xylitol dehydrogenase from P. tannophilus. Preliminary studies indicate that this method may be easily adapted to purify similar enzymes from other xylose-fermenting yeasts. 相似文献
19.
Raquel M. Cadete Monaliza A. Melo-Cheab Adriana L. Viana Evelyn S. Oliveira César Fonseca Carlos A. Rosa 《World journal of microbiology & biotechnology》2016,32(12):207
This study assessed the efficiency of Scheffersomyces amazonensis UFMG-CM-Y493T, cultured in xylose-supplemented medium (YPX) and rice hull hydrolysate (RHH), to convert xylose to xylitol under moderate and severe oxygen limitation. The highest xylitol yields of 0.75 and 1.04 g g?1 in YPX and RHH, respectively, were obtained under severe oxygen limitation. However, volumetric productivity in RHH was ninefold decrease than that in YPX medium. The xylose reductase (XR) and xylitol dehydrogenase (XDH) activities in the YPX cultures were strictly dependent on NADPH and NAD+ respectively, and were approximately 10% higher under severe oxygen limitation than under moderate oxygen limitation. This higher xylitol production observed under severe oxygen limitation can be attributed to the higher XR activity and shortage of the NAD+ needed by XDH. These results suggest that Sc. amazonensis UFMG-CM-Y493T is one of the greatest xylitol producers described to date and reveal its potential use in the biotechnological production of xylitol. 相似文献
20.
Xylose fermentation by Saccharomyces cerevisiae 总被引:1,自引:0,他引:1
We have performed a comparative study of xylose utilization in Saccharomyces cerevisiae transformants expressing two key enzymes in xylose metabolism, xylose reductase (XR) and xylitol dehydrogenase (XDH), and in a prototypic xylose-utilizing yeast, Pichia stipitis. In the absence of respiration (see text), baker's yeast cells convert half of the xylose to xylitol and ethanol, whereas P. stipilis cells display rather a homofermentative conversion of xylose to ethanol. Xylitol production by baker's yeast is interpreted as a result of the dual cofactor dependence of the XR and the generation of NADPH by the pentose phosphate pathway. Further limitations of xylose utilization in S. cerevisiae cells are very likely caused by an insufficient capacity of the non-oxidative pentose phosphate pathway, as indicated by accumulation of sedoheptulose-7-phosphate and the absence of fructose-1,6-bisphosphate and pyruvate accumulation. By contrast, uptake at high substrate concentrations probably does not limit xylose conversion in S. cerevisiae XYL1/XYL2 transformants.
Correspondence to: M. Ciriacy 相似文献