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1.
Chen Y 《Journal of industrial microbiology & biotechnology》2011,38(5):581-597
This article reviews current co-culture systems for fermenting mixtures of glucose and xylose to ethanol. Thirty-five co-culture
systems that ferment either synthetic glucose and xylose mixture or various biomass hydrolysates are examined. Strain combinations,
fermentation modes and conditions, and fermentation performance for these co-culture systems are compared and discussed. It
is noted that the combination of Pichia stipitis with Saccharomyces cerevisiae or its respiratory-deficient mutant is most commonly used. One of the best results for fermentation of glucose and xylose
mixture is achieved by using co-culture of immobilized Zymomonas mobilis and free cells of P. stipitis, giving volumetric ethanol production of 1.277 g/l/h and ethanol yield of 0.49–0.50 g/g. The review discloses that, as a
strategy for efficient conversion of glucose and xylose, co-culture fermentation for ethanol production from lignocellulosic
biomass can increase ethanol yield and production rate, shorten fermentation time, and reduce process costs, and it is a promising
technology although immature. 相似文献
2.
Novel two‐stage fermentation process for bioethanol production using Saccharomyces pastorianus
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Yogender Kumar Gowtham Kristen P. Miller David B. Hodge J. Michael Henson Sarah W. Harcum 《Biotechnology progress》2014,30(2):300-310
Bioethanol produced from lignocellulosic materials has the potential to be economically feasible, if both glucose and xylose released from cellulose and hemicellulose can be efficiently converted to ethanol. Saccharomyces spp. can efficiently convert glucose to ethanol; however, xylose conversion to ethanol is a major hurdle due to lack of xylose‐metabolizing pathways. In this study, a novel two‐stage fermentation process was investigated to improve bioethanol productivity. In this process, xylose is converted into biomass via non‐Saccharomyces microorganism and coupled to a glucose‐utilizing Saccharomyces fermentation. Escherichia coli was determined to efficiently convert xylose to biomass, which was then killed to produce E. coli extract. Since earlier studies with Saccharomyces pastorianus demonstrated that xylose isomerase increased ethanol productivities on pure sugars, the addition of both E. coli extract and xylose isomerase to S. pastorianus fermentations on pure sugars and corn stover hydrolysates were investigated. It was determined that the xylose isomerase addition increased ethanol productivities on pure sugars but was not as effective alone on the corn stover hydrolysates. It was observed that the E. coli extract addition increased ethanol productivities on both corn stover hydrolysates and pure sugars. The ethanol productivities observed on the corn stover hydrolysates with the E. coli extract addition was the same as observed on pure sugars with both E. coli extract and xylose isomerase additions. These results indicate that the two‐stage fermentation process has the capability to be a competitive alternative to recombinant Saccharomyces cerevisiae‐based fermentations. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:300–310, 2014 相似文献
3.
Fangqing Wei Menglei Li Ming Wang Hongxing Li Zailu Li Wensheng Qin Tiandi Wei Jianzhi Zhao Xiaoming Bao 《Global Change Biology Bioenergy》2021,13(1):83-97
During second‐generation bioethanol production from lignocellulosic biomass, the desired traits for fermenting microorganisms, such as Saccharomyces cerevisiae, are high xylose utilization and high robustness to inhibitors in lignocellulosic hydrolysates. However, as observed previously, these two traits easily showed the antagonism, one rising and the other falling, in the C6/C5 co‐fermenting S. cerevisiae strain. In this study, LF1 obtained in our previous study is an engineered budding yeast strain with a superior co‐fermentation capacity of glucose and xylose, and was then mutated by atmospheric and room temperature plasma (ARTP) mutagenesis to improve its robustness. The ARTP‐treated cells were grown in 50% (v/v) leachate from lignocellulose pretreatment with high inhibitors content for adaptive evolution. After 30 days, the generated mutant LF1‐6 showed significantly enhanced tolerance, with a six‐fold increase in cell density in the above leachate. Unfortunately, its xylose utilization dropped markedly, indicating the recurrence of the negative correlation between xylose utilization and robustness. To alleviate this antagonism, LF1‐6 cells were iteratively mutated with ARTP mutagenesis and then anaerobically grown using xylose as the sole carbon source, and xylose utilization was restored in the resulting strain 6M‐15. 6M‐15 also exhibited increased co‐fermentation performance of xylose and glucose with the highest ethanol productivity reported to date (0.525 g g?1 h?1) in high‐level mixed sugars (80 g L?1 glucose and 40 g L?1 xylose) with no inhibitors. Meanwhile, its fermentation time was shortened by 8 h compared to that of LF1. During the fermentation of non‐detoxified lignocellulosic hydrolysate with high inhibitor concentrations at pH ~3.5, 6M‐15 can efficiently convert glucose and xylose with an ethanol yield of 0.43 g g?1. 6M‐15 is also regarded as a potential chassis cell for further design of a customized strain suitable for production of second‐generation bioethanol or other high value‐added products from lignocellulosic biomass. 相似文献
4.
Alcoholic fermentation of carbon sources in biomass hydrolysates by Saccharomyces cerevisiae: current status 总被引:1,自引:0,他引:1
van Maris AJ Abbott DA Bellissimi E van den Brink J Kuyper M Luttik MA Wisselink HW Scheffers WA van Dijken JP Pronk JT 《Antonie van Leeuwenhoek》2006,90(4):391-418
Fuel ethanol production from plant biomass hydrolysates by Saccharomyces cerevisiae is of great economic and environmental significance. This paper reviews the current status with respect to alcoholic fermentation of the main plant biomass-derived monosaccharides by this yeast. Wild-type S. cerevisiae strains readily ferment glucose, mannose and fructose via the Embden–Meyerhof pathway of glycolysis, while galactose is fermented via the Leloir pathway. Construction of yeast strains that efficiently convert other potentially fermentable substrates in plant biomass hydrolysates into ethanol is a major challenge in metabolic engineering. The most abundant of these compounds is xylose. Recent metabolic and evolutionary engineering studies on S. cerevisiae strains that express a fungal xylose isomerase have enabled the rapid and efficient␣anaerobic fermentation of this pentose. l-Arabinose fermentation, based on the expression of a prokaryotic pathway in S. cerevisiae, has also been established, but needs further optimization before it can be considered for industrial implementation. In addition to these already investigated strategies, possible approaches for metabolic engineering of galacturonic acid and rhamnose fermentation by S. cerevisiae are discussed. An emerging and major challenge is to achieve the rapid transition from proof-of-principle experiments under ‘academic’ conditions (synthetic media, single substrates or simple substrate mixtures, absence of toxic inhibitors) towards efficient conversion of complex industrial substrate mixtures that contain synergistically acting inhibitors. 相似文献
5.
《Critical reviews in biotechnology》2013,33(1):22-48
Lignocellulosic biomass from agricultural and agro-industrial residues represents one of the most important renewable resources that can be utilized for the biological production of ethanol. The yeast Saccharomyces cerevisiae is widely used for the commercial production of bioethanol from sucrose or starch-derived glucose. While glucose and other hexose sugars like galactose and mannose can be fermented to ethanol by S. cerevisiae, the major pentose sugars D-xylose and L-arabinose remain unutilized. Nevertheless, D-xylulose, the keto isomer of xylose, can be fermented slowly by the yeast and thus, the incorporation of functional routes for the conversion of xylose and arabinose to xylulose or xylulose-5-phosphate in Saccharomyces cerevisiae can help to improve the ethanol productivity and make the fermentation process more cost-effective. Other crucial bottlenecks in pentose fermentation include low activity of the pentose phosphate pathway enzymes and competitive inhibition of xylose and arabinose transport into the cell cytoplasm by glucose and other hexose sugars. Along with a brief introduction of the pretreatment of lignocellulose and detoxification of the hydrolysate, this review provides an updated overview of (a) the key steps involved in the uptake and metabolism of the hexose sugars: glucose, galactose, and mannose, together with the pentose sugars: xylose and arabinose, (b) various factors that play a major role in the efficient fermentation of pentose sugars along with hexose sugars, and (c) the approaches used to overcome the metabolic constraints in the production of bioethanol from lignocellulose-derived sugars by developing recombinant S. cerevisiae strains. 相似文献
6.
Aloke Kumar Bera Miroslav Sedlak Aftab Khan Nancy W. Y. Ho 《Applied microbiology and biotechnology》2010,87(5):1803-1811
Cost-effective and efficient ethanol production from lignocellulosic materials requires the fermentation of all sugars recovered
from such materials including glucose, xylose, mannose, galactose, and l-arabinose. Wild-type strains of Saccharomyces cerevisiae used in industrial ethanol production cannot ferment d-xylose and l-arabinose. Our genetically engineered recombinant S. cerevisiae yeast 424A(LNH-ST) has been made able to efficiently ferment xylose to ethanol, which was achieved by integrating multiple
copies of three xylose-metabolizing genes. This study reports the efficient anaerobic fermentation of l-arabinose by the derivative of 424A(LNH-ST). The new strain was constructed by over-expression of two additional genes from
fungi l-arabinose utilization pathways. The resulting new 424A(LNH-ST) strain exhibited production of ethanol from l-arabinose, and the yield was more than 40%. An efficient ethanol production, about 72.5% yield from five-sugar mixtures containing
glucose, galactose, mannose, xylose, and arabinose was also achieved. This co-fermentation of five-sugar mixture is important
and crucial for application in industrial economical ethanol production using lignocellulosic biomass as the feedstock. 相似文献
7.
O. V. Dmytruk K. V. Dmytruk A. Ya. Voronovsky A. A. Sibirny 《Cytology and Genetics》2008,42(2):127-138
Plant biomass possesses huge potential as a source for the production of biofuels. Glucose and the five-carbon sugar xylose are the principal constituents of biomass. The yeast Saccharomyces cerevisiae, which is used for industrial production of ethanol from glucose is not capable of fermenting xylose. Thus, it is necessary to find in Nature or to create microorganisms capable of achieving efficient fermentation of glucose and xylose, as a means of achieving economically feasible biomass conversion into ethanol. Active fermentation of xylose may be achieved if the initial stages of metabolism are efficiently performed [1]. In this review, the enzymes of the initial stages of xylose metabolism in yeast (xylose reductase, xylitol dehydrogenase, and xylulokinase) and bacteria (xylose isomerase and xylulokinase) are characterized. The ways for constructing yeast strains capable of achieving efficient alcoholic xylose fermentation are discussed. 相似文献
8.
Krzysztof Berezka Marta Semkiv Mariia Borbuliak Johanna Blomqvist Tomas Linder Justyna Ruchała Kostyantyn Dmytruk Volkmar Passoth Andriy Sibirny 《Cell biology international》2021,45(3):507-517
Amid known microbial bioethanol producers, the yeast Scheffersomyces (Pichia) stipitis is particularly promising in terms of alcoholic fermentation of both glucose and xylose, the main constituents of lignocellulosic biomass hydrolysates. However, the ethanol yield and productivity, especially from xylose, are still insufficient to meet the requirements of a feasible industrial technology; therefore, the construction of more efficient S. stipitis ethanol producers is of great significance. The aim of this study was to isolate the insertional mutants of S. stipitis with altered ethanol production from glucose and xylose and to identify the disrupted gene(s). Mutants obtained by random insertional mutagenesis were screened for their growth abilities on solid media with different sugars and for resistance to 3-bromopyruvate. Of more than 1,300 screened mutants, 17 were identified to have significantly changed ethanol yields during the fermentation. In one of the best fermenting strains (strain 4.6), insertion was found to occur within the ORF of a homolog to the Saccharomyces cerevisiae gene HEM25 (YDL119C), encoding a mitochondrial glycine transporter required for heme synthesis. The role of HEM25 in heme accumulation, respiration, and alcoholic fermentation in the yeast S. stipitis was studied using strain 4.6, the complementation strain Comp—a derivative from the 4.6 strain with expression of the WT HEM25 allele and the deletion strain hem25Δ. As hem25Δ produced lower amounts of ethanol than strain 4.6, we assume that the phenotype of strain 4.6 may be caused not only by HEM25 disruption but additionally by some point mutation. 相似文献
9.
Karhumaa K Fromanger R Hahn-Hägerdal B Gorwa-Grauslund MF 《Applied microbiology and biotechnology》2007,73(5):1039-1046
Xylose fermentation performance was studied of a previously developed Saccharomyces cerevisiae strain TMB 3057, carrying high xylose reductase (XR) and xylitol dehydrogenase (XDH) activity, overexpressed non-oxidative
pentose phosphate pathway (PPP) and deletion of the aldose reductase gene GRE3. The fermentation performance of TMB 3057 was significantly improved by increased ethanol production and reduced xylitol
formation compared with the reference strain TMB 3001. The effects of the individual genetic modifications on xylose fermentation
were investigated by comparing five isogenic strains with single or combined modifications. All strains with high activity
of both XR and XDH had increased ethanol yields and significantly decreased xylitol yields. The presence of glucose further
reduced xylitol formation in all studied strains. High activity of the non-oxidative PPP improved the xylose consumption rate.
The results indicate that ethanolic xylose fermentation by recombinant S. cerevisiae expressing XR and XDH is governed by the efficiency by which xylose is introduced in the central metabolism. 相似文献
10.
Jingping G Hongbing S Gang S Hongzhi L Wenxiang P 《Journal of industrial microbiology & biotechnology》2012,39(5):777-787
Genome shuffling is an efficient approach for the rapid improvement of industrially important microbial phenotypes. This report
describes optimized conditions for protoplast preparation, regeneration, inactivation, and fusion using the Saccharomyces cerevisiae W5 strain. Ethanol production was confirmed by TTC (triphenyl tetrazolium chloride) screening and high-performance liquid
chromatography (HPLC). A genetically stable, high ethanol-producing strain that fermented xylose and glucose was obtained
following three rounds of genome shuffling. After fermentation for 84 h, the high ethanol-producing S. cerevisiae GS3-10 strain (which utilized 69.48 and 100% of the xylose and glucose stores, respectively) produced 26.65 g/L ethanol,
i.e., 47.08% higher than ethanol production by S. cerevisiae W5 (18.12 g/L). The utilization ratios of xylose and glucose were 69.48 and 100%, compared to 14.83 and 100% for W5, respectively.
The ethanol yield was 0.40 g/g (ethanol/consumed glucose and xylose), i.e., 17.65% higher than the yield by S. cerevisiae W5 (0.34 g/g). 相似文献
11.
Candida shehatae and Saccharomyces cerevisiae work synergistically to improve ethanol fermentation from sugarcane bagasse and rice straw hydrolysate in immobilized cell bioreactor
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Pareena Meethit Pirayaprach Ratanaprasit Chularat Sakdaronnarong 《Engineering in Life Science》2016,16(8):706-719
Sugarcane bagasse (SCB) and rice straw (RS), abundant lignocellulosic agro‐industrial residues in South‐East Asia, are potent feedstocks for bioethanol production as they contain significant amount of glucose and xylose monomers after fractionation and subsequent enzymatic hydrolysis. To simultaneously convert glucose and xylose to ethanol, it requires co‐cultivation of Saccharomyces cerevisiae and Candida shehatae which are hexose and pentose‐fermenting yeasts, respectively. Xylose‐fermenting strain grows slower than glucose‐fermenting one, therefore low efficiency of xylose‐to‐ethanol conversion was found. To enhance the efficiency of ethanol fermentation, the present work proposed to improve xylose assimilation by using co‐immobilization of two strains in a packed bed bioreactor and to increase oxygenation of the medium by applying a recycled batch system when the recycle stream was intervened by a mixing system in a naturally aerated vessel. Initially, conversion of glucose and xylose to ethanol using pure culture was investigated. Subsequently, influence of different immobilization techniques was investigated. Cells entrapment in Ca‐alginate beads provided considerably high ethanol yield over cells immobilized on delignified cellulose, and thus it was selected to use as inoculum in an immobilized cell bioreactor (ICB). The results showed that continuous ethanol production yielded 0.38 and 0.40 g/g corresponding to 74.5% and 78.4% theoretical yields from SCB and RS hydrolysate, respectively. However, recycled batch system produced significantly improved ethanol yield to 0.49 g/g and 0.50 g/g corresponding to 96.1% and 98.0% theoretical yields for SCB and RS hydrolysate, respectively. In this study, higher ethanol concentration and less unfermented sugar concentration was successfully achieved in the ICB with recycled batch system when using SCB and RS hydrolysate as the substrate. 相似文献
12.
Stephan Lane Yanfei Zhang Eun Ju Yun Leah Ziolkowski Guochang Zhang Yong-Su Jin José L. Avalos 《Biotechnology and bioengineering》2020,117(2):372-381
Bioconversion of xylose—the second most abundant sugar in nature—into high-value fuels and chemicals by engineered Saccharomyces cerevisiae has been a long-term goal of the metabolic engineering community. Although most efforts have heavily focused on the production of ethanol by engineered S. cerevisiae, yields and productivities of ethanol produced from xylose have remained inferior as compared with ethanol produced from glucose. However, this entrenched focus on ethanol has concealed the fact that many aspects of xylose metabolism favor the production of nonethanol products. Through reduced overall metabolic flux, a more respiratory nature of consumption, and evading glucose signaling pathways, the bioconversion of xylose can be more amenable to redirecting flux away from ethanol towards the desired target product. In this report, we show that coupling xylose consumption via the oxidoreductive pathway with a mitochondrially-targeted isobutanol biosynthesis pathway leads to enhanced product yields and titers as compared to cultures utilizing glucose or galactose as a carbon source. Through the optimization of culture conditions, we achieve 2.6 g/L of isobutanol in the fed-batch flask and bioreactor fermentations. These results suggest that there may be synergistic benefits of coupling xylose assimilation with the production of nonethanol value-added products. 相似文献
13.
Zong-wen Pang Jing-juan Liang Ri-bo Huang 《Journal of industrial microbiology & biotechnology》2011,38(8):927-933
A new fungus, Pestalotiopsis sp. XE-1, which produced ethanol from xylose with yield of 0.47 g ethanol/g of consumed xylose was isolated. It also produced
ethanol from arabinose, glucose, fructose, mannose, galactose, cellobiose, maltose, and sucrose with yields of 0.38, 0.47,
0.45, 0.46, 0.31, 0.25, 0.31, and 0.34 g ethanol/g of sugar consumed, respectively. It produced maximum ethanol from xylose
at pH 6.5, 30°C under a semi-aerobic condition. Acetic acid produced in xylose fermenting process inhibited ethanol production
of XE-1. The ethanol yield in the pH-uncontrolled batch fermentation was about 27% lower than that in the pH-controlled one.
The ethanol tolerance of XE-1 was higher than most xylose-fermenting, ethanol-producing microbes, but lower than Saccharomyces cerevisiae and Hansenula polymorpha. XE-1 showed tolerance to high concentration of xylose, and was able to grow and produce ethanol even when it was cultivated
in 97.71 g/l xylose. 相似文献
14.
Takanori Tanino Atsushi Hotta Tomonori Ito Jun Ishii Ryosuke Yamada Tomohisa Hasunuma Chiaki Ogino Naoto Ohmura Takayuki Ohshima Akihiko Kondo 《Applied microbiology and biotechnology》2010,88(5):1215-1221
A yeast with the xylose isomerase (XI) pathway was constructed by the multicopy integration of XI overexpression cassettes
into the genome of the Saccharomyces cerevisiae MT8-1 strain. The resulting yeast strain successfully produced ethanol from both xylose as the sole carbon source and a mixed
sugar, consisting of xylose and glucose, without any adaptation procedure. Ethanol yields in the fermentation from xylose
and mixed sugar were 61.9% and 62.2% of the theoretical carbon recovery, respectively. Knockout of GRE3, a gene encoding nonspecific aldose reductase, of the host yeast strain improved the fermentation profile. Not only specific
ethanol production rates but also xylose consumption rates was improved more than twice that of xylose-metabolizing yeast
with the XI pathway using GRE3 active yeast as the host strain. In addition, it was demonstrated that xylitol in the medium exhibits a concentration-dependent
inhibition effect on the ethanol production from xylose with the yeast harboring the XI-based xylose metabolic pathway. From
our findings, the combination of XI-pathway integration and GRE3 knockout could be result in a consolidated xylose assimilation pathway and increased ethanol productivity. 相似文献
15.
Matsushika A Watanabe S Kodaki T Makino K Inoue H Murakami K Takimura O Sawayama S 《Applied microbiology and biotechnology》2008,81(2):243-255
A recombinant Saccharomyces cerevisiae strain transformed with xylose reductase (XR) and xylitol dehydrogenase (XDH) genes from Pichia stipitis has the ability to convert xylose to ethanol together with the unfavorable excretion of xylitol, which may be due to cofactor
imbalance between NADPH-preferring XR and NAD+-dependent XDH. To reduce xylitol formation, we have already generated several XDH mutants with a reversal of coenzyme specificity
toward NADP+. In this study, we constructed a set of recombinant S. cerevisiae strains with xylose-fermenting ability, including protein-engineered NADP+-dependent XDH-expressing strains. The most positive effect on xylose-to-ethanol fermentation was found by using a strain
named MA-N5, constructed by chromosomal integration of the gene for NADP+-dependent XDH along with XR and endogenous xylulokinase genes. The MA-N5 strain had an increase in ethanol production and
decrease in xylitol excretion compared with the reference strain expressing wild-type XDH when fermenting not only xylose
but also mixed sugars containing glucose and xylose. Furthermore, the MA-N5 strain produced ethanol with a high yield of 0.49 g
of ethanol/g of total consumed sugars in the nonsulfuric acid hydrolysate of wood chips. The results demonstrate that glucose
and xylose present in the lignocellulosic hydrolysate can be efficiently fermented by this redox-engineered strain. 相似文献
16.
Cornelis Verduyn Timotheus P. L. Zomerdijk Johannes P. van Dijken W. Alexander Scheffers 《Applied microbiology and biotechnology》1984,19(3):181-185
Summary An alcohol electrode was constructed which consisted of an oxygen probe onto which alcohol oxidase was immobilized. This enzyme electrode was used, in combination with a reference oxygen electrode, to study the short-term kinetics of alcoholic fermentation by aerobic yeast suspensions after pulsing with glucose. The results demonstrate that this device is an excellent tool in obtaining quantitative data on the short-term expression of the Crabtree effect in yeasts.Samples from aerobic glucose-limited chemostat cultures of Saccharomyces cerevisiae not producing ethanol, immediately (within 2 min) exhibited aerobic alcoholic fermentation after being pulsed with excess glucose. With chemostat-grown Candida utilis, however, ethanol production was not detectable even at high sugar concentrations. The Crabtree effect in S. cerevisiae was studied in more detail with commercial baker's yeast. Ethanol formation occurred only at initial glucose concentrations exceeding 150 mg·l-1, and the rate of alcoholic fermentation increased with increasing glucose concentrations up to 1,000 mg·l-1 glucose.Similar experiments with batch cultures of certain non-fermentative yeasts revealed that these organisms are capable of alcoholic fermentation. Thus, even under fully aerobic conditions, Hansenula nonfermentans and Candida buffonii produced ethanol after being pulsed with glucose. In C. buffonii ethanol formation was already apparent at very low glucose concentrations (10 mg·l-1) and alcoholic fermentation even proceeded at a higher rate than in S. cerevisiae. With Rhodotorula rubra, however, the rate of ethanol formation was below the detection limit, i.e., less than 0.1 mmol·g cells-1·h-1. 相似文献
17.
N. Meinander M. Linko H. Ojamo B. Hahn-Hägerdal P. Linko 《Applied microbiology and biotechnology》1994,42(2-3):334-339
The bioconversion of xylose into xylitol in fed-batch fermentation with a recombinantSaccharomyces cerevisiae strain, transformed with the xylose-reductase gene ofPichia stipitis, was studied. When only xylose was fed into the fermentor, the production of xylitol continued until the ethanol that had been produced during an initial growth phase on glucose, was depleted. It was concluded that ethanol acted as a redox-balance-retaining co-substrate. The conversion of high amounts of xylose into xylitol required the addition of ethanol to the feed solution. Under O2-limited conditions, acetic acid accumulated in the fermentation broth, causing poisoning of the yeast at low extracellular pH. Acetic acid toxicity could be avoided by either increasing the pH from 4.5 to 6.5 or by more effective aeration, leading to the further metabolism of acetic acid into cell mass. The best xylitol/ethanol yield, 2.4 gg–1 was achieved under O2-limited conditions. Under anaerobic conditions ethanol could not be used as a co-substrate, because the cell cannot produce ATP for maintenance requirements from ethanol anaerobically. The specific rate of xylitol production decreased with increasing aeration. The initial volumetric productivity increased when xylose was added in portions rather than by continuous feeding, due to a more complete saturation of the transport system and the xylose reductase enzyme. 相似文献
18.
19.
Efficient fermentation of xylose, which is abundant in hydrolysates of lignocellulosic biomass, is essential for producing
cellulosic biofuels economically. While heterologous expression of xylose isomerase in Saccharomyces cerevisiae has been proposed as a strategy to engineer this yeast for xylose fermentation, only a few xylose isomerase genes from fungi
and bacteria have been functionally expressed in S. cerevisiae. We cloned two bacterial xylose isomerase genes from anaerobic bacteria (Bacteroides stercoris HJ-15 and Bifidobacterium longum MG1) and introduced them into S. cerevisiae. While the transformant with xylA from B. longum could not assimilate xylose, the transformant with xylA from B. stercoris was able to grow on xylose. This result suggests that the xylose isomerase (BsXI) from B. stercoris is functionally expressed in S. cerevisiae. The engineered S. cerevisiae strain with BsXI consumed xylose and produced ethanol with a good yield (0.31 g/g) under anaerobic conditions. Interestingly, significant
amounts of xylitol (0.23 g xylitol/g xylose) were still accumulated during xylose fermentation even though the introduced
BsXI might not cause redox imbalance. We investigated the potential inhibitory effects of the accumulated xylitol on xylose fermentation.
Although xylitol inhibited in vitro BsXI activity significantly (K
I = 5.1 ± 1.15 mM), only small decreases (less than 10%) in xylose consumption and ethanol production rates were observed when
xylitol was added into the fermentation medium. These results suggest that xylitol accumulation does not inhibit xylose fermentation
by engineered S. cerevisiae expressing xylA as severely as it inhibits the xylose isomerase reaction in vitro. 相似文献
20.
木糖是纤维素原料水解液中最主要的五碳糖成分,由于野生的酿酒酵母缺乏有效的木糖利用途径,将外源木糖代谢途径整合至酿酒酵母中使其具有发酵木糖生产乙醇的能力是构建纤维素乙醇发酵菌株的关键。国内外学者的研究表明,同一木糖代谢途径导入不同酿酒酵母菌株中,所得到的重组菌发酵性能存在明显差异,表明宿主的遗传背景对菌株利用木糖能力和发酵性能具有重要的影响。就酿酒酵母宿主对重组菌株的木糖发酵性能的影响进行了综述,分析了产生宿主差异的内在机理,为进一步选育高效木糖共发酵菌种提供借鉴。 相似文献