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d-xylose andl-arabinose are the major constituents of plant lignocelluloses, and the related fungal metabolic pathways have been extensively examined. AlthoughPichia stipitisCBS 6054 grows usingd-arabinose as the sole carbon source, the hypothetical pathway has not yet been clarified at the molecular level. We herein purified NAD(P)H-dependentd-arabinose reductase from cells grown ond-arabinose, and found that the enzyme was identical to the knownd-xylose reductase (XR). The enzyme activity of XR withd-arabinose was previously reported to be only 1% that withd-xylose. Thekcat/Kmvalue withd-arabinose (1.27 min−1 mM−1), which was determined using the recombinant enzyme, was 13.6- and 10.5-fold lower than those withl-arabinose andd-xylose, respectively. Among the 34 putative sugar transporters fromP. stipitis, only seven genes exhibited uptake ability not only ford-arabinose, but also ford-glucose and other pentose sugars includingd-xylose andl-arabinose inSaccharomyces cerevisiae. d-Xylose reductase, encoded byXYL1gene, plays as an aldose reductase involved not only ind-xylose andl-arabinose but alsod-arabinose metabolism. [ABSTRACT FROM PUBLISHER]

Xylose, recovered from Meranti wood sawdust (MWS), can be used as a promising and alternative carbon source for yeast growth as well as for the production of xylose reductase (XR). This enzyme has potential applications in the bioproduction of various high value products, especially xylitol. The aim of this study was to isolate XR from adapted yeast Candida tropicalis and to characterize it. The XR enzyme was prepared from C. tropicalis strain, grown in MWS hydrolysate-based medium, by ultrasonic homogenization. The isolated XR was characterized based on enzyme activity, stability, and kinetic constants. The activity of NADPH-dependent crude XR measured was 11.16 U/mL. It was stable at pH 5.0–7.0 and temperature of 25–40 °C for 24 h, and retained above 95% of its original activity after 4 months of storage at –80 °C. The apparent K m values of XR for xylose and NADPH were 81.78 mM and 7.29 μM while the V max for xylose and NADPH were 178.57 and 12.5 μM/min, respectively. The low K m,app and high V max,app values of XR for xylose as a substrate indicates a strong binding affinity for xylose and good productivity of the reaction. [ABSTRACT FROM AUTHOR]

In this article, the authors focus on the metablolomic and transcriptomic analyses of rate-limiting metabolic steps during xylose utilization by recombinant Candida utilis strain expressing xylose reductase genes. They inform that the strain accumulated pentose phosphate pathway intermediates as analyzed by capillary electrophoresis time-of-flight mass spectrometry. They mention that microarray analyses have showed that expression of tricarboxylic acid cycle enzymes increases in the strain.

Abstract: We constructed one wild-type xylose reductase (XR) and eight XR variants in a recombinant industrial Saccharomyces cerevisiae strain along with xylitol dehydrogenase and xylulokinase overexpression. In the current study, we found that K270R XR (hereafter referred to as “XR-1”) appeared to utilize more NADH than NADPH when xylose was the carbon source. After 72h of fermentation, XR-1 produced an ethanol yield of 0.34g/g and a xylitol yield of 0.08g/g from 55g/L xylose, while it gave an ethanol yield of 0.44g/g and a xylitol yield of 0.04g/g under a mixture of 40g/L xylose and 40g/L glucose. Notably, the findings presented here suggest that the XR-1 variant produced approximately 76% more ethanol from xylose than the wild-type XR strain. Comparing with other widely divergent XR mutations, the XR-1(K270R) exhibited improved xylose consumption rate, balanced redox system and increased ethanol yield and production rate when engineered into S. cerevisiae, suggesting the significance of mutations to the XR gene in xylose utilization. [Copyright &y& Elsevier]

Abstract: Supply of NAD(P)H is a key factor in microbial production of xylitol from xylose. To facilitate NAD(P)H supplementation, acetaldehyde dehydrogenase 6 (ALD6) and acetyl-CoA synthetase 1 (ACS1) were overexpressed in recombinant Saccharomyces cerevisiae harboring the Pichia stipitis xylose reductase (XR) gene. In-vitro activity analysis confirmed the functional expression of both enzymes. Glucose-limited fed-batch fermentations of Saccharomyces cerevisiae BJ3505:δXR strains overexpressing ACS1 and/or ALD6 were performed by feeding 600g/L glucose in the presence of 100g/L xylose. Among them, ACS1 overexpression gave the best result of xylitol production: 91.3g/L xylitol concentration and 1.76g/Lh xylitol productivity, which were 25% and 11% increase, relative to those of the control and ALD6-overexpressing strains. Considering the changes of cell growth, ethanol and acetate production, a remarkable enhancement of xylitol production by ACS1 overexpression seemed be ascribed to energy and NAD(P)H generation through a metabolism from acetaldehyde to acetyl-CoA and TCA cycle. [Copyright &y& Elsevier]

The article presents a study that examines the ethanol production from xylose by a recombinant industrial yeast Candida utilis (C. utilis). It notes that xylose is one of the most abundant sugars derived from lignocellulose where fungi and bacteria dwells on it aerobically. Furthermore , analysis of the genes responsible for ethanol production has confirmed that the introduction of CsheXDH was important as overexpression of such improved the efficiency of ethanol production.

At present, yeast is the main microorganism involved in ethanol production using xylose as carbon source. The filamentous fungi have been less studied compared to yeast. Duchenne tube and ethanol yield assay methods were applied to screen different microbes for xylose fermentation. The microorganism producing the highest amount of ethanol was identified by microscopy and 18s rRNA amplification and analysis. Fermentation assays of this microorganism were studied by the Potassium dichromate method. The screening results showed that the organism code named cs -- 28 was Fusarium oxysporum. It was found that this fungus could ferment xylose, glucose, sucrose and corn stalk to produce ethanol. The optimal nitrogen source was yeast extract. The ethanol production rate was highest at initial pH 6.0 and 30 °C, when initial xylose concentration was 20 g · L-1. Thus, cs -- 28 can be used as a new strain for transformation of cellulose materials to ethanol. Moreover, characterization of cs -- 28 on xylose fermentation can be applied in technological advancement. [ABSTRACT FROM AUTHOR]

The article investigates the effects of a mutation of xylose reductase from Pichia stipitis (PxXR) on xylose-to-ethanol fermentation using recombinant Saccharomyces cerevisiae transformed with PsXR and PxXDH (xylitol dehydrogenase from P. stipitis) genes. It details the design of several single PxXR mutants based on inherent NADH-preferring XR and several site-directed muta-genetic studies using other aldo-keto reductase enzymes.

The article presents a study which aims to explore the heterologous expression of Aspergillus oryza. It notes that the cDNA encrypting a putative xylose reductase (xyrA) from Aspergillus oryza which was cloned and coexpressed in the yeast Saccharomyces cerevisiae with Aspergillus oryza xylitol dehydrogenase cDNA (xyhA). The strain in Saccharomyces cerevisiae which was overexpressing xyrA and xdhA developed on xylose as sole carbon source and bring about ethanol.

Meyerozyma caribbica is prominently used for the production of xylitol from agro waste hydrolysate of the corncob. M. caribbica was isolated from fermented apple juice, the nicotinamide adenine dinucleotide phosphate (NADP) dependent xylose reductase (XR) enzyme act as a catalyst for the production of xylitol from xylose during xylose fermentation by M. caribbica. The enzyme XR was extracted, partially purified, sequenced and molecular weight was determined by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). This study explores the in silico and in vitro comparative analysis of the cofactor NADP binding mechanism in rossmann fold of isolated M. caribbica and other xylose fermenting Debaryomycetaceae family yeast. The rossmaan fold analysis of M. caribbica and Debaryomycetaceae family of yeast revealed, xylose fermenting organisms such as Scheffersomyces stipitis, Debaryomyces hansenii, Debaryomyces nepalensis, Candida parapsilosis, Candida maltos a have divergence structure of rosmann fold. Whereas M. caribbica and Candida tenuis has unique structure of rossmann fold. Also, the identified rossmann fold of Debaryomycetaceae family yeast and isolated M. caribbica are conserved to interact with cofactor NADP by H 2 bonding, which displays the proximity evolutionary relationship of the enzyme in Debaryomycetaceae family yeast. Annotation analysis showed the isolated M. caribbica has the ability of aldopentose fermentation for xylitol production. Image 1 • Isolation of xylose fermenting yeast M. caribbica for xylitol production. • The isolated yeast were identified using 16s rRNA gene sequences. • M. caribbica and C. tenuis have close evolution relationship in rossmann fold. • Acidophilic yeast M. caribbica acts as the potential strain for xylose fermentation. [ABSTRACT FROM AUTHOR]