Five-carbon Sugar Research Articles

Research progress in the biosynthesis of xylitol: feedstock evolution from xylose to glucose.

Xylitol, as an important food additive and fine chemical, has a wide range of applications, including food, medicine, chemical, and feed. This review paper focuses on the research progress of xylitol biosynthesis, from overcoming the limitations of traditional chemical hydrogenation and xylose bioconversion, to the full biosynthesis of xylitol production using green and non-polluting glucose as substrate. In the review, the molecular strategies of wild strains to increase xylitol yield, as well as the optimization strategies and metabolic reconfiguration during xylitol biosynthesis are discussed. Subsequently, on the basis of existing studies, the paper further discusses the current status of research and future perspectives of xylitol production using glucose as a single substrate. The evolution of raw materials from xylose-based five-carbon sugars to glucose is not only cost-saving, but also safe and environmentally friendly, which brings new opportunities for the green industrial chain of xylitol.

Advances in the Synthesis of Spirocyclic Nucleosides

AbstractThe nucleosides are the building blocks for nucleic acids and composed of a five-carbon sugar bearing either pyrimidine or purine nucleobase. The biological properties of nucleosides can be tailored by chemically modifying the five-carbon sugar to influence its sugar pucker. The spirocyclic scaffold is an indispensable scaffold in more than ten approved drugs, and its inherent three-dimensionality makes it an ideal modification to influence the sugar pucker and biological properties of nucleosides. However, the introduction of spirocyclic scaffold is often synthetically challenging due to increase in synthetic steps and stereocenters. The present review highlights the advances in synthetic methodologies developed during the past decades for accessing various members of the spiro-functionalized nucleoside family.1 Introduction2 C-1′-Spirocyclic Nucleosides3 C-2′-Spirocyclic Nucleosides4 C-3′-Spirocyclic Nucleosides5 C-4′-Spirocyclic Nucleosides6 Miscellaneous Spirocyclic Nucleosides7 Conclusion and Future Perspectives

331 Investigating the Ruminal Metagenome of Grass and Forage-Fed Bison to Uncover Metabolic Activities That Impact the Efficiency of Plant Fiber Utilization

Abstract The ability of bison to thrive on grass and forage-based diets is of great interest for the bison industry. However, raising bison on pasture presents challenges, including longer finishing times. While some producers overcome this by feeding grain or concentrate to bison, this practice conflicts with the concept of natural production. Considering that bison maintain better on feed of poor quality compared with domesticated grazers, it can be inferred that there is great potential for improving their productivity on pastures. Because ruminants rely on symbiotic microorganisms to break down and ferment plant polysaccharides into nutrients they can absorb and assimilate, the metabolic capabilities of rumen microbial communities in bison would likely have an important role in contributing to the efficiency of their host. To gain further insight, we investigated the ruminal metagenome of six grass-fed bison. Raw sequence reads generated using an Illumina Miseq (2x250) platform from ruminal microbial genomic DNA were assembled into genomic contigs using custom written Perl scripts. A total of 6,297 contigs, representing a combined total length of 23,822,104 nucleotides, were obtained for all samples. Coding sequences were identified and annotated using RAST (Rapid Annotation using Subsystem Technology), which was followed by assignment to metabolic pathways using references from KEGG (Kyoto Encyclopedia of Genes and Genomes), with a particular focus on carbohydrate metabolism and amino acid synthesis. This analysis resulted in the identification of nine of the ten enzymes necessary for glycolysis, indicating the capacity to metabolize glucose into pyruvate. Two outcomes were predicted for pyruvate: conversion to lactate through lactate dehydrogenases (EC 1.1.1.27, EC 1.1.1.28), as well as the production of acetate through the sequential activity of pyruvate-flavodoxin oxidoreductase (EC 1.2.7.1), phosphate acetyltransferase (EC 2.3.1.8), and acetate kinase (EC 2.7.2.1). Propionate and butyrate were also predicted as end-products being produced in bison rumen, as well as synthesis of precursors for aromatic amino synthesis through the Chorismate-Shikimate pathway. In addition, enzymes involved in the fermentation of five-carbon sugars, such as arabinose (EC 5.1.3.4, EC 2.7.1.16, and EC 5.3.1.4) and xylose (EC 2.7.1.17 and EC 5.3.1.5), were also identified. Characterization of the metabolic potential of ruminal bacteria from pasture-fed bison, such as the utilization of glucose and pentose sugars that form the backbone of structural polysaccharides to produce short chain fatty acids and essential amino acids, will provide further insight on the use of forage and grass-based diets by these animals.

Physicochemical Pretreatment of Vietnamosasa pusilla for Bioethanol and Xylitol Production.

The consumption of fossil fuels has resulted in severe environmental consequences, including greenhouse gas emissions and climate change. Therefore, transitioning to alternative energy sources, such as cellulosic ethanol, is a promising strategy for reducing environmental impacts and promoting sustainable low-carbon energy. Vietnamosasa pusilla, an invasive weed, has been recognized as a high potential feedstock for sugar-based biorefineries due to its high total carbohydrate content, including glucan (48.1 ± 0.3%) and xylan (19.2 ± 0.4%). This study aimed to examine the impact of NaOH pretreatment-assisted autoclaving on V. pusilla feedstock. The V. pusilla enzymatic hydrolysate was used as a substrate for bioethanol and xylitol synthesis. After treating the feedstock with varying concentrations of NaOH at different temperatures, the glucose and xylose recovery yields were substantially higher than those of the untreated material. The hydrolysate generated by enzymatic hydrolysis was fermented into bioethanol using Saccharomyces cerevisiae TISTR 5339. The liquid byproduct of ethanol production was utilized by Candida tropicalis TISTR 5171 to generate xylitol. The results of this study indicate that the six- and five-carbon sugars of V. pusilla biomass have great potential for the production of two value-added products (bioethanol and xylitol).

Dietary intake of xylose impacts the transcriptome and proteome of tissues involved in xylose metabolism in swine

Xylose is a primary component of arabinoxylan in swine diets. As arabinoxylan is a significant component of fiber, and fiber is generally rising in practical pig diets globally, the study of arabinoxylan and xylose is of increasing interest. However, the mechanisms by which free xylose may be absorbed and the pathways impacted by xylose have yet to be elucidated in pigs. The objective of this study was to determine the impact of xylose supplementation on gene expression and protein abundance in jejunum, kidney, liver, and muscle tissues which have previously been identified as possible sites of xylose absorption or metabolism. This study aimed to expand the preliminary understanding of dietary xylose metabolism and utilization in pigs. One study, replicated twice with 24 crossbred gilts, was used to assess two dietary treatments: a xylose-free (0%) control and 8% D-xylose. The impact of xylose on growth was monitored by measuring initial and final body weight, serum IGF-1, and liver glycogen concentrations. The rate and efficiency of weight gain were reduced on the xylose diet but not to a level that would occur if xylose was not used at all; the detection of xylose systemically further supports this conclusion. This study confirmed that pigs can utilize dietary xylose. To determine the impact of xylose on tissue metabolism, samples were collected from all four tissues for gene expression analysis by RNA-sequencing, and kidney and liver samples were subjected to proteomic analysis using 2D-DIGE and mass spectrometry. The majority of differentially expressed (DE) genes were identified in the kidney samples (n = 157), with a few identified in the jejunum (n = 16), liver (n = 1), and muscle (n = 20) samples. The DE genes in the kidney were mainly identified as being involved in lipid biosynthesis and fatty acid metabolism. Proteomic results corroborated these findings. Although the inclusion of xylose in a diet at practical levels is shown to impact energy metabolic processes, it has been confirmed that this five-carbon sugar can support levels of growth only slightly below those of glucose, a six-carbon sugar that is more commonly utilized as an energy source in pig diets.

Regulation of photosynthetic and hemolytic activity of Phaeocystis globosa under different light spectra.

Phaeocystis globosa frequently proliferates in eutrophic waters and forms ichthyotoxic algal blooms that cause massive fish mortalities in marine ecosystems. One of the ichthyotoxic metabolites was identified as the glycolipid-like hemolytic toxin, reported to be initiated under light conditions. However, the association between hemolytic activity (HA) and photosynthesis of P. globosa remained unclear. Light spectra (blue, red, green, and white) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) were selected as the stressors to stimulate the hemolytic response of P. globosa in relation to the light and dark photosynthesis reaction. Hemolytic activity in P. globosa was sensitive to the light spectrum as it decreased from 93% to nearly undetectable (1.6%) within 10 min of transfer from red (630 nm) to green light (520 nm). This indicates that the vertical transformation of P. globosa from deep to surface waters (dominated by green light and all light spectra, respectively) may drive the hemolytic response in coastal waters. However, regulation of photosynthetic electron transfer in the light reaction of P. globosa was excluded by the evidence of inconsistent response of HA to photosynthetic activity. The biosynthesis of HA may interfere with the pathway of photopigments diadinoxanthin or fucoxanthin, and the metabolism of three- and five-carbon sugars (GAP and Ru5P, respectively), which ultimately lead to changes in the alga's hemolytic carbohydrate metabolism.

Production of Hemicellulose Sugars Combined with the Alkaline Extraction Lignin Increased the Hydro-Depolymerization of Cellulose from Corn Cob

Hydro-depolymerization is a novel method for converting agricultural waste into eco-friendly and promising products. Due to the complex structure and composition of corn cob (CC), a three-step process was developed, which involved pre-hydro-depolymerization of hemicellulose, alkaline extraction of lignin, and hydro-depolymerization of cellulose. The pre-hydro-depolymerization step was at first optimized to produce five-carbon and six-carbon sugars, achieving a maximum hemicellulose conversion rate of 78.48 ± 3.92%, and reducing a sugar yield of 59.12 ± 2.95%. Alkaline treatment achieved a maximum lignin extraction efficiency of 73.76 ± 3.68%. After hemicellulose removal and delignification, the cellulose conversion rate increased to 36.63% and further increased to 76.97% after five cycles. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were performed to confirm physical and chemical changes in CC residues. The integrated process of hydro-depolymerization and alkaline treatment enables the complete exploitation of cellulose, hemicellulose, and lignin, and thus holds great potential for application in the agriculture industry.

Detoxification of areca nut acid hydrolysate and production of xylitol by Candida tropicalis (MTCC 6192)

Areca nut husk is the most promising alternative source of low-cost raw materials because it contains a considerable amount of five-carbon monosaccharide sugar in the form of xylose. This polymeric sugar can be isolated and transformed into a value-added chemical using fermentation. To extract sugars from areca nut husk fibers, preliminary pretreatment, such as dilute acid hydrolysis (H2SO4), was performed. The hemicellulosic hydrolysate of areca nut husk can produce xylitol through fermentation, but toxic components inhibit the growth of microorganisms. To overcome this, a series of detoxification treatments, including pH adjustment, activated charcoal, and ion exchange resin, were carried out to reduce the concentration of inhibitors in the hydrolysate. This study reports a remarkable 99% removal of inhibitors in the hemicellulosic hydrolysate. Subsequently, a fermentation process using Candida tropicalis (MTCC6192) was executed with the detoxified hemicellulosic hydrolysate of areca nut husk, yielding an optimum xylitol yield of 0.66 g/g. This study concludes that detoxification techniques like pH adjustment, activated charcoal, and ion exchange resins are the most economical and effective methods for eliminating toxic compounds in hemicellulosic hydrolysates. Therefore, the medium derived after detoxification from areca nut hydrolysate may be considered to have significant potential for xylitol production.

Analysis of Single-Step Pretreatments for Lignocellulosic Platform Isolation as the Basis of Biorefinery Design.

Biorefinery feasibility is highly influenced by the early design of the best feedstock transformation pathway to obtain value-added products. Pretreatment has been identified as the critical stage in biorefinery design since proper pretreatment influences subsequent reaction, separation, and purification processes. However, many pretreatment analyses have focused on preserving and valorizing six-carbon sugars for future use in bioconversion processes, leaving aside fractions such as hemicellulose and lignin. To date, there has been no pretreatment systematization for the removal of lignocellulosic fractions. This work defines pretreatment efficacy through operational, economic, environmental, and social indicators. Thus, using the data reported in the literature, as well as the results of the simulation schemes, a multi-criteria weighting of the best-performing schemes for the isolation or removal of cellulose, hemicellulose, and lignin was carried out. As a main result, it was concluded that dilute acid is the most effective for cellulose isolation and hemicellulose removal for producing platform products based on six- and five-carbon sugars, respectively. Additionally, the kraft process is the best methodology for lignin removal and its future use in biorefineries. The results of this work help to elucidate a methodological systematization of the pretreatment efficacy in the design of biorefineries as an early feasibility stage considering sustainability aspects.

Carbon/nitrogen ratio as a tool to enhance the lipid production in Rhodosporidium toruloides-1588 using C5 and C6 wood hydrolysates

The interest in microbial lipids has recently increased because of their wide use to produce several value-added compounds in the biofuel, pharmaceutical and food industries. Oleaginous yeast such as Rhodosporidium toruloides could be an efficient option because of its ability to consume five-carbon sugars, high lipid accumulation, and tolerance to toxic compounds such as furans, phenolic compounds, and organic acids. The present study aims to investigate the effect of different initial sugar ratios, in combination with different carbon/nitrogen ratios, and the use of dibasic sodium phosphate (Na2HPO4) as an inducer on cell biomass production, sugar consumption, and lipid accumulation by Rhodosporidium toruloides-1588. The investigation showed a maximum lipid accumulation of 5.35 gL-1 (0.28 g of lipids/g of sugar) under the culture conditions of initial glucose: xylose ratio of 1:1, C/N ratio of 70, and Na2HPO4 concentration of 1.05 gL-1. The predominant lipids composition was palmitic, stearic, oleic, and linoleic acids which could be used as a suitable feedstock for biofuel production. Additionally, under the optimal conditions (initial glucose: xylose ratio of 1:1, 1.19 gL-1 of Na2HPO4 and C/N ratio of 70.50) an increase of 10.5% and 7.5% in lipid accumulation was observed, compared with control treatments (glucose and xylose, respectively). In addition, the study shows the ability of R. toruloides-1588 to tolerate inhibitors, a feature that could be a promising alternative to increase the feasibility of the microbial lipid production process using undetoxified wood hydrolysate as a sustainable culture media.

Genomic, probiotic, and metabolic potentials of Liquorilactobacillus nagelii AGA58, a novel bacteriocinogenic motile strain isolated from lactic acid-fermented shalgam

This study aimed to perform genomic, probiotic, and metabolic characterization of a novel Liquorilactobacillus nagelii AGA58 isolated from a lactic acid-fermented shalgam beverage to understand its metabolic potentials and probiotic features. AGA58 is gram-positive, motile, catalase-negative and appears as short rods under the light-microscope. The AGA58 chromosome comprises a single linear chromosome of 2,294,635 bp that is predicted to carry 2135 coding sequences, including 45 tRNA genes, 3 mRNA, and 3 rRNA operons. The genome has a G+C content of 36.9%, including 55 pseudogenes and a single intact prophage. AGA58 is micro-anaerobic due to achieving a shorter doubling time and faster growth rate than micro-aerophilic conditions. It carries flagellar biosynthesis protein-encoding genes predicting motile behavior, which was confirmed with the in vitro motility test. AGA58 is an obligatory homofermentative lactobacillus that can ferment hexose sugars such as galactose, glucose, fructose, sucrose, mannose, N-acetyl glucosamine, maltose, and trehalose to lactate through glycolysis. No acid production from pentoses implies that five-carbon sugars are being utilized for purine and pyrimidine synthesis. Putative pyruvate metabolism revealed formate, malate, oxaloacetate, acetate, acetaldehyde, acetoin, and lactate forms from pyruvate. AGA58 is predicted to encode the LuxS gene and biosynthesis of class IIa and Blp family class-II bacteriocins suggesting this bacterium's antimicrobial potential, linked to antagonism tests that AGA58 can inhibit Escherichia coli ATCC 43895, Salmonellaenterica serovar Typhimurium ATCC 14028, and Klebsiellapneumonia ATCC 13883. Moreover, AGA58 is tolerant to acid and bile concentrations simulating the human gastrointestinal conditions depicting the probiotic potential of the organism as the first report in literature within the same species.

Crystalline xylitol production from corncob biomass with oral toxicity analysis

Xylitol, a five-carbon sugar alcohol, has a steady global market and finds application as a natural sugar substitute in various food and confectionery products. Biocatalytic xylitol production, although touted as a greener alternative to conventional chemical catalysis, suffers from certain challenges, the primary being high cost of production. This study demonstrates a process for food-grade xylitol production from corncob biomass with energy reduction through two major process modifications. A non-conventional fermentation strategy was adopted whereby adjusting aeration without agitation, xylitol with high yield (0.86 ± 0.015 g/g), and productivity (0.74 gL-1h-1) could be produced by a GRAS Pichia caribbica MTCC 5703 strain. Xylitol was recovered from the broth in the form of crystals using a combination of membrane-based filtration and crystallization. The crystals demonstrated ~98 % purity when quantified with 1H NMR. Oral toxicity analysis of the crystals demonstrated no adverse effect in female Winstar rats (at a loading of 2000 mg/kg body weight of animals). Overall process statistics showed that 0.584 kg of food-grade xylitol crystals could be produced from 3.5 kg of corncob biomass. The two-process modifications during fermentation and xylitol recovery enabled an energy saving of ~20.842 kW/kg of crystals, providing tremendous advantages for biorefinery-based large-scale xylitol production from corncob biomass.

Improved fed-batch processes with Wickerhamomyces anomalus WC 1501 for the production of d-arabitol from pure glycerol

Backgroundd-Arabitol, a five-carbon sugar alcohol, represents a main target of microbial biorefineries aiming to valorize cheap substrates. The yeast Wickerhamomyces anomalus WC 1501 is known to produce arabitol in a glycerol-based nitrogen-limited medium and preliminary fed-batch processes with this yeast were reported to yield 18.0 g/L arabitol.ResultsFed-batch fermentations with W. anomalus WC 1501 were optimized using central composite design (CCD). Dissolved oxygen had not a significant effect, while optimum values were found for glycerol concentration (114.5 g/L), pH (5.9), and temperature (32.5 °C), yielding 29 g/L d-arabitol in 160 h, a conversion yield of 0.25 g of arabitol per g of consumed glycerol, and a volumetric productivity of 0.18 g/L/h. CCD optimal conditions were the basis for further improvement, consisting in increasing the cellular density (3✕), applying a constant feeding of glycerol, and increasing temperature during production. The best performing fed-batch fermentations achieved 265 g/L d-arabitol after 325 h, a conversion yield of 0.74 g/g, and a volumetric productivity of 0.82 g/L/h.ConclusionW. anomalus WC 1501 confirmed as an excellent producer of d-arabitol, exhibiting a remarkable capability of transforming pure glycerol. The study reports among the highest values ever reported for microbial transformation of glycerol into d-arabitol, in terms of arabitol titer, conversion yield, and productivity.Graphical

Production of Hydroxymethylfurfural Derivatives From Furfural Derivatives via Hydroxymethylation.

Hydroxymethylfurfural (HMF) derivatives such as 2,5-bis(hydroxymethyl)furan (BHMF) and furandicarboxylic acid (FDCA) are promising alternative of fossil-based diols and dicarboxylic acids for synthesis of polyesters such as polyethylene terephthalate (PET). However, high cost for preparing HMF from biomass discourages the commercialization of HMF-derived polyesters. Since producing furfural (FUR) from five-carbon sugars (e.g., xylose) via dehydration is an inexpensive and commercialized process, we herein reported a method to synthesize BHMF derivatives (5-(ethoxymethyl)furan-2-methanol (EMFM), 2,5-bis(hydroxymethyl)furan monoacetate (BHMFM) and 2,5-bis(hydroxymethyl)furan diacetate (BHMFD) from furfural derivatives, i.e., (2-(ethoxymethyl)furan (EMF) and furfuryl acetate (FA)). To avoid strong acid-induced side reactions (e.g., furan ring opening, condensation and carbonization), two reaction systems, i.e., a low-concentration HCl aqueous solution combined with formaldehyde and anhydrous acetic acid combined with paraformaldehyde, were found to be suitable for such a hydroxymethylation reaction and could lead to decent product yields. In order to improve the carbon utilization, condensed furanic byproducts were further converted into hydrocarbon fuels via a reported two-step hydrodeoxygenation (HDO) process. This study not only validates the possibility of synthesizing functional HMF derivatives (EMFM, BHMFM, and BHMFD) from commercially-available FUR derivatives (EMF and FA), but also provide a new way to transform condensed furanics to value-added hydrocarbon fuels.

D-Xylose Sensing in Saccharomyces cerevisiae: Insights from D-Glucose Signaling and Native D-Xylose Utilizers.

Extension of the substrate range is among one of the metabolic engineering goals for microorganisms used in biotechnological processes because it enables the use of a wide range of raw materials as substrates. One of the most prominent examples is the engineering of baker’s yeast Saccharomyces cerevisiae for the utilization of d-xylose, a five-carbon sugar found in high abundance in lignocellulosic biomass and a key substrate to achieve good process economy in chemical production from renewable and non-edible plant feedstocks. Despite many excellent engineering strategies that have allowed recombinant S. cerevisiae to ferment d-xylose to ethanol at high yields, the consumption rate of d-xylose is still significantly lower than that of its preferred sugar d-glucose. In mixed d-glucose/d-xylose cultivations, d-xylose is only utilized after d-glucose depletion, which leads to prolonged process times and added costs. Due to this limitation, the response on d-xylose in the native sugar signaling pathways has emerged as a promising next-level engineering target. Here we review the current status of the knowledge of the response of S. cerevisiae signaling pathways to d-xylose. To do this, we first summarize the response of the native sensing and signaling pathways in S. cerevisiae to d-glucose (the preferred sugar of the yeast). Using the d-glucose case as a point of reference, we then proceed to discuss the known signaling response to d-xylose in S. cerevisiae and current attempts of improving the response by signaling engineering using native targets and synthetic (non-native) regulatory circuits.

High D-arabitol production with osmotic pressure control fed-batch fermentation by Yarrowia lipolytica and proteomic analysis under nitrogen source perturbation

D-arabitol, a five-carbon sugar alcohol, is widely used in food and pharmacy industry as a lower calorie sweetener or intermediate. Appropriate osmotic pressure was confirmed to facilitate polyol production by an osmophilic yeast strain of Yarrowia lipolytica with glycerol. In this study, an osmotic pressure control fed-batch fermentation strategy was used for high D-arabitol producing by Y. lipolytica ARA9 with crude glycerol. Glycerol was added to the broth quantitatively not only as a substrate but also as an osmotic agent. Meanwhile, NH3·H2O was fed as a nitrogen source and pH regulator. The maximum D-arabitol production reached 118.5 g/L at 108 h with the yield of 0.49 g/g and productivity of 1.10 g/L/h, respectively. Furthermore, a comparative proteomic analysis was used to study the cellular responses under excess and deficient nitrogen sources. Thirty-one differentially expressed protein spots belonging to seven different biological processes were identified. Excess nitrogen source enhanced gluconeogenesis and pentose phosphate pathways, both of which were involved in arabitol synthesis. In addition, cell growth was facilitated by increased expression of nucleotide and structural proteins. Enhanced energy and NADPH biosynthesis were employed to create a reductive environment and quell reactive oxygen species, improving D-arabitol production. Nitrogen deficiency resulted in cell rescue and stress response mechanisms such as reactive oxygen species elimination and heat shock protein response. The identified differentially expressed proteins provide information to reveal the mechanisms of the cellular responses under nitrogen source perturbation, and also provide guidance to improve D-arabitol production in metabolic engineering or process optimization methodologies.

Production of bio-xylitol from d-xylose by an engineered Pichia pastoris expressing a recombinant xylose reductase did not require any auxiliary substrate as electron donor

BackgroundXylitol is a five-carbon sugar alcohol that has numerous beneficial health properties. It has almost the same sweetness as sucrose but has lower energy value compared to the sucrose. Metabolism of xylitol is insulin independent and thus it is an ideal sweetener for diabetics. It is widely used in food products, oral and personal care, and animal nutrition as well. Here we present a two-stage strategy to produce bio-xylitol from d-xylose using a recombinant Pichia pastoris expressing a heterologous xylose reductase gene. The recombinant P. pastoris cells were first generated by a low-cost, standard procedure. The cells were then used as a catalyst to make the bio-xylitol from d-xylose.ResultsPichia pastoris expressing XYL1 from P. stipitis and gdh from B. subtilis demonstrated that the biotransformation was very efficient with as high as 80% (w/w) conversion within two hours. The whole cells could be re-used for multiple rounds of catalysis without loss of activity. Also, the cells could directly transform d-xylose in a non-detoxified hemicelluloses hydrolysate to xylitol at 70% (w/w) yield.ConclusionsWe demonstrated here that the recombinant P. pastoris expressing xylose reductase could transform d-xylose, either in pure form or in crude hemicelluloses hydrolysate, to bio-xylitol very efficiently. This biocatalytic reaction happened without the external addition of any NAD(P)H, NAD(P)+, and auxiliary substrate as an electron donor. Our experimental design & findings reported here are not limited to the conversion of d-xylose to xylitol only but can be used with other many oxidoreductase reactions also, such as ketone reductases/alcohol dehydrogenases and amino acid dehydrogenases, which are widely used for the synthesis of high-value chemicals and pharmaceutical intermediates.

Oxidative Pentose Phosphate Pathway Enzyme 6-Phosphogluconate Dehydrogenase Plays a Key Role in Breast Cancer Metabolism.

Simple SummaryCancer cells alter their metabolism to maintain their high need for energy, produce enough macromolecules for biosynthesis, and preserve their redox status. The investigation of cancer cell-specific metabolic alterations has vital importance to identify targets to be exploited for therapeutic development. The pentose phosphate pathway (PPP) is often highly activated in tumor cells to maintain redox level, as this pathway takes an important role in reactive oxygen species detoxification. PPP also yields ribose-5-phosphate, a five-carbon sugar essential for synthesizing nucleotides necessary for DNA replication and cell proliferation. In this study, we inhibited one of the key enzymes of this biochemical pathway and observed the main functions of this enzyme in breast cancer cells. We have demonstrated that inhibition of this enzyme reduces cell proliferation and leads to cell cycle arrest and apoptosis. Besides that, we showed that the inhibition of this enzyme causes an alteration in cellular metabolism. All these findings indicate that targeting this enzyme with specific pharmacological inhibitors is an effective strategy in fighting cancer.The pentose phosphate pathway (PPP) plays an essential role in the metabolism of breast cancer cells for the management of oxidative stress and the synthesis of nucleotides. 6-phosphogluconate dehydrogenase (6PGD) is one of the key enzymes of the oxidative branch of PPP and is involved in nucleotide biosynthesis and redox maintenance status. Here, we aimed to analyze the functional importance of 6PGD in a breast cancer cell model. Inhibition of 6PGD in MCF7 reduced cell proliferation and showed a significant decrease in glucose consumption and an increase in glutamine consumption, resulting in an important alteration in the metabolism of these cells. No difference in reactive oxygen species (ROS) production levels was observed after 6PGD inhibition, indicating that 6PGD, in contrast to glucose 6-phosphate dehydrogenase, is not involved in redox balance. We found that 6PGD inhibition also altered the stem cell characteristics and mammosphere formation capabilities of MCF7 cells, opening new avenues to prevent cancer recurrance after surgery or chemotherapy. Moreover, inhibition of 6PGD via chemical inhibitor S3 resulted in an induction of senescence, which, together with the cell cycle arrest and apoptosis induction, might be orchestrated by p53 activation. Therefore, we postulate 6PGD as a novel therapeutic target to treat breast cancer.

Mechanism of solvothermal conversion of xylose to furfural in rich-methanol solution: A study based on density functional theory

The hydrothermal conversion of biomass is an important method for furfural (FF) production. The development of methods for converting five-carbon sugars to FF can improve the utilization rate of biomass polysaccharides, which has important research value. FF is a valuable furan organic compound in the decomposition of xylose and can be produced in large quantities under hydrothermal conditions. In this study, density functional theory (DFT) method was used to study the mechanism of xylose forming FF and the effect of methanol-water mixed solution on FF formation. In this paper, through quantitative calculations, the best way to convert xylose to FF is explored, in order to understand the basic conversion way of biomass hydrothermal conversion to high-value molecular FF. It shows that water molecules participate in the catalytic reaction, and the Gibbs free energy is significantly reduced. This is consistent with the experimental results. In the gas phase, the catalytic reaction shows excellent effects. The Gibbs free energy in the solution is significantly lower than the Gibbs free energy in the gas phase. Combining experimental results and theoretical calculations, it is confirmed that the yield of FF produced by hydrothermal liquefaction of xylose is significantly higher than that of gas-phase pyrolysis. It was also confirmed that methanol played a role in protecting active functional groups, while water played a role as a catalyst. At the same time, methanol and water have a synergistic effect on the solvent.

Effectiveness of Baffled Flasks on the Growth of Scheffersomyces stipitis CBS 6054 Inoculum for Ethanol Production in Corncob Hemicellulosic Hydrolysate

Corncob is an agricultural byproduct, a result of maize grains processing. It is a lignocellulosic biomass, and its hydrolysis releases a great amount of xylose, a five-carbon sugar that is not readily assimilated by industrial yeasts for bioethanol production. Scheffersomyces stipitis CBS 6054, however, is a yeast that can directly assimilate xylose. It is also known that aeration control has a positive effect on ethanol production during the fermentation process. However, it is rare to find research integrating the inoculum preparation with fermentation processes, and the physiological condition of the inoculum on the very moment of the culture transference can trigger off-target effects on fermentation performance. In this work, we evaluate the inoculum production of S. stipitis CBS 6054 in corncob hemicellulosic hydrolysate (CHH), containing glucose and xylose, and employing Erlenmeyer flasks with and without baffles. Baffles tend to cause an increase in oxygen transfer rate. The inoculum prepared on CHH using baffled flasks (BF) achieved faster exponential phase than unbaffled flasks (UF; 7–14 h versus 12–18 h). Cell density in this phase was also higher (0.2–2.8 versus 0.01–0.70 g L−1) compared with UF. Fermentations conducted with these inoculums presented a significant increase in ethanol production and yield (YP/S of 0.17 to 0.23), proving the important role of oxygen transfer rates on inoculum preparation. Color images are available online