Xylose Oxidation Research Articles

In-situ carbon-doped poly(triazine imide) modified with silver nanoparticles for synergistic efficient photocatalytic CO2 reduction coupled with biomass refining

Solar-driven CO2 reduction to fuels holds critical importance in addressing climate and energy challenges. However, the practical application faces limitations due to the difficulty in activating CO2, the slow kinetics of the oxidation half-reaction, and the generation of undesired by-products. Herein, we report a functionally-oriented approach for the deliberate fabrication of in-situ carbon-doped poly(triazine imide) modified with silver nanoparticles (Ag NPs) (Ag/C@PTI), aimed at solar-driven CO2 reduction synchronized with xylose oxidation within a single redox cycle. The strategic in-situ carbon doping and the deposition of Ag NPs significantly reduce the bandgap of PTI to 1.60 eV, thereby markedly enhancing charge carrier separation and refining product selectivity. Consequently, the optimally formulated Ag10/C@PTI-10 catalyst demonstrates superior photocatalytic performance in xylose oxidation coupled with CO2 reduction, achieving a xylonic acid yield of 51.4 % and a CO evolution rate of 31.4 μmol g-1h-1. The 13CO2 isotope labeling experiments confirm that a portion of the CO is derived from the xylose conversion process. Moreover, ESR characterization along with capture tests reveal that h+ and ·O2- are pivotal in the photooxidation of xylose to xylonic acid.

Constructing heterostructure of Mo-doped Co(CO3)0.5OH on NiCo2S4 nanowires towards electrocatalytic biomass upgrading

The development of an advanced electrocatalyst is crucial to achieve low-cost and efficient biomass electrooxidation for assisting its practical application. In this study, we design a unique heterostructure of Mo-doped Co(CO3)0.5OH coating on NiCo2S4 nanowires for efficient xylose oxidation reaction (XOR). The as-prepared electrocatalyst requires only 1.28 V for XOR to achieve current density of 50 mA cm−2, and the electrocatalytic system exhibits the high formic acid (FA) yield of 63.22 % and excellent selectivity of 96.52 %, which still maintains unchanged after seven cycles. Furthermore, the two-electrode system by coupling XOR and hydrogen evolution reaction (HER) shows that product selectivity remained at least 96 %, while the hydrogen production rate higher than the original. This remarkable performance is attributed to the synergic effect of heterostructure and multi-component as confirmed by XPS and XRD analysis. This work puts forward an attractive approach for designing high electrocatalytic activity and selectivity electrocatalyst for biomass electrooxidation.

Influence of Reaction Parameters on Nanogold-Catalyzed Glucose and Xylose Oxidation: A Joint Experimental and DFT Study

Influence of Reaction Parameters on Nanogold-Catalyzed Glucose and Xylose Oxidation: A Joint Experimental and DFT Study

Adaptive laboratory evolution to obtain furfural tolerant Saccharomyces cerevisiae for bioethanol production and the underlying mechanism.

Furfural, a main inhibitor produced during pretreatment of lignocellulose, has shown inhibitory effects on S. cerevisiae. In the present study, new strains named 12-1 with enhanced resistance to furfural were obtained through adaptive laboratory evolution, which exhibited a shortened lag phase by 36 h, and an increased ethanol conversion rate by 6.67% under 4 g/L furfural. To further explore the mechanism of enhanced furfural tolerance, ADR1_1802 mutant was constructed by CRISPR/Cas9 technology, based on whole genome re-sequencing data. The results indicated that the time when ADR1_1802 begin to grow was shortened by 20 h compared with reference strain (S. cerevisiae CEN.PK113-5D) when furfural was 4 g/L. Additionally, the transcription levels of GRE2 and ADH6 in ADR1_ 1802 mutant were increased by 53.69 and 44.95%, respectively, according to real-time fluorescence quantitative PCR analysis. These findings suggest that the enhanced furfural tolerance of mutant is due to accelerated furfural degradation. Importance: Renewable carbon worldwide is vital to achieve "zero carbon" target. Bioethanol obtained from biomass is one of them. To make bioethanol price competitive to fossil fuel, higher ethanol yield is necessary, therefore, monosaccharide produced during biomass pretreatment should be effectively converted to ethanol by Saccharomyces cerevisiae. However, inhibitors formed by glucose or xylose oxidation could make ethanol yield lower. Thus, inhibitor tolerant Saccharomyces cerevisiae is important to this process. As one of the main component of pretreatment hydrolysate, furfural shows obvious impact on growth and ethanol production of Saccharomyces cerevisiae. To get furfural tolerant Saccharomyces cerevisiae and find the underlying mechanism, adaptive laboratory evolution and CRISPR/Cas9 technology were applied in the present study.

Integrating electrocatalytic seawater splitting and biomass upgrading via bifunctional nickel cobalt phosphide nanorods

A hybrid electrolyser using NiCoP as a bifunctional electrode was constructed by coupling xylose oxidation with hydrogen evolution from seawater, aiming to boost the efficiency of seawater electrolysis.

Recent progress in the microbial production of xylonic acid.

Interest in the production of renewable chemicals from biomass has increased in the past years. Among these chemicals, carboxylic acids represent a significant part of the most desirable bio-based products. Xylonic acid is a five-carbon sugar-acid obtained from xylose oxidation that can be used in several industrial applications, including food, pharmaceutical, and construction industries. So far, the production of xylonic acid has not yet been available at an industrial scale; however, several microbial bio-based production processes are under development. This review summarizes the recent advances in pathway characterization, genetic engineering, and fermentative strategies to improve xylonic acid production by microorganisms from xylose or lignocellulosic hydrolysates. In addition, the strengths of the available microbial strains and processes and the major requirements for achieving biotechnological production of xylonic acid at a commercial scale are discussed. Efficient native and engineered microbial strains have been reported. Xylonic acid titers as high as 586 and 171g L-1 were obtained from bacterial and yeast strains, respectively, in a laboratory medium. Furthermore, relevant academic and industrial players associated with xylonic acid production will be presented.

Energy-efficient monosaccharides electrooxidation coupled with green hydrogen production by bifunctional Co9S8/Ni3S2 electrode

Water electrolysis is a sustainable strategy for renewable energy conversion and storage that can be replenished by intermittent electricity sources. Despite the decades-long progress, the commercialization of water electrolysis remains fraught with difficulties owing to its high electricity consumption. We couple the hydrogen evolution reaction with the electrooxidation of xylose obtained from regenerated hemicellulose to organic acids, utilizing a bifunctional electrode consisting of Co9S8/Ni3S2. The electrochemically activated anodic sites, including Co2+/Co3+, Co3+/Co4+, Ni2+/Ni3+, and Ni3+/Ni4+ redox species, are responsible for xylose electrooxidation, with the required potential reduced by 290 mV at 100 mA cm−2 compared with water oxidation. Moreover, the process yields over 60% towards formic acid at the anode, is accompanied by the production of hydrogen at the cathode. Xylose oxidation is kinetically and thermodynamically more favorable than water oxidation, significantly reducing the overall energy consumption relative to conventional water electrolysis. This study provides a promising strategy for the scalable and energy-efficient process of biomass electrooxidation coupled with hydrogen production.

Well-Arranged Hollow Au@Zn/Ni-MOF-2-NH2 Core–Shell Nanocatalyst with Enhanced Catalytic Activity for Biomass-Derived d-Xylose Oxidation

Well-Arranged Hollow Au@Zn/Ni-MOF-2-NH₂ Core–Shell Nanocatalyst with Enhanced Catalytic Activity for Biomass-Derived <scp>d</scp>-Xylose Oxidation

Xylonic acid production by recombinant Komagataella phaffii strains engineered with newly identified xylose dehydrogenases

Microbial production of xylonic acid can be achieved via xylose oxidation catalyzed by the xylose dehydrogenase enzyme. In the present study, 11 putative xylose dehydrogenases (XDH) from bacterial and fungi were identified through in silico analysis using the sequences of the two XDH previously described. Among them, 6 genes were successfully cloned and expressed in Komagataella phaffii (Pichia pastoris) as demonstrated by the ability of the strains to produce xylonic acid. The best strain was capable of producing up to 37.1 ± 1.9 and 11.7 ± 1.6 g/L of xylonic acid with yields of 0.96 ± 0.02 and 0.40 ± 0.06 g/g in mineral medium and sugarcane bagasse hydrolysate, respectively. The results presented here demonstrated the functionality of 6 newly identified xylose dehydrogenases, increasing the number of XDH described. In addition, the efficiency of K. phaffii as a xylonic acid producer is showed for the first time.

Highly selective oxidation of monosaccharides to sugar acids by nickel-embedded carbon nanotubes under mild conditions

The preparation of inexpensive, high-performance non-noble metal catalysts for selective oxidation of biomass-derived monosaccharides to high value-added chemicals is challenging but in high demand. Herein, we successfully synthesized a nickel-embedded carbon nanotube (Ni-NCNT) catalyst to selectively convert the monosaccharides into sugar acids under mild condition. The Ni-NCNT catalyst was highly reactive towards glucose and xylose oxidation, reaching 90.8% yield of gluconic acid and 88.4% yield of xylonic acid under the optimal condition. Theoretical calculations revealed that the intrinsic reaction mechanism of xylose oxidation involves the activation of the oxidant, adsorption of xylose, dissociation of the formyl C–H bond in xylose, formation of chemisorbed xylonic acid, and desorption of xylonic acid. The dissociation of the formyl C–H bond and the formation of adsorbed xylonic acid are key steps in the oxidation of xylose. The OH−, instead of O2, acted as a direct oxidant and was crucial for the xylose oxidation. The highly active and cost-effective Ni-NCNT developed in this study provided a promising route to generate valuable chemicals from biomass.

Biotransformation of d-xylose to d-xylonate coupled to medium-chain-length polyhydroxyalkanoate production in cellobiose-grown Pseudomonas putida EM42.

SummaryCo‐production of two or more desirable compounds from low‐cost substrates by a single microbial catalyst could greatly improve the economic competitiveness of many biotechnological processes. However, reports demonstrating the adoption of such co‐production strategy are still scarce. In this study, the ability of genome‐edited strain Pseudomonas putida EM42 to simultaneously valorize d‐xylose and d‐cellobiose – two important lignocellulosic carbohydrates – by converting them into the platform chemical d‐xylonate and medium‐chain‐length polyhydroxyalkanoates, respectively, was investigated. Biotransformation experiments performed with P. putida resting cells showed that promiscuous periplasmic glucose oxidation route can efficiently generate extracellular xylonate with a high yield. Xylose oxidation was subsequently coupled to the growth of P. putida with cytoplasmic β‐glucosidase BglC from Thermobifida fusca on d‐cellobiose. This disaccharide turned out to be a better co‐substrate for xylose‐to‐xylonate biotransformation than monomeric glucose. This was because unlike glucose, cellobiose did not block oxidation of the pentose by periplasmic glucose dehydrogenase Gcd, but, similarly to glucose, it was a suitable substrate for polyhydroxyalkanoate formation in P. putida. Co‐production of extracellular xylose‐born xylonate and intracellular cellobiose‐born medium‐chain‐length polyhydroxyalkanoates was established in proof‐of‐concept experiments with P. putida grown on the disaccharide. This study highlights the potential of P. putida EM42 as a microbial platform for the production of xylonate, identifies cellobiose as a new substrate for mcl‐PHA production, and proposes a fresh strategy for the simultaneous valorization of xylose and cellobiose.

Highly efficient and selective electrooxidation of glucose and xylose in alkaline medium at carbon supported alloyed PdAu nanocatalysts

The effect of the composition of carbon supported PdAu nanomaterials toward electrocatalytic oxidation of glucose and xylose was evaluated in alkaline medium. PdxAu10-x/C catalysts were synthesized by a water-in-oil microemulsion method and characterized by physical (TGA, AAS, TEM, XRD) and electrochemical methods. Bulk Pd/Au alloys were formed, but the surface composition was different than the bulk one. The surface of PdxAu10-x/C catalysts as determined by electrochemical method were enriched in Pd with respect to the nanoparticle bulk composition as determined by atomic absorption spectroscopy (AAS). Electrochemical experiments combined with in situ infrared spectroscopy measurements showed the dissociative adsorption of aldoses on Pd-rich catalysts at low potentials (appearance of the typical band of COads on Pd surface). For catalysts with Au at. % ≥70%, this band was not visible. Pd3Au7/C catalyst provided the lowest oxidation onset potential, the highest activity and the best selectivity towards gluconate and xylonate. Therefore, long term chronoamperometry measurements of glucose and xylose electrooxidation were performed on this catalyst in a 25 cm2 geometric active surface area electrolysis cell at a voltage of 0.4 V and at 293 K. Reaction products were analyzed by HPLC every hour, and by 1H NMR at the end of the experiments. The main products were gluconate and xylonate. Glucose oxidation led to selectivity in gluconate of 87% for 67% conversion, and higher for lower conversion. Xylose oxidation led to selectivity in xylonate of 100% after 1 and 2 h electrolysis and of 92% after 6 h (52% conversion). The conversion of glucose and xylose into gluconate and xylonate was performed with high selectivity and an energy cost below 36 € per ton of reaction products.

Refactoring the upper sugar metabolism of Pseudomonas putida for co-utilization of cellobiose, xylose, and glucose

Given its capacity to tolerate stress, NAD(P)H/ NAD(P) balance, and increased ATP levels, the platform strain Pseudomonas putida EM42, a genome-edited derivative of the soil bacterium P. putida KT2440, can efficiently host a suite of harsh reactions of biotechnological interest. Because of the lifestyle of the original isolate, however, the nutritional repertoire of P. putida EM42 is centered largely on organic acids, aromatic compounds and some hexoses (glucose and fructose). To enlarge the biochemical network of P. putida EM42 to include disaccharides and pentoses, we implanted heterologous genetic modules for D-cellobiose and D-xylose metabolism into the enzymatic complement of this strain. Cellobiose was actively transported into the cells through the ABC complex formed by native proteins PP1015-PP1018. The knocked-in β-glucosidase BglC from Thermobifida fusca catalyzed intracellular cleavage of the disaccharide to D-glucose, which was then channelled to the default central metabolism. Xylose oxidation to the dead end product D-xylonate was prevented by deleting the gcd gene that encodes the broad substrate range quinone-dependent glucose dehydrogenase. Intracellular intake was then engineered by expressing the Escherichia coli proton-coupled symporter XylE. The sugar was further metabolized by the products of E. coli xylA (xylose isomerase) and xylB (xylulokinase) towards the pentose phosphate pathway. The resulting P. putida strain co-utilized xylose with glucose or cellobiose to complete depletion of the sugars. These results not only show the broadening of the metabolic capacity of a soil bacterium towards new substrates, but also promote P. putida EM42 as a platform for plug-in of new biochemical pathways for utilization and valorization of carbohydrate mixtures from lignocellulose processing.

Selection and characterisation of a xylitol-derepressed Aspergillus niger mutant that is apparently impaired in xylitol transport

Aspergillus niger is known for its biotechnological applications, such as the use of xylanase enzyme for the degradation of hemicellulose. Depending on culture conditions, several polyols may also be accumulated, such as xylitol during D: -xylose oxidation. Also during industrial fermentation of xylose for the production of fuel ethanol by recombinant yeast, xylitol is a by-product. We studied xylitol metabolism by isolating mutants that have impaired xylitol-mediated repression. Genetic and biochemical characterisation revealed that one of these mutants was affected not only in xylitol-mediated carbon repression, but also had impaired xylitol transport.

Energy generation by extracellular aldose oxidation in N(2)-fixing Gluconacetobacter diazotrophicus.

Gluconacetobacter diazotrophicus PAL3 was grown in a chemostat with N(2) and mixtures of xylose and gluconate. Xylose was oxidized to xylonate, which was accumulated in the culture supernatants. Biomass yields and carbon from gluconate incorporated into biomass increased with the rate of xylose oxidation. By using metabolic balances it is demonstrated that extracellular xylose oxidation led N(2)-fixing G. diazotrophicus cultures to increase the efficiency of energy generation.

Effect of thiosulphate as electron acceptor on glucose and xylose oxidation by Thermoanaerobacter finnii and a Thermoanaerobacter sp. isolated from oil field water

During glucose and xylose fermentation, Thermoanaerobacter finnii was observed to produce lactate, acetate, H 2 and CO 2, with ethanol being the major end product. Thermoanaerobacter strain SEBR 5268, an isolate from an oil field, also produced a similar range of end product from glucose and xylose fermentation, with the exception that both ethanol and lactate were the major products of sugar metabolism. Both these strains were able to reduce thiosulphate to sulphide in the presence of these two substrates, with acetate being the dominant metabolite in that case. In addition, a faster growth rate and increased cell yield were obtained in the presence of thiosulphate, than in its absence. The higher concentrations of acetate produced in the presence of thiosulphate rather than without any electron acceptor indicated that more ATP was generated from substrate-level phosphorylation. These results have implications for our understanding of the breakdown of carbohydrates present in organic matter found in the natural ecological niches of Thermoanaerobacter species (sulphide-, elemental sulphur- or sulphate-rich thermal hot springs and oil fields).

Large-scale applicable purification and characterization of a membrane-bound PQQ-dependent aldose dehydrogenase

A membrane-bound xylose oxidizing PQQ-dependent dehydrogenase from Gluconobacter oxydans was purified with a simple large-scale applicable purification procedure. The activity recovery from membrane extract was 33% with 130-fold purification. Important characteristics with respect to the application of the dehydrogenase in biosensor technology were studied. The purified enzyme was most stable in the pH range 3.5–6.5. The pH optimum for xylose oxidation was in the range 7.5–8 for the solubilized enzyme. Optimal pH for the electrochemical detection of xylose oxidation was 6.5. Dimethyl and carboxylic acid derivatives of ferrocene were able to mediate electrons transferred in xylose oxidation from the enzyme immobilized on graphite electrode to the electrode. Hence the purified enzyme appeared to be suitable for biosensor applications.

Energy conservation by pyrroloquinoline quinol-linked xylose oxidation in Pseudomonas putida NCTC 10936 during carbon-limited growth in chemostat culture

Energy conservation by pyrroloquinoline quinol-linked xylose oxidation in Pseudomonas putida NCTC 10936 during carbon-limited growth in chemostat culture

Energy conservation by pyrroloquinoline quinol-linked xylose oxidation in Pseudomonas putida NCTC 10936 during carbon-limited growth in chemostat culture.

When grown in carbon source-limited chemostat cultures with lactate or glucose as the carbon and energy source and xylose as an additional source of reducing equivalents. Pseudomonas putida NCTC 10936 oxidized xylose to xylonolactone and xylonate. No other products were formed from this pentose, nor was it incorporated into biomass. The presence of xylose in these cultures resulted in higher Yglucose and Ylactate values as compared to cultures without xylose indicating that biologically useful energy was conserved during the periplasmic oxidation of xylose. As the Y0 values for growth on glucose or on lactate alone were equal to the Y0 values for growth with xylose as co-substrate, it is concluded that for glucose- or lactate-limited growth energy conservation by PQQH2 oxidation is as efficient as by NADH2 oxidation.

Achromobacter xylosoxidans isolates in Hawaii.

Clinical and bacteriological features of nine cases in which Achromobacter xylosoxidans were isolated in Hawaii are described. Five cases were ear infections mixed with other gram-negative bacteria. Colonial morphology, xylose oxidation, peritrichous flagella staining, and antibiotic susceptibility pattern assisted in separating this bacterium from other nonfermentative, oxidase-positive, gram-negative rods.