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Photocatalysis has emerged as an effective approach to sustainably convert biomass into value-added products. CoSe2 is a promising non-precious, efficient cocatalyst for photooxidation, which can facilitate the separation of photogenerated electron–holes, increase the reaction rates, and enhance photocatalytic efficiency. In this work, we synthesized a stable and efficient photocatalysis system of CoSe2/g-C3N4 through attaching CoSe2 on g-C3N4 sheets, with a yield of 50.12% for the selective photooxidation of xylose to xylonic acid. Under light illumination, the photogenerated electrons were prone to migrating from g-C3N4 to CoSe2 due to the higher work function of CoSe2, resulting in the accelerated separation of photogenerated electron–holes and the promoted photooxidation. Herein, this study reveals the unique function of CoSe2, which can significantly promote oxygen adsorption, work as an electron sink and accelerate the generation of ·O2−, thereby improving the selectivity toward xylonic acid over other by-products. This work provides useful insights into the design of selective photocatalysts by engineering g-C3N4 for biomass high-value utilization. [ABSTRACT FROM AUTHOR]

Rare earth vanadates are promising for solar‐to‐fuel conversions, yet their photocatalytic efficiency is limited by the substantial recombination of photo‐generated carriers. Constructing heterojunctions is recognized as an effective approach to improving charge carrier separation in vanadates. Nonetheless, inefficient charge transfer often results from the poor quality of interfaces and non‐directional charge transfer within these heterojunctions. Herein, an S‐scheme AgInS2/CeVO4@Biocharx (AIS/CV@Cx) heterojunction photocatalyst is designed and synthesized through a straightforward freeze‐drying and calcination three‐step process, aimed at photocatalytic co‐production of xylonic acid and carbon monoxide (CO) from xylose. The AIS/CV@C2 heterojunction achieves an optimal yield of 67.74% for xylonic acid and a CO release of 29.76 µmol from xylose. The enhanced photocatalytic performance of the AIS/CV@C2 heterojunction is attributed to three key factors: I) the high‐quality interface and intimate contact within the AIS/CV@C2 heterojunction significantly reduce undesirable carriers recombination, II) the staggered band structures and directed carriers transfer in the AIS/CV@C2 heterojunction notably improve spatial carriers separation/migration, and III) the incorporation of biochar boosts the conductivity of the AIS/CV@C2 heterojunction. This work presents a straightforward yet effective method for fabricating vanadate heterojunctions, highlighting the importance of quality interfacial contact and directed charge transfer in amplifying photocatalytic performance. [ABSTRACT FROM AUTHOR]

A significant reaction in the synthesis of biomass-based chemicals is the catalyst-based and targeted oxidation of monosaccharides into valuable sugar acids. In this study, an activated carbon supported gold catalyst was used to oxidize glucose and xylose to gluconic acid and xylonic acid under neutral condition. Optimization of reaction conditions for the catalysts was performed using both a batch reactor and a flow-through reactor. In a batch reactor, the yields of gluconic and xylonic acid reached 93% and 92%, respectively, at 90 °C within 180 min. In a flow reactor, both reactions reached a similar yield at 80 °C with the weight hourly space velocity of 47.1 h−1. The reaction kinetics were explored in the flow reactor. The oxidation of glucose and xylose to gluconic and xylonic acid followed a first-order kinetics and the turnover frequency was 0.195 and 0.161 s−1, respectively. The activation energy was evaluated to be 60.58 and 59.30 kJ·mol−1, respectively. This study presents an environmentally friendly and feasible method for the selective oxidation of monosaccharides using an activated carbon supported gold catalyst, benefiting the high-value application of carbohydrates. [ABSTRACT FROM AUTHOR]

This study explores the mechanical properties, as well as the water-reducing and setting delay mechanism, of a novel xylonic acid-based water reducer applied to cementitious materials. Four xylonic acid water reducers were synthesized in this study: XACa (PX) from pure xylose, XACa (HS) from hemicellulose hydrolysate, XANa (PX) from pure xylose, and XANa (HS) from hemicellulose hydrolysate. These were generated through the whole-cell catalysis of Gluconobacter oxydans bacteria, using pure xylose and hemicellulose hydrolysate as substrates. The findings indicate that the xylonic acid-based water reducer can attain a water-reducing capability between 14% and 16% when the dosage (expressed as a mass fraction of cement) is roughly 0.2%. In initial and final setting tests, XACa (PX) demonstrated a pronounced retarding influence at admixture levels below 0.15%, reaching its apex at 0.10%. This delayed the initial setting time by 76% and the final setting time by 136% relative to the control group. However, a slight pro-setting effect was noted beyond a 0.2% dosage. In the compressive and flexural tests of concrete, under the same slump, the XA group improved its mechanical properties by 5% to 10% compared to the SodiuM lignosulfonate (SL) group. In the air content and chloride ion migration resistance tests, the XA group reduced the air content by 38% compared to the SL group, but also increased the data of rapid chloride migration (DRCM) by 16%. Characterization studies revealed that the carboxyl and hydroxyl groups in xylonic acid undergo chemisorption with the Si-O bonds on the surface of cement particles. These groups interact with the Si-O bonds on cement particles, contributing to water-reducing effects and delaying the setting process by impeding Ca2+ ion aggregation in the calcium-silicate-hydrate gel. Its significant water-reducing effect, adjustable setting time, and excellent mechanical and durability properties suggest its viability as an alternative to lignosulfonate series water-reducing agents. [ABSTRACT FROM AUTHOR]

In this study, the synthesis of xylonic acid from xylose by Gluconobacter oxydans NL71 has been investigated. According to the relationship between oxygen transfer rate and oxygen uptake rate, three different kinetic models of product formation were established and the nonlinear fitting was carried out. The results showed that G. oxydans has critical dissolved oxygen under different strain concentrations, and the relationship between respiration intensity and dissolved oxygen conformed to the Monod equation q O 2 = q O 2 , max C L K O 2 + C L . The maximum reaction rate per unit cell mass and the theoretical maximum specific productivity of G. oxydans obtained by the kinetic model are 0.042 mol/L/h and 6.97 g/gx/h, respectively. These results will assist in determining the best balance between the airflow rate and cell concentration in the reaction and improve the production efficiency of xylonic acid. [ABSTRACT FROM AUTHOR]

In this work, the effect of activated carbon particles on the production of xylonic acid from xylose by Gluconobacter oxydans in a stirred tank bioreactor was investigated. The enhancement of the oxygen transfer coefficient by activated carbon particles was experimentally evaluated under different solids volume fractions, agitation and aeration rates conditions. The experimental conditions optimized by response surface methodology (agitation speed 800 rpm, aeration rate 7 L min−1, and activated carbon 0.002%) showed a maximum oxygen transfer coefficient of 520.7 h−1, 40.4% higher than the control runs without activated carbon particles. Under the maximum oxygen transfer coefficient condition, the xylonic acid titer reached 108.2 g/L with a volumetric productivity of 13.53 g L−1 h−1 and a specific productivity of 6.52 g/gx/h. In conclusion, the addition of activated carbon particles effectively enhanced the oxygen mass transfer rate. These results demonstrate that activated carbon particles enhanced cultivation for xylonic acid production an inexpensive and attractive alternative. [ABSTRACT FROM AUTHOR]

Pentose oxidation and reduction, processes yielding value-added sugar-derived acids and alcohols, typically involve separate procedures necessitating distinct reaction conditions. In this study, a novel one-pot reaction for the concurrent production of xylonic acid and xylitol from xylose is proposed. This reaction was executed at ambient temperature in the presence of a base, eliminating the need for external gases, by leveraging Pt-supported catalysts. Initial experiments using commercially available metal-supported carbon catalysts validated the superior activity of Pt. However, a notable decline in recycling performance was observed in Pt/C, which is attributed to the sintering of Pt nanoparticles. In contrast, the synthesized Pt-supported ZrO 2 catalysts exhibited enhanced recycling performance because of the strong metal-support interaction between Pt and the ZrO 2 support. Furthermore, mechanistic insights and density functional theory calculations show that product desorption involves a significantly higher energy barrier compared to substrate adsorption and hydrogenation, highlighting an efficient transfer hydrogenation mechanism leading to equivalent yields of both xylonic acid and xylitol. This study introduces a promising approach for the simultaneous production of sugar-derived acids and alcohols, with implications for sustainable catalysis and process optimization., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

g-C 3 N 4 has broad prospects in photocatalytic upgrading of biomass but suffers from the large exciton binding energy and high charge recombination rate. Herein, we integrated the biomass-derived carbocyclic rings with heptazine units via π-conjugation, constructing biochar-welded electron donor (D)-acceptor (A) structures in g-C 3 N 4. This structure can induce intrinsic driving forces that promoted electron delocalization and transport. Meanwhile, the interlayer π-π stacking interaction of the carbocyclic rings provided a channel for electrons to migrate on the vertically layered structure. The g-C 3 N 4 with biochar-welded D-A configuration exhibited an improved yield of 87.52 % for xylonic acid from biomass monosaccharide. The mechanism study confirmed the dominant role of superoxide radicals (·O 2 -) and distinguished singlet oxygen (1O 2) from the generation path, demonstrating the supporting role of 1O 2 originated from an energy transfer process. This work proposed a universal strategy to construct g-C 3 N 4 -based photocatalysts with D-A configuration to achieve efficient photocatalytic reforming of biomass. [Display omitted] • The biomass-derived carbocyclic rings were integrated with heptazine units, forming electron donor (D)-acceptor (A) configuration in g-C 3 N 4. • The interlayer π-π stacking interaction of the carbocyclic rings provided a channel for electrons to migrate vertically. • Mechanism study distinguished 1O 2 from the generation path, demonstrating the supporting role of 1O 2 originated fromenergy transfer process. [ABSTRACT FROM AUTHOR]

Xylomyrocins, a unique group of nonribosomal peptide secondary metabolites, were discovered in Paramyrothecium and Colletotrichum spp. fungi by employing a combination of high-resolution tandem mass spectrometry (HRMS/MS)-based chemometrics, comparative genome mining, gene disruption, stable isotope feeding, and chemical complementation techniques. These polyol cyclodepsipeptides all feature an unprecedented D-xylonic acid moiety as part of their macrocyclic scaffold. This biosynthon is derived from D-xylose supplied by xylooligosaccharide catabolic enzymes encoded in the xylomyrocin biosynthetic gene cluster, revealing a novel link between carbohydrate catabolism and nonribosomal peptide biosynthesis. Xylomyrocins from different fungal isolates differ in the number and nature of their amino acid building blocks that are nevertheless incorporated by orthologous nonribosomal peptide synthetase (NRPS) enzymes. Another source of structural diversity is the variable choice of the nucleophile for intramolecular macrocyclic ester formation during xylomyrocin chain termination. This nucleophile is selected from the multiple available alcohol functionalities of the polyol moiety, revealing a surprising polyspecificity for the NRPS terminal condensation domain. Some xylomyrocin congeners also feature N-methylated amino acid residues in positions where the corresponding NRPS modules lack N-methyltransferase (M) domains, providing a rare example of promiscuous methylation in the context of an NRPS with an otherwise canonical, collinear biosynthetic program. [ABSTRACT FROM AUTHOR]

Abstract Background Biological routes for ethylene glycol production have been developed in recent years by constructing the synthesis pathways in different microorganisms. However, no microorganisms have been reported yet to produce ethylene glycol naturally. Results Xylonic acid utilizing microorganisms were screened from natural environments, and an Enterobacter cloacae strain was isolated. The major metabolites of this strain were ethylene glycol and glycolic acid. However, the metabolites were switched to 2,3-butanediol, acetoin or acetic acid when this strain was cultured with other carbon sources. The metabolic pathway of ethylene glycol synthesis from xylonic acid in this bacterium was identified. Xylonic acid was converted to 2-dehydro-3-deoxy-d-pentonate catalyzed by d-xylonic acid dehydratase. 2-Dehydro-3-deoxy-d-pentonate was converted to form pyruvate and glycolaldehyde, and this reaction was catalyzed by an aldolase. d-Xylonic acid dehydratase and 2-dehydro-3-deoxy-d-pentonate aldolase were encoded by yjhG and yjhH, respectively. The two genes are part of the same operon and are located adjacent on the chromosome. Besides yjhG and yjhH, this operon contains four other genes. However, individually inactivation of these four genes had no effect on either ethylene glycol or glycolic acid production; both formed from glycolaldehyde. YqhD exhibits ethylene glycol dehydrogenase activity in vitro. However, a low level of ethylene glycol was still synthesized by E. cloacae ΔyqhD. Fermentation parameters for ethylene glycol and glycolic acid production by the E. cloacae strain were optimized, and aerobic cultivation at neutral pH were found to be optimal. In fed batch culture, 34 g/L of ethylene glycol and 13 g/L of glycolic acid were produced in 46 h, with a total conversion ratio of 0.99 mol/mol xylonic acid. Conclusions A novel route of xylose biorefinery via xylonic acid as an intermediate has been established.

Abstract In bacterial system, direct conversion of xylose to xylonic acid is mediated through NAD-dependent xylose dehydrogenase (xylB) and xylonolactonase (xylC) genes. Heterologous expression of these genes from Caulobacter crescentus into recombinant Corynebacterium glutamicum ATCC 13032 and C. glutamicum ATCC 31831 (with an innate pentose transporter, araE) resulted in an efficient bioconversion process to produce xylonic acid from xylose. Process parameters including the design of production medium was optimized using a statistical tool, Response Surface Methodology (RSM). Maximum xylonic acid of 56.32 g/L from 60 g/L xylose, i.e. about 76.67% of the maximum theoretical yield was obtained after 120 h fermentation from pure xylose with recombinant C. glutamicum ATCC 31831 containing the plasmid pVWEx1 xylB. Under the same condition, the production with recombinant C. glutamicum ATCC 13032 (with pVWEx1 xylB) was 50.66 g/L, i.e. 69% of the theoretical yield. There was no significant improvement in production with the simultaneous expression of xylB and xylC genes together indicating xylose dehydrogenase activity as one of the rate limiting factor in the bioconversion. Finally, proof of concept experiment in utilizing biomass derived pentose sugar, xylose, for xylonic acid production was also carried out and obtained 42.94 g/L xylonic acid from 60 g/L xylose. These results promise a significant value addition for the future bio refinery programs.

S-scheme heterojunctions have become an emerging type of effective photocatalysts to convert biomass. However, there are few reports on the synergistic S-type heterojunction and oxygen vacancy enhanced photocatalytic biomass conversion. Here, an AgInS 2 @CeO 2 -x S-scheme heterojunction photocatalyst with abundant oxygen vacancies was developed through a simple thermal and mild annealing process, allowing for the simultaneous production of xylonic acid and CO. Under visible light, the xylonic acid yield and CO evolution rate reached 60.0% and 3689.9 μmol g−1 h−1, respectively, through the decomposition of xylose. It was found that the S-scheme staggered band structure could improve sunlight utilization, increase the reduction power of photogenerated electrons, and enhance the separation and transfer of photogenerated charge carriers. Furthermore, oxygen vacancies on the surface of CeO 2 for AgInS 2 @CeO 2 -x heterojunction can suppress the recombination of generated electrons and holes. This study offers a promising approach for designing artificial photosynthetic systems to promote photocatalytic biomass conversion. [Display omitted] • The AgInS 2 @CeO 2 -x S-scheme heterojunctions with enhanced CeO 2 oxygen defects were designed. • The synergism between S-scheme heterojunctions and oxygen vacancies accelerated charge separation of AgInS 2 @CeO 2 -x. • The CO evolution and xylonic acid yield reached 3689.9 μmol g−1 h−1 and 60.0%. • The yields of xylonic acid and CO via AgInS 2 @CeO 2 -20 were 1.39 and 1.44 times greater than AgInS 2. [ABSTRACT FROM AUTHOR]

Abstract Background Obtaining high-value products from lignocellulosic biomass is central for the realization of industrial biorefinery. Acid pretreatment has been reported to yield xylooligosaccharides (XOS) and improve enzymatic hydrolysis. Moreover, xylose, an inevitable byproduct, can be upgraded to xylonic acid (XA). The aim of this study was to valorize sugarcane bagasse (SB) by starting with XA pretreatment for XOS and glucose production within a multi-product biorefinery framework. Results SB was primarily subjected to XA pretreatment to maximize the XOS yield by the response surface method (RSM). A maximum XOS yield of 44.5% was achieved by acid pretreatment using 0.64 M XA for 42 min at 154 °C. Furthermore, XA pretreatment can efficiently improve enzymatic digestibility, and achieved a 90.8% cellulose conversion. In addition, xylose, the inevitable byproduct of the acid-hydrolysis of xylan, can be completely converted to XA via bio-oxidation of Gluconobacter oxydans (G. oxydans). Subsequently, XA and XOS can be simultaneously separated by electrodialysis. Conclusions XA pretreatment was explored and exhibited a promising ability to depolymerize xylan into XOS. Mass balance analysis showed that the maximum XOS and fermentable sugars yields reached 10.5 g and 30.9 g per 100 g raw SB, respectively. In summary, by concurrently producing XOS and fermentable sugars with high yields, SB was thus valorized as a promising feedstock of lignocellulosic biorefinery for value-added products.

Large amounts of xylose cannot be efficiently metabolized and fermented due to strain limitations in lignocellulosic biorefinery. The conversion of xylose into high value chemicals can help to reduce the cost of commercialization. Therefore, xylonic acid with potential value in the construction industry offers a valuable alternative for xylose biorefinery. However, low productivity is the main challenge for xylonic acid fermentation. This study investigated the effect of three reaction parameters (agitation, aeration, and biomass concentration) on xylose acid production and optimized the key process parameters using response surface methodology The second order polynomial model was able to fit the experimental data by using multiple regression analysis. The maximum specific productivity was achieved with a value of 6.64 ± 0.20 g gx−1 h−1 at the optimal process parameters (agitation speed 728 rpm, aeration rate 7 L min−1, and biomass concentration 1.11 g L−1). These results may help to improve the production efficiency during xylose acid biotransformation from xylose.

Ethylene glycol and glycolic acid are bulk chemicals with a broad range of applications. The ethylene glycol and glycolic acid biosynthesis pathways have been produced by microorganisms and used as a biological route for their production. Unlike the methods that use xylose or glucose as carbon sources, xylonic acid was used as a carbon source to produce ethylene glycol and glycolic acid in this study. Amounts of 4.2 g/L of ethylene glycol and 0.7 g/L of glycolic acid were produced by a wild‐type Escherichia coli W3110 within 10 H of cultivation with a substrate conversion ratio of 0.5 mol/mol. Furthermore, E. coli strains that produce solely ethylene glycol or glycolic acid were constructed. 10.3 g/L of glycolic acid was produced by E. coli ΔyqhD+aldA, and the achieved conversion ratio was 0.56 mol/mol. Similarly, the E. coli ΔaldA+yqhD produced 8.0 g/L of ethylene glycol with a conversion ratio of 0.71 mol/mol. Ethylene glycol and glycolic acid production by E. coli on xylonic acid as a carbon source provides new information on the biosynthesis pathway of these products and opens a novel way of biomass utilization. [ABSTRACT FROM AUTHOR]

The xylose oxidative pathway (XOP) has been engineered in microorganisms for the production of a wide range of industrially relevant compounds. However, the performance of metabolically engineered XOP-utilizing microorganisms is typically hindered by D-xylonic acid accumulation. It acidifies the media and perturbs cell growth due to toxicity, thus curtailing enzymatic activity and target product formation. Fortunately, from the growing portfolio of genetic tools, several strategies that can be adapted for the generation of efficient microbial cell factories have been implemented to address D-xylonic acid accumulation. This review centers its discussion on the causes of D-xylonic acid accumulation and how to address it through different engineering and synthetic biology techniques with emphasis given on bacterial strains. In the first part of this review, the ability of certain microorganisms to produce and tolerate D-xylonic acid is also tackled as an important aspect in developing efficient microbial cell factories. Overall, this review could shed some insights and clarity to those working on XOP in bacteria and its engineering for the development of industrially applicable product-specialist strains. Key points: D-Xylonic acid accumulation is attributed to the overexpression of xylose dehydrogenase concomitant with basal or inefficient expression of enzymes involved in D-xylonic acid assimilation. Redox imbalance and insufficient cofactors contribute to D-xylonic acid accumulation. Overcoming D-xylonic acid accumulation can increase product formation among engineered strains. Engineering strategies involving enzyme engineering, evolutionary engineering, coutilization of different sugar substrates, and synergy of different pathways could potentially address D-xylonic acid accumulation. [ABSTRACT FROM AUTHOR]

For high value utilization of depectinized celery, in this work. Sulfuric acid (1%, 160 °C, 60 min) treatments, followed by high pressure homogenization, were used to isolate lignin-rich nanocellulose (LRNC) from depectinized celery. LRNC yield from celery was 43.9%. LRNC solutions containing up to 20% xylonic acid (XA) were cast into films, which exhibited significantly improved flexibility, transparency, and hydrophilic properties. Moreover, the antibacterial property of the hybrid films was determined by the content of XA, and better antibacterial property were gained with higher amounts of XA. In total, > 61.6% depectinized celery was used as the storage of food yield. This study provided a value-added utilization technology for celery and other vegetables. [ABSTRACT FROM AUTHOR]

Background: Biotechnologically produced microbial lipids are of interest as potential alternatives for crude and plant oils. Their lipid profile is similar to plant oils and can therefore be a substitute for the production of biofuels, additives for food and cosmetics industry as well as building blocks for oleochemicals. Commercial microbial lipids production, however, is still not profitable and research on process optimization and cost reduction is required. This study reports on the process optimization using glucose or xylose with the unconventional oleaginous yeast Saitozyma podzolica DSM 27192 aiming to reduce the applied carbon source amount without sacrificing lipid productivity. Results: By optimizing the process parameters temperature and pH, lipid productivity was enhanced by 40%. Thereupon, by establishing a two-phase strategy with an initial batch phase and a subsequent fed-batch phase for lipid production in which a constant sugar concentration of about 10 g/L was maintained, resulted in saving of ~ 41% of total glucose and ~ 26% of total xylose. By performing the automated continuous sugar feed the total sugar uptake was improved to ~ 91% for glucose and ~ 92% for xylose and thus, prevented waste of unused carbon source in the cultivation medium. In addition, reduced glucose cultivation resulted in to 28% higher cell growth and 19% increase of lipid titer. By using xylose, the by-product xylonic acid was identified for the first time as by-product of S. podzolica. Conclusions: These findings provide a broad view of different cultivation process strategies with subsequent comparison and evaluation for lipid production with S. podzolica. Additionally, new biotechnological characteristics of this yeast were highlighted regarding the ability to produce valuable organic acids from sustainable and renewable sugars. [ABSTRACT FROM AUTHOR]

• Glutamate together with ammonium is a suitable nitrogen source for Gluconobacter oxydans. • >200 g/L xylonic acid is feasible by application of defined media (Productivity > 2.9 g·L−1 h−1). • G. oxydans is not sensitive towards acetic acid and HMF up to 5 g·L−1 and 2.5 g·L−1 respectively. • A 25 % substitution of pure xylose by hemicellulose-derived xylose did not affect G. oxydans. • Pulse feed increased the feasible substitution percentage of pure xylose by hemicellulosic xylose. Xylonic acid is a promising compound for the substitution of gluconic acid. Gluconobacter oxydans DSM 2343 has proven to be a highly potent biocatalyst for the conversion of xylose to xylonic acid. In the present study, different nitrogen sources for the growth of G. oxydans and subsequent xylonic acid production were investigated for the first time with minimal medium. Application of 0.32 g/L glutamate supplemented with 0.15 g/L ammonium sulfate as a cheap nitrogen source enabled a xylonic acid productivity of 2.92 g/(Lh) which is similar to findings involving a complex medium (3.20 g/(Lh)). The study further investigated the impact of the xylose source on the growth and production of G. oxydans. Dose-response curves confirmed that G. oxydans is mainly insensitive towards the main inhibitory compounds, acetate and hydroxymethylfurfural, up to a concentration of 5 g/L and 2.5 g/L, respectively. However, batch investigations indicated that substitution of 25 % of the pure xylose with hemicellulosic xylose resulted in a xylonic acid yield of 90 % compared to the control approach without hemicellulosic xylose. The feeding of hemicellulosic xylose in a pulsed fed-batch mode even enabled the use of 50 g/L demonstrating that the proper selection of a feeding strategy for the hemicellulosic xylose greatly improves the production of xylonic acid. [ABSTRACT FROM AUTHOR]

Efficient utilization of lignocellulose is an economically relevant practice for improving the financial prospects of biorefineries. Lignocellulose contains significant levels of xylose that can be converted into valuable xylonic acid. However, some inhibitors of bioconversion processes are produced after pretreatment. Xylonic acid production in bacteria, such as Gluconobacter oxydans, is hindered by poor bacterial tolerance to contaminants. Therefore, in order to enhance bacterial resistance to inhibitors, a recombinant strain of G. oxydans was created by the introduction of the thioredoxin gene. Thioredoxin is a key protein responsible for maintaining cellular redox potential and is critical to the conversion of xylose to xylonate. Overexpression of thioredoxin was confirmed at the enzymatic level, while the recombinant strain showed increased catalytic activity when inhibitors, such as formic acid or p-hydroxybenzaldehyde (PHBA), were added to the synthetic xylose medium (17% and 7% improvement in xylonic acid yield, respectively). To probe the molecular mechanism behind the recombinant strain response to inhibitors, the expression levels of various genes were analyzed by qRT-PCR, which revealed five differentially expressed genes (DEGs) upon exposure to formic acid or PHBA. [ABSTRACT FROM AUTHOR]

In bacterial system, direct conversion of xylose to xylonic acid is mediated through NAD-dependent xylose dehydrogenase (xylB) and xylonolactonase (xylC) genes. Heterologous expression of these genes from Caulobacter crescentus into recombinant Corynebacterium glutamicum ATCC 13032 and C. glutamicum ATCC 31831 (with an innate pentose transporter, araE) resulted in an efficient bioconversion process to produce xylonic acid from xylose. Process parameters including the design of production medium was optimized using a statistical tool, Response Surface Methodology (RSM). Maximum xylonic acid of 56.32 g/L from 60 g/L xylose, i.e. about 76.67% of the maximum theoretical yield was obtained after 120 h fermentation from pure xylose with recombinant C. glutamicum ATCC 31831 containing the plasmid pVWEx1 xylB. Under the same condition, the production with recombinant C. glutamicum ATCC 13032 (with pVWEx1 xylB) was 50.66 g/L, i.e. 69% of the theoretical yield. There was no significant improvement in production with the simultaneous expression of xylB and xylC genes together indicating xylose dehydrogenase activity as one of the rate limiting factor in the bioconversion. Finally, proof of concept experiment in utilizing biomass derived pentose sugar, xylose, for xylonic acid production was also carried out and obtained 42.94 g/L xylonic acid from 60 g/L xylose. These results promise a significant value addition for the future bio refinery programs. [ABSTRACT FROM AUTHOR]

Background: Biological routes for ethylene glycol production have been developed in recent years by constructing the synthesis pathways in different microorganisms. However, no microorganisms have been reported yet to produce ethylene glycol naturally. Results: Xylonic acid utilizing microorganisms were screened from natural environments, and an Enterobacter cloacae strain was isolated. The major metabolites of this strain were ethylene glycol and glycolic acid. However, the metabolites were switched to 2,3-butanediol, acetoin or acetic acid when this strain was cultured with other carbon sources. The metabolic pathway of ethylene glycol synthesis from xylonic acid in this bacterium was identified. Xylonic acid was converted to 2-dehydro-3-deoxy-d-pentonate catalyzed by d-xylonic acid dehydratase. 2-Dehydro-3-deoxy-d-pentonate was converted to form pyruvate and glycolaldehyde, and this reaction was catalyzed by an aldolase. d-Xylonic acid dehydratase and 2-dehydro-3-deoxy-d-pentonate aldolase were encoded by yjhG and yjhH, respectively. The two genes are part of the same operon and are located adjacent on the chromosome. Besides yjhG and yjhH, this operon contains four other genes. However, individually inactivation of these four genes had no effect on either ethylene glycol or glycolic acid production; both formed from glycolaldehyde. YqhD exhibits ethylene glycol dehydrogenase activity in vitro. However, a low level of ethylene glycol was still synthesized by E. cloacae ΔyqhD. Fermentation parameters for ethylene glycol and glycolic acid production by the E. cloacae strain were optimized, and aerobic cultivation at neutral pH were found to be optimal. In fed batch culture, 34 g/L of ethylene glycol and 13 g/L of glycolic acid were produced in 46 h, with a total conversion ratio of 0.99 mol/mol xylonic acid. Conclusions: A novel route of xylose biorefinery via xylonic acid as an intermediate has been established. [ABSTRACT FROM AUTHOR]

This study assesses the environmental impact of pine chip-based biorefinery processes, focusing on bioethanol, xylonic acid, and lignin production. A cradle-to-gate Life Cycle Assessment (LCA) is employed, comparing a novel biphasic pretreatment method (p -toluenesulfonic acid (TsOH)/pentanol, Sc-1) with conventional sulfuric acid pretreatment (H 2 SO 4 , Sc-2). The analysis spans biomass handling, pretreatment, enzymatic hydrolysis, yeast fermentation, and distillation. Sc-1 yielded an environmental impact of 1.45E+01 kPt, predominantly affecting human health (96.55%), followed by ecosystems (3.07%) and resources (0.38%). Bioethanol, xylonic acid, and lignin contributed 32.61%, 29.28%, and 38.11% to the total environmental burdens, respectively. Sc-2 resulted in an environmental burden of 1.64E+01 kPt, with a primary impact on human health (96.56%) and smaller roles for ecosystems (3.07%) and resources (0.38%). Bioethanol, xylonic acid, and lignin contributed differently at 22.59%, 12.5%, and 64.91%, respectively. Electricity generation was predominant in both scenarios, accounting for 99.05% of the environmental impact, primarily driven by its extensive usage in biomass handling and pretreatment processes. Sc-1 demonstrated a 13.05% lower environmental impact than Sc-2 due to decreased electricity consumption and increased bioethanol and xylonic acid outputs. This study highlights the pivotal role of pretreatment methods in wood-based biorefineries and underscores the urgency of sustainable alternatives like TsOH/pentanol. Additionally, adopting greener electricity generation, advanced technologies, and process optimization are crucial for reducing the environmental footprint of waste-based biorefineries while preserving valuable bioproduct production. [Display omitted] • Pinewood biorefinery producing bioethanol, xylonic acid, and lignin are environmentally analyzed. • LCA compares the environmental impacts of monophasic and biphasic pretreatment methods. • TsOH/pentanol pretreatment was environmentally superior to H 2 SO 4 (13.05 % reduction). • Lignin production exhibited the highest environmental burden in both scenarios. • Electricity production was a hotspot in both scenarios, with a share of 99.05 %. [ABSTRACT FROM AUTHOR]

Sugarcane bagasse is an agricultural residue rich in xylose, which may be used as a feedstock for the production of high-value-added chemicals, such as xylonic acid, an organic acid listed as one of the top 30 value-added chemicals on a NREL report. Here, Zymomonas mobilis was engineered for the first time to produce xylonic acid from sugarcane bagasse hydrolysate. Seven coding genes for xylose dehydrogenase (XDH) were tested. The expression of XDH gene from Paraburkholderia xenovorans allowed the highest production of xylonic acid (26.17 ± 0.58 g L−1) from 50 g L−1 xylose in shake flasks, with a productivity of 1.85 ± 0.06 g L−1 h−1 and a yield of 1.04 ± 0.04 gAX/gX. Deletion of the xylose reductase gene further increased the production of xylonic acid to 56.44 ± 1.93 g L−1 from 54.27 ± 0.26 g L−1 xylose in a bioreactor. Strain performance was also evaluated in sugarcane bagasse hydrolysate as a cheap feedstock, which resulted in the production of 11.13 g L−1 xylonic acid from 10 g L−1 xylose. The results show that Z. mobilis may be regarded as a potential platform for the production of organic acids from cheap lignocellulosic biomass in the context of biorefineries.

Candida glycerinogenes , an industrial yeast with excellent multi-stress tolerance, has been applied to glycerol production for decades. However, its genetic manipulation was limited by the absence of meiosis, the diploid genome, and the lack of molecular tools. We described here the implementation of a transient CRISPR-Cas9 system for efficient genome editing in C. glycerinogenes. By targeting the counterselectable marker genes (TRP1 , URA3), single and double gene knock-outs were achieved and the auxotroph obtained can be used as a background for targeting other gene (HOG1) at a mutation efficiency of 80%. Further, a xylonic acid producing C. glycerinogenes strain was constructed by knock-in of the xylose dehydrogenase gene, which produced up to 28 g/L ethanol and 9 g/L xylonic acid simultaneously from simulated lignocellulosic hydrolysate (contained 70 g/L glucose and 24 g/L xylose). These results indicated that the CRSIPR-Cas9 system developed here can facilitate the study of gene functions and metabolic pathways in C. glycerinogenes. [ABSTRACT FROM AUTHOR]

Highlights • Immobilized whole-cell G. oxydans could be efficiently reused for XA production. • POA-SSB can improve the production efficiency of XA with immobilized cells. • 276.5 g/L XA was produced in 48 h by fed-batch fermentation in the POA-SSB. • Successive XA production was achieved by coupling electrodialysis and POA-SSB. Abstract Immobilized whole-cell fermentation has been proven to be an effective method to improve the performance and cost-effectiveness of Gluconobacter oxydans ATCC 621. In the bio-oxidation of xylose to xylonic acid, the oxygen supply through the immobilized beads is a well-known factor that limits the biocatalytic performance of Gluconobacter oxydans as obligate aerobic bacteria. The activity of immobilized cells could be efficiently improved by execution of pressurized pure oxygen supply strategy. Subsequently, in order to further enhance the production efficiency of xylonic acid and reduce end-product inhibition, online-electrodialysis was employed. Finally, a design of pressurized oxygen supply bioreactor combining with online-electrodialysis was put forward for implementing successive production of xylonic acid. The central features of this a highly integrated design are feasible and thus might enable cost-competitive bacterial xylonic acid production. [ABSTRACT FROM AUTHOR]

Preparation of xylonic acid from xylonate fermentation broth was studied in a four-chamber bipolar membrane electrodialysis (BMED) setup. The effects of metal-ion size, current density, and xylonate concentration on BMED were evaluated principally with respect to acid yield and partially with respect to efficiency and energy consumption. Sodium xylonate was more successful than potassium xylonate because of its smaller size and easier membrane penetrability for BMDE. Efficient electrodialysis was achieved using 50 mA/cm2 current density for 14 min; thus, we obtained 92% xylonic acid from 100 g/L sodium xylonate fermentation broth. In conclusion, BMED can be used for producing xylonic acid from fermentation broth. Moreover, this study highlights ways of improving the efficiency of BMED. [ABSTRACT FROM AUTHOR]

A sustainable and efficient two-stage fermentation was developed to produce gluconic acid (GA) and xylonic acid (XA) from dilute acid pretreated corn stover (DA-CS) using Gluconobacter oxydans. Cells (6.2 g/L) were obtained after four cycles of fermentation in DA-CS enzyme hydrolysate at 50 ml scale in a shake flask. With each cycle showing complete utilization of glucose with GA productivity rate at 5.3 g/L/h. The enriched cells were then collected and used to ferment DA-CS liquid stream (generated during pretreatment containing mostly xylose) at 50 ml scale in a shake flask to produce XA at a rate of 1.9 g/L/h. Subsequently, the process was scaled up to 1 L. Both GA and XA was produced at the rate of 8.7 g/L/h and 3.7 g/L/h respectively in 36 h. From 1 kg of corn stover we were able to produce 296.2 g GA and 167.4 g XA by two stage fermentation. [ABSTRACT FROM AUTHOR]

The complete valorization of lignocellulosic biomass (LCB) to valuable bio-products with one-step fractionation is still challenging. This study represents sustainable waste-free biorefinery routes for efficient fractionation of LCB, employing a novel pretreatment method using hydrotropic p– toluenesulfonic acid (TsOH) mixed with pentanol. The potential of LCB pretreatment using TsOH/pentanol reagent as lignin absorbent with co-production of bioethanol and xylonic acid was investigated. Biomass pretreatment at 120 °C for 40 min with 20% TsOH dosage was the optimal condition that significantly dissolved more than 88.2% of lignin and 95.1% of hemicellulose in the biphasic phase, while 95.6% of cellulose was retained in the solid phase. Further fermentation of cellulose-rich fraction using Saccharomyces cerevisiae resulted in 225 g kg−1 bioethanol yield. In addition, xylose-rich phase was converted into xylonic acid by Gluconobacter oxydans fermentation with a yield of 202 g kg−1. Importantly, the isolated lignin was altered by acid groups during sulphonation through TsOH/pentanol pretreatment, which makes lignin a potential adsorbent for cationic contaminants in wastewater. In particular, the isolated lignin achieved high adsorption capacity (300 mg/g) of methylene blue. The proposed biorefinery routes showed a high net positive energy of 3.65 MJ kg−1 dry biomass with an energy ratio of 1.70. Therefore, this study provides an innovative synergistic pretreatment using TsOH/pentanol as a promising fractionation process for efficient cascade valorization of LCB into valuable bio-products. [Display omitted] • A novel TsOH/pentanol pretreatment was introduced for complete valorization of LCB. • Cellulose-rich fraction obtained a bioethanol yield of 225 g kg−1. • Xylose-rich phase converted into xylonic acid with a yield of 202 g kg−1. • Modified lignin showed excellent adsorption of methylene blue (300 mg/g). • Proposed biorefinery routes showed a high net positive energy of 3.65 MJ kg−1. [ABSTRACT FROM AUTHOR]

A novel bio-refinery sequence yielding varieties of co-products was developed using straw pulping solid residue. This process utilizes neutral sulfite pretreatment which under optimal conditions (160 °C and 3% (w/v) sulfite charge) provides 64.3% delignification while retaining 90% of cellulose and 67.3% of xylan. The pretreated solids exhibited excellent enzymatic digestibility, with saccharification yields of 86.9% and 81.1% for cellulose and xylan, respectively. After pretreatment, the process of semi-simultaneous saccharification and fermentation (S-SSF) and bio-catalysis was investigated. The results revealed that decreased ethanol yields were achieved when solid loading increased from 5% to 30%. An acceptable ethanol yield of 76.8% was obtained at 20% solid loading. After fermentation, bio-catalysis of xylose remaining in fermentation broth resulted in near 100% xylonic acid (XA) yield at varied solid loadings. To complete the co-product portfolio, oxidation ammoniation of the dissolved lignin successfully transformed it into biodegradable slow-release nitrogen fertilizer with excellent agricultural properties. [ABSTRACT FROM AUTHOR]

The thermodynamic dissociation constants of xylonic acid and gluconic acid were studied via potentiometric methods, and the results were verified using lactic acid, which has a known p Ka value, as a model compound. Solutions of xylonic acid and gluconic acid were titrated with a standard solution of sodium hydroxide. The determined p Ka data were processed via the method of derivative plots using computer software, and the accuracy was validated using the Gran method. The dissociation constants associated with the carboxylic acid group of xylonic and gluconic acids were determined to be p Ka = 3.56 ± 0.07 and p Ka = 3.74 ± 0.06, respectively. Further, the experimental data showed that the second deprotonation constants associated with a hydroxyl group of each of the two acids were p Ka = 8.58 ± 0.12 and p Ka = 7.06 ± 0.08, respectively. The deprotonation behavior of polyhydroxy carboxylic acids was altered using various ratios with Cu(II) to form complexes in solution, and this led to proposing a hypothesis for further study. [ABSTRACT FROM AUTHOR]

Oxygen supply for microbial cultures is often identified as a limiting factor for aerobic fermentation. Through implementation of an integrated oxygen control strategy, the high oxygen mass transfer rate satisfied cellular metabolic demands. Gluconobacter oxydans NL71 fermentation of xylose to xylonic acid was improved remarkably. Finally, the productivity of xylonic acid from xylose by biooxidation was markedly increased to 32.5 ± 3.1 g/L/h compared to production levels using conventional laboratory-scale bioreactors. By improving microbial fermentative vitality, we successfully bio-converted 1800 g xylose to 1813 ± 36 g xylonic acid by combination of a fed-batch addition of xylose substrate as well as a cell-recycling strategy. Bioconversion results demonstrated a highly efficient fermentation model that performs continuous bioreaction, assisting the effort to industrialize microbial xylonic acid production. [ABSTRACT FROM AUTHOR]

Efficient utilization (over needless disposal) of biorefinery pre-hydrolysate is an economically relevant practice for improving biorefinery financial prospects. The liquid fraction obtained after acid hydrolysis pretreatment of lignocellulosic biomass, called pre-hydrolysate, are predominantly comprised of hemicellulosic carbohydrates. Using a two-step bioprocess, the hexoses were selectively fermented to ethanol by S. cerevisiae to clear the path for Gluconobacter oxydans transformation of pentoses to a high purity pentonic acids solution. Finally, approximately 180 g pentonic acids and 19 g ethanol could be produced starting from pre-hydrolysate produced from 1 kg corn stover. The results demonstrate execution of our objective to prove this bioconversion method for producing high purity pentonic acids starting from crude lignocellulosic pre-hydrolysate, a wastefully disregarded biorefinery process stream. [ABSTRACT FROM AUTHOR]

With Zn(II)-selective inhibition on the whole-cell catalysis of Gluconobacter oxydans NL71, gluconic acid and xylonic acid were coproduced efficiently from the hydrolysate of corn stover. Further metabolism of gluconic acid to the by-product 2-ketogluconic acid was prevented by addition of 10 g/L ZnCl 2 . Remarkably, yields of 93.91% of gluconic acid and 93.36% of xylonic acid were obtained with the supplement of ZnCl 2 in the synthetic medium, without by-product production. After optimization of the concentrations of ZnCl 2 and inocula of the strain, maximum amounts of gluconic acid and xylonic acid were coproduced at titers of 63.01 g/L and 33.81 g/L, with an overall utilization of 100% of the sugars in the enzymatic hydrolysate of corn stover. The results showed execution of our objective to prove this novel bioconversion method for simultaneously producing gluconic acid and xylonic acid, which would benefit subsequent studies on the comprehensive utilization of lignocellulosic materials. [ABSTRACT FROM AUTHOR]

In this work, an easily implemented and cost-effective activated carbon (AC) enhanced technique was proposed for C5 sugar acid production from corncob hemicellulose hydrolysates. The optimum AC detoxification conditions were obtained by response surface methodology, and the fermentation kinetics behaviors were comparatively evaluated using two fermentation modes: separate detoxification and fermentation (SDF) and in-situ detoxification and fermentation (In-situDF). An investigation of the AC function demonstrates it offers synchronous detoxification and oxygen transfer enhancement, with a final increase of XA fermentation yield and productivity. This study shows a potential of detoxification and oxygen transfer enhancement in one-pot in C5 sugar acid production, which may smooth the way for commercial utilization of C5 sugars from lignocellulosic biomass in the future. • A novel integrated process was developed to produce C5 sugar acid by AC addition. • 100% removal of furfural and HMF coupled with 6.4% xylose loss was achieved. • AC acted as an oxygen transfer enhancement additive, in addition to a detoxifier. • XA production in the in-situDF process reached that of the SDF process. [ABSTRACT FROM AUTHOR]

Efficient production of poly-3-hydroxybutyrate (P(3HB)) based on glucose-xylose mixtures simulating different types of lignocellulosic hydrolysate (LCH) was addressed using Burkholderia sacchari , a wild strain capable of metabolizing both sugars and producing P(3HB). Carbon catabolite repression was avoided by maintaining glucose concentration below 10 g/L. Xylose concentrations above 30 g/L were inhibitory for growth and production. In fed-batch cultivations, pulse size and feed addition rate were controlled in order to reach high productivities and efficient sugar consumptions. High xylose uptake and P(3HB) productivity were attained with glucose-rich mixtures (glucose/xylose ratio in the feed = 1.5 w/w) using high feeding rates, while with xylose-richer feeds (glucose/xylose = 0.8 w/w), a lower feeding rate is a robust strategy to avoid xylose build-up in the medium. Xylitol production was observed with xylose concentrations in the medium above 30–40 g/L. With sugar mixtures featuring even lower glucose/xylose ratios, i.e . xylose-richer feeds (glucose/xylose = 0.5), xylonic acid (a second byproduct) was produced. This is the first report of the ability of Burkholderia sacchari to produce both xylitol and xylonic acid. [ABSTRACT FROM AUTHOR]