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D‐Glucose‐to‐L‐sorbose isomerization on Lewis acidic zeolite is a highly attractive avenue for sorbose production. But the L‐sorbose yield is limited by the competing D‐glucose‐to‐D‐fructose isomerization and reaction equilibrium. In this work, it is suggested that ethanol directs the glucose conformation for selective D‐glucose‐to‐L‐sorbose isomerization. It also reacts with the produced L‐sorbose to form ethyl‐sorboside, which allows the D‐glucose‐to‐L‐sorbose isomerization to proceed beyond the thermodynamic equilibrium limit. It is shown that a bifunctional zeolite Beta containing framework titanium (Ti) and boron (B) is a selective catalyst for this tandem reaction: Lewis acidic framework Ti catalyzes the D‐glucose‐to‐L‐sorbose isomerization via an intramolecular 5,1‐hydride shift process as confirmed by isotopic tracing experiments followed by 13C‐NMR, while weak Brønsted acid framework B selectively promotes the sorbose ketalization with ethanol. A remarkably high yield of L‐sorbose with a high fraction of sugar (>95 %: 27 % unreacted glucose, 11.4 % fructose, 57 % sorbose) was obtained after the mixture produced in ethanol was hydrolyzed. [ABSTRACT FROM AUTHOR]

L-Sorbose is an essential intermediate for the industrial production of vitamin C (L-ascorbic acid). However, the formation of fructose and some unknown by-products significantly reduces the conversion ratio of D-sorbitol to Lsorbose. This study aimed to identify the key D-sorbitol dehydrogenases in Gluconobacter oxydans WSH-003 by gene knockout. Then, a total of 38 dehydrogenases were knocked out in G. oxydans WSH-003, and 23 dehydrogenase-deficient strains could increase L-sorbose production. G. oxydans-30, wherein a pyrroloquinoline quinone-dependent glucose dehydrogenase was deleted, showed a significant reduction of a by-product with the extension of fermentation time. In addition, the highest conversion ratio of 99.60% was achieved in G. oxydans MD-16, in which 16 different types of dehydrogenases were inactivated consecutively. Finally, the gene vhb encoding hemoglobin was introduced into the strain. The titer of L-sorbose was 298.61 g/L in a 5-L bioreactor. The results showed that the systematic engineering of dehydrogenase could significantly enhance the production of L-sorbose. [ABSTRACT FROM AUTHOR]

6-Deoxy-l-sorbose (6-DLS) is an imperative rare sugar employed in food, agriculture, pharmaceutical and cosmetic industeries. However, it is a synthetic and very expensive rare sugars, previously synthesized by chemo-enzymatic methods through a long chain of chemical processes. Recently, enzymatic synthesis of rare sugars has attracted a lot of attention due to its advantages over synthetic methods. In this work, a promising approach for the synthesis of 6-DLS from an inexpensive sugar l-fucose was identified. The genes for l-fucose isomerase from Paenibacillus rhizosphaerae (Pr-LFI) and genes for d-tagatose-3-epimerase from Caballeronia fortuita (Cf-DTE) have been used for cloning and co-expression in Escherichia coli, developed a recombinant plasmid harboring pANY1-Pr-LFI/Cf-DTE vector. The recombinant co-expression system exhibited an optimum activity at 50 °C of temperature and pH 6.5 in the presence of Co 2+ metal ion which inflated the catalytic activity by 6.8 folds as compared to control group with no metal ions. The recombinant co-expressed system was stable up to more than 50 % relative activity after 12 h and revealed a melting temperature (T m ) of 63.38 °C exhibiting half-life of 13.17 h at 50 °C. The co-expression system exhibited, 4.93, 11.41 and 16.21 g/L of 6-DLS production from initial l-fucose concentration of 30, 70 and 100 g/L, which equates to conversion yield of 16.44 %, 16.30 % and 16.21 % respectively. Generally, this study offers a promising strategy for the biological production of 6-DLS from an inexpensive substrate l-fucose in slightly acidic conditions with the aid of co-expression system harboring Pr-LFI and CF-DTE genes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Aqueous‐phase isomerization of d‐glucose to d‐fructose and l‐sorbose is catalyzed in parallel by Lewis acidic Ti sites in siliceous frameworks. Glucose isomerization rates (per Ti, 373 K) are undetectable when Ti sites are confined within mesoporous voids (Ti‐MCM‐41, TiO2‐SiO2) and increase to detectable values when Ti sites are confined within the smaller 12‐membered ring (12‐MR) micropores of Ti‐Beta. Isomerization rates decrease to lower values (by ≈20×) with further decreases in micropore size as Ti sites are confined within 10‐MR pores (Ti‐MFI, Ti‐CON), likely because of intrapore reactant diffusion restrictions, and reach undetectable values within the 8‐MR pores of Ti‐CHA as size exclusion prevents glucose from accessing active sites. Remarkably, the selectivity toward l‐sorbose over d‐fructose increases systematically as spatial constraints around Ti sites become tighter, and is >10 on Ti‐MFI. These findings demonstrate the marked influence of confinement around Ti active sites on the selectivity between parallel stereoselective sugar isomerization pathways. [ABSTRACT FROM AUTHOR]

We have studied mutarotation in anhydrous supercooled L-sorbose by means of dielectric spectroscopy. The phenomenon observed in L-sorbose is much faster than in the structurally similar D-fructose. The kinetics of this process has been determined by applying 1st order kinetics model. Activation energy equal to 68 kJ/mol was obtained from temperature dependence of rate constants. To understand differences in mutarotation rate between D-fructose and L-sorbose, quantum mechanical calculations were performed to study mechanism of this phenomenon. The possible impact of water absorbed from air on the mutarotation in supercooled liquid state has been checked. It turned out that the process is probably intermolecular and the water molecules or other carbohydrate molecules assist in the proton transfer process. Finally we have shown that the rate constant can be alternatively determined from frequency of the maximum of peak, obtained by performing Fourier transform of kinetic curve. [ABSTRACT FROM AUTHOR]

The stable and complex EPR signals produced by the action of ionizing radiation on crystalline L-sorbose (C6H12O6) separated from rowan berries (Sorbus aucuparia) were studied. Isothermal heating of the samples at the temperature close to the melting point of L-sorbose (140°C) results in the modification and simplification of the EPR signal involved. In the EPR signal of heated L-sorbose, the isotropic quartet was distinguished. In the differential spectrum obtained by subtraction of normalized spectra of unheated and heated L-sorbose, the isotropic doublet was identified in addition. The DFT fitting offers the probable assignment of the EPR signals to specific radical structures.

Highlights • COS-SSB can improve the productivity of sorbose by enhanced oxygen supply. • 432.8 g/L sorbose and 8.8 g/L biomass can be obtained in 1 L broth within 72 h. • Successive biomass and sorbose production is well conducted in COS-SSB. Abstract High-efficiency cell proliferation of Gluconobacter oxydans was carried out in a compressed oxygen supply and sealed bioreactor to co-produce biomass and corresponding metabolite (sorbose). Higher cell density of Gluconobacter oxydans was achieved by implementing high-oxygen tension supply strategy resulting into high sorbose production from bio-oxidation of sorbitol. The highest biomass of 8.8 g/L and highest sorbose production of 432.8 g/L were simultaneously obtained after 72 h of fed-batch operation. Moreover, continuous co-production of biomass and sorbose was successfully conducted with retaining 10% sorbitol fermentation broth as the seed of next stage culture. The key features of this bioprocess application would enable cost-competitive Gluconobacter oxydans industrial applications. [ABSTRACT FROM AUTHOR]

ABSTRACT Thermotolerant microorganisms are beneficial to the fermentation industry because they reduce the need for cooling and offer other operational advantages. Previously, we obtained a thermally adapted Gluconobacter frateurii strain by experimental evolution. In the present study, we found only a single G insertion in the adapted strain, which causes a frameshift in a gene encoding a putative drug transporter. A mutant derivative strain with the single G insertion in the transporter gene (Wild-G) was constructed from the wild-type strain and showed increased thermotolerance. We found that the thermotolerant strains accumulated substantial intracellular trehalose and manifested a defect in sorbose assimilation, suggesting that the transporter is partly involved in trehalose efflux and sorbose uptake and that the defect in the transporter can improve thermotolerance. The ΔotsAB strain, constructed by elimination of the trehalose synthesis gene in the wild type, showed no trehalose production but, unexpectedly, much better growth than the adapted strain at high temperatures. The ΔotsAB mutant produced more acetate as the final metabolite than the wild-type strain did. We hypothesized that trehalose does not contribute to thermotolerance directly; rather, a metabolic change including increased carbon flux to the pentose phosphate pathway may be the key factor. The NADPH/NADP+ ratio was higher in strain Wild-G, and much higher in the ΔotsAB strain, than in the wild-type strain. Levels of reactive oxygen species (ROS) were lower in the thermotolerant strains. We propose that the defect of the transporter causes the metabolic flux to generate more NADPH, which may enhance thermotolerance in G. frateurii. IMPORTANCE The biorefinery industry has to ensure that microorganisms are robust and retain their viability and function at high temperatures. Here we show that Gluconobacter frateurii, an industrially important member of the acetic acid bacteria, exhibited enhanced thermotolerance through the reduction of trehalose excretion after thermal adaptation. Although intracellular trehalose may play a key role in thermotolerance, the molecular mechanisms of action of trehalose in thermotolerance are a matter of debate. Our mutated strain that was defective in trehalose synthase genes, producing no trehalose but a larger amount of acetic acid as the end metabolite instead, unexpectedly showed higher thermotolerance than the wild type. Our adapted and mutated thermotolerant strains showed increased NADPH/NADP+ ratios and reductions in ROS levels. We concluded that in G. frateurii, treha-lose does not contribute to thermotolerance directly; rather, the metabolic change increases the NADPH/NADP+ ratio to enhance thermotolerance. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Rare sugars including d‐allulose, d‐tagatose, and d‐sorbose are present in limited quantities in nature; some of these rare sugars are now commercially produced using microbial enzymes. Apart from the anti‐obesity and anti‐hyperglycaemic activities of d‐allulose, effects of these sugars on lipid metabolism have not been investigated. Therefore, we aimed to determine if and how d‐tagatose and d‐sorbose modulate lipid metabolism in rats. After feeding these rare sugars to rats, parameters on lipid metabolism were determined. RESULTS: No diet‐related effects were observed on body weight and food intake. Hepatic lipogenic enzyme activity was lowered by d‐allulose and d‐sorbose but increased by d‐tagatose. Faecal fatty acid excretion was non‐significantly decreased by d‐allulose, but significantly increased by d‐sorbose without affecting faecal steroid excretion. A trend toward reduced adipose tissue weight was observed in groups fed rare sugars. Serum adiponectin levels were decreased by d‐sorbose relative to the control. Gene expression of cholesterol metabolism‐related liver proteins tended to be down‐regulated by d‐allulose and d‐sorbose but not by d‐tagatose. In the small intestine, SR‐B1 mRNA expression was suppressed by d‐sorbose. CONCLUSION: Lipid metabolism in rats varies with rare sugars. Application of rare sugars to functional foods for healthy body weight maintenance requires further studies. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

2-Keto-L-gulonic acid (the precursor of vitamin C) is bio-converted from L-sorbose by mixed fermentation of Ketogulonicigenium vulgare and a helper strain. The helper strain promotes the conversion of 2-KLG by enhancing the growth of K. vulgare, but its growth is greatly inhibited by high concentration of L-sorbose, which consequently influence the 2-KLG production. The aim of this study is to obtain L-sorbose-tolerant helper strain (LHS) by experimental evolution for reduced L-sorbose-inhibition-effect and enhanced 2-KLG productivity in high concentration of L-sorbose. After three steps screening by using our devised screening strategy, three strains (i.e., Bc 21, Bc 47, Bc 50) with high resistance to high concentration of L-sorbose were obtained. The fermentation tests by co-culturing Bc 21 and K. vulgare 418 showed that the production of 2-KLG was increased by 17.9% in 11% L-sorbose medium than that in 8% after 55 h of fermentation and the conversion rate was 89.5%. The results suggested that Bc 21 could be an ideal helper strain for 2-KLG production under high concentration of L-sorbose and demonstrated the feasibility of using experimental evolution to breed LHS for vitamin C production. [ABSTRACT FROM AUTHOR]

1-Deoxynojirimycin (1-DNJ) is a glycoprocessing inhibitor, and it serves as a synthetic precursor to two of three currently marketed iminosugar drugs, miglustat (N-butyl DNJ/Zavesca®) and miglitol (Glyset®). Herein a continuous flow procedure is presented that shortens a synthesis of 1-DNJ from an intermediate prepared from l-sorbose. Batch reactions involving an azide reduction, subsequent reductive amination-based cyclisation, and O-benzyl deprotection in a previous report required two steps and the use of an acid. Here, this sequence is achieved in one step using the H-Cube® MiniPlus continuous flow reactor. Subsequent reductive amination of 1-DNJ with butanal using the H-Cube® gave NB-DNJ., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jack Bennett reports financial support was provided by Pfizer Ringaskiddy Ireland., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

One-step fermentation to produce 2-keto-l-gulonic acid (2-KLG), the precursor of vitamin C, is a long-term goal. Improvement of the enzyme's activity through engineering could benefit 2-KLG production. This study aimed to conduct a semi-rational design of l-sorbose dehydrogenase (SDH) through structure-directed, to screen mutants that could enhance the 2-KLG titer. First, the predicted structure of SDH was obtained using AlphaFold2. The key mutation sites in the substrate pocket were identified by Ala scanning. Subsequently, the mutant V336I/V368A was obtained by iterative saturation mutagenesis, which increased the yield of 2-KLG 1.9-fold. Finally, 5.03 g/L of 2-KLG was obtained by a two-stage temperature control fermentation method, and the conversion rate was 50%. Furthermore, experiments showed that knockdown of the l-sorbose-associated phosphotransferase system delays 2-KLG production. The results show that the production of 2-KLG was effectively increased through a combination of SDH engineering and fermentation optimization., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Improving the yield of 2-keto- l-gulonic acid (2-KGA), the direct precursor of vitamin C, draws more and more attention in industrial production. In this study, we try to increase the 2-KGA productivity by computer-aided selection of genes encoding l-sorbose dehydrogenases (SDH) of Ketogulonicigenium vulgare. First, six SDHs were modeled by docking strategy to predict the binding mode with co-factor PQQ. The binding energy between SSDA1-H/SSDA1-L and PQQ was the highest, followed by SSDA3/SSDA2. The binding energy between SSDA1-P/SSDB and PQQ was the lowest. Then, these genes were overexpressed, respectively, in an industrial strain K. vulgare HKv604. Overexpression of ssda1- l and ssda1- h enhanced the 2-KGA production by 7.89 and 12.56 % in mono-cultured K. vulgare, and by 13.21 and 16.86 % when K. vulgare was co-cultured with Bacillus endophyticus. When the engineered K. vulgare SyBE_Kv000116013 (overexpression of ssda1- p) or SyBE_Kv000116016 (overexpression of ssdb) was co-cultured with B. endophyticus, the 2-KGA production decreased significantly. The docking results were in accordance with the experimental data, which indicated that computer-aided modeling is an efficient strategy for screening more efficient enzymes. [ABSTRACT FROM AUTHOR]

A two-step enzymatic strategy for the efficient and convenient synthesis of 6-deoxy- l -sorbose was reported herein. In the first reaction step, the isomerization of l -fucose (6-deoxy- l -galactose) to l -fuculose (6-deoxy- l -tagatose) catalyzed by l -fucose isomerase (FucI), and the epimerization of l -fuculose to 6-deoxy- l -sorbose catalyzed by d -tagatose 3-epimerase (DTE) were coupled with the targeted phosphorylation of 6-deoxy- l -sorbose by fructose kinase from human (HK) in a one-pot reaction. The resultant 6-deoxy- l -sorbose 1-phosphate was purified by silver nitrate precipitation method. In the second reaction step, the phosphate group of the 6-deoxy- l -sorbose 1-phosphate was hydrolyzed with acid phosphatase (AphA) to produce 6-deoxy- l -sorbose in 81% yield with regard to l -fucose. [ABSTRACT FROM AUTHOR]

Pyrroloquinoline quinone (PQQ) is a cofactor of various membrane-bound dehydrogenases. The amount of endogenous PQQ is generally regarded as a bottleneck to achieving higher catalytic efficiency of PQQ-dependent dehydrogenases. Proteins that biosynthesize PQQ in Gluconobacter oxydans WSH-003 are encoded by the pqqABCDE gene cluster and the tldD gene. In this study, PQQ overproduction in G. oxydans was attempted by overexpressing PQQ biosynthetic genes using the promoter of pqqA and the elongation factor TU ( tufB ). Overexpression of each single gene could enhance PQQ biosynthesis except for the tldD gene. Overexpression of pqqA , pqqB , pqqC , pqqD and pqqE with the pqqA promoter enhanced the extracellular PQQ concentration by 38.5%, 68.4%, 19.9%, 30.3% and 8.2%, respectively, whereas production was enhanced by 59.4%, 85.7%, 30.9%, 42.2% and 19.3%, respectively, using the tufB promoter. In addition, the results show that PQQ biosynthesis could be enhanced by overexpressing some of the individual genes in the gene cluster in G. oxydans and the PQQ levels were positively correlated with the efficiency of conversion of d -sorbitol to l -sorbose. The results demonstrated that cofactor engineering of PQQ in G. oxydans is beneficial for enhancing the production of quinoprotein-related products. [ABSTRACT FROM AUTHOR]

The use of l-sorbose in the synthesis of functionalized cyclopentene derivatives was accomplished. These cyclopentene derivatives are related to those found in naturally occurring jatrophane frameworks and in other bioactive compounds. The formation of allyl α- l-sorbopyranoside was a key synthetic step. Regioselective introduction of protecting groups was followed by the hydrolysis of the allyl glycoside to furnish a fully protected acyclic l-sorbose derivative. This acyclic intermediate was subsequently used to give an orthogonally protected polyhydroxylated cyclopentene, which has potential for further synthesis of bioactive compounds. The protected cyclopentene itself showed a clear cytotoxic activity when tested against a panel of human cancer cell lines (HT29, LS174T, SW620, A549, and HeLa cells). [ABSTRACT FROM AUTHOR]

We developed an in vitro method to assess pet food ingredients safety. Canine bone marrow-derived mesenchymal stem cells (BMSC) were differentiated into enterocyte-like cells (ELC) to assess toxicity in cells representing similar patterns of exposure in vivo. The toxicological profile of clove leave oil, eugenol, guanosine monophosphate (GMP), GMP+ inosine monophosphate, sorbose, ginger root extract, cinnamon bark oil, cinnamaldehyde, thyme oil, thymol and citric acid was assessed in BMSC and ELC. The LC50 for GMP+ inosine monophosphate was 59.42 ± 0.90 and 56.7± 3.5mgml-1 for BMSC and ELC; 56.84 ± 0.95 and 53.66± 1.36mgml-1 for GMP; 0.02 ± 0.001 and 1.25± 0.47mgml-1 for citric acid; 0.077 ± 0.002 and 0.037 ± 0.01mgml-1 for cinnamaldehyde; 0.002 ± 0.0001 and 0.002 ± 0.0008mgml-1 for thymol; 0.080 ± 0.003 and 0.059 ± 0.001mgml-1 for thyme oil; 0.111 ± 0.002 and 0.054 ± 0.01mgml-1 for cinnamon bark oil; 0.119 ± 0.0004 and 0.099 ± 0.011mgml-1 for clove leave oil; 0.04 ± 0.001 and 0.028 ± 0.002mg ml-1 for eugenol; 2.80 ± 0.11 and 1.75 ± 0.51mgml-1 for ginger root extract; > 200 and 116.78 ± 7.35mgml-1 for sorbose. Lemon grass oil was evaluated at 0.003-0.9 in BMSC and .03-0.9 mgml-1 in ELC and its mechanistic effect was investigated. The gene toxicology studies showed regulation of 61% genes in CYP450 pathway, 37% in cholestasis and 33% in immunotoxicity pathways for BMSC. For ELC, 80% for heat shock response, 69% for beta-oxidation and 65% for mitochondrial energy metabolism. In conclusion, these studies provide a baseline against which differential toxicity of dietary feed ingredients can be assessed in vitro for direct effects on canine cells and demonstrate differential toxicity in differentiated cells that represent gastrointestinal epithelial cells. [ABSTRACT FROM AUTHOR]

Background: In the industry, the conventional two-step fermentation method was used to produce 2-keto-L-gulonic acid (2-KGA), the precursor of vitamin C, by three strains, namely, Gluconobacter oxydans, Bacillus spp. and Ketogulonicigenium vulgare. Despite its high production efficiency, the long incubation period and an additional second sterilization process inhibit the further development. Therefore, we aimed to reorganize a synthetic consortium of G. oxydans and K. vulgare for one-step fermentation of 2-KGA and enhance the symbiotic interaction between microorganisms to perform better. Results: During the fermentation, competition for sorbose of G. oxydans arose when co-cultured with K. vulgare. In this study, the competition between the two microbes was alleviated and their mutualism was enhanced by deleting genes involved in sorbose metabolism of G. oxydans. In the engineered synthetic consortium (H6 + Kv), the yield of 2-KGA (mol/mol) against d-sorbitol reached 89.7 % within 36 h, increased by 29.6 %. Furthermore, metabolomic analysis was used to verify the enhancement of the symbiotic relationship and to provide us potential strategies for improving the synthetic consortium. Additionally, a significant redistribution of metabolism occurred by co-culturing the K. vulgare with the engineered G. oxydans, mainly reflected in the increased TCA cycle, purine, and fatty acid metabolism. Conclusions: We reorganized and optimized a synthetic consortium of G. oxydans and K. vulgare to produce 2-KGA directly from d-sorbitol. The yield of 2-KGA was comparable to that of the conventional two-step fermentation. The metabolic interaction between the strains was further investigated by metabolomics, which verified the enhancement of the mutualism between the microbes and gave us a better understanding of the synthetic consortium. [ABSTRACT FROM AUTHOR]

We biosynthesized 6-deoxy- l -talose, 6-deoxy- l -sorbose, 6-deoxy- l -gulose, and 6-deoxy- l -idose, which rarely exist in nature, from l -fucose by coupling and sequential enzymatic reactions. The first product, 6-deoxy- l -talose, was directly produced from l -fucose by the coupling reactions of immobilized d -arabinose isomerase and immobilized l -rhamnose isomerase. In one-pot reactions, the equilibrium ratio of l -fucose, l -fuculose, and 6-deoxy- l -talose was 80:9:11. In contrast, 6-deoxy- l -sorbose, 6-deoxy- l -gulose, and 6-deoxy- l -idose were produced from l -fucose by sequential enzymatic reactions. d -Arabinose isomerase converted l -fucose into l -fuculose with a ratio of 88:12. Purified l -fuculose was further epimerized into 6-deoxy- l -sorbose by d -allulose 3-epimerase with a ratio of 40:60. Finally, purified 6-deoxy- l -sorbose was isomerized into both 6-deoxy- l -gulose with an equilibrium ratio of 40:60 by l -ribose isomerase, and 6-deoxy- l -idose with an equilibrium ratio of 73:27 by d -glucose isomerase. Based on the amount of l -fucose used, the production yields of 6-deoxy- l -talose, 6-deoxy- l -sorbose, 6-deoxy- l -gulose, and 6-deoxy- l -idose were 7.1%, 14%, 2%, and 2.4%, respectively. [ABSTRACT FROM AUTHOR]

Pt nanoparticles were prepared by a sol immobilization route, deposited on supports with different acid/base properties (MgO, activated carbon, TiO2, Al2O3, H-Mordenite), and tested in the selective oxidation of sorbose to 2-keto-gulonic acid (2- KGUA), an important precursor for vitamin C. In general, as the basicity of the support increased, a higher catalytic activity occurred. However, in most cases, a strong deactivation was observed. The best selectivity to 2-KGUA was observed with acidic supports (TiO2 and H-Mordenite) that were able to minimize the formation of C1/C2 products. We also demonstrated that, by alloying Pt to Au, it is possible to enhance significantly the selectivity of Pt-based catalysts. Moreover, the AuPt catalyst, unlike monometallic Pt, showed good stability in recycling because of the prevention of metal leaching during the reaction. [ABSTRACT FROM AUTHOR]

• SDH_1927 has the highest specific activity (56.72 ± 1.2 U/mg) among the eight L-sorbose dehydrogenases. • The 2-KGA production can be significantly increase by PMS under the condition of avoiding light. • The product 2-KGA could inhibit SDH activity by competing for the same hydrogen bonding sites with the substrate of L-sorbose. • The cell-recycling catalysis system is proposed to convert L-sorbose to 2-KGA, with the yield of 80.12 g/L and the productivity of 6.68 g/L/h. There are five L-sorbose dehydrogenases (SDH_2764, SDH_2744, SDH_0718, SDH_1927, SDH_0337) in Ketogulonicigenium vulgare SPU B805 and three L-sorbose dehydrogenases (SDH_02251, SDH_02271, SDH_P100164) in K. robustum SPU_B003, which play essential roles in the classical two-step fermentation for 2-keto-L-gulonic acid (2-KGA, the precursor of vitamin C) synthesis. In this work, the above eight SDH enzymes were cloned and purified, and their optimal pH values and reaction temperatures, kinetic properties (K m and K cat), thermal stabilities, substrate spectra, and effects of metal ions were determined. Eight SDH-harboring recombinant E.coli strains were verified to be capable to catalyze L-sorbose to 2-KGA. Additionally, the molecular docking results showed that the product 2-KGA could inhibit SDH activity by competing for the same hydrogen bonding sites with substrate L-sorbose. Finally, a novel and efficient whole-cell recycling catalysis system to overcome the product inhibition was proposed, the yield of 2-KGA reached up to 80.12 g/L with the productivity of 6.68 g/L/h. The results provide a promising prospect for selection and modification sorbose dehydrogenase for construction a one-step biotransformation system of 2-KGA. [Display omitted] [ABSTRACT FROM AUTHOR]

Glucotoxicity, impaired insulin secretion, suppression of insulin gene expression, and apoptosis, in pancreatic β-cells caused by chronic hyperglycemia is a key component of the pathogenesis of type 2 diabetes. Recently, it has been reported that rare sugar d-allulose has antihyperglycemic and antihyperlipidemic effects in diabetic rats. However, the direct effects of rare sugars including d-allulose on pancreatic β-cell function are unclear. In this study, we investigated whether chronic exposure to ketohexoses causes glucotoxicity, suppression of insulin gene expression, and apoptosis, in INS-1 rat pancreatic insulinoma cells. d-Fructose, d-tagatose, l-allulose, and l-sorbose treatment for 1-week reduced insulin gene expression, whereas d-allulose, d-sorbose, l-fructose, and l-tagatose did not. All ketohexoses were transported into INS-1 cells, but were not metabolized. In addition, the ketohexoses did not induce apoptosis and did not affect glucose metabolism. These results suggest that long-term administration of d-allulose, d-sorbose, l-fructose, and l-tagatose does not affect pancreatic β-cell function., (© The Author(s) 2022. Published by Oxford University Press on behalf of Japan Society for Bioscience, Biotechnology, and Agrochemistry.)

α,α-Disubstituted piperidinesand conformationallyconstrained polyhydroxylated indolizidines bearing a hydroxymethylsubstituent in position 8a were synthesized from a readily available l-sorbose-derived ketonitrone. Diastereoselective vinylationunder two sets of complementary conditions allowed access to bothconfigurations of the newly formed quaternary stereocenter. Subsequent N-allylation and ring-closing metathesis afforded 8a-branchedindolizidines in high yield. The newly prepared iminosugars demonstratedhighly potent inhibition of α-glucosidases. Most interestingly,compound 9bexhibits very high selectivity toward thisclass of enzymes, with an unusual mode of binding. [ABSTRACT FROM AUTHOR]

The article discusses the results of a study revealing an NADPH (nicotinamide adenine dinucleotide phospate)-dependent sorbose reductase (SOU1) from Candida albicans to catalyze the reduction of ethyl 4-chloro-3-oxobutanoate (COBE). Topics mentioned include SOU1 activity toward COBE, bioconversion of COBE to (S)-CHBE with two coexisting Escherichia coli strains, and the effect of cell mass ratio on (S)-CHBE yield.

Gluconobacter oxydans is capable of rapidly incomplete oxidation of many sugars and alcohols, which means the strain has great potential for industrial purposes. Strong promoters are one of the essential factors that can improve strain performance by overexpression of specific genes. In this study, a pipeline for screening strong promoters by proteomics analysis was established. Based on the procedure, a new strong promoter designated as P was identified in G. oxydans WSH-003. The promoter region was characterized based on known genome sequence information using BPROM. The strength of P was further assessed by analysis of enhanced green fluorescent protein ( egfp) expression and comparison with egfp expression by two commonly used strong promoters, P and P. Both quantitative real-time PCR and fluorescence intensities for egfp gene expression showed that P promoter is stronger than the other two. Overexpression of d-sorbitol dehydrogenase ( sldh) by P in G. oxydans WSH-003 enhanced the titer and productivity of l-sorbose synthesis from d-sorbitol by 12.0 % and 33.3 %, respectively. These results showed that proteomics analysis is an efficient way to identify strong promoters. The isolated promoter P could further facilitate the metabolic engineering of G. oxydans. [ABSTRACT FROM AUTHOR]

The property of loose stereochemical control at aldol products from aldolases helped to synthesize multiple polyhydroxylated compounds with nonnatural stereoconfiguration. In this study, we discovered for the first time that some fructose 1,6-diphosphate aldolases (FruA) and tagatose 1,6-diphosphate (TagA) aldolases lost their strict stereoselectivity when using L-glyceraldehyde and synthesized not only L-sorbose but also a high proportion of L-psicose. Among the aldolases tested, TagA from Bacillus licheniformis (BGatY) showed the highest enzyme activity with L-glyceraldehyde. Subsequently, a "one-pot" reaction based on BGatY and fructose-1-phosphatase (YqaB) generated 378 mg/liter L-psicose and 199 mg/liter L-sorbose from dihydroxyacetonephosphate (DHAP) and L-glyceraldehyde. Because of the high cost and instability of DHAP, a microbial fermentation strategy was used further to produce L-sorbose/L-psicose from glucose and L-glyceraldehyde, in which DHAP was obtained from glucose through the glycolytic pathway, and some recombination pathways based on FruA or TagA and YqaB were constructed in Escherichia coli and Corynebacterium glutamicum strains. After evaluation of different host cells and combinations of FruA or TagA with YqaB and optimization of gene expression, recombinant C. glutamicum strain WT(pXFTY) was selected and produced 2.53 g/liter total ketoses, with a yield of 0.50 g/g L-glyceraldehyde. Moreover, deletion of gene cgl0331, encoding the Zn-dependent alcohol dehydrogenase in C. glutamicum, was confirmed for the first time to significantly decrease conversion of L-glyceraldehyde to glycerol and to increase yield of target products. Finally, fed-batch culture of strain SY14(pXFTY) produced 3.5 g/liter L-sorbose and 2.3 g/liter L-psicose, with a yield of 0.61 g/g L-glyceraldehyde. This microbial fermentation strategy also could be applied to efficiently synthesize other L-sugars. [ABSTRACT FROM AUTHOR]

An optimal scheduling approach for the 2-keto-L-gulonic acid (2-KGA) fermentation process is proposed to improve allocation of L-sorbose resources with the aim of profit maximization in a multi-bioreactor workshop. The empirical operation in 2-KGA cultivation under study is to assign the same quantity of L-sorbose to each batch without taking batch-to-batch variations into account, while the optimal scheduling approach presented in this paper will determine L-sorbose feeding according to the evaluation of the profit-making ability of the individual batch. Each 2-KGA batch is classified online according to the prediction of the profit function, so that each batch is assigned into different profit-making categories. Pseudo-online scheduling is implemented with the data of industrial 2-KGA cultivations. A total profit increase of 6-7 % is found to be achievable for the workshop in comparison with the empirical operation. [ABSTRACT FROM AUTHOR]

The co-culture system of the fermentation process of vitamin C can be regarded as an artificial microbial ecosystem (AME). To extend our understanding of this AME, an investigation of the relationship between strains, substrate and product was carried out in this study. The results showed that both Ketogulonicigenium vulgare and 2-keto- l-gulonic acid (2-KLG, the precursor of vitamin C) can inhibit the growth of the helper strain, while the helper strain promoted the growth of K. vulgare and 2-KLG production. Moreover, l-sorbose is not only a substrate for 2-KLG production in the AME, but also a promoter of K. vulgare and an inhibitor of the helper strain. In the earlier stage of fermentation, the inhibition of l-sorbose on the helper strain's growth is a key factor for ensuring an efficient fermentation. In the condition of adding the extra helper strain (OD: 0.57, ratio of inoculation: 2 %), the yields of 2-KLG is increased by 9 % in the 14 % l-sorbose medium. To the best of our knowledge, this is the first report about the inhibition of substrate in the AME of 2-KLG production. [ABSTRACT FROM AUTHOR]

In the current work, the in vitro synthetic system for rare sugars was successfully transformed into an engineeredEscherichia coliwith a plasmid containing both the aldolase RhaD and phosphatase YqaB. By taking advantage of the inherent biosynthetic pathways inE. coli, this approach permits the use of simple and cheap glycerol for the synthesis of DHAP in vivo. Moreover, the introduction of the phosphatase into theE. colisystem allows for the removal of the phosphate group on the synthetic intermediate to yield the neutral rare sugars, which can be readily secreted to the medium without accumulation in the cell. [ABSTRACT FROM AUTHOR]

A new electrocatalytic method for the selective electrochemical oxidation of sorbitol to fructose and sorbose is demonstrated by using a platinum electrode promoted by p-block metal atoms. By the studying a range of C4, C5 and C6 polyols, it is found that the promoter interferes with the stereochemistry of the polyol and thereby modifies its reactivity. [ABSTRACT FROM AUTHOR]

Two rare sugars - 1-deoxy- L-fructose and L-sorbose - were synthesized from inexpensive starting materials by a carbonyl translocation method developed in our laboratory. Reduction of a known starting compound gave a 1,5-diol derivative. Selective protection of the corresponding primary alcohol and oxidation of the secondary alcohol provided the desired product in acyclic, protected form. Subsequent deprotection resulted in the production of 1-deoxy- L-fructose from the known starting material in five steps and in a total yield of 42 %. This approach represents the first report of a chemical synthesis of 1-deoxy- L-fructose. A similar strategy was applied to convert inexpensive D-glucose into L-sorbose, which was prepared in five steps from a known starting material in a total yield of 55 %. The synthetic methods represent a complementary method to biological approaches for the synthesis of vitamin C. [ABSTRACT FROM AUTHOR]

Ndt80p, a known transcriptional factor, regulates various targets involved in stress responses, filamentous growth, and virulence in Candida albicans . Potential targets of Ndt80p have been identified at the transcriptional level. The present study was conducted to identify genes regulated by Ndt80p from the protein level. We found that the levels of Ahp1p, Fma1p, Hsp21p, Rfa2p, Snz1p, Sod1p, Sou1p, Trp99p, orf19.251, orf19.1862, and orf19.5620, were affected by the null mutation of NDT80 by two-dimensional polyacrylamide gel-electrophoresis analysis. Among the 11 proteins, all but Sou1p and Rfa2p are suggested to be involved in known functions of Ndt80p. Here, we demonstrate that Ndt80p plays a role in l -sorbose utilization through regulating SOU1 in C. albicans . [ABSTRACT FROM AUTHOR]