Glucose Conversion Rate Research Articles

Investigating the catalytic influence of MIL-101(Cr) and MIL-101(Cr)-NH2 on glucose dehydration into 5-hydroxymethylfurfural and modelled through response surface methodology

Dehydration of glucose into 5-hydroxymethylfurfural (5-HMF) is an effective approach for generating bio-based chemicals. Metal-organic frameworks (MOFs) are notable catalysts for this process due to their unsaturated metal centers. Functionalized MOFs further enhance these catalytic properties. This study investigates the catalytic abilities of MIL-101(Cr) and MIL-101(Cr)-NH2 for glucose dehydration into 5-HMF using an H2O + DMSO solvent system. Using Response Surface Methodology (RSM), the reaction parameters (temperature, time, and catalyst amount) were optimized to maximize 5-HMF yield. Results showed that at 180 °C, MIL-101(Cr) achieved a 5-HMF yield of 21 % with a selectivity of 22 %, while MIL-101(Cr)-NH2 achieved a 5-HMF yield of 55 % with a selectivity of 56 %. MIL-101(Cr) demonstrated a glucose conversion rate of 92 %, and MIL-101(Cr)-NH2 achieved a conversion rate of 99 % after 3 h at 180 °C. The optimized 5-HMF yield predicted by RSM for MIL-101(Cr) was 53.8 %, whereas the experimentally obtained value was 24.23 %. For MIL-101(Cr)-NH2, the predicted 5-HMF yield was 35.46 %, with an experimental value of 47.51 %. The Lewis acidic nature of MIL-101(Cr) arises from the Cr sites, while MIL-101(Cr)-NH2 exhibits both Lewis acidic characteristics from the Cr sites and Brønsted basic characteristics from the non-coordinated primary amine groups. The experimental results highlight the potential of MIL-101(Cr)-NH2, which produced a higher 5-HMF yield compared to MIL-101(Cr). The dual nature of MIL-101(Cr)-NH2 enhances glucose dehydration to 5-HMF, resulting in significantly higher yields. This study underscores the effectiveness of MIL-101(Cr)-NH2 in converting glucose to 5-HMF, advancing biomass utilization efficiency.

Efficient carbon flux allocation towards D-pantothenic acid production via growth-decoupled strategy in Escherichia coli

For industrial strain construction, rational allocation of carbon flux is of paramount importance especially for decoupling cell growth and chemical productions to get maximum titer, rate, yield (TRY), which become Gordian Knot. Here, a temperature-sensitive switch and genetic circuits was used for effectively decoupling cell growth from D-pantothenic acid (DPA) production, along with systematically metabolic engineering including blocking redundant pathways of pyruvate and enhancing DPA driving force. Afterwards, rapid biomass accumulation only happened during growth stage, and subsequent high-efficient DPA production was initiated with reducing fermentation temperature. Finally, 97.20 g/L DPA and 0.64 g/g glucose conversion rate were achieved in 5-liter fed-batch fermentation. These undisputedly represent a milestone for the biosynthesis of DPA. With using strategies for decoupling cell growth from chemical productions, it would serve as “Alexander’s sword” to cut Gordian Knot to get industrial chassis cells with excellent TRY for de novo biosynthesis of valuable chemicals.

Highly selective oxidation of glucose to formic acid and exploring reaction pathways using continuous flow microreactors

The process of converting glucose into formic acid (FA) has been explored as a promising route for using biomass as a renewable feedstock for green chemical manufacturing. However, the most commonly used batch-tank reactor systems currently suffer from several drawbacks, including extended processing time, limited product selectivity, and high energy consumption, while the underlying reaction paths have been poorly understood. In this work, a continuous flow microchannel reactor was employed for the glucose conversion catalyzed by H5PV2Mo10O40 with O2 as an oxidant. The influence of various parameters on the conversion rate of glucose and the FA yield was characterized. Experimental results indicated that with a residence time of less than 3 min, the glucose was completely converted, and the highest FA yield reached 82.40 %. Extensive examination on the apparent by-products revealed that most of them acted as intermediates to produce FA through various pathways, including glyoxal, glyceraldehyde and glycolaldehyde as key intermediates for the oxidation of glucose to FA. Furthermore, the density functional theory (DFT) method was used to determine the bond energies of different C–C bond cleavage modes of substrate glucose and fructose produced by the isomerization of glucose. Experimentally, the conversion of three main intermediates and some other possible intermediates and their FA yield were measured with different residence time. It was also found that the CO2 was produced through the decarboxylation of α-hydroxy and α-carbonyl carboxylic acid compounds, while the aldehyde groups in the compounds were more likely converted to FA by the α-carbon bond cleavage. Finally, plausible reaction pathways were proposed for the process of glucose-to-FA catalyzed by HPA-2, providing useful guidance for the identification of side reaction pathways and further improvement of FA yield.

Effect of addition of γ-poly glutamic acid on bacterial nanocellulose production under agitated culture conditions.

Bacterial nanocellulose (BNC), a natural polymer material, gained significant popularity among researchers and industry. It has great potential in areas, such as textile manufacturing, fiber-based paper, and packaging products, food industry, biomedical materials, and advanced functional bionanocomposites. The main current fermentation methods for BNC involved static culture, as the agitated culture methods had lower raw material conversion rates and resulted in non-uniform product formation. Currently, studies have shown that the production of BNC can be enhanced by incorporating specific additives into the culture medium. These additives included organic acids or polysaccharides. γ-Polyglutamic acid (γ-PGA), known for its high polymerization, excellent biodegradability, and environmental friendliness, has found extensive application in various industries including daily chemicals, medicine, food, and agriculture. In this particular study, 0.15g/L of γ-PGA was incorporated as a medium additive to cultivate BNC under agitated culture conditions of 120rpm and 30℃. The BNC production increased remarkably by 209% in the medium with 0.15g/L γ-PGA and initial pH of 5.0 compared to that in the standard medium, and BNC production increased by 7.3% in the medium with 0.06g/L γ-PGA. The addition of γ-PGA as a medium additive resulted in significant improvements in BNC production. Similarly, at initial pH levels of 4.0 and 6.0, the BNC production also increased by 39.3% and 102.3%, respectively. To assess the characteristics of the BNC products, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis were used. The average diameter of BNC fibers, which was prepared from the medium adding 0.15g/L γ-PGA, was twice thicker than that of BNC fibers prepared from the control culture medium. That might be because that polyglutamic acid relieved the BNC synthesis from the shear stress from the agitation. This experiment held great significance as it explored the use of a novel medium additive, γ-PGA, to improve the production and the glucose conversion rate in BNC fermentation. And the BNC fibers became thicker, with better thermal stability, higher crystallinity, and higher degree of polymerization (DPv). These findings lay a solid foundation for future large-scale fermentation production of BNC using bioreactors.

Screening of enhanced biohydrogen production from anaerobic fermentation amended with nano-sized barium ferrite supported by aluminum oxide

Anaerobic fermentation has attracted wide attention to effectively reduce carbon footprint and alleviate potential energy shortages, which is being regarded as a sustainable and promising technology to obtain high biohydrogen production from widespread organic wastes. However, biohydrogen commercial uptake is now dominantly inhibited by the low hydrogen yield and process instability. In this work, Al2O3/BaFe2O4 nanoparticles (NPs) are successfully applied to anaerobic fermentation for investigating their effects on hydrogen yield, activity of bacteria and microbial community structure. The benefits of Al2O3/BaFe2O4 NPs with respect to microbial metabolism, reactivity of enzymes and process optimization are systematically researched through batch experiments. In addition, various characterizations are used to verify the physical and chemical properties of Al2O3/BaFe2O4 NPs. The results show that the activity of hydrogenases and microbe metabolism can be significantly inhibited by excess addition of Al2O3/BaFe2O4 NPs (150 mg/L and 200 mg/L) while the optimum addition 100 mg/L of Al2O3/BaFe2O4 NPs can boost the biohydrogen yield by 49% via facilitating microorganism growth and enhancing key enzymatic activities, which indicate that the Al2O3/BaFe2O4 NPs display a beneficial influence on electron transfer efficiency and process stability. The existence of Fe3+, Al3+and Ba2+ derived from the corrosion of Al2O3/BaFe2O4 NPs by organic acids synergistically improve the microbial transmembrane transportation and substrate utilization, which contribute to higher conversion rate of glucose into acetate, butyrate and H2. Meanwhile, the complementary functions of Fe3+ and Al3+ can powerfully shorten the lag phase and promote the glycolysis, which finally accelerate the dark fermentation process. Compared with the control group, Clostridium_sensu_stricto_1 is selectively enriched by the addition of Al2O3/BaFe2O4 NPs, which keep heavily involved in the synthesis of H2. On balance, this study provides an effective strategy to enhance hydrogen productivity and maintain process stability, which offer the valuable information for the sustainable utilization of sewage sludge.

Tolerance of hyperosmolar Candida krusei

The utilization of industrial microorganisms for the conversion of lignocellulose into high value-added chemicals is an essential pathway towards achieving carbon neutrality and promoting sustainable bioeconomy. However, the pretreated lignocellulase hydrolysate often contains various sugars, salts, phenols/aldehydes and other substances, which requires microorganisms to possess strong tolerance for direct fermentation. This study aims to investigate the tolerance of Candida krusei to substrate, salt, and high temperature shock, in order to validate its potential for utilizing the enzymatic hydrolysate of Pennisetum giganteum in seawater for fermentation. The experimental results showed that the adaptively domesticated C. krusei exhibited tolerance to glucose at a concentration of 200 g/L and became a hypertonic strain. When seawater was used instead of freshwater without sterilization, the yield of glycerol in fermentation was 109% higher than that in freshwater with sterilization. Moreover, the combined thermal shock at 32 hours of fermentation and addition of 10 Na2SO3 at 48 hours resulted in a yield of glycerol to glucose 0.37 g/g, which was 225% higher than the control group. By fermenting the enzymatic hydrolysate of P. giganteum pretreated in seawater, the total conversion rate of glucose into glycerol and ethanol reached 0.45 g/g. This study indicates that hypertonic C. krusei exhibits remarkable adaptability to substrate, salt, and temperature. It not only can directly utilize complex lignocellulosic hydrolysates, but also exhibits strong tolerance to them. Therefore, it provides a potential candidate strain for the production of bio-based chemicals using lignocellulosic processes.

Biochar-based solid-acid catalysts for the selective oxidation of glucose to α,β-unsaturated carboxylic acids in water

H2SO4-modified biochar loaded with TiO2nanoparticles (SBC) was synthesized via anoxic pyrolysis of rice straw biomass. This SBC material was employed for the photo-Fenton-like oxidative conversion of D(+)-glucose intoα,β-unsaturated carboxylic acids (UCAs). Varying catalyst and peroxide loadings generated multiple reactive oxygen species (ROS), including •OH and •O2–, as well as photogenerated electrons and holes. Remarkably, a 90.8 % glucose conversion rate was achieved within 4 h, with an overall carboxylic acid production rate of 463.0μ mol.gcat-1.h-1 and 330.3μ mol.gcat-1.h-1 for UCAs, while maintaining a high selectivity of 71 %. This study elucidated the mechanism through UHPLC-MS/MS analysis, demonstrating the potential of SBC for sustainable glucose valorization and renewable chemicals production.

Strategy for production of high-purity rare sugar D-allulose from corn stover

Here, we report a strategy for producing high-value and high-purity rare sugar D-allulose from inexpensive corn stover. To eliminate the negative impact of xylan hydrolysis products on the production of D-allulose, NH4Cl treatment was employed to thoroughly remove xylan from corn stover. By using 0.6 M NH4Cl to treat the corn stover at 160 °C for 1 h, 97.2% of xylan was removed. After the pretreatment, 92% of cellulose in the corn stover was degraded into glucose by CTec2 and 17.9% (close to the theoretical conversion rate) of glucose was further transformed into D-allulose by D-Tagatose 3-epimerase and D-glucose isomerase. After separation and purification through MCK-35 calcium ion resin, followed by freeze-drying, the obtained solid D-allulose had a purity of 99.4%. This study establishes a low-cost and affordable source for D-allulose production, while simultaneously presenting a new direction for enhancing the high-value utilization of lignocellulosic biomass.

Two birds with one stone: A magneto-optical dual-stimuli-responsive intelligent Pickering emulsion for efficient conversion of glucose to 5-hydroxymethylfurfural

The efficient conversion of glucose to 5-hydroxymethylfurfural (HMF) is a critical process for maximizing the value of lignocellulosic biomass. However, the existing systems of binary solvent and ionic liquids (ILs) commonly employed for this conversion often encounter significant interphase mass transfer resistance and exhibit lower utilization efficiency of ILs. Herein, the study presents the precise fabrication of a novel Pickering interfacial catalyst, P(0.8[CL8]-[ILs]2-[SP])@SiO2@Fe3O4 with immobilized magneto-optical bi-sensitizer and Brønsted&di-superimposed-Lewis acid functionalized ILs (B-L-ILs), realized through surface-initiated reversible addition-fragmentation chain transfer polymerization. The construction of an intelligent Pickering emulsion with dual-stimuli-responsive properties was effectively accomplished by accurate manipulation under Vis-light radiation, utilizing P(0.8[CL8]-[ILs]2-[SP])@SiO2@Fe3O4. The presence of this emulsion significantly enhances interphase mass transfer in a binary solvent system, while the incorporation of B-L-ILs at interphase interfaces in Pickering emulsion greatly facilitates the efficient conversion of glucose to HMF. The Pickering interfacial catalyst demonstrates exceptional and unprecedented performance, as evidenced by its ability to achieve a glucose conversion rate of 96.3% and HMF yield of 86.7%. Various characterizations, experimental analyses, and kinetic studies synergistically confirm the efficient conversion of glucose to HMF in the Pickering emulsion. The effective control of Pickering demulsification can be intelligently achieved by simultaneously applying magnetic stimulation and UV-light irradiation, while its catalytic activity remains unaltered even after undergoing five consecutive cycles. This study presents a novel approach to enhance the efficiency of HMF production by combining a cutting-edge Pickering emulsion with B-L-ILs, thereby accomplishing two objectives simultaneously.

Comprehensive insight into synergistic enhancement of nickel and iron doped lanthanum manganese oxide for biohydrogen production via anaerobic fermentation

Anaerobic fermentation offers an effective strategy to produce H2 from organic wastes, which facilitates waste utilization and the development of sustainable energy. However, the low hydrogen yield and instability of fermentation systems block the further industrial and commercial application. In this work, nickel and iron doped lanthanum manganese oxide nanoparticles (NPs) are successfully fabricated for researching their effects on H2 production and process stability. The advantages of lanthanum manganese oxides doped by nickel and iron in terms of bacterial activity and microbial community structures are studied in a fermentation system. The physicochemical properties of LaMn0.7Fe0.3O3 NPs and LaMn0.7Ni0.3O3 NPs are summarized and analyzed. The results show that the moderate addition of nanoparticles can both effectively increase the final H2 yield and stabilize the fermentation process simultaneously. The highest H2 yield of 223.08 mL/g and 246.10 mL/g correspond to 100 mg/L supplementation of LaMn0.7Fe0.3O3 NPs and LaMn0.7Ni0.3O3 NPs, respectively, which confirms that the LaMn0.7Ni0.3O3 NPs exhibit a more positive impact on anaerobic fermentation, while excess dosage nanoparticles (over 100 mg/L) may hamper the H2 production and inhibit the electron transfer to microbe. The underlying mechanism analysis reveals that Fe3+ and Ni2+ significantly improve the microbial transmembrane transportation and conversion rate of glucose into acetate, butyrate and H2 through stimulating the activity of related enzymes, leading to an enhanced H2 productivity. Meanwhile, Ni2+ and Fe3+ are helpful to the synthesis of ferredoxin and hydrogenase, which increase the activity of critical enzymes. The microbial community discloses that LaMn0.7Fe0.3O3 NPs and LaMn0.7Ni0.3O3 NPs separately make a 7.71%, 9.65% increase of Clostridium_sensu_stricto_1 compared to the control group, which is deeply involved in the sustainable H2 generation. Based on comprehensive evaluation, LaMn0.7Ni0.3O3 NPs will have a huge potential market for H2 production enhancement in anaerobic fermentation system.

Bioconversion of cellulose and hemicellulose in corn cob into L-lactic acid and xylo-oligosaccharides

With the banning of antibiotic chemical feed additives, multi-functional bioactive feed additives have been extensively sought after by the feed industry. In this study, low-cost and renewable corn cobs were treated with liquid hot water and converted into bioactive xylo-oligosaccharides and L-lactic acid after enzymatic hydrolysis, strain activation, and fermentation under mild conditions, which achieved a full utilization of cellulose and hemicellulose in corn cobs. Simultaneous saccharification fermentation after strain activation with enzymatic hydrolysate delivered the highest conversion rate of glucose to L-lactic acid (93.00 %) and yielded 17.38 g/L L-lactic acid and 2.68 g/L xylo-oligosaccharides. On this basis, batch-feeding fermentation resulted in a 78.03 % conversion rate of glucose to L-lactic acid, 18.99 g/L L-lactic acid, and 2.84 g/L xylo-oligosaccharides. This work not only provided a green and clean bioconversion strategy to produce multi-functional feed additives but can also boost the full utilization of renewable and cheap biomass resources.

Production of Sorbitol via Hydrogenation of Glucose over Ruthenium Coordinated with Amino Styrene-co-maleic Anhydride Polymer Encapsulated on Activated Carbon (Ru/ASMA@AC) Catalyst.

Sorbitol, a product primarily derived from glucose hydrogenation, has extensive applications in the pharmaceutical, chemical and other industries. Amino styrene-co-maleic anhydride polymer encapsulated on activated carbon (Ru/ASMA@AC) catalysts were developed for efficient glucose hydrogenation and were prepared and confined Ru by coordination with styrene-co-maleic anhydride polymer (ASMA). Through single-factor experiments, optimal conditions were determined to be 2.5 wt.% ruthenium loading and a catalyst usage of 1.5 g, 20% glucose solution at 130 °C, reaction pressure of 4.0 MPa, and a stirring speed of 600 rpm for 3 h. These conditions achieved a high glucose conversion rate of 99.68% and a sorbitol selectivity of 93.04%. Reaction kinetics testing proved that the hydrogenation of glucose catalyzed by Ru/ASMA@AC was a first-order reaction, with a reaction activation energy of 73.04 kJ/mol. Furthermore, the catalytic performance of the Ru/ASMA@AC and Ru/AC catalysts for glucose hydrogenation were compared and characterized by various detection methods. The Ru/ASMA@AC catalyst exhibited excellent stability after five cycles, whereas the traditional Ru/AC catalyst suffered from a 10% decrease in sorbitol yield after three cycles. These results suggest that the Ru/ASMA@AC catalyst is a more promising candidate for high-concentration glucose hydrogenation due to its high catalytic performance and superior stability.

Luteolin-7-O-rutinoside Protects RIN-5F Cells from High-Glucose-Induced Toxicity, Improves Glucose Homeostasis in L6 Myotubes, and Prevents Onset of Type 2 Diabetes.

Luteolin-7-O-rutinoside (lut-7-O-rutin), a flavonoid commonly present in Mentha longifolia L. and Olea europaea L. leaves has been used as a flavoring agent with some biological activity. The present study is the first attempt to analyze the protective effect of lut-7-O-rutin on high-glucose-induced toxicity to RIN-5F cells in vitro. We found that lut-7-O-rutin improved insulin secretion in both normal and high-glucose conditions in a dose-dependent manner, without toxicity observed. In addition, 20 µmol of lut-7-O-rutin improves insulin sensitization and glucose uptake significantly (p ≤ 0.01) in L6 myotubes cultured in a high-glucose medium. Lut-7-O-rutin has shown a significant (p ≤ 0.05) effect on glucose uptake in L6 myotubes compared to the reference drug, rosiglitazone (20 µmol). Gene expression analysis confirmed significantly lowered CYP1A, TNF-α, and NF-κb expressions in RIN-5F cells, and increased mitochondrial thermogenesis-related LPL, Ucp-1 and PPARγC1A mRNA expressions in L6 myotubes after 24 h of lut-7-O-rutin treatment. The levels of signaling proteins associated with intracellular glucose uptakes, such as cAMP, ChREBP-1, and AMPK, were significantly increased in L6 myotubes. In addition, the levels of the conversion rate of glucose to lactate and fatty acids were raised in insulin-stimulated conditions; the rate of glycerol conversion was found to be higher at the basal level in L6 myotubes. In conclusion, lut-7-O-rutin protects RIN-5F cells from high-glucose-induced toxicity, stimulates insulin secretion, and promotes glucose absorption and homeostasis via molecular mechanisms.

Preparation of High Value Added Chemicals by Layered G-C3N4 Photocatalytic Oxidation of Glucose

This study used cyanamide as the precursor and SiO2 as the template to prepare a layered structure g-C3N4, and characterized its crystal structure, morphology, optical performance, and electrochemical performance. Photocatalytic oxidation experiments were conducted on biomass derivatives (glucose).Orthogonal experiments were used to study the effects of factors such as illumination time, catalyst concentration, and photocurrent on photocatalytic reactions, and the reaction mechanism was explored. The product was qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS) and quantitatively analyzed by High-performance liquid chromatography (HPLC). The results showed that the prepared g-C3N4 exhibited a layered structure with a band gap of 2.78 eV. When the catalyst concentration is 10mg, the photocurrent intensity is 4 A, and the illumination time is 24 hours, the glucose conversion rate is 49.09 %. The active group capture experiment shows that the main active species of g-C3N4 under visible light is ·O -. In this study, commercial P25 catalyst was used for photocatalytic oxidation of glucose under optimal conditions. The experimental results indicate that the catalytic oxidation performance of P25 for glucose is lower than that of layered structure g-C3N4.

Bioconversion of cellulose and hemicellulose in reed sawdust to xylo-oligosaccharides and L-lactic acid

Much of the carbohydrate-rich reed sawdust (RS) produced from the reed pulping mills is burned or buried, causing a waste of resources. The aim of this work is to effectively bio-convert cellulose and hemicellulose of RS to L-lactic acid and xylo-oligosaccharide (XOS) after liquid hot water (LHW) pretreatment. The experiments were carried out via separation hydrolysis fermentation (SHF) and simultaneous saccharification fermentation (SSF) by optimizing the culture and fermentation conditions of a probiotics compound composed of a consortium of lactic acid bacteria. In the end, functional feed additives containing 69.33 wt% L-lactic acid and 26.82 wt% XOS can easily be obtained without additional handling by SSF configuration at 40 ℃ for 82 h with the initial fermentation pH 7.0. The conversion rate of glucose to L-lactic acid reached 72.33%. The bioconversion of available portion in RS into XOS and L-lactic acid paves a new way for high-value utilization of reed residue resources.

Ethanol Production from the Mixture of Waste French Fries and Municipal Wastewater via Separate Hydrolysis and Fermentation.

The potential of bioethanol generation using the mixture of waste French fries (WFF) and municipal wastewater (MWW) via separate hydrolysis and fermentation (SHF) was evaluated in this study. The effect of WFF substrate loading (SL, 10%, 16%, and 20%, w/v) on the SHF was also examined. Both glucose production and hydrolysis efficiency increased with increasing of SL from 10 to 16% and the maximum glucose yield of 0.236g glucose/g WFF and hydrolysis efficiency of 91.9% were obtained at SL of 16%. However, the glucose production and hydrolysis efficiency decreased when the SL further increased to 20% due to the inhibition on enzyme caused by higher glucose production. The mixture hydrolysate was then used as feedstock for ethanol fermentation. The maximum ethanol production of 22.69g/L was obtained from SL of 16%. The highest rate of glucose conversion to ethanol was 84.2%. The results demonstrated that the mixture of WFF and MWW could be used for ethanol production by the SHF.

Bioconversion of Lactose into Glucose-Galactose Syrup by Two-Stage Enzymatic Hydrolysis.

Fermentation technology enables the better use of resources and the conversion of dairy waste into valuable food products. The aim of this study is to evaluate the conversion rate of glucose into fructose by immobilised glucose isomerase (GI) in sweet and acid whey permeates for glucose–galactose syrup production. The experiments demonstrated that the highest concentration of glucose and galacto-oligosaccharides (GOSs) in sweet and acid whey permeates was reached by GODO-YNL2 β-galactosidase, 32 ± 2% and 28 ± 1%, respectively. After glucose isomerisation, the highest fructose yield was 23 ± 0.3% and 13 ± 0.4% in sweet and acid whey permeates, where Ha-Lactase 5200 β-galactosidase was used for lactose hydrolysis in sweet and acid whey permeates. Finally, the results of this study highlight the potential for two-stage enzymatic hydrolysis to increase the sweetness of glucose–galactose syrup made from sweet and acid whey permeates.

Effects of heat shock treatment on the survival rate of Lactobacillus acidophilus after freeze-drying

Herein we investigated the effects of heat shock treatment on the resistance of Lactobacillus acidophilus ATCC4356 to freeze-drying and the underlying mechanisms. We assessed the survival rate, cell morphology, enzyme activities, and metabolites in glycometabolism and energy metabolism. Heat shock treated at 45 °C for 30 min has increased the survival rate from 39.1% to 56.3% and had a certain protective effect on the integrity of the cell wall and membrane after freeze-drying. Activities of key enzymes, namely glucose-6-phosphate isomerase and lactate dehydrogenase in the glycolytic pathway; phosphoglucomutase, UDP-glucose pyrophosphorylase, and glycosyltransferases in the glycogen biosynthetic pathway; and Na+ -K+ -ATPase in energy metabolism were significantly altered. Further, the utilization rate of extracellular glucose in the broth decreased 7.59% but the conversion rate of intracellular glucose increased 24.04%, which led to the production of lactic acid and energy. Meanwhile, the production of polysaccharides with potential protectant function was increased by 47.6% and the proportion of glucose in the monosaccharide fraction decreased from 21% to 17%. However, the production of galactose increased from 17% to 26%, consequently enhancing the activities and survival rate of bacterial cells in a freeze-drying environment. This is the first study to determine the potential mechanisms and metabolic changes induced by heat shock treatment that make LAB tolerant to freeze-drying, and providing a new insight on the anti-adversity for LAB during the process.

Directing cell catalysis of glucose to 2-keto-d-gluconic acid using Gluconobacter oxydans NL71

2-Keto-d-gluconic acid (2-KGA) is a high-value-added product from lignocellulosic straw-based biorefining process obtained via cell catalysis using Gluconobacter oxydans (G. oxydans); nonetheless, the economical production has some limitations because of the formation of undesirable mixture products of keto-gluconic acid from glucose. In this study, it was demonstrated that pulse addition of hydrogen peroxide (H2O2) to synthetic media was beneficial to improve the conversion rate of glucose to 2-KGA by 1.47-fold in G. oxydans. Moreover, some lignocellulosic degradation compounds served as substitute and played the role of H2O2 on corn stover hydrolysate for the production of 2-KGA. By conducting qRT-PCR analysis, eight dehydrogenase genes were identified in G. oxydans, which were responsible for regulating 2-KGA production. Moreover, most of the identified genes were found to produce membrane-bound glucose dehydrogenase and gluconate 2-dehydrogenase, and were up-regulated by adding H2O2 or degradation compounds. These up-regulated genes could be responsible for directing cell catalysis of glucose to 2-KGA in G. oxydans.

Truncating the Structure of Lipopolysaccharide in Escherichia coli Can Effectively Improve Poly-3-hydroxybutyrate Production.

Poly-3-hydroxybutyrate is an environmentally friendly polymer with many promising applications and can be produced in Escherichia coli cells after overexpressing the heterologous gene cluster phaCAB. In this study, we found that truncating the structure of lipopolysaccharide in E. coli can effectively enhance poly-3-hydroxybutyrate production. E. coli mutant strains WJW00, WJD00, and WJJ00 were constructed by deleting rfaD from E. coli strain W3110, DH5α, and JM109, respectively. Compared to the controls W3110/pDXW-8-phaCAB, DH5a/pDXW-8-phaCAB, and JM109/pDXW-8-phaCAB, the yield of poly-3-hydroxybutyrate in WJW00/pDXW-8-phaCAB, WJD00/pDXW-8-phaCAB, and WJJ00/pDXW-8-phaCAB cells increased by 200%, 81.5%, and 75.6%, respectively, and the conversion rate of glucose to poly-3-hydroxybutyrate was increased by ∼250%. Further analysis revealed that LPS truncation in E. coli rebalanced carbon and nitrogen metabolism, increased the levels of acetyl-CoA, γ-aminobutyric acid, NADPH, NADH, and ATP, and decreased the levels of organic acids and flagella, resulting in the high ratio of carbon to nitrogen. These metabolic changes in these E. coli mutants led to the significant increase of poly-3-hydroxybutyrate production.