Transporter mining and metabolic engineering of Escherichia coli for high-level D-allulose production from D-fructose by thermo-swing fermentation.

D-Allulose is an ultra-low-calorie sweetener with broad market prospects in the fields of food, beverage, health care, and medicine. The fermentative synthesis of D-allulose is still under development and considered as an ideal route to replace enzymatic approaches for large-scale production of D-allulose in the future. Generally, D-allulose is synthesized from D-fructose through Izumoring epimerization. This biological reaction is reversible, and a high temperature is beneficial to the conversion of D-fructose. Mild cell growth conditions seriously limit the efficiency of producing D-allulose through fermentation. FryABC permease was identified to be responsible for the transport of D-allulose in Escherichia coli by comparative transcriptomic analysis. A cell factory was then developed by expression of ptsG-F, dpe, and deletion of fryA, fruA, manXYZ, mak, and galE. The results show that the newly engineered E. coli was able to produce 32.33 ± 1.33 g L-1 of D-allulose through a unique thermo-swing fermentation process, with a yield of 0.94 ± 0.01 g g-1 on D-fructose.

Switching the memory behaviour from binary to ternary by triggering S62- relaxation in polysulfide-bearing zinc-organic complex molecular memories.

The use of crystalline metal-organic complexes with definite structures as multilevel memories can enable explicit structure-property correlations, which is significant for designing the next generation of memories. Here, four Zn-polysulfide complexes with different degrees of conjugation have been fabricated as memory devices. ZnS6(L)2-based memories (L = pyridine and 3-methylpyridine) can exhibit only bipolar binary memory performances, but ZnS6(L)-based memories (L = 2,2'-bipyridine and 1,10-phenanthroline) illustrate non-volatile ternary memory performances with high ON2/ON1/OFF ratios (104.22/102.27/1 and 104.85/102.58/1) and ternary yields (74% and 78%). Their ON1 states stem from the packing adjustments of organic ligands upon the injection of carriers, and the ON2 states are a result of the ring-to-chain relaxation of S62- anions. The lower conjugated degrees in ZnS6(L)2 result in less compact packing; consequently, the adjacent S62- rings are too long to trigger the S62- relaxation. The deep structure-property correlation in this work provides a new strategy for implementing multilevel memory by triggering polysulfide relaxation based on the conjugated degree regulation of organic ligands.

Engineering of Escherichia coli for D-allose fermentative synthesis from D-glucose through izumoring cascade epimerization.

D-Allose is a potential alternative to sucrose in the food industries and a useful additive for the healthcare products in the future. At present, the methods for large-scale production of D-allose are still under investigation, most of which are based on in vitro enzyme-catalyzed Izumoring epimerization. In contrast, fermentative synthesis of D-allose has never been reported, probably due to the absence of available natural microorganisms. In this work, we co-expressed D-galactose: H+ symporter (GalP), D-glucose isomerase (DGI), D-allulose 3-epimerase (DAE), and ribose-5-phosphate isomerase (RPI) in Escherichia coli, thereby constructing an in vivo Izumoring pathway for yielding D-allose from D-glucose. The carbon fluxes and carbon catabolite repression (CCR) were rationally regulated by knockout of FruA, PtsG, Glk, Mak, PfkA, and PfkB involved in the pathways capable of phosphorylating D-fructose, D-glucose, and fructose-6-phosphate. Moreover, the native D-allose transporter was damaged by inactivation of AlsB, thus driving the reversible Izumoring reactions towards the target product. Fermentation was performed in the M9 medium supplemented with glycerol as a carbon source and D-glucose as a substrate. The results show that the engineered E. coli cell factory was able to produce approximately 127.35 mg/L of D-allose after 84 h. Our achievements in the fermentative production of D-allose in this work may further promote the green manufacturing of rare sugars.

Methanol-Dependent Carbon Fixation for Irreversible Synthesis of d-Allulose from d-Xylose by Engineered Escherichia coli.

d-Allulose is a rare hexose with great application potential, owing to its moderate sweetness, low energy, and unique physiological functions. The current strategies for d-allulose production, whether industrialized or under development, utilize six-carbon sugars such as d-glucose or d-fructose as a substrate and are usually based on the principle of reversible Izumoring epimerization. In this work, we designed a novel route that coupled the pathways of methanol reduction, pentose phosphate (PP), ribulose monophosphate (RuMP), and allulose monophosphate (AuMP) for Escherichia coli to irreversibly synthesize d-allulose from d-xylose and methanol. After improving the expression of AlsE by SUMO fusion and regulating the carbon fluxes by knockout of FrmRAB, RpiA, PfkA, and PfkB, the titer of d-allulose in fed-batch fermentation reached ≈70.7 mM, with a yield of ≈0.471 mM/mM on d-xylose or ≈0.512 mM/mM on methanol.

Metabolically Engineered Escherichia coli for Conversion of D-Fructose to D-Allulose via Phosphorylation-Dephosphorylation.

D-Allulose is an ultra-low calorie sweetener with broad market prospects. As an alternative to Izumoring, phosphorylation-dephosphorylation is a promising method for D-allulose synthesis due to its high conversion of substrate, which has been preliminarily attempted in enzymatic systems. However, in vitro phosphorylation-dephosphorylation requires polyphosphate as a phosphate donor and cannot completely deplete the substrate, which may limit its application in industry. Here, we designed and constructed a metabolic pathway in Escherichia coli for producing D-allulose from D-fructose via in vivo phosphorylation-dephosphorylation. PtsG-F and Mak were used to replace the fructose phosphotransferase systems (PTS) for uptake and phosphorylation of D-fructose to fructose-6-phosphate, which was then converted to D-allulose by AlsE and A6PP. The D-allulose titer reached 0.35 g/L and the yield was 0.16 g/g. Further block of the carbon flux into the Embden-Meyerhof-Parnas (EMP) pathway and introduction of an ATP regeneration system obviously improved fermentation performance, increasing the titer and yield of D-allulose to 1.23 g/L and 0.68 g/g, respectively. The E. coli cell factory cultured in M9 medium with glycerol as a carbon source achieved a D-allulose titer of ≈1.59 g/L and a yield of ≈0.72 g/g on D-fructose.

Intelligent self-control of carbon metabolic flux in SecY-engineered Escherichia coli for xylitol biosynthesis from xylose-glucose mixtures.

Xylitol is a salutary sugar substitute that has been widely used in the food, pharmaceutical, and chemical industries. Co-fermentation of xylose and glucose by metabolically engineered cell factories is a promising alternative to chemical hydrogenation of xylose for commercial production of xylitol. Here, we engineered a mutant of SecY protein-translocation channel (SecY [ΔP]) in xylitol-producing Escherichia coli JM109 (DE3) as a passageway for xylose uptake. It was found that SecY (ΔP) channel could rapidly transport xylose without being interfered by XylB-catalyzed synthesis of xylitol-phosphate, which is impossible for native XylFGH and XylE transporters. More importantly, with the coaction of SecY (ΔP) channel and carbon catabolite repression (CCR), the flux of xylose to the pentose phosphate (PP) pathway and the xylitol synthesis pathway in E. coli could be automatically controlled in response to glucose, thereby ensuring that the mutant cells were able to fully utilize sugars with high xylitol yields. The E. coli cell factory developed in this study has been proven to be applicable to a broad range of xylose-glucose mixtures, which is conducive to simplifying the mixed-sugar fermentation process for efficient and economical production of xylitol.

Engineering Escherichia coli for d-Allulose Production from d-Fructose by Fermentation.

d-Allulose is considered an ideal alternative to sucrose and has shown tremendous application potential in many fields. Recently, most efforts on production of d-allulose have focused on in vitro enzyme-catalyzed epimerization of cheap hexoses. Here, we proposed an approach to efficiently produce d-allulose through fermentation using metabolically engineered Escherichia coli JM109 (DE3), in which a SecY (ΔP) channel and a d-allulose 3-epimerase (DPEase) were co-expressed, ensuring that d-fructose could be transported in its nonphosphorylated form and then converted into d-allulose by cells. Further deletion of fruA, manXYZ, mak, galE, and fruK and the use of Ni2+ in a medium limited the carbon flux flowing into the byproduct-generating pathways and the Embden-Meyerhof-Parnas (EMP) pathway, achieving a ≈ 0.95 g/g yield of d-allulose on d-fructose using E. coli (DPEase, SecY [ΔP], ΔFruA, ΔManXYZ, ΔMak, ΔGalE, ΔFruK) and 8 µM Ni2+. In fed-batch fermentation, the titer of d-allulose reached ≈23.3 g/L.

Thermal-Responsive Polyoxometalate-Metalloviologen Hybrid: Reversible Intermolecular Three-Component Reaction and Temperature-Regulated Resistive Switching Behaviors.

The development of new-type memristors with special performance is of great interest. Herein, an inorganic-organic hybrid crystalline polyoxometalate (POM) with usual dynamic structures is reported and used as active material for fabricating memristor with unique temperature-regulated resistive switching behaviors. The hybrid POM not only exhibits tunable thermochromic properties, but also thermal-induced reversible aggregation and disaggregation reactions, leading to reversible structural transformations in SCSC fashion. Further, the memory device using the hybrid POM as active layer exhibits uncommon performance, which can keep resistive switching silent in the low temperature range of 30-150 °C, but show nonvolatile memory behavior in the high temperature range of 150-270 °C. Particularly, the silent and working states at three special temperatures (30, 150 and 270 °C) can be monitored by chromism. The correlation between structure and resistive switching property of the material has been discussed. The work demonstrates that crystalline inorganic-organic hybrid POMs are promising materials for making memristors with superior performance.

[Damage of deltamethrin on tissue and cell DNA in hepatopancreas of Pagrosomus major]. / æº´æ°°èŠé ¯å¯¹çœŸé²·è‚èƒ°è„ç»„ç»‡åŠç»†èƒžDNA的损伤.

In order to study the toxic effect of deltamethrin on the hepatopancreas of Pagrosomus major with sub-acute exposure, Pagrosomus major were divided into 5 groups with different doses of semi-static exposure. The damage of the hepatopancreas tissue of Pagrosomus major was analyzed by microscopy observation and the DNA damage of the cells was analyzed by comet assay technique after 25 days exposure. The results showed that different degrees of congestion, nuclear enrichment and cell necrosis appeared in hepatopancreas of 0.025, 0.125, 0.250, 0.375 Μg·L-1 exposure concentrations. The higher the exposure concentration, the variations of tissue and cell were more significant. DNA damages in the hepatopancreas cells of all exposed group were observed. The co-met rate, percentage of tail DNA and the olive moment were significantly different from the control group (P<0.05). Linear regression analysis showed that the exposure concentration was significantly positively correlated with the tailing rate and the tail length (P<0.01). The indexes were significantly related to the concentration of deltamethrin exposure with the coefficient of determination between 0.909-0.996. It was suggested that deltamethrin could cause various degree of damage to the tissue and cellular DNAs in the hepatopancreas of Pagrosomus major in a linear responsive manner.

Three silver iodides with zero and one-dimensional hybrid structures directed by conjugated organic templates: synthesis and theoretical study.

Under the direction of large conjugated organic cationic SDAs (structure-directing agents), three silver(I) iodides, (ipq)4(Ag2I6 x 2I2) (1), {[pql][Ag2I3]}n (2), [(npql)2(Ag4I6)]n (3) (ipq+ = N-(isopentyl)-quinolinium, pql+ = N-propyl-quinolinium, npql+ = N-(n-pentyl)-quinolinium) have been synthesized. 1 presents a zero-dimensional structure constituting of ipq+ cations, [Ag2I6]4- anions and molecular iodine. But 2 and 3 consist of one-dimensional coordination polymers that could be described as edge-sharing AgI4 tetrahedra. Electrostatic interactions between organic counter cations and inorganic moieties are present and contribute to the crystal packing. The structural differences between 1, 2 and 3 illustrate the influences of substituents of SDAs on the linkage modes of AgI4 tetrahedra. DFT calculations were carried out to reveal their electronic structures.