Engineering Escherichia coli for succinate production from hemicellulose via consolidated bioprocessing

<p>Abstract</p> <p>Background</p> <p>The recalcitrant nature of hemicellulosic materials and the high cost in depolymerization are the primary obstacles preventing the use of xylan as feedstock for fuel and chemical production. Consolidated bioprocessing, incorporating enzyme-generating, biomass-degrading and bioproduct-producing capabilities into a single microorganism, could potentially avoid the cost of the dedicated enzyme generation in the process of xylan utilization. In this study, we engineered <it>Escherichia coli </it>strains capable of exporting three hemicellulases to the broth for the succinate production directly from beechwood xylan.</p> <p>Results</p> <p>Xylanases were extracellular environment-directed by fusing with OsmY. Subsequently, twelve variant OsmY fused endoxylanase-xylosidase combinations were characterized and tested. The combination of XynC-A from <it>Fibrobacter succinogenes </it>S85 and XyloA from <it>Fusarium graminearum </it>which appeared to have optimal enzymatic properties was identified as the best choice for xylan hydrolysis (0.18 ± 0.01 g/l protein in the broth with endoxylanase activity of 12.14 ± 0.34 U/mg protein and xylosidase activity of 92 ± 3 mU/mg protein at 8 h after induction). Further improvements of hemicellulases secretion were investigated by <it>lpp </it>deletion, <it>dsbA </it>overexpression and expression level optimization. With co-expression of α-arabinofuranosidase, the engineered <it>E. coli </it>could hydrolyze beechwood xylan to pentose monosaccharides. The hemicellulolytic capacity was further integrated with a succinate-producing strain to demonstrate the production of succinate directly from xylan without externally supplied hydrolases and any other organic nutrient. The resulting <it>E. coli </it>Z6373 was able to produce 0.37 g/g succinate from xylan anaerobically equivalent to 76% of that from xylan acid hydrolysates.</p> <p>Conclusions</p> <p>This report represents a promising step towards the goal of hemicellulosic chemical production. This engineered <it>E. coli </it>expressing and secreting three hemicellulases demonstrated a considerable succinate production on the released monosaccharides from xylan. The ability to use lower-cost crude feedstock will make biological succinate production more economically attractive.</p

Epitaxial crystallization of precisely fluorine substituted polyethylene induced by carbon nanotube and reduced graphene oxide

Crystallization of well-defined precision polyethylene with fluorine substituent on every 21st backbone carbon (PE21F) induced by low-dimensional carbonaceous nanofillers (carbon nanotube (CNT) and reduced graphene oxide (RGO)) via solution crystallization and supercritical CO2 assisted solution crystallization were investigated. Transmission electron microscopy was used to investigate the morphology of carbonaceous nanofiller-induced PE21F crystals. The kebab-like and rod-like crystals formed on the CNT and RGO, respectively. Selected area electron diffraction (SAED) pattern revealed that the c-axis of polymer chain is parallel to the surface of the RGO. Differential scanning calorimetry (DSC) revealed the melting temperatures (T-m) of PE21F lamellae nanocomposites increased with crystallization temperature increasing. The X-ray diffraction (XRD) results showed that the incorporation of nanofillers did not influence the crystal structure of PE21F. The chemical composition of the PE21F nanocomposites measured by X-ray photoelectron spectra (XPS) confirmed substituent F as a defect of chain was accommodated into the crystal lattice. (C) 2015 Elsevier Ltd. All rights reserved

Epitaxial crystallization of precisely bromine-substituted polyethylene induced by carbon nanotubes and graphene

Precisely substituted polyethylenes have well-defined primary structures and aggregation architecture. Herein, precisely bromine-substituted polyethylene (PE21Br) was chosen as an ideal model to investigate the substituent impact on epitaxial crystallization upon one-dimensional carbon nanotubes (CNT) and two-dimensional reduced graphene oxide (RGO) via solution crystallization. The abilities of different dimensional nanofillers to induce ordered chain packing structures were compared. Transmission electron microscopy (TEM) images showed that kebab-like and rod-like nanofiller-induced crystals were separately observed on the surfaces of CNT and graphene, and selected area electron diffraction (SAED) pattern revealed that the c-axis of the polymer chain was parallel to the surface of RGO. Fast-scan differential scanning calorimetry (Flash DSC) revealed that the melting points of the crystals grown on CNT and graphene were increased by 19 and 99 degrees C, respectively. More importantly, X-ray diffraction (XRD) suggested that CNT and RGO induced the transition of the crystal structure of PE21Br from the triclinic to orthorhombic form, but with different orderness. More ordered lattice structures and higher melting temperatures of PE21Br/RGO nanocomposites are ascribed to the perfect lattice matching between PE21Br and RGO. This study not only provides a method for fabricating bromine-functionalized polyolefin nanocomposites, but is also anticipated to open up a new opportunity for improving the service temperature of substituted polyethylene by means of epitaxial crystallization

Epitaxial crystallization of precisely chlorine-substituted polyethylene induced by carbon nanotube and graphene

We report morphology, thermal analysis and beam diffraction of polyethylene chlorine-substituted precisely on every 21st backbone carbon, after solution crystallization induced by low-dimensional carbonaceous nanofillers (carbon nanotube and graphene). Kebab-like and rod-like nanofiller-induced crystals were separately observed on the surfaces of carbon nanotube and graphene. Fast-scan differential scanning calorimetry revealed that while the melting point of crystals grown on carbon nanotube remains close to that in the bulk phase, the melting point of crystals grown on graphene is 75 degrees C higher. X-ray diffraction and selected area electron diffraction suggested that graphene induces the formation of orthorhombic form, which is of higher density than the triclinic form in the bulk. (C) 2016 Elsevier Ltd. All rights reserved

Structure of Amorphous Selenium: Small Ring, Big Controversy

Selenium (Se) discovered in 1817 belongs to the family of chalcogens. Surprisingly, despite the long history of over two centuries and the chemical simplicity of Se, the structure of amorphous Se (a-Se) remains controversial to date regarding the dominance of chains versus rings. Here, we find that vapor-deposited a-Se is composed of disordered rings rather than chains in melt-quenched a-Se. We further reveal that the main origin of this controversy is the facile transition of rings to chains arising from the inherent instability of rings. This transition can be inadvertently triggered by certain characterization techniques themselves containing above-bandgap illumination (above 2.1 eV) or heating (above 50 °C). We finally build a roadmap for obtaining accurate Raman spectra by using above-bandgap excitation lasers with low photon flux (below 1017 phs m–2 s–1) and below-bandgap excitation lasers measured at low temperatures (below −40 °C) to minimize the photoexcitation- and heat-induced ring-to-chain transitions

NMR-based metabolomics Reveals Alterations of Electro-acupuncture Stimulations on Chronic Atrophic Gastritis Rats

Chronic atrophic gastritis (CAG) is a common gastrointestinal disease which has been considered as precancerous lesions of gastric carcinoma. Previously, electro-acupuncture stimulation has been shown to be effective in ameliorating symptoms of CAG. However the underlying mechanism of this beneficial treatment is yet to be established. In the present study, an integrated histopathological examination along with molecular biological assay, as well as 1H NMR analysis of multiple biological samples (urine, serum, stomach, cortex and medulla) were employed to systematically assess the pathology of CAG and therapeutic effect of electro-acupuncture stimulation at Sibai (ST 2), Liangmen (ST 21), and Zusanli (ST 36) acupoints located in the stomach meridian using a rat model of CAG. The current results showed that CAG caused comprehensive metabolic alterations including the TCA cycle, glycolysis, membrane metabolism and catabolism, gut microbiota-related metabolism. On the other hand, electro-acupuncture treatment was found able to normalize a number of CAG-induced metabolomics changes by alleviating membrane catabolism, restoring function of neurotransmitter in brain and partially reverse the CAG-induced perturbation in gut microbiota metabolism. These findings provided new insights into the biochemistry of CAG and mechanism of the therapeutic effect of electro-acupuncture stimulations