Metabolic engineering of Escherichia coli for high-level production of the biodegradable polyester monomer 2-pyrone-4,6-dicarboxylic acid.

2-Pyrone-4,6-dicarboxylic acid (PDC), a chemically stable pseudo-aromatic dicarboxylic acid, is a promising building block compound for manufacturing biodegradable polyesters. This study aimed to construct high-performance cell factories enabling the efficient production of PDC from glucose. Firstly, the effective enzymes of the PDC biosynthetic pathway were overexpressed on the chromosome of the 3-dehydroshikimate overproducing strain. Consequently, the one-step biosynthesis of PDC from glucose was achieved. Further, the PDC production was enhanced by multi-copy integration of the key gene PsligC encoding 4-carboxy-2-hydroxymuconate-6-semialdehyde dehydrogenase and co-expression of Vitreoscilla hemoglobin. Subsequently, the PDC production was substantially improved by redistributing the metabolic flux for cell growth and PDC biosynthesis based on dynamically downregulating the expression of pyruvate kinase. The resultant strain PDC50 produced 129.37 g/L PDC from glucose within 78 h under fed-batch fermentation conditions, with a yield of 0.528 mol/mol and an average productivity of 1.65 g/L/h. The findings of this study lay the foundation for the potential industrial production of PDC.

Efficient formaldehyde sensor based on PtPd nanoparticles-loaded nafion-modified electrodes.

The noble metal-based electrochemical sensor design for efficient and stable formaldehyde(FA) detection is important ongoing research. In this paper, PtPd/Nafion/GCE is prepared by electrochemical cyclic voltammetry deposition method based on electrodepositing nanostructured platinum (Pt)-palladium (Pd) nanoparticles in Nafion film-coated glassy carbon electrode (GCE). The influence of deposition parameters and chemical composition (atomic ratio of Pt and Pd) on the electrochemical behaviour of PtPd/Nafion/GCE has been investigated. PtPd/Nafion/GCE displays a remarked electrocatalytic activity for the oxidation of FA and exhibits a linear relationship in the range of 10-5000µM, with a detection limit of 3.3µM in 0.1 M H2SO4solution. It is proved that the detection performance of PtPd/Nafion/GCE electrode is valuable for further application with low detection limit, wide linear range, favourable selectivity and high response.

The Molecular Model of Organic Matter in Coal-Measure Shale: Structure Construction and Evaluation Based on Experimental Characterization.

To investigate the molecular structure and micropore structure of organic matters in coal-measure shale, the black shale samples of the Shanxi formation were collected from Xishan Coalfield, Taiyuan, and a hybrid experimental-simulation method was used for realistic macromolecular models of organic matter (OM). Four experimental techniques were used to determine the structural information of OM, including elemental analysis, state 13C nuclear magnetic resonance (13CNMR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). With structural parameters, two-dimensional (2D) average molecular models of OM were established as C177H160O8N2S with a molar weight of 2474, which agreed well with the experimental 13C-NMR spectra. A realistic three-dimensional (3D) OM macromolecular model was also reconstructed, containing 20 2D molecules with a density of 1.41 g/cm3. To determine the connectivity and spatial disposition of the OM pores, focused ion beam microscope (FIB-SEM) and transmission electron micrographs (TEM) were utilized. The 3D OM pores models were developed. The results show that whether the OM pores varied from 20 to 350 nm as obtained from FIB-SEM images or less than 10 nm as observed in the TEM images, both were of poor connectivity. However, the ultra-micro pores from the 3D OM macromolecular model varied from 3Å to 10 Å and showed certain connectivity, which may be the main channel of diffusion. Furthermore, with the pressure increased, the methane adsorption capacity of the 3D OM model increased with a maximum value of 103 cm3/g at 7 MPa, indicating that OM pores less than 1 nm have a huge methane adsorption capacity. Therefore, our work provides an analysis method that is a powerful and superior tool in further research on gas migration.

[Construction of seamless genome editing system for fast-growing Vibrio natriegens].

Recently, fast-growing Vibrio natriegens, as the great potential chassis, has shown a wide application in synthetic biology. Genome editing is an indispensable tool for genetic modification in synthetic biology. However, genome editing tools with high efficiency and fidelity are still to be developed for V. natriegens synthetic biology. To deal with this problem, the physiological characteristics of 6 V. natriegens strains were evaluated, and CICC 10908 strain with fast and stable growth was selected as the host strain for genome editing study. Then, the natural transformation system of V. natriegens was established and optimized. The efficiencies of optimized natural transformation that integrates antibiotic resistance marker cat-sacB or Kan(R) onto the chromosome of V. natriegens could reach 4×10⁻5 and 4×10⁻4, respectively. Based on the optimized natural transformation, a double-selection cassette was used to achieve seamless genome editing with high efficiency and fidelity. The positive rates of four different types of genetic manipulation, including gene deletion, complementation, insertion and substitution, were 93.8%, 100%, 95.7% and 100%, respectively. Finally, transformation and elimination of the recombinant plasmid could be easily achieved in V. natriegens. This work provides a seamless genome editing system with high efficiency and fidelity for V. natriegens synthetic biology.

Growth Mechanisms and the Effects of Deposition Parameters on the Structure and Properties of High Entropy Film by Magnetron Sputtering.

Despite intense research on high entropy films, the mechanism of film growth and the influence of key factors remain incompletely understood. In this study, high entropy films consisting of five elements (FeCoNiCrAl) with columnar and nanometer-scale grains were prepared by magnetron sputtering. The high entropy film growth mechanism, including the formation of the amorphous domain, equiaxial nanocrystalline structure and columnar crystal was clarified by analyzing the microstructure in detail. Besides, the impacts of the important deposition parameters including the substrate temperature, the powder loaded in the target, and the crystal orientation of the substrate on the grain size and morphology, phase structure, crystallinity and elemental uniformity were revealed. The mechanical properties of high entropy films with various microstructure features were investigated by nanoindentation. With the optimized grain size and microstructure, the film deposited at 350 °C using a power of 100 W exhibits the highest hardness of 11.09 GPa. Our findings not only help understanding the mechanisms during the high entropy film deposition, but also provide guidance in manufacturing other novel high entropy films.

Comparison of Vacancy Sink Efficiency of Cu/V and Cu/Nb Interfaces by the Shared Cu Layer.

This paper provides a new method to compare and then reveal the vacancy sink efficiencies quantitively between different hetero-interfaces with a shared Cu layer in one sample, in contrast to previous studies, which have compared the vacancy sink efficiencies of interfaces in different samples. Cu-Nb-Cu-V nanoscale metallic multilayer composites (NMMCs) containing Cu/V and Cu/Nb interfaces periodically were prepared as research samples and bombarded with helium ions to create vacancies which were filled by helium bubbles. A special Cu layer shared by adjoining Cu/V and Cu/Nb interfaces exists, in which the implanted helium concentration reaches its maximum and remains nearly constant with a well-designed incident energy. The results show that bubble-denuded zones (BDZ) close to interfaces exist, and that the width of the BDZ close to the Cu/V interface is less than that of Cu/Nb interface. This result is explained by one-dimensional diffusion theory, and the ratio of vacancy sink efficiency between Cu/V and Cu/Nb interfaces is calculated. Conclusively, Cu/Nb interfaces are more efficient than Cu/V interfaces in eliminating vacancies induced by radiation.

High electrocatalytic performance inspired by crystalline/amorphous interface in PtPb nanoplate.

Nanoscale PtPb catalysts with core-shell structure have been actively explored in recent years owing to their outstanding catalytic activity. We report on a new class of PtPb nanoplate (NP) catalyst with a novel structure realized by ion irradiation modification, which contains an interface formed by a crystalline phase and an amorphous phase simultaneously in an annular state. Significantly, the PtPb NP with the new structure shows superior catalytic activity towards the methanol oxidation reaction (MOR). The specific activity of PtPb NPs with the new structure reaches 4.32 mA cm-2 towards the MOR and the mass activity reaches 1.31 A mg-1, which is 1.9-fold and 1.4-fold greater than those for the original crystalline PtPb NPs, respectively. The outstanding catalytic activity could be attributed to the presence of the interface between a crystalline phase and an amorphous phase with a special electronic structure created by ion irradiation. Density functional theory calculations reveal that the novel interface activates the C-H and O-H bonds, leading to high electrocatalytic activity, and optimizes the adsorption of hydroxyl and intermediates on the surface to facilitate the oxidation reaction. The novel structure with an interface formed by a crystalline phase and an amorphous phase opens up a new approach to improve electrocatalytic activity.

Defects and Interfaces on PtPb Nanoplates Boost Fuel Cell Electrocatalysis.

Nanostructured Pt is the most efficient single-metal catalyst for fuel cell technology. Great efforts have been devoted to optimizing the Pt-based alloy nanocrystals with desired structure, composition, and shape for boosting the electrocatalytic activity. However, these well-known controls still show the limited ability in maximizing the Pt utilization efficiency for achieving more efficient fuel cell catalysis. Herein, a new strategy for maximizing the fuel cell catalysis by controlling/tuning the defects and interfaces of PtPb nanoplates using ion irradiation technique is reported. The defects and interfaces on PtPb nanoplates, controlled by the fluence of incident C+ ions, make them exhibit the volcano-like electrocatalytic activity for methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR), and oxygen reduction reaction (ORR) as a function of ion irradiation fluence. The optimized PtPb nanoplates with the mixed structure of dislocations, subgrain boundaries, and small amorphous domains are the most active for MOR, EOR, and ORR. They can also maintain high catalytic stability in acid solution. This work highlights the impact and significance of inducing/controlling the defects and interfaces on Pt-based nanocrystals toward maximizing the catalytic performance by advanced ion irradiation strategy.