The Facile Three-Dimensional Printing of the Composite of Copper Nanosized Powder and Micron Powder with Enhanced Properties.

Three-dimensional (3D) printing of Cu items is a new way to build up the structured Cu materials, but 3D printing of Cu items is usually a challenge because of the high melting point, high thermal conductivity, and high light reflection rate of Cu material. In this study, the composite of Cu microspheres powder and Cu nanoparticles (micro/nano Cu powder) is used to realize the 3D printing of Cu items with the selective laser melting technology. The sintering temperature and the thermal conductivity of micro/nano Cu powder are evidently decreased due to Cu nanoparticles' addition in the micron Cu powder. The results reveal that the 3D printing of 50%/50% micro/nano Cu powder needs laser power range of 100-240 W, which is in contrast to 200-340 W for 3D printing of 100% Cu microspheres powder. Furthermore, the conductivity, mechanical strength, and density of 3D-printed Cu items are improved with the addition of Cu nanoparticles into the micron Cu powder. The increasement of 34% on electrical conductivity and 17% on tensile strength are reached by the addition of 50% Cu nanoparticles with the laser power of 240 W.

Electrochemical Preparation and Post-treatment of Composite Porous Foam NiZn Alloy Electrodes with High Activity for Hydrogen Evolution.

Composite porous foam NiZn alloy electrodes with nano pore structure were prepared by the combination of eletrodeposition, heat treatment and HCl etching. The morphology of the electrodes was examined by scanning electron microscopy (SEM). And the component of the electrodes was analyzed by Energy Dispersive Spectrum (EDS). The specific surface area and pore size of the electrode were investigated by nitrogen adsorption. The phase constituents were analyzed by X ray diffraction (XRD), and the electrocatalytic characteristics for hydrogen evolution reaction of the electrodes in 30% (mass fraction) KOH solution were investigated by cathode polarization curve. The experimental results showed that the pores were formed on surface of the foam NiZn alloy electrodes after heat treatment at 600 °C, and with the etching by 10% HCl, nano layered structure was formed on the surface of the porous skeleton. Compared with the nickel foam, the surface area of the NiZn foam alloy electrode became larger, and the nano pore structure had good catalytic activity. At current density of 200 mA·dm-2, the hydrogen evolution overpotential of the NiZn foam alloy electrodes were reduced by 222 mV and 276 mV, respectively, through heat treatment of 600 °C and etching in 10% HCl solution, which indicated that the hydrogen evolution overpotential was effectively reduced because of the composite nano porous structure, while the activity of hydrogen evolution of the electrodes was obviously improved.

ß-Galactosidase BMG without galactose and glucose inhibition: Secretory expression in Bacillus subtilis and for synthesis of oligosaccharide.

ß-Galactosidases can catalyze the hydrolysis of lactose and the synthesis of galacto-oligosaccharides (GOS) from lactose. The catalytic activity of ß-galactosidases is usually inhibited by galactose and glucose, which hampers the complete hydrolysis of lactose in food products. In this report, a ß-galactosidase (denoted as BMG) from Bacillus megaterium YZ08 without the inhibition by galactose and glucose is the first to our knowledge reported. Efficient secretory expression of BMG was successfully achieved in Bacillus subtilis WB800. With the increasing of galactose and glucose, the activity of BMG dramatically enhanced. With addition of 0.6 M galactose or 1 M glucose, the initial activity to oNPG hydrolysis was increased by 2.1-fold and 4.3-fold, respectively. Moreover, the synthetic rate of galacto-oligosaccharides was enhanced by 1.1-fold and 1.9-fold with the addition of 0.7 M galactose or glucose, respectively. The GOS (278 g/L) from 600 g/L lactose by BMG were efficiently produced within 12 h, and the substrate lactose was completely used up. These results suggest that BMG shows a potential application in the food industry.

Ca2+-induced stabilization of the nucleoside 2'- deoxyribosyltransferase from Lactobacillus hilgardii ZJS01: Characteristics and application in nucleosides synthesis.

A novel nucleoside 2'-deoxyribosyltransferase (LhNDT) from Lactobacillus hilgardii ZJS01 was cloned and expressed in Escherichia coli BL21 (DE3). The amino acid sequence of LhNDT displayed the highest identity of 26% to other reported NDTs. LhNDT was a monomer as revealed by gel filtration chromatography with or without addition of Ca2+ in elution buffer. This enzyme showed a high activity and stability over a broad pH range and was sensitive to temperature. With the addition of 15mM Ca2+, the thermostability of LhNDT was greatly promoted by 63 times and 46 times at 30°C and 35°C, respectively. With the use of 2'-deoxyuridine as sugar donor at an economic molar ratio of 1:1, 5-aza-2'-deoxycytidine (46%) and 5-fluoro-2'- deoxycytidine (58%) were efficiently synthesized from 5-azacytosine and 5-fluorocytosine, respectively, by LhNDT for 2h.

A thermostable pyrimidine nucleoside phosphorylase from Brevibacillus borstelensis LK01 for synthesizing halogenated nucleosides.

OBJECTIVE: To isolate a thermostable pyrimidine nucleoside phosphorylase (PyNP) from mesophilic bacteria by gene mining. RESULTS: BbPyNP from Brevibacillus borstelensis LK01 was isolated by gene mining. BbPyNP had a highest 60% identity with that of reported PyNPs. BbPyNP could catalyze the phosphorolysis of thymidine, 2'-deoxyuridine, uridine and 5-methyuridine. BbPyNP had good thermostability and retained 73% of its original activity after 2 h incubation at 50 °C. BbPyNP had the highest activity at an optimum alkaline pH of 8.5. BbPyNP was stable from pH 7 to 9.8. Under preliminary optimized conditions, the biosynthesis of various 5-halogenated pyrimidine nucleosides by BbPyNP reached the yield of 61-84%. CONCLUSION: An efficient approach was estimated in isolating thermostable PyNP from mesophilic bacteria.

Mg2+-induced stabilization of ß-galactosidase from Bacillus megaterium and its application in the galactosylation of natural products.

OBJECTIVE: To improve the stability of ß-galactosidase from Bacillus megaterium YZ08 (BMG) in aqueous hydrophilic solvents and promote its application in the galactosylation of natural products. RESULTS: The addition of 5 mM Mg2+ significantly enhanced the stability of BMG in aqueous hydrophilic solvents, and the half-lives of BMG in these solutions reached 56 min to 208 h, while they were only 7 min to 5.9 h without addition of Mg2+. Studies on the kinetic parameters in buffer solution and 30% dimethyl sulfoxide (DMSO) indicated that the affinity of BMG to 2-nitrophenyl-ß-D-galactopyranoside and its catalytic efficiency (κ cat/K m) increased with the addition of Mg2+. Furthermore, the addition of Mg2+ facilitated galactosylation reactions in 30% DMSO and increased product conversions by 24-41% due to the reversal of the thermodynamic equilibrium of hydrolysis. CONCLUSION: A convenient approach was established to improve the stability of BMG in aqueous hydrophilic solvents.

[Effects of knockout genes related to outer membrane on extracellular secretion of recombinant proteins in Escherichia coli BL21 (DE3)].

OBJECTIVE: We knocked out the genes related to lipopolysaccharide in outer membrane of Escherichia coli BL21 (DE3) to study the effects on extracellular secretion of recombinant proteins. METHODS: We generated waaF or msbB knockout mutants [E. coli BL21 (ΔwaaF) or E. coli BL21 (ΔmsbB) ] of E. coli BL21 (DE3) by using lambda-Red recombination system. Then, we transformed recombinant plasmids pET-ffase or pET-pga into E. coli BL21 (AmsbB) , E. coli BL21 (ΔwaaF) and E. coli BL21 (DE3) respectively, to generate the engineering strains E. coli BL21 (ΔmsbB)/ pET-ffase, E. coli BL21 (ΔwaaF)/pET-ffase, E. coli BL21 (DE3)/pET-ffase, E. coli BL21 (ΔmsbB)/pET-pga, E. coli BL21 (ΔwaaF)/pET-pga and E. coli BL21 (DE3)/pET-pga. Finally, we studied the effects of mutants on extracellular secretion of beta-fructofuranosidase (EC 3. 2. 1. 26, beta-FFase) and penicillin G acylase (EC 3. 5. 1. 11) in shaking flask fermentation. RESULTS: After induced expression for 4 hours, up to 19.7% of the beta-FFase activity was found in the culture medium with the msbB deletion mutant, and 50.9% with the waaF deletion mutant, compared to the original 2.6%. Besides, after induced expression for 24 hours, up to 1708 U/L extracellular activity of penicillin G acylase was found in the culture medium with the waaF deletion mutant, which was 4.1 times of the original. CONCLUSION: Knockout mutants (ΔmsbB and ΔwaaF) had significantly higher excretion of beta-FFase and the waaF deletion mutant had higher excretion of penicillin G acylase.