Complete microbial synthesis of crocetin and crocins from glycerol in Escherichia coli.

BACKGROUND: Crocin, a glycosylated apocarotenoid pigment predominantly found in saffron, has garnered significant interest in the field of biotechnology for its bioactive properties. Traditional production of crocins and their aglycone, crocetin, typically involves extraction from crocin-producing plants. This study aimed to develop an alternative biosynthetic method for these compounds by engineering the metabolic pathways of zeaxanthin, crocetin, and crocin in Escherichia coli strains. RESULTS: Employing a series of genetic modifications and the strategic overexpression of key enzymes, we successfully established a complete microbial pathway for synthesizing crocetin and four glycosylated derivatives of crocetin, utilizing glycerol as the primary carbon source. The overexpression of zeaxanthin cleavage dioxygenase and a novel variant of crocetin dialdehyde dehydrogenase resulted in a notable yield of crocetin (34.77 ± 1.03 mg/L). Further optimization involved the overexpression of new types of crocetin and crocin-2 glycosyltransferases, facilitating the production of crocin-1 (6.29 ± 0.19 mg/L), crocin-2 (5.29 ± 0.24 mg/L), crocin-3 (1.48 ± 0.10 mg/L), and crocin-4 (2.72 ± 0.13 mg/L). CONCLUSIONS: This investigation introduces a pioneering and integrated microbial synthesis method for generating crocin and its derivatives, employing glycerol as a sustainable carbon feedstock. The substantial yields achieved highlight the commercial potential of microbial-derived crocins as an eco-friendly alternative to plant extraction methods. The development of these microbial processes not only broadens the scope for crocin production but also suggests significant implications for the exploitation of bioengineered compounds in pharmaceutical and food industries.

Comparative Genomic Analysis of Agarolytic Flavobacterium faecale WV33T.

Flavobacteria are widely dispersed in a variety of environments and produce various polysaccharide-degrading enzymes. Here, we report the complete genome of Flavobacterium faecale WV33T, an agar-degrading bacterium isolated from the stools of Antarctic penguins. The sequenced genome of F. faecale WV33T represents a single circular chromosome (4,621,116 bp, 35.2% G + C content), containing 3984 coding DNA sequences and 85 RNA-coding genes. The genome of F. faecale WV33T contains 154 genes that encode carbohydrate-active enzymes (CAZymes). Among the CAZymes, seven putative genes encoding agarases have been identified in the genome. Transcriptional analysis revealed that the expression of these putative agarases was significantly enhanced by the presence of agar in the culture medium, suggesting that these proteins are involved in agar hydrolysis. Pangenome analysis revealed that the genomes of the 27 Flavobacterium type strains, including F. faecale WV33T, tend to be very plastic, and Flavobacterium strains are unique species with a tiny core genome and a large non-core region. The average nucleotide identity and phylogenomic analysis of the 27 Flavobacterium-type strains showed that F. faecale WV33T was positioned in a unique clade in the evolutionary tree.

Few-Layer Graphene Island Seeding for Dendrite-Free Li Metal Electrodes.

Li metal batteries such as Li-air and Li-S systems have increasingly attracted the attention of researchers because of their high energy densities, which are enhanced by the use of Li metal negative electrodes. However, poor cycle efficiency and safety concerns, which are mainly related to dendritic Li growth during cycling, need to be addressed. Here we propose a solution to the Li dendrite problems. We distributed chemically prepared nitrogen-doped few-layer graphene (N-FLG) sheets on Cu substrates to create island structures. The island-type FLG on the Cu electrode was prepared via spin-coating using slurries that included a polymer binder. When the electrode was used for Li deposition, Li ions were first inserted into the graphene layers. Then, Li metal nucleation occurred at the N-FLG sheets owing to their high electrical conductivity; meanwhile, an insulating polymer layer on the Cu prevented the growth of metallic Li there. Lastly, Li metal grew from the edges of N-FLG sheets in both the lateral and vertical direction, and Li metal deposits filled the gaps between the N-FLG islands as well as covering the remainder of the electrode surface. Thus, stable cycling with flat voltage profiles was demonstrated over 100 cycles at a current density of 2 mA cm-2. The materials and electrochemical characterization results highlight the effectiveness of this method, which paves the way for the development of robust, dendrite-free Li metal electrodes.

Effect of multilayer structure on cyclic performance of Si/Fe anode electrode in lithium-ion secondary batteries.

A buffer-strengthened Si/Fe multilayer film, consisting of amorphous silicon layers and polycrystalline Fe layers, is investigated as the anode for Li-ion batteries. This film can achieve a stable cycle-life performance with a high capacity. Decreasing the thickness of the Fe layer can lead to a higher capacity, which is related to the fast transport of the Li ion, but the cyclic performance deteriorates with repeated cycling. In contrast, increasing the thickness of the Fe buffer layers and the number of deposit stacks improves the cycle life with high reversibility. Because of the strain in the Si layers suppressed by the primary multilayer structure, the long-term strength is preserved and the substantial fracture toughness is enhanced by the increasing numbers of effective grain boundaries and interfacial layers. In addition, we demonstrate that the Ti underlayer promotes the electrochemical properties in the Si/Fe multilayer for various Fe layer thicknesses because of the enhanced adhesion of the interfacial electrode and current collector. The mechanically optimized Si/Fe multilayer films can have superior cycle-life performances and higher capacities. Notably, the 16-bilayer deposited electrode exhibits an excellent capacity retention of ~95% with ~204 mAh g(-1) over 300 cycles at a 1 C rate.

Effect of sintering conditions on the magnetic and microstructural properties of Nd-Fe-B sintered magnets doped with DyF(3) powders.

The microstructural and magnetic property changes of DyF(3)-doped (Nd(26.06), Dy(6.51))-Fe(bal) -B(0.97)-M(2.39) (wt. %) (M = Cu, Al, Co, and Nb) sintered magnets as functions of the sintering conditions were studied. The sintering conditions for the optimum core-shell microstructure were determined. When the magnets were sintered at 1050 °C for 4 h, a coercivity of 35.1 kOe was obtained without sacrificing the remanence. When the magnets were doped with DyF(3), the formation of the RE-rich phase (Nd-Dy-O) was effectively suppressed and, hence, saving the Dy. In addition, the formation of a cubic-NdOF triple-junction phase (TJP) improves the interface uniformity and enhances the coercivity.

Perpendicular magnetic anisotropy properties of CoFeB/Pd multilayers.

The perpendicular magnetic anisotropy (PMA) properties of CoFeB/Pd multilayers are investigated as functions of the thickness of the constituent layers of the multilayers and of the substrate type. A relatively strong PMA is formed at small CoFeB thicknesses of 0.3 and 0.5 nm over the entire Pd thickness range of 0.47 to 1.26 nm. At a fixed CoFeB thickness, the PMA tends to increase with increasing Pd thickness and this behavior can be attributed to the fact that the interface tends to become flatter and smoother at a higher Pd thicknesss, leading to a stronger surface anisotropy. A stronger PMA is observed for the glass substrate than for the MgO substrate. Since the thermal stress formed at the CoFeB layer is tensile for both the glass and MgO substrates, the magnetoelastic interactions suggest the possibility of forming a Co-Pd alloy with a negative saturation magnetostriction at the CoFeB/Pd interfaces.

Field emission characteristics of electrochemically synthesized nickel nanowires with oxygen plasma post-treatment.

The field emissive, electrical, magnetic, and structural characteristics of nickel (Ni) nanowires synthesized using the electrochemical deposition method with an alumina nanoporous template are reported. The synthesis and formation of Ni nanowires were confirmed by XRD, SEM, and HR-TEM experiments. Ferromagnetic hysteresis curves and the metallic temperature dependence of the current-voltage characteristics were observed for the Ni nanowire systems. The nanotip emitters of the field emission cells of the Ni nanowires after O(2) plasma treatment were easily patterned using the solution drop casting (SDC) method, in which the Ni nanowires were homogeneously dispersed in organic solvents, and then dropped and dried on an n-type doped Si substrate as the cathode. For the O(2) plasma treated Ni nanowires, we observed that the inhomogeneous oxidized layer on their surface was reduced, that the current density of the field emission cell increased from approximately 3.0 x 10(-9) to approximately 1.0 x 10(-3) A cm(-2) due to field emission, and that the lowest threshold electric field was approximately 4 V microm(-1). The field enhancement factor was estimated as approximately 1300 for the O(2) plasma treated Ni nanowires. The evolution of the field emission obtained from the phosphor screen was observed at different applied electric fields.