Yunlin Chen

Enhanced FK506 production in Streptomyces tsukubaensis by rational feeding strategies based on comparative metabolic profiling analysis

FK506, a widely used immunosuppressant, is produced by industrial fermentation processes using various Streptomyces species. However, the low titer becomes a bottleneck for its application and industrialization. It urgently required a full understanding of the biological mechanisms for FK506 overproduction. Towards this end, comparative metabolomics approach was employed to analyze metabolite concentrations difference of Streptomyces tsukubaensis cultivated in two media with low and high productivities. Initially, 98 intracellular metabolites were identified and 13 metabolites involved in five pathways were determined to be directly correlated with FK506 biosynthesis. Then in‐depth analysis elucidated how those key factors exerted influence on FK506 biosynthesis. Many previously unreported metabolites were shown to play an important role in FK506 biosynthesis and provided potential regulation points for external manipulation. Based on such key information, rationally designed feeding strategy was carried out. Results showed that the FK506 yield increased from 251 to 405 mg/L, whereas, by‐products FK520 and 37,38‐dihydro‐FK506 decreased by 31% and 39%, respectively, compared with the values of control. To our knowledge, it is the first study to apply the comparative metabolomics method to identify key metabolites to promote the FK506 production. The strategies developed here can easily be extended to titer improvement of other important microbial natural products and process optimization. Biotechnol. Bioeng. 2013;110: 2717–2730.

Rational medium optimization based on comparative metabolic profiling analysis to improve fumaric acid production.

To rationally guide fumaric acid production improvement, metabolic profiling approach was performed to analyze metabolite changes of Rhizopus oryzae FM19 under different fermentation conditions. A correlation between the metabolic profiling and fumaric acid production was revealed by principal component analysis as well as partial least squares. Citric acid, oxaloacetic acid, 2-oxoglutarate, lactic acid, proline, alanine, valine, leucine were identified to be mainly responsible for the metabolism difference, which were involved in the Embden-Meyerhof-Parnas, tricarboxylic acid cycle, amino acid metabolism and fatty acid metabolism. Through the further analysis of metabolites changes together with the above pathways, exogenous addition strategies were developed, which resulted in 14% increase of fumaric acid (up to 56.5 g/L) and less by-products. These results demonstrated that metabolic profiling analysis could be successfully applied to the rational guidance of medium optimization and the productivity improvement of value-added compounds.

Effect of Li diffusion on the composition of LiNbO3 at high temperature

Abstract LiNbO 3 crystals with a variety of compositions were prepared by the vapor transport equilibration (VTE) technique. Crystals were characterized through the measurements of fundamental absorption edge, lattice parameters and the electric field required for ferroelectric domain switching. The techniques employed for characterization served as tools for the determination of the composition and homogeneity of the crystals. We discussed the Li diffusion mechanisms in LiNbO 3 crystals at high temperature and found that the Li vacancy model is consistent with the experimental results for the VTE-grown LiNbO 3 crystal.

Domain reversion process in near-stoichiometric LiNbO3 crystals

Abstract LiNbO 3 single crystals with a composition close to stoichiometry ([Li]/[Li+Nb]=0.496) were grown by Czochralski method with K 2 O flux for the domain reversal characteristics investigation. The switching field for the domain reversal in the near-stoichiometric crystal was 8.0±0.5 kV/mm, which is about one-third of the switching field required for the congruent LiNbO 3 crystals. The resulted long switching time enabled us to observe, for the first time, clear domain growth process in near-stoichiometric LiNbO 3 crystals. Slow growth is also found of both the needle-shaped nuclei into larger domains on the existing domain wall and along the electrode fingers.

Metabolic flux analysis and principal nodes identification for daptomycin production improvement by Streptomyces roseosporus.

In the present work, a comprehensive metabolic network of Streptomyces roseosporus LC-54-20 was proposed for daptomycin production. The analysis of extracellular metabolites throughout the batch fermentation was evaluated in addition to daptomycin and biomass production. Metabolic flux distributions were based on stoichiometrical reaction as well as the extracellular metabolites fluxes. Experimental and calculated values for both the specific growth rate and daptomycin production rate indicated that the in silico model proved a powerful tool to analyze the metabolic behaviors based on the analysis under different initial glucose concentrations throughout the fermentation. Through manipulating different pH values, the production rates of various extracellular metabolites were also presented in this paper. Flux distribution variations revealed that the daptomycin production could be significantly influenced by the branch points of glucose 6-phosphate, 3-phosphoglycerate, phosphoenolpyruvate, pyruvate, and oxaloacetate. The five principal metabolites were certified as the flexible nodes and could form potential bottlenecks for a further enhancement of daptomycin production. Furthermore, various concentrations of the five precursors were added into the batch fermentation and led to the enhancement of daptomycin concentration and production rate.

Effect of Mg concentration on the domain reversal of Mg-doped LiNbO3

MgO-doped LiNbO3 (MgLN) crystal has been produced using the Czochralski method. The domain reversal characteristics of the MgO-doped LiNbO3 single crystals with different Mg doping levels have been investigated, and the switching field is found to decrease with the increasing of Mg concentration. The switching field for the domain reversal in the MgLN crystal doped with 6.5 mol % MgO was ∼4.6kV∕mm. This is about one-fifth of the switching field for the congruent crystal. The resistance of the poling MgLN crystals as a function of Mg concentration was measured, and the influence of doping Mg on domain reversion for Mg-doped LiNbO3 is discussed, and explain the physical mechanism of the polarization switching of the MgLN crystals.

Optical band gap transition from direct to indirect induced by organic content of CH3NH3PbI3 perovskite films

Most of the systematic studies on tuning the band gap in the family of organolead halide perovskites have focused on changing the compositions of halogens. Here, the effects of varying the organic content on the band gap of CH3NH3PbI3 were studied. The methylammonium lead iodide (CH3NH3PbI3) films were fabricated with different molar ratios of CH3NH3I to PbI2. We found that the films become compact and the crystalline size decreased from 6.0 to 0.2 μm and the optical band gap of CH3NH3PbI3 could be transferred from direct to indirect with increasing CH3NH3I content in the precursor. The experimental results demonstrated that the existence of the indirect band gap in CH3NH3PbI3 film and the CH3NH3I content plays a key role in adjusting the film morphology and optical band. The investigation of the optical band transition induced by changing organic content could provide a different view on studying CH3NH3PbI3 materials.

Improving the Photoluminescence Properties of Perovskite CH3NH3PbBr3-xClx Films by Modulating Organic Cation and Chlorine Concentrations

The photoluminescence (PL) properties of inorganic-organic perovskites can be drastically changed by tuning the halogen composition, especially the Cl content. However, our research demonstrated that in addition to the influence of Cl concentration, the PL emission intensity of CH3NH3PbBr3 strongly depends on the content of CH3NH3Br in the coating solution. The effects of CH3NH3Br and Cl concentrations on the PL properties of CH3NH3PbBr3-xClx were investigated. We found that a strong PL emission intensity of CH3NH3PbBr3 can be obtained from solutions with a high CH3NH3Br concentration. The PL emission intensities of CH3NH3PbBr3-xClx films were enhanced by adjusting the molar ratio of PbBr to PbCl2 only in a highly concentrated CH3NH3Br environment. Moreover, it was found that an optimum CH3NH3Br/PbBr2/PbCl2 ratio in the precursor solutions can be used to obtain the strongest PL emission intensity of CH3NH3PbBr3-xClx films. Further studies revealed that both CH3NH3Br and Cl concentrations significantly influence the CH3NH3PbBr3-xClx films evolution, which affects their PL properties.

Refractive index modulation in periodically poled MgO-doped congruent LiNbO3 crystal

An optical diffraction method is exploited to characterize periodically poled MgO-doped congruent LiNbO3 crystal fabricated by electric induced technique. The optical diffraction patterns indicate that the refractive index changes occur in periodic domain structures. Light diffraction from this type of refractive index modulation is simulated, thus providing an effective and nondestructive technique to determine the refractive index changes and domain structures. From the normalized diffraction intensity, we estimate the refractive index change to be in the magnitude of 10−5.

Enhanced second-harmonic generation by means of high-power confinement in a photovoltaic soliton-induced waveguide.

We present the first experimental demonstration of enhanced second-harmonic generation (SHG) by means of power confinement with a femtosecond laser in a photovoltaic soliton-induced waveguide. A dark spatial soliton created with a weak cw laser beam in a photovoltaic lithium niobate crystal induces an efficient waveguide for SHG, leading to a 60% enhancement of the conversion efficiency.