Arbitrary-order three-point finite difference method for the modal analysis of chiral waveguides.

A three-point finite difference method with an arbitrary order of accuracy is proposed for the modal analysis of chiral planar waveguides. The elaborate application of a nonuniform grid, compact finite difference technique, and boundary conditions results in an efficient, easily implemented, and versatile tool for the modal analysis of chiral planar waveguides with an arbitrarily discontinuous profile of permittivity, permeability, and chirality. In particular, this method efficiently resolves the fine structures in plasmon and photonic crystal waveguides. For the test model of a chiral-metallic plasmon waveguide, stable convergence up to a sixteenth order of accuracy can be obtained, which produces a relative error on the effective index that approaches the machine precision with only eighty grid points.

Efficient full-vectorial modal analysis based on immersed interface method for dielectric chiral optical fibers.

This paper presents the application of an immersed interface method in efficient modal analysis of dielectric chiral optical fibers. Under the easily implemented finite-difference framework, the second- and fourth-order accuracy formulations are developed, which in principle are applicable for automatically computing various types of modes in dielectric chiral optical fibers with an arbitrary, electromagnetic parameters piecewise constant profile. To validate the developed formulations, numerical examples are given for the guided, leaky, and surface modes in dielectric chiral step-profile and Bragg fibers.

Porphyrinic Probe for Fluorescence "Turn-On" Monitoring of Cu+ in Aqueous Buffer and Mitochondria.

A zinc(II) porphyrin derivative (ZPSN) was designed and synthesized, and this probe exhibited rapid, selective and reversible binding to Cu+ for fluorescence monitoring in pure aqueous buffer. The detection mechanism is based on Cu+-activated disruption of axial coordination between the pyridyl ligand and the zinc center, which changes the molecular geometry and inhibits intramolecular electron transfer (ET), leading to fluorescence enhancement of the probe. The proposed sensing mechanism was supported by UV-vis spectroscopy/fluorescence spectral titration, NMR spectroscopy, mass spectrometry, and time-resolved fluorescence decay studies. The dissociation constant was calculated to be 6.53 × 10-11 M. CLSM analysis strongly suggested that ZPSN could penetrate live cells and successfully visualize Cu+ in mitochondria. This strategy may establish a design and offer a potential building block for construction of other metal sensors based on a similar mechanism.

Partially overlapping primer-based PCR for genome walking.

Current genome walking methods are cumbersome to perform and can result in non-specific products. Here, we demonstrate the use of partially overlapping primer-based PCR (POP-PCR), a direct genome walking technique for the isolation of unknown flanking regions. This method exploits the partially overlapping characteristic at the 3' ends of a set of POP primers (walking primers), which guarantees that the POP primer only anneals to the POP site of the preceding PCR product at relatively low temperatures. POP primer adaptation priming at the genomic DNA/POP site occurs only once due to one low-/reduced-stringency cycle in each nested PCR, resulting in the synthesis of a pool of single-stranded DNA molecules. Of this pool, the target single-stranded DNA is replicated to the double-stranded form bound by the specific primer and the POP primer in the subsequent high-stringency cycle due to the presence of the specific primer-binding site. The non-target single stranded DNA does not become double stranded due to the absence of a binding site for any of the primers. Therefore, the POP-PCR enriches target DNA while suppressing non-target products. We successfully used POP-PCR to retrieve flanking regions bordering the gadA locus in Lactobacillus brevis NCL912, malQ in Pichia pastoris GS115, the human aldolase A gene, and hyg in rice.

Rapid removal of aniline from contaminated water by a novel polymeric adsorbent.

Dummy molecularly imprinted polymers (DMIPs) for aniline were synthesized by a thermal polymerization method using acrylamide as a functional monomer, ethylene dimethacrylate as a crosslinker, 2,2-azobisisobutyronitrile as a free radical initiator, acetonitrile as a porogenic solvent, and analogues of aniline, namely sulfadiazine, as the template. The DMIPs that were obtained showed a high affinity to aniline compared to non-imprinted polymers. It was proven that the DMIPs obtained using sulfadiazine as the template were much better than the molecularly imprinted polymers using aniline as the template. The results indicated that the Freundlich model was fit for the adsorption model of DMIP for aniline and the adsorption model of the DMIP for aniline was multilayer adsorption. Furthermore, the results showed that the DMIP synthesized by bulk polymerization could be used as a novel adsorbent for removal of aniline from contaminated water.

Transverse electromagnetic modes in chiral negatively refractive fibers and a new type of space-division multiplexing.

We investigated theoretically chiral negatively refractive fibers that guide transverse electromagnetic modes. In this Letter, novel properties of such fibers are presented, including arbitrariness of modal field and arbitrarily scalable core radius. Based on these novel properties, we conceptually propose a new type of space-division multiplexing that uses different spatial positions of the core of such fascinating fibers as different data paths.

gadA gene locus in Lactobacillus brevis NCL912 and its expression during fed-batch fermentation.

Normally, Lactobacillus brevis has two glutamate decarboxylase (GAD) genes; gadA and gadB. Using PCR, we cloned the gadA gene from L. brevis strain NCL912, a high yield strain for the production of gamma-aminobutyric acid (GABA). However, despite using 61 different primer pairs, including degenerate primers from conserved regions, we were unable to use PCR to clone gadB from the NCL912 strain. Furthermore, we could not clone it by genomic walking over 3000 bp downstream of the aldo-keto reductase gene, a single-copy gene that is located 1003 bp upstream of gadB in L. brevis ATCC367. Altogether, the data suggest that L. brevis NCL912 does not contain a gadB gene. By genomic walking, we cloned regions upstream and downstream of the gadA gene to obtain a 4615 bp DNA fragment that included the complete gadA locus. The locus contained the GAD gene (gadA) and the glutamate:GABA antiporter gene (gadC), which appear to be transcribed in an operon (gadCA), and a transcriptional regulator (gadR) of gadCA. During whole fed-batch fermentation, the expression of gadR, gadC and gadA was synchronized and correlated well with GABA production. The gadA locus we cloned from NCL912 has reduced homology compared with gadA loci of other L. brevis strains, and these differences might explain the ability of NCL912 to produce higher levels of GABA in culture.

[Isolation and characterisation of an aflatoxin B1-degrading bacterium].

OBJECTIVE: Aflatoxins are toxic and carcinogenic fungal metabolites. The aim of this research was to isolate aflatoxin B1 (AFB1)-degrading bacteria. METHODS: Samples from various sources were screened by using coumarin as the sole carbon source. The strains that could grow in the medium with coumarin carbon source were detected for their degradation of AFB1 ability by addition of AFB1 (2.5 microg/mL) to the cultured broth. Among the positive strains, F4 strain with the highest activities was identified according to its morphological, physiological and biochemical properties together with phylogenetic analysis of its 16S rRNA sequence. The effects of degradation conditions such as bacterial cell concentration, pH, temperature, metal ions on the degrading AFB, were investigated. RESULTS: Ten isolates showed good AFB, reduction activity and they could grow well on coumarin carbon source. Strain F4, obtained from Budorcas taxicolor feces could reduce AFB1 by 90.03% after incubation in the liquid medium at 37 degrees C for 72 h. F4 was preliminary identified to be Pseudomonas stutzeri with morphology, physiological and biochemical properties and 16S rRNA gene sequence. The active degrading component existed in the cell of F4, and the degrading activity was interrelated with cell concentration, temperature, pH and metal ions. CONCLUSION: An AFB1-degrading strain F4 was isolated from animal feces and identified as Pseudomonas stutzeri. The activive component of AFB1 degradation was mainly in the cell of F4.

Method for screening of bacterial strains biosynthesizing specific conjugated linoleic acid isomers.

A simple and accurate method for screening of bacterial strains with the ability to convert free linoleic acid into specific conjugated linoleic acid (CLA) isomers has been developed by combining the ultraviolet spectral scan and capillary electrophoresis analysis. The ultraviolet spectral scan was carried out for preliminary screening of bacterial strains with the capacity to biosynthesize CLA, and the absorption peak at 228-235 nm was used for assessing the possible production of CLA by bacteria. The capillary electrophoresis analysis was used as the follow-up confirmation to definitively conclude CLA production and the composition of CLA isomers. Linoleic acid at the concentration of 25 µg/mL, which showed little inhibitory effect on the growth of bacteria, was used for initial screening of CLA-producing strains. The strains with the ability to produce specific CLA isomers can be selected quickly from a large number of bacteria by this high-throughput method.

[Identification and denitrification of an aerobic bacterium].

OBJECTIVE: Denitrifying bacteria play an important role in the biological nitrogen removal process, especially the aerobic denitrifying bacteria. However, there are few studies on aerobic denitrifying bacteria. The present study aimed at the isolation of aerobic denitrifying bacteria with high ammonium and nitrite nitrogen removing ability from environmental samples, and its phylogeny and denitrifying characteristics. METHODS: Based on the aerobic denitrifying activity, ammonium and nitrite nitrogen removing ability, the strains were isolated from sludge, water and sediment in a eutrophicated pond. A strain with the highest activities was identified according to its morphological, physiological and biochemical properties and phylogenetic analysis of its 16S rRNA sequence. By using NO(3-)-N, NH(4+)-N and NO(2-)-N as the sole nitrogen source respectively, its denitrifying characteristics, and the effects of culture conditions such as initial pH of medium, temperature, carbon source, shaking speed on the ability of removing ammonium and nitrite nitrogen, were investigated under aerobic condition. RESULTS: Among the isolated strains, strain C-4 showed the highest ability of removing ammonium and nitrite nitrogen. Strain C-4 was identified as Acinetobacter sp.. Under the conditions of sodium citrate as carbon source, temperature 30 degres C, shaking speed 120 r/min, cell age of 18 h, pH 8.5 for 200 mg/L NH(4+)-N medium and pH 7.5 for 100 mg/L NO(2-)-N medium, the net removal efficiency of nitrogen were 65.8% and 47.8% after 15 h and 12 h, respectively. CONCLUSION: An aerobic denitrifying strain Acinetobacter sp. C-4 (HQ896038) was isolated from water pond, and it exhibited high net removal efficiency of nitrogen in relative media. The net removal efficiency of nitrogen of strain C-4 was 73.04% in dealing with a eutrophicated pond water.

[Analysis of differential expression proteins and functions in Lactobacillus brevis NCL912 under acid stress].

OBJECT: We investigated the proteomic profile of Lactobacillus brevis NCL912 under optimum pH and acidic pH in the media without the addition of sodium L- glutamate to characterize the differential expression proteins and function by two-dimensional gel electrophoresis. METHODS: The differential expression proteins were separated and analyzed by two-dimensional gel electrophoresis, mass spectrum and bioinformatics. RESULTS: The results showed that the two-dimensional gel electrophoresis profiles of L. brevis NCL912 were uniformity, well-resolution and repeatability. 25 proteins were differently expressed in the two profiles. Among them, 8 proteins were identified and analyzed by the mass spectrum and bioinformatics due to the lack of genome sequence data of L. brevis NCL912. These proteins played the roles of the synthesis of protein and DNA, glycolysis and regulating the cellular energy level. CONCLUSION: The differential expression proteins might play the important role in the acid stress resistance mechanism which may protect cell against acid stress.

Separation of gamma-aminobutyric acid from fermented broth.

Gamma-aminobutyric acid (GABA) is a non-proteinaceous amino acid that is widely distributed in nature and acts as the major inhibitory neurotransmitter in the mammalian brain. This study aimed to find a separation method for getting high-purity GABA from a fermented broth. Firstly, a fermented broth with a high content of GABA (reaching 997 ± 51 mM) was prepared by fermentation with Lactobacillus brevis NCL912. GABA purification was conducted by successive centrifugation, filtration, decoloration, desalination, ion-exchange chromatography (IEC), and crystallization. Inorganic salt (Na2SO4) was removed from the both by desalination with 70% ethanol solution. A ninhydrin test strip was designed for the real-time detection of GABA during IEC. The recovery rate for the whole purification process was about 50%. The purified product was characterized by thin-layer chromatography and HPLC, and its purity reached 98.66 ± 2.36%.

Proteomic analysis of differentially expressed proteins in Lactobacillus brevis NCL912 under acid stress.

Protein expression of Lactobacillus brevis NCL912 under acid stress was analysed by two-dimensional gel electrophoresis and MS. Twenty-five proteins were differentially expressed under acid stress. Among them, eight protein spots were identified by matrix-assisted laser desorption/ionization time-of-flight MS, of which seven were upregulated and one was downregulated. The function of the downregulated protein was unknown and the putative functions of the upregulated proteins were categorized as stress response, DNA repair, protein synthesis and glycolysis. Quantitative real-time PCR was used to further validate these differentially expressed proteins at the mRNA level and a positive correlation between the content of the proteins and their mRNA levels was found. The results suggest that these proteins are involved in the acid stress response mechanisms of this bacterium.

Production of gamma-aminobutyric acid by Lactobacillus brevis NCL912 using fed-batch fermentation.

BACKGROUND: Gamma-aminobutyric acid is a major inhibitory neurotransmitter in mammalian brains, and has several well-known physiological functions. Lactic acid bacteria possess special physiological activities and are generally regarded as safe. Therefore, using lactic acid bacteria as cell factories for gamma-aminobutyric acid production is a fascinating project and opens up a vast range of prospects for making use of GABA and LAB. We previously screened a high GABA-producer Lactobacillus brevis NCL912 and optimized its fermentation medium composition. The results indicated that the strain showed potential in large-scale fermentation for the production of gamma-aminobutyric acid. To increase the yielding of GABA, further study on the fermentation process is needed before the industrial application in the future. In this article we investigated the impacts of pyridoxal-5'-phosphate, pH, temperature and initial glutamate concentration on gamma-aminobutyric acid production by Lactobacillus brevis NCL912 in flask cultures. According to the data obtained in the above, a simple and effective fed-batch fermentation method was developed to highly efficiently convert glutamate to gamma-aminobutyric acid. RESULTS: Pyridoxal-5'-phosphate did not affect the cell growth and gamma-aminobutyric acid production of Lb. brevis NCL912. Temperature, pH and initial glutamate concentration had significant effects on the cell growth and gamma-aminobutyric acid production of Lb. brevis NCL912. The optimal temperature, pH and initial glutamate concentration were 30-35 °C, 5.0 and 250-500 mM. In the following fed-batch fermentations, temperature, pH and initial glutamate concentration were fixed as 32 °C, 5.0 and 400 mM. 280.70 g (1.5 mol) and 224.56 g (1.2 mol) glutamate were supplemented into the bioreactor at 12 h and 24 h, respectively. Under the selected fermentation conditions, gamma-aminobutyric acid was rapidly produced at the first 36 h and almost not produced after then. The gamma-aminobutyric acid concentration reached 1005.81 ± 47.88 mM, and the residual glucose and glutamate were 15.28 ± 0.51 g L-1 and 134.45 ± 24.22 mM at 48 h. CONCLUSIONS: A simple and effective fed-batch fermentation method was developed for Lb. brevis NCL912 to produce gamma-aminobutyric acid. The results reveal that Lb. brevis NCL912 exhibits a great application potential in large-scale fermentation for the production of gamma-aminobutyric acid.

Circularly polarized guided modes in dielectrically chiral photonic crystal fiber.

The effect of dielectric chirality on the polarization states and mode indices of guided modes in photonic crystal fiber (PCF) is investigated by a modified plane-wave expansion (PWE) method. Using a solid-core chiral PCF as a numerical example, we show that circular polarization is the eigenstate of the fundamental mode. Mode index divergence between right-handed circularly polarized (RCP) and left-handed circularly polarized (LCP) states is demonstrated. Chirality's effect on mode index and circular birefringence (CB) in such a PCF is found to be similar to that in bulk chiral media.

Antioxidant activity of peptide fractions derived from cottonseed protein hydrolysate.

BACKGROUND: Cottonseed protein is widely regarded as a potential source of nutrients for humans and animals, but it is mainly used as forage in China. In the present study, Neutrase was employed to hydrolyse cottonseed protein to produce a hydrolysate with antioxidant activity suitable for conversion to high-value products. The antioxidant potential of the cottonseed protein hydrolysate (CPH) and its fractions was investigated using different in vitro methods. Furthermore, the amino acid composition of the CPH fractions was determined to evaluate the relationship between antioxidant activity and amino acid composition. RESULTS: The CPH prepared using Neutrase was separated into four fractions (I, II, III and IV) by gel filtration on Sephadex G-25. All fractions were effective antioxidants, with fraction III (0.8-1.2 kDa) showing the strongest activity. The amino acid analysis showed that fraction III also had the highest total amino acid content (616.8 g kg(-1) protein) and was rich in Phe, His, Pro, Met, Ile and Cys compared with the other fractions. CONCLUSION: The results showed that the hydrolysate derived from cottonseed protein, particularly fraction III, could be a natural antioxidant source suitable for use as a food additive.

Lactic acid bacterial cell factories for gamma-aminobutyric acid.

Gamma-aminobutyric acid is a non-protein amino acid that is widely present in organisms. Several important physiological functions of gamma-aminobutyric acid have been characterized, such as neurotransmission, induction of hypotension, diuretic effects, and tranquilizer effects. Many microorganisms can produce gamma-aminobutyric acid including bacteria, fungi and yeasts. Among them, gamma-aminobutyric acid-producing lactic acid bacteria have been a focus of research in recent years, because lactic acid bacteria possess special physiological activities and are generally regarded as safe. They have been extensively used in food industry. The production of lactic acid bacterial gamma-aminobutyric acid is safe and eco-friendly, and this provides the possibility of production of new naturally fermented health-oriented products enriched in gamma-aminobutyric acid. The gamma-aminobutyric acid-producing species of lactic acid bacteria and their isolation sources, the methods for screening of the strains and increasing their production, the enzymatic properties of glutamate decarboxylases and the relative fundamental research are reviewed in this article. And the potential applications of gamma-aminobutyric acid-producing lactic acid bacteria were also referred to.

Synthesis, antitumor evaluation and crystal structure of hydroxyurea derivatives.

A series of hydroxyurea derivatives have been synthesized and elucidated by means of FT-IR, (1)H-, (13)C-NMR and MS. The exact stereostructures of representative compounds have been determined by X-ray crystal structure analysis. In the crystals, inversion dimers linked by pairs of N-H...O hydrogen bonds occurred, and further N-H...O links led to chains of molecules. In vitro antitumor activities against Tca8113 human tongue cancer cells and L1210 murine leukemia cells were evaluated. A total of 8 of the 12 compounds had higher inhibitory activities than hydroxyurea against L1210 cells. Among them, the most promising compounds were 3e, 3d, 3a and 2d.

Medium optimization for production of gamma-aminobutyric acid by Lactobacillus brevis NCL912.

Production of gamma-aminobutyric acid (GABA) was carried out in Erlenmeyer flasks by Lactobacillus brevis NCL912. Traditional methods were first adopted to select the key factors that impact the GABA production to preliminarily determine the suitable concentration ranges of the key factors. It was found that glucose, soya peptone, Tween-80 and MnSO(4).4H(2)O were the key factors affecting GABA production. Then, response surface methodology was applied to analyze the optimum contents of the four key factors in the medium, and the production of GABA was predicted as 349.69 mM under the optimized conditions with this model. Afterward, the experiment was performed under the optimized conditions, and the yield of GABA reached 345.83 mM, which was 130% higher than the initial medium. The results showed that experimental yield and predicted values of GABA yield were in good agreement.

Pre-staining paper chromatography method for quantification of gamma-aminobutyric acid.

The routine method of paper chromatography includes five steps: spotting, separating, drying, spraying/immersing and color development. In this paper, a pre-staining paper chromatography which only consisted of spotting, separating and color development was developed for quantitative analysis of gamma-aminobutyric acid. Compared to the routine paper chromatography, the improved method is clean, rapid, inexpensive and reproducible. The effects of ninhydrin concentration, color temperature, color time and Cu(2+) concentration on the color yield in the ninhydrin reaction were optimized. And then the pre-staining paper chromatography coupled with vis spectrophotometry was applied to gamma-aminobutyric acid quantification. The results indicated that the limit of detection was 0.05 mg mL(-1) and the linear range was from 0.5 to 20.0 mg mL(-1). Furthermore, an excellent correlation coefficient was observed with an R(2)=0.998. The method is accurate (RSD<2.64%), and has good recoveries (102.7-103.9%). The validation of the modified technique was verified by a HPLC method.