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Host System (host + system)
Selected AbstractsPure and Saturated Red Electroluminescent Polyfluorenes with Dopant/Host System and PLED Efficiency/Color Purity Trade-OffsADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Lei Chen Abstract Three kinds of red electroluminescent (EL) polymers based on polyfluorene as blue host and 2,1,3-benzothiadiazole derivatives with different emission wavelengths as red dopant units on the side chain are designed and synthesized. The influence of the photoluminescence (PL) efficiencies and emission wavelengths of red dopants on the EL efficiencies and color purities of the resulting polyfluorene copolymers of dopant/host system is investigated by adjusting the electron donating ability of the donor units in D- , -A-D typed 2,1,3-benzothiadiazole derivatives. The devices of these red-emitting polymers realize remarkable EL efficiency/color purity trade-offs. The single-layer devices with the configuration of ITO/PEDOT:PSS/Polymer/Ca/Al show pure red emission at 624 nm with a luminous efficiency of 3.83 cd A,1 and CIE of (0.63, 0.35) for PFR1, saturated red emission at 636 nm with a luminous efficiency of 2.29 cd A,1 and CIE of (0.64, 0.33) for PFR2, respectively. By introduction of an additional electron injection layer PF-EP(Ethanol soluble phosphonate-functionalized polyfluorene), high performance pure and saturated red emission two-layer devices (ITO/PEDOT:PSS/Polymer/PF-EP/LiF/Al) were achieved with maximum luminous efficiencies of 5.50 cd A,1 and CIE of (0.62, 0.35) for PFR1, 3.10 cd A,1 and CIE of (0.63, 0.33) for PFR2, respectively, which are the best results for pure and saturated fluorescent red EL polymers reported so far. [source] Characterizing the regulation of the Pu promoter in Acinetobacter baylyi ADP1ENVIRONMENTAL MICROBIOLOGY, Issue 7 2008Wei E. Huang Summary Effective gene trapping and screening requires sensory and regulatory compatibility of both host and exogenous systems. The naturally competent bacterium Acinetobacter baylyi ADP1 is able to efficiently take up and integrate exogenous DNA into the chromosome, making it an attractive host system for a wide range of metagenomic applications. To test the ability of A. baylyi ADP1 to express the XylR-regulated Pu promoter from Pseudomonas putida mt-2, we have constructed and examined an A. baylyi ADP1 strain, ADPWH- Pu-lux-xylR. The Pu promoter in ADPWH- Pu-lux-xylR was specifically induced by toluene, m -, p - and o- xylene. The substrate-induced Pu promoter was highly dependent on the growth medium: it was repressed in rich media until stationary phase, but was immediately induced in minimal medium with glucose as the sole carbon source (MMG). However, the Pu promoter was repressed in MMG when it was supplemented with 5 g l,1 yeast extract. Further investigation showed that the Pu promoter in MMG was repressed by 0.5 g l,1 aspartic acid or asparagine, but not repressed by glutamine. Changing the carbon/nitrogen ratios by addition of ammonia did not significantly affect the Pu promoter activity but addition of nitrate did. These results show that A. baylyi ADP1 reproduced characteristics of the XylR-regulated Pu promoter observed in its original host. It demonstrates that A. baylyi could provide an excellent genetic host for a wide range of functional metagenomic applications. [source] Novel archaeal plasmid pAH1 and its interactions with the lipothrixvirus AFV1MOLECULAR MICROBIOLOGY, Issue 1 2009Tamara Basta Summary At present very little is known about interactions between extrachromosomal genetic elements in Archaea. Here we describe an Acidianus strain which carries naturally a novel 28 kb conjugative plasmid-like element, pAH1, and also serves as a laboratory host for lipothrixvirus AFV1. In an attempt to establish a system for studying plasmid,virus interactions we characterized the genome of pAH1 which closely resembles those of the Sulfolobus conjugative plasmids pARN3 and pARN4. pAH1 integrates site specifically into, and excises from, the host chromosome indicating a dynamic interaction with the latter. Although nucleotide sequence comparisons revealed extensive intergenomic exchange during the evolution of archaeal conjugative plasmids, pAH1 was shown to be stably maintained suggesting that the host system is suitable for studying plasmid,virus interactions. AFV1 infection and propagation leads to a loss of the circular form of pAH1 and this effect correlates positively with the increase in the intracellular quantity of AFV1 DNA. We infer that the virus inhibits plasmid replication since no pAH1 degradation was observed. This mechanism of archaeal viral inhibition of plasmid propagation is not observed in bacteria where relevant bacteriophages either are dependent on a conjugative plasmid for successful infection or are excluded by a resident plasmid. [source] Quantitative proteomes and in vivo secretomes of progressive and regressive UV-induced fibrosarcoma tumor cells: Mimicking tumor microenvironment using a dermis-based cell-trapped system linked to tissue chamberPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 24 2007Yang Shi Abstract The alterations of tumor proteome and/or in vivo secretome created by host-tumor cell interaction may be crucial factors for tumors to undergo progression or regression in a host system. Two UV-induced fibrosarcoma tumor cell lines (UV-2237 progressive cells and UV-2240 regressive cells) were used as models to address this issue. Hundreds of proteins including in vivo secretome have been identified and quantified via an isotope-coded protein label (ICPL) in conjunction with high-throughput NanoLC-LTQ MS analysis. A newly designed technology using a dermis-based cell-trapped system was employed to encapsulate and grow 3-D tumor cells. A tissue chamber inserted with a tumor cell-trapped dermis was implanted into mice to mimic the tumor microenvironment. The in vivo secretome created by host-tumor interaction was characterized from samples collected from tissue chamber fluids via ICPL labeling mass spectrometric analysis. Twenty-five proteins including 14-3-3 proteins, heat shock proteins, profilin-1, and a fragment of complement C3 with differential expression in proteomes of UV-2237 and UV-2240 cells were revealed. Three secreted proteins including myeloperoxidase, alpha-2-macroglobulin, and a vitamin D-binding protein have different abundances in the in vivo secretome in response to UV-2237 and UV-2240 cells. Differential tumor proteomes and in vivo secretome were thus accentuated as potential therapeutic targets to control tumor growth. [source] Ectoparasite load is linked to ontogeny and cell-mediated immunity in an avian host system with pronounced hatching asynchronyBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2008RADOVAN VÁCLAV Several contrasting hypotheses have been proposed to account for host age-biased parasite distribution, with some of them suggesting a key role of ectoparasites in the evolution and maintenance of weight hierarchies within broods. We examined parasite distribution among individual hosts across the whole period of host exposure to the parasite in a host system that shows distinct within-brood differences in age and age-related mortality. By contrast to previous hypotheses, we found that the abundance of a haematophagous, mobile ectoparasite Carnus haemapterus on nestling European rollers (Coracias garrulus) was highest approximately during the mid-nestling stage of their host, coinciding with the inflection point of the host growth phase. Parasite load increased neither with absolute resource availability (i.e. body size), nor body condition index. By contrast to previous evidence, higher parasite load under natural conditions was associated with a stronger cell-mediated immune response. However, this association was moderated by low parasite densities, as well as a better brood body condition index. Overall, although we revealed remarkable host ontogenetic effects on parasite distribution, the present study suggests that a highly mobile ectoparasite generally prefers healthier hosts. We propose that, in host systems with a marked asynchrony of hatching and background mortality within the brood, parasites favour persistence rather than nutritional attractiveness of the host. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 463,473. [source] A-ring ortho -specific monohydroxylation of daidzein by cytochrome P450s of Nocardia farcinica IFM10152BIOTECHNOLOGY JOURNAL, Issue 11 2009Kwon-Young Choi Abstract The bioconversion of the isoflavonoid daidzein using whole cell Nocardia farcinica IFM10152 showed two kinds of major metabolic modifications, i.e. mono-hydroxylation and subsequent O -methylation. The major hydroxylated products of daidzein prior to the O -methylation reaction were 3',4',7-trihydroxyisoflavone (3'-ODI), 4',6,7-trihydroxyisoflavone (6-ODI) and 4',7,8-trihydroxyisoflavone (8-ODI), which are mono-hydroxylated at the ortho position of each hydroxyl group of daidzein. To identify monooxygenases playing a key role in the monohydroxylation of the A-ring of daidzein, all genes of 27 cytochrome P450s from N. farcinica IFM10152 were cloned and transformed into a E. coli BL21 (DE3) host system. By this enzymatic reaction using the mutants and the genome sequence analysis of N. farcinica IFM10152, it was revealed that nfa12130 and nfa33880 P450 genes clustered with their own ferredoxins and ferredoxin reductases (nfa12140+nfa12150 and nfa338870+nfa33860, respectively) are responsible for the hydroxylation of the A-ring of daidzein, and their major reaction products were 6-ODI and 8-ODI, respectively. [source] Biosynthesis of the Vitamin E Compound ,-Tocotrienol in Recombinant Escherichia coli CellsCHEMBIOCHEM, Issue 15 2008Christoph Albermann Dr. Abstract The biosynthesis of natural products in a fast growing and easy to manipulate heterologous host system, such as Escherichia coli, is of increasing interest in biotechnology. This procedure allows the investigation of complex natural product biosynthesis and facilitates the engineering of pathways. Here we describe the cloning and the heterologous expression of tocochromanol (vitamin E) biosynthesis genes in E. coli. Tocochromanols are synthesized solely in photosynthetic organisms (cyanobacteria, algae, and higher green plants). For recombinant tocochromanol biosynthesis, the genes encoding hydroxyphenylpyruvate dioxygenase (hpd), geranylgeranylpyrophosphate synthase (crtE), geranylgeranylpyrophosphate reductase (ggh), homogentisate phytyltransferase (hpt), and tocopherol-cyclase (cyc) were cloned in a stepwise fashion and expressed in E. coli. Recombinant E. coli cells were cultivated and analyzed for tocochromanol compounds and their biosynthesis precursors. The expression of only hpd from Pseudomonas putida or crtE from Pantoea ananatis resulted in the accumulation of 336 mgL,1 homogentisate and 84 ,gL,1 geranylgeranylpyrophosphate in E. coli cultures. Simultaneous expression of hpd, crtE, and hpt from Synechocystis sp. under the control of single tac-promoter resulted in the production of methyl-6-geranylgeranyl-benzoquinol (67.9 ,g,g,1). Additional expression of the tocopherol cyclase gene vte1 from Arabidopsis thaliana resulted in the novel formation of a vitamin E compound,,-tocotrienol (15 ,g,g,1),in E. coli. [source] Seasonality and the dynamics of infectious diseasesECOLOGY LETTERS, Issue 4 2006Sonia Altizer Abstract Seasonal variations in temperature, rainfall and resource availability are ubiquitous and can exert strong pressures on population dynamics. Infectious diseases provide some of the best-studied examples of the role of seasonality in shaping population fluctuations. In this paper, we review examples from human and wildlife disease systems to illustrate the challenges inherent in understanding the mechanisms and impacts of seasonal environmental drivers. Empirical evidence points to several biologically distinct mechanisms by which seasonality can impact host,pathogen interactions, including seasonal changes in host social behaviour and contact rates, variation in encounters with infective stages in the environment, annual pulses of host births and deaths and changes in host immune defences. Mathematical models and field observations show that the strength and mechanisms of seasonality can alter the spread and persistence of infectious diseases, and that population-level responses can range from simple annual cycles to more complex multiyear fluctuations. From an applied perspective, understanding the timing and causes of seasonality offers important insights into how parasite,host systems operate, how and when parasite control measures should be applied, and how disease risks will respond to anthropogenic climate change and altered patterns of seasonality. Finally, by focusing on well-studied examples of infectious diseases, we hope to highlight general insights that are relevant to other ecological interactions. [source] Ecology of invasive mosquitoes: effects on resident species and on human healthECOLOGY LETTERS, Issue 5 2005Steven A. Juliano Abstract Investigations of biological invasions focus on patterns and processes that are related to introduction, establishment, spread and impacts of introduced species. This review focuses on the ecological interactions operating during invasions by the most prominent group of insect vectors of disease, mosquitoes. First, we review characteristics of non-native mosquito species that have established viable populations, and those invasive species that have spread widely and had major impacts, testing whether biotic characteristics are associated with the transition from established non-native to invasive. Second, we review the roles of interspecific competition, apparent competition, predation, intraguild predation and climatic limitation as causes of impacts on residents or as barriers to invasion. We concentrate on the best-studied invasive mosquito, Aedes albopictus, evaluating the application of basic ecological theory to invasions by Aedes albopictus. We develop a model based on observations of Aedes albopictus for effects of resource competition and predation as barriers to invasion, evaluating which community and ecosystem characteristics favour invasion. Third, we evaluate the ways in which invasive mosquitoes have contributed to outbreaks of human and animal disease, considering specifically whether invasive mosquitoes create novel health threats, or modify disease transmission for existing pathogen,host systems. [source] Polythiacrown Macro- and Gigantocycles with Chiral Diacetal CoresEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2007Sarah Abramson Abstract We present a unique class of polythiacrown macro- and gigantocyclic[9] systems, consisting of ethylene 1,2-dithioglycol (ETG) to poly(ethylene thioglycol) (ETGn) bridges over one to six diacetal units of the cis -1,3,5,7-tetraoxadecalin (TOD) type. The latter is a dissymmetric, chiral moiety, incorporating a cavity with built-in high electron lone pair concentration, serving as the "core" of chiral macrocyclic host systems with good inclusion ability of ions and polar molecules. We describe two approaches: (i) the reactions of the 2,6-bis(bromomethyl)- cis -TOD podand (6) with ETG or higher ETGns (12n), in Cs2CO3 promoted processes, leading to the innate but uncontrolled formation of polythiacrown-TOD macrocycles having ETG/TOD ratios of 1:1 (7), 2:2 (8) and further 3:3,6:6 (111/m)10 macrocycles via open dithiol intermediates, and (ii) judicious preparation, using K2CO3, of oligomeric dibromide intermediates with ETGn:TOD ratios 1:2, 2:3 or 3:4 (14n/m), which led (with further ETGn) in a controlled way to the 2:2 (8n), or 3:3, 4:4 and 6:6 (11n/m) macro- and gigantocyclic systems. Altogether, the outcome of these processes depends on the relative concentrations of the reactants. Synthesis was accompanied by detailed (NMR and MS) spectroscopy. X-ray crystallographic analysis of a number of macrocycles, complemented by (MM & MD) computation, made possible valuable structural, stereochemical and conformational analysis. While sophisticated in their stereochemical features, these systems are readily prepared in enantiopure form and hold great promise of chemical reactivity in metal ion inclusion and molecular and chiral recognition.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Controlling Light Emission in Luminescent Solar Concentrators Through Use of Dye Molecules Aligned in a Planar Manner by Liquid CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Paul P. C. Verbunt Abstract A luminescent solar concentrator (LSC) is a potential low-cost enhancement of the standard large-area silicon photovoltaic panels for the generation of electricity from sunlight. In this work, guest,host systems are investigated using anisotropic fluorescent dyes and liquid crystal mesogens to control the direction of emitted light in the LSC. It is determined that up to 30% more light is emitted from the edge of an LSC waveguide with planar dye alignment parallel to the alignment direction than from any edge of an LSC with no alignment (isotropic). The aligned samples continue to show dichroic performance after additions of both edge mirrors and rear scattering layer. [source] Macrocyclic vs. dendrimeric effect.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2004A DFT study Abstract Macrocycles up to 15 members with different heteroatoms (N, O, and S) and dendrimeric functionalized branches were assembled, resulting in unique "collective" supramolecular hosts with several active sites for transition metal ions complexation. The nature of the interactions between these kinds of systems and metal ions of the first transition series (Fe, Ni, Cu, Zn) was evaluated by calculations of the binding energies at the B3LYP/LACVP* level of theory, resulting in a preference of metal ions for macrocyclic cavity in terms of complexation; however, there is a favorable contribution in energy due to the cooperative effect of dendrimeric branches (DBs) in the inclusion process by means of long-range interactions between metal ions and the heteroatoms present in DBs. According to calculated binding energies, even when the complexation in the middle of DBs appears as a less favored situation, still competes with the complexation occurred in several known macrocycles traditionally used in the formation of inclusion complexes. The capability of macrocycles as host entities is related to some criteria like: (1) the compatibility in orbital symmetry between host and guest molecules; (2) the cavity dimensions and the negative charge inside; and (3) the hardness,softness affinity between host and guest molecules. When DBs are included in host systems, their flexibility seems to be very important, in addition to localized negative charge, which permits the occurrence of long-range interactions. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1215,1226, 2004 [source] Ectoparasite load is linked to ontogeny and cell-mediated immunity in an avian host system with pronounced hatching asynchronyBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2008RADOVAN VÁCLAV Several contrasting hypotheses have been proposed to account for host age-biased parasite distribution, with some of them suggesting a key role of ectoparasites in the evolution and maintenance of weight hierarchies within broods. We examined parasite distribution among individual hosts across the whole period of host exposure to the parasite in a host system that shows distinct within-brood differences in age and age-related mortality. By contrast to previous hypotheses, we found that the abundance of a haematophagous, mobile ectoparasite Carnus haemapterus on nestling European rollers (Coracias garrulus) was highest approximately during the mid-nestling stage of their host, coinciding with the inflection point of the host growth phase. Parasite load increased neither with absolute resource availability (i.e. body size), nor body condition index. By contrast to previous evidence, higher parasite load under natural conditions was associated with a stronger cell-mediated immune response. However, this association was moderated by low parasite densities, as well as a better brood body condition index. Overall, although we revealed remarkable host ontogenetic effects on parasite distribution, the present study suggests that a highly mobile ectoparasite generally prefers healthier hosts. We propose that, in host systems with a marked asynchrony of hatching and background mortality within the brood, parasites favour persistence rather than nutritional attractiveness of the host. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 463,473. [source] Real-time PCR-based determination of gene copy numbers in Pichia pastorisBIOTECHNOLOGY JOURNAL, Issue 4 2010Sandra Abad Abstract Pichia pastoris is a preferred host for heterologous protein production. Expression cassettes are usually integrated into the genome of this methylotrophic yeast. This manuscript describes a method for fast and reliable gene copy number determinations for P. pastoris expression strains. We believe that gene copy number determinations are important for all researchers working with P. pastoris and also many other research groups using similar gene integration techniques for the transformation of other yeasts. The described method uses real-time PCR to quantify the integrated expression cassettes. Similar methods were employed previously for other host systems such as animal and plant cells but no such method comparing different detection methods and describing details for yeast analysis by quantitative PCR is known to us, especially for methylotrophic yeasts such as P. pastoris. Neglecting gene copy numbers can easily lead to false interpretations of experimental results from codon optimization or promoter studies and co-expression of helper proteins as demonstrated in an application example, which is also described here. [source] Quantifying Viral Propagation in Vitro: Toward a Method for Characterization of Complex PhenotypesBIOTECHNOLOGY PROGRESS, Issue 6 2001Karen A. Duca For a eukaryotic virus to successfully infect and propagate in cultured cells several events must occur: the virion must identify and bind to its cellular receptor, become internalized, uncoat, synthesize viral proteins, replicate its genome, assemble progeny virions, and exit the host cell. While these events are taking place, intrinsic host defenses activate in order to defeat the virus, e.g., activation of the interferon system, induction of apoptosis, and attempted elicitation of immune responses via chemokine and cytokine production. As a first step in developing an imaging methodology to facilitate direct observation of such complex host/virus dynamics, we have designed an immunofluorescence-based system that extends the traditional plaque assay, permitting simultaneous quantification of the rate of viral spread, as indicated by the presence of a labeled viral protein, and cell death in vitro, as indicated by cell loss. We propose that our propagation and cell death profiles serve as phenotypic read-outs, complementing genetic analysis of viral strains. As our virus/host system we used vesicular stomatitis virus (VSV) propagating in hamster kidney epithelial (BHK-21) and murine astrocytoma (DBT) cell lines. Viral propagation and death profiles were strikingly different in these two cell lines, displaying both very different initial titer and cell age effects. The rate of viral spread and cell death tracked reliably in both cell lines. In BHK-21 cells, the rate of viral propagation, as well as maximal spread, was relatively insensitive to initial titer and was roughly linear over several days. In contrast, viral plaque expansion in DBT cells was contained early in the infections with high titers, while low titer infections spread in a manner similar to the BHK-21 cells. The effect of cell age on infection spread was negligible in BHK-21 cells but not in DBTs. Neither of these effects was clearly observed by plaque assay. [source] | |||||||||||||