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Competition Experiments (competition + experiment)

Distribution by Scientific Domains

Life Sciences	46%
Chemistry	40%
Medical Sciences	11%

Selected Abstracts

Competition and character displacement in two species of scincid lizards

ECOLOGY LETTERS, Issue 3 2002
Jane Melville
Abstract The role of competition in habitat occupation and character displacement is investigated in two species of alpine lizards (Niveoscincus microlepidotus and N. greeni), using both controlled competition experiments and field-based ecological work. Competition experiments demonstrate that interspecific aggression occurs between these closely related species, with the larger and more aggressive N. greeni being socially dominant. When these species occur in sympatry, N. microlepidotus was found to shift its habitat occupation to the heathlands, which provide less thermal opportunities. In addition, a reduction in body size occurred in both adult and neonatal N. microlepidotus at sympatric field sites. Differences in body size between N. microlepidotus and N. greeni in sympatry were significantly greater than in allopatry, indicating that character displacement is occurring. Results, combined with previous molecular and biogeographical data, suggest that there is a trend towards a reduction in body size and a restriction in habitat occupation in N. microlepidotus in the north-east periphery of its distribution, which is shaped by competition with N. greeni. [source]

Temporal and selective association of multiple sigma factors with RNA polymerase during sporulation in Bacillus subtilis

GENES TO CELLS, Issue 2 2000
Masaya Fujita
Background During sporulation in Bacillus subtilis, an asymmetric division produces two cells, a forespore and mother cell, with which follow different developmental paths. The highly ordered programme of temporal and spatial gene activation during sporulation is governed by the principal RNA polymerase holoenzyme (E,A) and alternative holoenzyme forms containing the developmental sigma factors ,H, ,F, ,E, ,G and ,K, which appear successively during development. The control mechanism(s) of temporal and selective association of multiple sigma factors with core RNA polymerase is unclear. As a first step to addressing these issues, this report quantifies the amount of each subunit of RNA polymerase that is present in the sporangium during sporulation, and analyses in vitro the relative affinities of each sigma subunit for core RNA polymerase. Results Using quantitative immunoblot analysis, the amounts of E,A, E,H, E,E and E,K in relation to the total amount of RNA polymerase at appropriate time-points were found to be 15%, 1%, 6% and 2%, respectively. Therefore, the core RNA polymerase is predicted to be in excess. The level of core RNA polymerase and ,A remained constant during the transition from vegetative growth to sporulation, whereas the sporulation-specific sigma factors appeared successively, in the order ,H, ,E and ,K. Competition experiments between sigma factors in an in vitro transcription system revealed the dominance of ,A over ,H and ,E for open promoter complex formation. These results are inconsistent with the idea that late appearing sigma factors can displace earlier appearing sigmas from the core enzyme. Conclusions As the core RNA polymerase is in excess, the results suggest that successive sigma factors can bind to core RNA polymerase without having to displace earlier appearing sigma factors. Thus, the programme of gene expression during sporulation might not require mechanisms for the substitution of one sigma factor by another on the core RNA polymerase. [source]

NF-,B DNA-binding activity after high peak power pulsed microwave (8.2 GHz) exposure of normal human monocytes

BIOELECTROMAGNETICS, Issue 4 2002
Mohan Natarajan
Abstract The hypothesis investigated is that exposure of a mammalian cell to high peak power pulsed RF, at the frequency of 8.2 GHz, can result in the activation of an important eukaryotic transcriptional regulator, nuclear factor kappa B (NF-,B). This DNA-binding protein controls genes involved in long term cellular regulation. The selection of 8.2 GHz was based on the availability of a high peak power pulsed RF transmitter. In these studies, triplicate cultures of human monocytes (Mono Mac-6) were exposed to the pulsed wave radiation. The peak to average power ratio was 455:1 (2.2 ,s pulse width and pulse repetition rate of 1000 pulses/s). The average power density at the position of exposure was 50 W/m2, and the mean SAR at the bottom of the culture flask was 10.8,±,7.1 W/kg. The FDTD analysis indicated that 10% of the cells had an SAR of 22,29 W/kg. The cells were exposed continuously for 90 min at 37 °C, reincubated at this temperature, and harvested 4 h postexposure. The nuclear extracts were analyzed by electrophoretic mobility shift assay. The results showed a profound increase (3.6-fold) in the DNA binding activity of NF-,B in monocytes at 4 h after the pulsed RF exposure compared to sham irradiated controls. Competition experiments with cold NF-,B- specific oligonucleotides confirmed the specificity of the DNA binding activity. These results provide evidence that high peak power pulsed radiofrequency radiation can perturb the cell and initiate cell signaling pathways. However, at this point, we are not prepared to advocate that the cause is a nonthermal mechanism. Because of the broad distribution of SAR's in the flask, experiments need to be performed to determine if the changes observed are associated with cells exposed to high or low SARs. Bioelectromagnetics 23:271,277, 2002. © 2002 Wiley-Liss, Inc. [source]

Determination of isokinetic ratios necessary for equimolar incorporation of carboxylic acids in the solid-phase synthesis of mixture-based combinatorial libraries

BIOPOLYMERS, Issue 1 2002
Achyuta N. Acharya
Abstract The methods used to study the relative reaction rates of 45 different aliphatic and aromatic carboxylic acids when coupled to resin-bound amino acid amides is described. Competition experiments involving the coupling of incoming carboxylic acids to resin-bound amino acid amides were performed. The relative composition of each N-acylated amino acid amide in the resulting mixtures was compared to controls prepared by physically mixing equal aliquots of individual compounds in order to study the relative reaction rates of the incoming carboxylic acids. The ratios of the incoming carboxylic acids were then iteratively adjusted to yield as close to equimolar products as possible. As expected, the steric and electronic nature of the incoming carboxylic acids was found to influence their relative reaction rates. The steric hindrance of the resin-bound amino acid appears to have a proportional effect on the reaction rates of the incoming carboxylic acids. N-acylated amino acid amides in the final mixtures, prepared using the final isokinetic ratios, were found to be approximately equimolar. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 32,39, 2002 [source]

Structure,Reactivity Relationships in Negishi Cross-Coupling Reactions

CHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2010
Zhi-Bing Dong Dr.
Abstract Competition experiments have been performed to determine the relative reactivities of substituted bromobenzenes and of different arylzinc reagents in the [Pd(PPh3)4]-catalyzed Negishi cross-coupling reaction in THF at 25,°C. The cross-coupling reactions are accelerated by electron acceptors in the bromobenzenes, the effect of which increases in the order ortho [source]

Palladium-Catalyzed Cyclopropanation of Alkenyl Silanes by Diazoalkanes: Evidence for a Pd0 Mechanism

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2009
Guillaume Berthon-Gelloz Dr.
Abstract Pd0does the trick! Alkenyl silanes are efficiently cyclopropanated by diazoalkanes at low Pd loadings (see scheme). Clear evidence for the involvement of a Pd0 resting state for this reaction is given. Alkenyl silanes are efficiently converted to the corresponding silyl cyclopropanes in the presence of a slight excess of diazomethane (2,4,equiv) and a low loading of Pd(OAc)2 (<0.5,mol,%). Diazoethane and diazobutane can also be employed and yield silyl cyclopropanes with diastereoselectivities of up to 10:1 for the trans isomer. When conducted on a 4,g scale, the reaction only required a catalyst loading of 5×10,3,mol,%, which corresponds to a turnover frequency of 40,000,h,1. Competition experiments revealed that vinyl silanes can be selectively cyclopropanated in the presence of an aliphatic terminal alkene and styrene. The complex [Pd02(DVTMS)3] (38, DVTMS=divinyltetramethyldisiloxane) proved to be an exceptionally active catalyst for the cyclopropanation reaction, giving complete conversion at ,35,°C in 1,min. Intermolecular and intramolecular competition experiments with DVTMS (36), both with Pd(OAc)2 and 38, provided strong evidence for a Pd0(alkenyl silane)3 resting state. Detailed density functional calculations on the reaction pathways for the cyclopropanation of trimethylvinylsilane and DVTMS by diazomethane with Pd0 corroborated the experimental observations. [source]

Palladium-Catalyzed Cross-Coupling Reactions of Amines with Alkenyl Bromides: A New Method for the Synthesis of Enamines and Imines

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2004
José Barluenga Prof. Dr.
Abstract The palladium-catalyzed cross-coupling reaction of alkenyl bromides with secondary and primary amines gives rise to enamines and imines, respectively. This new transformation expands the applicability of palladium-catalyzed CN bond forming reactions (the Buchwald,Hartwig amination), which have mostly been applied to aryl halides. After screening of different ligands, bases, and solvents, the catalytic combination [Pd2(dba)3]/BINAP in the presence of NaOtBu in toluene gave the best results in the cross-coupling of secondary amines with 1-bromostyrene (dba=dibenzylideneacetone, BINAP=2,2,-bis(diphenylphosphino)-1,1,-binaphthyl). The corresponding enamines are obtained cleanly and in nearly quantitative yields. However, steric hindrance seems to be a limitation of the reaction, as amines carrying large substituents are not well converted. The same methodology can be applied to the coupling of secondary amines with 2-bromostyrene. Moreover, the reaction with substituted 2-bromopropenes allows regioselective synthesis of isomerizable terminal enamines without isomerization of the double bond. The best catalytic conditions for the cross-coupling of 1-bromostyrene with primary amines include again the use of the Pd0/BINAP/NaOtBu system. The reaction gives rise to the expected imines in very short times and with low catalyst loadings. A set of structurally diverse imines can be prepared by this methodology through variations in the structure of both coupling partners. However, 2-bromostyrene failed to give good results in this coupling reaction, probably due to product inhibition of the catalytic cycle. Competition experiments of vinyl versus aryl amination reveal that the reaction occurs preferentially on vinyl bromides. La reacción de acoplamiento cruzado de bromuros de alquenilo con aminas secundarias y primarias da lugar a enaminas e iminas respectivamente. Esta nueva transformación expande las aplicaciones de la reacción de formación de enlaces CN catalizada por paladio (aminación Buchwald,Hartwig), que se había limitado fundamentalmente a haluros de arilo. Después de un estudio de diferentes ligandos. bases y disolventes, los mejores resultados en la reacción de acoplamiento cruzado de aminas secundarias con 1-bromoestireno, se obtuvieron para el catalizador constituido por la combinación Pd/BINAP en presencia de NaOtBu en tolueno. Las correspondientes enaminas se obtienen limpiamente y con rendimientos prácticamente cuantitativos. Sin embargo, los impedimentos estéricos en la amina parecen ser una limitación de la reacción, puesto que aminas con sustituyentes voluminosos proporcionan conversiones bajas. La misma metodología puede aplicarse al acoplamiento de aminas secundarias con 2-bromoestireno. Además, la reacción con 2-bromopropenos sustituidos permite obtener de forma regioselectiva enaminas terminales isomerizables, sin que la isomerización del doble enlace tenga lugar. Las mejores condiciones catalíticas para el acoplamiento de aminas primarias con 1-bromoestireno incluyen de nuevo la utilización del sistema Pd(0)/BINAP/NaOtBu. La reacción proporciona las iminas esperadas en tiempos de reacción muy cortos y con baja carga del catalizador. Mediante esta metodología pueden prepararse un conjunto de iminas de gran diversidad estructural, permitiendo variaciones en ambos reactivos de acoplamiento. Sin embargo, la reacción con 2-bromoestireno no produce buenos resultados en este acoplamiento, probablemente debido a inhibición del ciclo catalítico por parte del producto de reacción. Finalmente, experimentos de competencia de aminación vinílica frente a aminación arílica, ponen de manifiesto que esta reacción se produce de forma preferente sobre los bromuros de vinilo. [source]

DIEL RHYTHM OF ALGAL PHOSPHATE UPTAKE RATES IN P-LIMITED CYCLOSTATS AND SIMULATION OF ITS EFFECT ON GROWTH AND COMPETITION1

JOURNAL OF PHYCOLOGY, Issue 4 2002
Chi-Yong Ahn
Oscillations in the phosphate (Pi) uptake rates for three species of green algae were examined in a P-limited cyclostat. For Ankistrodesmus convolutus Corda and Chlorella vulgaris Beyerinck, the Pi uptake rates increased during the daytime and decreased at night. In contrast, Chlamydomonas sp. exhibited the opposite uptake pattern. Cell densities also oscillated under a light:dark cycle, dividing at a species-specific timing rather than continuously. In general, the cell densities exhibited an inverse relationship with the Pi uptake rates. A competition experiment between A. convolutus and C. vulgaris in a P-limited cyclostat resulted in the dominance of C. vulgaris, regardless of the relative initial cell concentrations. Chlorella vulgaris also dominated in a mixed culture with Chlamydomonas sp., irrespective of the initial seeding ratio and dilution rate. However, Chlamydomonas sp. and A. convolutus coexisted in the competition experiment with gradual decrease of Chlamydomonas sp. when equally inoculated. Mathematical expressions of the oscillations in the Pi uptake rate and species-specific cell division gate were used to develop a simulation model based on the Droop equation. The simulation results for each of the species conformed reasonably well to the experimental data. The results of the competition experiments also matched the competition simulation predictions quite well, although the experimental competition was generally more delayed than the simulations. In conclusion, the model simulation that incorporated the effect of diel rhythms in nutrient uptake clearly demonstrated that species diversity could be enhanced by different oscillation patterns in resource uptake, even under the condition of limitation by the same resource. [source]

More plant biomass results in more offspring production in annuals, or does it?

OIKOS, Issue 9 2008
Marina S. Neytcheva
Competitive ability in plants has been previously measured almost exclusively in terms of traits related to growth (biomass) or plant size. In this study, however, we used a multi-species competition experiment with six annuals to measure relative competitive ability in terms of reproductive output, i.e. the number of offspring produced for the next generation. Under greenhouse conditions, plants of each species were started in pots from germinating seeds and were grown singly (free of competition) and at high density in both monocultures and in mixtures with all study species. Several traits traditionally regarded as determinants of competitive ability in plants were recorded for each species grown singly, including: seed mass, germination time, early growth rate and potential plant size (biomass and height). Under competition, several traits were recorded as indicators of relative performance in both monocultures and mixtures, including: biomass of survivors, total number of survivors, number of reproductive survivors, and reproductive output (total seed production) of the survivors. As expected, species that grew to a larger biomass in isolation had higher seed production in isolation. However, none of the traditional plant growth/size-related traits, measured either in isolation or under competition, could predict between species variation in reproductive output under competition in either monocultures or mixtures. In mixtures, 97% of this variation in reproductive output could be explained by between-species variation in the number of reproductive survivors. The results indicate that traits measured on plants grown singly may be poor predictors of reproductive output under competition, and that species' rank order of competitive ability in terms of the biomass of survivors may bear no relationship to their rank order in terms of the number of offspring produced by these survivors. This has important implications for the interpretation of mechanisms of species coexistence and community assembly within vegetation. [source]

Synthesis, Structural Evaluation, and Estrogen Receptor Interaction of 4, 5-Bis(4-hydroxyphenyl)imidazoles

ARCHIV DER PHARMAZIE, Issue 10 2002
Ronald Gust
Abstract 4, 5-Bis(4-hydroxyphenyl)imidazoles with 2, 2,-H (1), 2, 2,-F (2), 2, 2,-Cl (3), and 2, 2,6-Cl (4) substituents in the aromatic rings were synthesized by oxidation of the respective methoxy-substituted (R, S)/(S, R)-4, 5-diaryl-2-imidazolines with MnO2 and subsequent ether cleavage with BBr3. N -alkylation of 1 and 3 with ethyl iodide yielded the compounds 5 and 6. The imidazoles were characterized by NMR spectroscopy and tested for estrogen receptor binding in a competition experiment with [3H]estradiol using calf uterine cytosol. Gene activation was verified in a luciferase assay using estrogen receptor positive MCF-7-2a cells stably transfected with the plasmid EREwtcluc. All halide substituted imidazoles competed with estradiol for the binding site at the estrogen receptor. The N -ethyl derivative 6 showed the highest relative binding affinity of 1.26 %. Treatment of MCF-7-2a cells, however, did not lead to gene activation. The relative activation of 6 amounted only to 10 % at 1,M compared to E2 (100 %). [source]

Competition and character displacement in two species of scincid lizards

The role of larval aggression and mobility in the transition between solitary and gregarious development in parasitoid wasps

ECOLOGY LETTERS, Issue 6 2000
G. Boivin
Models explaining the appearance of gregariousness in insect parasitoids assume the presence of a tolerance gene that enables nonsiblicidal behaviour in gregarious larvae. Under this assumption, nontolerant individuals should attack and kill tolerant individuals when sharing a host, making this behaviour susceptible to invasion by nontolerant individuals. We propose an alternative hypothesis where gregarious larvae retain their aggressiveness but are less mobile. We tested this hypothesis with two sympatric and congeneric species of Mymaridae, Anaphes victus and Anaphes listronoti, respectively, solitary and gregarious egg parasitoids of a Curculionidae, Listronotus oregonensis. Results obtained in competition experiments and from direct observation of movement in mymariform larvae of both species support the reduced mobility hypothesis. By being immobile while retaining their fighting capacity, A. listronoti mymariform larvae appear to optimize host utilization through gregarious development, but can still defend themselves against sympatric aggressive species. [source]

Transcription factor binding study by capillary zone electrophoretic mobility shift assay

ELECTROPHORESIS, Issue 1-2 2003
Zsolt Ronai
Abstract Regulation of gene expression through interaction of proteins with specific DNA sequences is a central issue in functional genomics. Capillary electrophoretic mobility shift assay is an efficient novel method for the investigation of sequence specific protein-DNA interactions, allowing rapid and sensitive quantification of the complex formation. In this paper, we present a pilot study on capillary zone electrophoretic mobility shift assay (CZEMSA) to investigate the interaction between the transcription factors of HeLa nuclear extract and Sp1-specific fluorescein-labeled oligonucleotide, using the unlabeled probe as competitor. The mobility shift assay was accomplished by CZE in coated capillaries without polymeric buffer additives. Specificity of the DNA protein complex formation was verified by competition experiments, as well as by supershift assay with an anti-Sp1 antibody. The applied electric field strength did not affect the stability of DNA-protein complex during the electrophoretic analysis, allowing rapid identification and quantification of the protein DNA interaction. A practical application to study the interaction between Oryza sativa MADS-box transcription factor 4 (OsMADS4) and its consensus sequence is also reported. [source]

d -Alanyl ester depletion of teichoic acids in Lactobacillus reuteri 100-23 results in impaired colonization of the mouse gastrointestinal tract

ENVIRONMENTAL MICROBIOLOGY, Issue 7 2007
Jens Walter
Summary The dlt operon of Gram-positive bacteria encodes proteins required for the incorporation of d -alanine esters into cell wall-associated teichoic acids (TA). d -Alanylation of TA has been shown to be important for acid tolerance, resistance to antimicrobial peptides, adhesion, biofilm formation, and virulence of a variety of pathogenic organisms. The aim of this study was to determine the importance of d -alanylation for colonization of the gastrointestinal tract by Lactobacillus reuteri 100-23. Insertional inactivation of the dltA gene resulted in complete depletion of d -alanine substitution of lipoteichoic acids. The dlt mutant had similar growth characteristics as the wild type under standard in vitro conditions, but formed lower population sizes in the gastrointestinal tract of ex- Lactobacillus -free mice, and was almost eliminated from the habitat in competition experiments with the parental strain. In contrast to the wild type, the dlt mutant was unable to form a biofilm on the forestomach epithelium during gut colonization. Transmission electron microscope observations showed evidence of cell wall damage of mutant bacteria present in the forestomach. The dlt mutant had impaired growth under acidic culture conditions and increased susceptibility to the cationic peptide nisin relative to the wild type. Ex vivo adherence of the dlt mutant to the forestomach epithelium was not impaired. This study showed that d -alanylation is an important cell function of L. reuteri that seems to protect this commensal organism against the hostile conditions prevailing in the murine forestomach. [source]

The RuO4 -Catalyzed Ketohydroxylation, Part II:A Regio-, Chemo- and Stereoselectivity Study

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2005
Bernd Plietker
Abstract The direct RuO4 -catalyzed ketohydroxylation of olefins is a new and convenient method for the preparation of a wide range of symmetrical and unsymmetrical ,-hydroxy ketones. Since reactions in which two different functional groups are introduced in one step always involve regio-, chemo- and stereoselectivity issues, this paper gives a full account of investigations of various selectivity aspects in the ketohydroxylation. Stereoselectivity issues were examined in the final part of the present report. The Kishi rules, known from OsO4 -catalyzed dihydroxylations, are found to be valid for the RuO4 -catalyzed ketohydroxylation and lead to moderate to good diastereomeric ratios in the oxidation of olefins possessing an allylic center of chirality. Furthermore, competition experiments between different substituted olefins led to a reactivity profile applicable to the prediction of which is the most reactive of different C=C double bonds present in a molecule. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Transcription of mammalian cytochrome c oxidase subunit IV-2 is controlled by a novel conserved oxygen responsive element

FEBS JOURNAL, Issue 21 2007
Maik Hüttemann
Subunit 4 of cytochrome c oxidase (CcO) is a nuclear-encoded regulatory subunit of the terminal complex of the mitochondrial electron transport chain. We have recently discovered an isoform of CcO 4 (CcO4-2) which is specific to lung and trachea, and is induced after birth. The role of CcO as the major cellular oxygen consumer, and the lung-specific expression of CcO4-2, led us to investigate CcO4-2 gene regulation. We cloned the CcO4-2 promoter regions of cow, rat and mouse and compared them with the human promoter. Promoter activity is localized within a 118-bp proximal region of the human promoter and is stimulated by hypoxia, reaching a maximum (threefold) under 4% oxygen compared with normoxia. CcO4-2 oxygen responsiveness was assigned by mutagenesis to a novel promoter element (5,-GGACGTTCCCACG-3,) that lies within a 24-bp region that is 79% conserved in all four species. This element is able to bind protein, and competition experiments revealed that, within the element, the four core bases 5,-TCNCA-3, are obligatory for transcription factor binding. CcO isolated from lung showed a 2.5-fold increased maximal turnover compared with liver CcO. We propose that CcO4-2 expression in highly oxygenated lung and trachea protects these tissues from oxidative damage by accelerating the last step in the electron transport chain, leading to a decrease in available electrons for free radical formation. [source]

Biophysical characterization of the interaction of high-density lipoprotein (HDL) with endotoxins

FEBS JOURNAL, Issue 23 2002
Klaus Brandenburg
The interaction of bacterial endotoxins [lipopolysaccharide (LPS) and the ,endotoxic principle' lipid A], with high-density lipoprotein (HDL) from serum was investigated with a variety of physical techniques and biological assays. HDL exhibited an increase in the gel to liquid crystalline phase transition temperature Tc and a rigidification of the acyl chains of the endotoxins as measured by Fourier-transform infrared spectroscopy and differential scanning calorimetry. The functional groups of the endotoxins interacting with HDL are the phosphates and the diglucosamine backbone. The finding of phosphates as target groups is in accordance to measurements of the electrophoretic mobility showing that the zeta potential decreases from ,50 to ,60 mV to ,20 mV at binding saturation. The importance of the sugar backbone as further target structure is in accordance with the remaining negative potential and competition experiments with polymyxin B (PMB) and phase transition data of the system PMB/dephosphorylated LPS. Furthermore, endotoxin binding to HDL influences the secondary structure of the latter manifesting in a change from a mixed ,-helical/,-sheet structure to a predominantly ,-helical structure. The aggregate structure of the lipid A moiety of the endotoxins as determined by small-angle X-ray scattering shows a change of a unilamellar/inverted cubic into a multilamellar structure in the presence of HDL. Fluorescence resonance energy transfer data indicate an intercalation of pure HDL, and of [LPS],[HDL] complexes into phospholipid liposomes. Furthermore, HDL may enhance the lipopolysaccharide-binding protein-induced intercalation of LPS into phospholipid liposomes. Parallel to these observations, the LPS-induced cytokine production of human mononuclear cells and the reactivity in the Limulus test are strongly reduced by the addition of HDL. These data allow to develop a model of the [endotoxin]/[HDL] interaction. [source]

Molecular cloning of the Matrix Gla Protein gene from Xenopus laevis

FEBS JOURNAL, Issue 7 2002
Functional analysis of the promoter identifies a calcium sensitive region required for basal activity
To analyze the regulation of Matrix Gla Protein (MGP) gene expression in Xenopus laevis, we cloned the xMGP gene and its 5, region, determined their molecular organization, and characterized the transcriptional properties of the core promoter. The Xenopus MGP (xMGP) gene is organized into five exons, one more as its mammalian counterparts. The first two exons in the Xenopus gene encode the DNA sequence that corresponds to the first exon in mammals whereas the last three exons show homologous organization in the Xenopus MGP gene and in the mammalian orthologs. We characterized the transcriptional regulation of the xMGP gene in transient transfections using Xenopus A6 cells. In our assay system the identified promoter was shown to be transcriptionally active, resulting in a 12-fold induction of reporter gene expression. Deletional analysis of the 5, end of the xMGP promoter revealed a minimal activating element in the sequence from ,70 to ,36 bp. Synthetic reporter constructs containing three copies of the defined regulatory element delivered 400-fold superactivation, demonstrating its potential for the recruitment of transcriptional activators. In gel mobility shift assays we demonstrate binding of X. laevis nuclear factors to an extended regulatory element from ,180 to ,36, the specificity of the interaction was proven in competition experiments using different fragments of the xMGP promoter. By this approach the major site of factor binding was demonstrated to be included in the minimal activating promoter fragment from ,70 to ,36 bp. In addition, in transient transfection experiments we could show that this element mediates calcium dependent transcription and increasing concentrations of extracellular calcium lead to a significant dose dependent activation of reporter gene expression. [source]

Helicobacter pylori mutagenesis by mariner in vitro transposition

FEMS IMMUNOLOGY & MEDICAL MICROBIOLOGY, Issue 2 2001
Betty P Guo
Abstract We have developed a method for generating transposon insertion mutants using mariner in vitro mutagenesis. The gene of interest was PCR-amplified and cloned. A kanamycin-marked mariner transposon was randomly inserted into the purified plasmid in an in vitro transposition reaction. After repair and propagation in Escherichia coli, purified mutagenized plasmid was introduced into Helicobacter pylori by natural transformation. Transformants were selected by plating on kanamycin. Mutants were predominantly the result of double homologous recombination, and multiple mutants (with insertions in distinct positions) were often obtained. The site of insertion was determined by PCR or sequencing. We have made mutations in known or potential virulence genes, including ureA, hopZ, and vacA, using kanamycin- and kanamycin/lacZ -marked transposons. Colonies carrying a kanamycin/lacZ transposon appeared blue on medium containing the chromogenic agent X-gal, allowing discrimination of mutant and wild-type H. pylori in mixed competition experiments. [source]

Competition in variable environments: experiments with planktonic rotifers

FRESHWATER BIOLOGY, Issue 6 2002
KEVIN L. KIRK
1.,In a constant environment, competition often tends to reduce species diversity. However, several theories predict that temporal variation in the environment can slow competitive exclusion and allow competing species to coexist. This study reports on laboratory competition experiments in which two pairs of planktonic rotifer species competed for a phytoplankton resource under different conditions of temporal variability in resource supply. 2.,For both species pairs, Keratella cochlearis dominated under all conditions of temporal variability, and the other species (Brachionus calyciflorus or Synchaeta sp.) almost always went extinct. Increasing temporal variation in resource supply slowed competitive exclusion but did not change competitive outcome or allow coexistence. 3.,Rotifers show a gleaner,opportunist trade-off, because gleaner species have low threshold resource levels (R*) and low maximum population growth rates, while opportunist species have the opposite characteristics. In the competition experiments, the gleaner always won and the opportunists always lost. Thus, a gleaner,opportunist trade-off was not sufficient to facilitate coexistence under conditions of resource variability. Instead, the winning species had both the lowest R* and the greatest ability to store resources and ration their use during times of extreme resource scarcity. [source]

Competitive relationships of Andropogon gerardii (Big Bluestem) from remnant and restored native populations and select cultivated varieties

FUNCTIONAL ECOLOGY, Issue 3 2004
D. J. GUSTAFSON
Summary 1Although genetic differentiation among plant populations is well known, its relevance for preserving the integrity of native ecosystems has received little attention. In a series of competition experiments with Andropogon gerardii Vitman, a dominant species of the North American Tallgrass Prairie, plant performance was related to seed provenance and restoration activities. 2Glasshouse experiments showed plant performance to be a function of seed source. Differential target plant performance relative to competitor identity was observed when plant performance was assessed across a range of competitor densities. Local and non-local plants were larger when competing against non-local plants relative to the local and cultivar plants, while cultivar plants were consistently larger than local and non-local plants regardless of competitor identity or density. The consistency of cultivar performance could reflect directional selection during cultivar development for consistently high fecundity, vigorous vegetative growth and resistance to pathogens. 3In a field experiment, non-local plants were half the size of local and cultivar plants, supporting recognition of seed provenances of A. gerardii based on differences in plant performance among source populations observed in the glasshouse study, and previous genetic analyses of the same populations. 4This study establishes that seed provenance and restoration activities influence the competitive ability of a dominant species which, in turn, may affect plant community structure and potential ecosystem function. [source]

Characterization of Arginine Transport in Helicobacter pylori

HELICOBACTER, Issue 4 2003
George L. Mendz
ABSTRACT Background. The amino acid L-arginine is an essential requirement for growth of Helicobacter pylori. Several physiological roles of this amino acid have been identified in the bacterium, but very little is known about the transport of L-arginine and of other amino acids into H. pylori. Methods. Radioactive tracer techniques using L-(U- 14C) arginine and the centrifugation through oil method were employed to measure the kinetic parameters, temperature dependence, substrate specificity, and effects of analogues and inhibitors on L-arginine transport. Results. The transport of arginine at millimolar concentrations was saturable with a Km of 2.4 ± 0.3 mM and Vmax of 1.3 ± 0.2 pmole min,1 (µl cell water),1 or 31 ± 3 nmole per minute (mg protein),1 at 20°C, depended on temperature between 4 and 40°C, and was susceptible to inhibitors. These characteristics suggested the presence of one or more arginine carriers. The substrate specificity of the transport system was studied by measuring the effects of L-arginine analogues and amino acids on the rates of transport of L-arginine. The absence of inhibition in competition experiments with L-lysine and L-ornithine indicated that the transport system was not of the Lysine-Arginine-Ornithine or Arginine-Ornithine types. The presence of different monovalent cations did not affect the transport rates. Several properties of L-arginine transport were elucidated by investigating the effects of potential inhibitors. Conclusions. The results provided evidence that the transport of L-arginine into H. pylori cells was carrier-mediated transport with the driving force supplied by the chemical gradient of the amino acid. [source]

Reproductive interference determines persistence and exclusion in species interactions

JOURNAL OF ANIMAL ECOLOGY, Issue 5 2009
Shigeki Kishi
Summary 1.,Reproductive interference is a negative interspecific sexual interaction that adversely affects the fitness of males and females during reproductive process. Theoretical studies suggest that because reproductive interference is characterized by positive frequency dependence it is far more likely to cause species exclusion than the density dependence of resource competition. However, the respective contributions of resource competition and reproductive interference to species exclusion, which have been frequently observed in many competition studies, remain unclear. 2.,We show that reproductive interference is a far more critical cause of species exclusion than resource competition in the competition between Callosobruchus bean weevil species. In competition experiments over several generations, we manipulated the initial relative abundance of the adzuki bean beetle, Callosobruchus chinensis, and the southern cowpea beetle, Callosobruchus maculatus. When the initial adult ratio of C. chinensis : C. maculatus were 6 : 2 and 4 : 4, C. chinensis excluded C. maculatus. However, when C. maculatus was four times more abundant than C. chinensis at the start, we observed the opposite outcome. 3.,A behavioural experiment using adults of the two species revealed asymmetric reproductive interference. The fecundity and longevity of C. maculatus females, but not those of C. chinensis females, decreased when the females were kept with heterospecific males. Fecundities of females of both species decreased as the number of heterospecific males increased. In contrast, resource competition at the larval stage resulted in higher survival of C. maculatus than of C. chinensis. 4.,These results suggest that the positive frequency-dependent effect of reproductive interference resulted in species exclusion, depending on the initial population ratio of the two species, and the asymmetry of the interference resulted in C. chinensis being dominant in this study, as in previous studies. Classical competition studies should be reviewed in light of this evidence for reproductive interference. [source]

Park's Tribolium competition experiments: a non-equilibrium species coexistence hypothesis

JOURNAL OF ANIMAL ECOLOGY, Issue 5 2003
Jeffrey Edmunds
Summary 1In this journal 35 years ago, P. H. Leslie, T. Park and D. B. Mertz reported competitive exclusion data for two Tribolium species. It is less well-known that they also reported ,difficult to interpret' coexistence data. We suggest that the species exclusion and the species coexistence are consequences of a stable coexistence two-cycle in the presence of two stable competitive exclusion equilibria. 2A stage-structured insect population model for two interacting species forecasts that as interspecific interaction is increased there occurs a sequence of dynamic changes (bifurcations) in which the classic Lotka,Volterra-type scenario with two stable competitive exclusion equilibria is altered abruptly to a novel scenario with three locally stable entities; namely, two competitive exclusion equilibria and a stable coexistence cycle. This scenario is novel in that it predicts the competitive coexistence of two nearly identical species on a single limiting resource and does so under circumstances of increased interspecific competition. This prediction is in contradiction to classical tenets of competition theory. [source]

Plant strategy theories: a comment on Craine (2005)

JOURNAL OF ECOLOGY, Issue 2 2007
J. PHILIP GRIME
Summary 1It is suggested that arguments concerning the nature of primary plant strategies could have been resolved more rapidly by reference to older literature relating to the behaviour of solutes in the rhizosphere and by more active programmes of plant trait screening. 2The critique of CSR theory in Craine (2005) is rejected largely on the basis that it misunderstands the role of fundamental and proximal controls on vegetation composition (sensu Welden & Slauson 1986). 3The ,way forward' advocated in Craine (2005) is flawed in its exclusive reliance on competition experiments. Recent progress in community and ecosystem ecology is strongly related to an increasing recognition of the declining importance of competition in unproductive or heavily disturbed environments. [source]

Molecular interactions of the neuronal GPI-anchored lipocalin Lazarillo

JOURNAL OF MOLECULAR RECOGNITION, Issue 5 2008
Diego Sanchez
Abstract Lazarillo, a glycoprotein involved in axon growth and guidance in the grasshopper embryo, is the only member of the lipocalin family that is attached to the cell surface by a GPI anchor. Recently, the study of Lazarillo homologous genes in Drosophila and mouse has revealed new functions in the regulation of lifespan, stress resistance and neurodegeneration. Here we report an analysis of biochemical properties of Lazarillo to gain insight into the molecular basis of its physiological function. Recombinant forms of the grasshopper protein were expressed in two different systems to test: (1) potential binding of several hydrophobic ligands; (2) protein,protein homophilic interactions; and (3) whether interaction with the function-blocking mAb 10E6 interferes with ligand binding. We tested 10 candidate ligands (retinoic acid, heme, bilirubin, biliverdin, ecdysterone, juvenile hormone, farnesol, arachidonic acid, linoleic acid and palmitic acid), and monitored binding using electrophoretic mobility shift, absorbance spectrum, and fluorimetry assays. Our work indicates binding to heme and retinoic acid, resulting in increased electrophoretic mobility, as well as to fatty acids, resulting in multimerization. Retinoic acid and fatty acids binding were confirmed by fluorescence titration, and heme binding was confirmed with absorbance spectrum assays. We demonstrate that Lazarillo oligomerizes in solution and can form clusters in the plasma membrane when expressed and GPI-anchored to the cell surface, however it is unable to mediate cell,cell adhesion. Finally, by ligand-mAb competition experiments we show that ligand-binding alone cannot be the key factor for Lazarillo to perform its function during axonal growth in the grasshopper embryo. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Characterization of nociceptin binding sites by novel peptide analogs and radioprobes

JOURNAL OF NEUROCHEMISTRY, Issue 2003
S. Benyhe
A number of new synthetic nociceptin ligands were studied in receptor binding and functional tests in rat brain membranes and in cloned systems. Ligand binding experiments were performed with three different radioprobes developed in our lab. The nociceptin derivatives exhibited high affinity in competition experiments. Receptor-mediated G-protein activation was determined in [35S]GTPgS binding assays. Among the new structures examined, Ac-RYYRIK-ol was found to be only a weak stimulator by itself, whereas this compound inhibited receptor-mediated G-protein activation. These data suggest that Ac-RYYRIK-ol is a high affinity peptide antagonist for the nociceptin receptor. Acknowledgements:, Supported by the Hungarian Scientific Research Fund OTKA T-035211, T-033078, T-030841, and the Ministry of Education, NKFP 1/027 Hungary. [source]

Impacts of Shewanella oneidensis c -type cytochromes on aerobic and anaerobic respiration

MICROBIAL BIOTECHNOLOGY, Issue 4 2010
Haichun Gao
Summary Shewanella are renowned for their ability to utilize a wide range of electron acceptors (EA) for respiration, which has been partially accredited to the presence of a large number of the c -type cytochromes. To investigate the involvement of c -type cytochrome proteins in aerobic and anaerobic respiration of Shewanella oneidensis Mr -1, 36 in-frame deletion mutants, among possible 41 predicted, c -type cytochrome genes were obtained. The potential involvement of each individual c -type cytochrome in the reduction of a variety of EAs was assessed individually as well as in competition experiments. While results on the well-studied c -type cytochromes CymA(SO4591) and MtrC(SO1778) were consistent with previous findings, collective observations were very interesting: the responses of S. oneidensis Mr -1 to low and highly toxic metals appeared to be significantly different; CcoO, CcoP and PetC, proteins involved in aerobic respiration in various organisms, played critical roles in both aerobic and anaerobic respiration with highly toxic metals as EA. In addition, these studies also suggested that an uncharacterized c -type cytochrome (SO4047) may be important to both aerobiosis and anaerobiosis. [source]

Growth, productivity, and competitiveness of introgressed weedy Brassica rapa hybrids selected for the presence of Bt cry1Ac and gfp transgenes

MOLECULAR ECOLOGY, Issue 10 2005
MATTHEW D. HALFHILL
Abstract Concerns exist that transgenic crop × weed hybrid populations will be more vigorous and competitive with crops compared with the parental weed species. Hydroponic, glasshouse, and field experiments were performed to evaluate the effects of introgression of Bacillus thuringiensis (Bt) cry1Ac and green fluorescent protein (GFP) transgenes on hybrid productivity and competitiveness in four experimental Brassica rapa × transgenic Brassica napus hybrid generations (F1, BC1F1, BC2F1 and BC2F2). The average vegetative growth and nitrogen (N) use efficiency of transgenic hybrid generations grown under high N hydroponic conditions were lower than that of the weed parent (Brassica rapa, AA, 2n = 20), but similar to the transgenic crop parent, oilseed rape (Brassica napus, AACC, 2n = 38). No generational differences were detected under low N conditions. In two noncompetitive glasshouse experiments, both transgenic and nontransgenic BC2F2 hybrids had on average less vegetative growth and seed production than B. rapa. In two high intraspecific competition field experiments with varied herbivore pressure, BC2F2 hybrids produced less vegetative dry weight than B. rapa. The competitive ability of transgenic and nontransgenic BC2F2 hybrids against a neighbouring crop species were quantified in competition experiments that assayed wheat (Triticum aestivum) yield reductions under agronomic field conditions. The hybrids were the least competitive with wheat compared with parental Brassica competitors, although differences between transgenic and nontransgenic hybrids varied with location. Hybridization, with or without transgene introgression, resulted in less productive and competitive populations. [source]

Stability and coexistence in a lawn community: mathematical prediction of stability using a community matrix with parameters derived from competition experiments

OIKOS, Issue 2 2000
Stephen H. Roxburgh
Community matrix theory has been proposed as a means of predicting whether a particular set of species will form a stable mixture. However, the approach has rarely been used with data from real communities. Using plant competition experiments, we use community matrix theory to predict the stability and competitive structuring of a lawn community. Seven species from the lawn, including the six most abundant, were grown in boxes, in conditions very similar to those on the lawn. They were grown alone (monocultures), and in all possible pairs. The species formed a transitive hierarchy of competitive ability, with most pairs of species showing asymmetric competition. Relative competitive ability (competitive effect) was positively correlated with published estimates of the maximum relative growth rate (RGRmax) for the same species. A seven-species community matrix predicted the mixture of species to be unstable. Simulations revealed two topological features of this community matrix. First, the matrix was closer to the stability/instability boundary than predicted from a range of null (random) models, suggesting that the lawn may be close to stability. Second, the tendencies of the lawn species to compete asymmetrically, and to be arranged in competitive hierarchies, were found to be positively associated with stability, and hence may be contributing factors to the near-stability seen in the matrix. The limitations of using competition experiments for constructing community matrices are discussed. [source]