1,721,007 research outputs found
Environmental burkholderia cenocepacia strain enhances fitness by serial passages during long-term chronic airways infection in mice
No full textBurkholderia cenocepacia is an important opportunistic pathogen in cystic fibrosis (CF) patients, and has also been isolated from natural environments. In previous work, we explored the virulence and pathogenic potential of environmental B. cenocepacia strains and demonstrated that they do not differ from clinical strains in some pathogenic traits. Here, we investigated the ability of the environmental B. cenocepacia Mex1 strain, isolated from the maize rhizosphere, to persist and increase its virulence after serial passages in a mouse model of chronic infection. B. cenocepacia Mex1 strain, belonging to the recA lineage IIIA, was embedded in agar beads and challenged into the lung of C57Bl/6 mice. The mice were sacrificed after 28 days from infection and their lungs were tested for bacterial loads. Agar beads containing the pool of B. cenocepacia colonies from the four sequential passages were used to infect the mice. The environmental B. cenocepacia strain showed a low incidence of chronic infection after the first passage, after the second, third and fourth passages in mice, its ability to establish chronic infection increased significantly and progressively up to 100%. Colonial morphology analysis and genetic profiling of the Mex1-derived clones recovered after the fourth passage from infected mice revealed that they were indistinguishable from the challenged strain both at phenotypic and genetic level. By testing the virulence of single clones in the Galleria mellonella infection model, we found that two Mex1-derived clones significantly increased their pathogenicity compared to the parental Mex1 strain and behaved similarly to the clinical and epidemic B. cenocepacia LMG16656 T. Our findings suggest that serial passages of the environmental B. cenocepacia Mex1 strain in mice resulted in an increased ability to determine chronic lung infection and the appearance of clonal variants with increased virulence in non-vertebrate hosts. © 2017 by the authors. Licensee MDPI, Basel, Switzerland
Involvement of peroxiredoxin bcp2 in oxidative stress in Sulfolobus solfataricus.
No full textReactive oxygen species (ROS) such as superoxide and hydroxyl radicals, hydrogen peroxide, are potent oxidant capable of damaging all cellular components including DNA, proteins and membrane lipids. In order to protect against the toxicity of ROS, organisms are equipped with an array of defence mechanisms. Among these, peroxiredoxins (Prxs) (1), a family of thiol-specific antioxidant proteins, have received significant attention in the last years. Prxs exert their protective antioxidant role in cells through their peroxidase activity, whereby hydrogen peroxide, peroxynitrite and a wide range of organic hydroperoxides are reduced and detoxified.
These enzymes have been identified in each domain of life: Eucarya (2), Bacteria (3)and Archaea (4). Prxs use a redox-active cysteine to reduce peroxides and can be divided into two groups, the 1-Cys and 2-Cys Prxs, based on the cysteinyl residues involved in the catalysis.
[i]S.[/i] [i]solfataricus[/i], is an aerobic hyperthermophilic Archaea whose genome has been sequenced. The genome analysis shows the presence of four putative Prxs (Bcp1, Bcp2, Bcp3, Bcp4) whose physiological roles in the oxidative stress are underway.
We report the involvement of [i]bcp2[/i] gene in oxidative stress, the characterization of the recombinant protein rSsBcp2, its capability to scavenge H2O2 and to protect DNA against the cleavage caused from thiol-mixed –function oxidation (MFO) system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Detection of Burkholderia cenocepacia in natural environment using culture-based and culture indipendent methods
No full textCharacterization of 1-cys peroxiredoxin from Sulfolobus solfataricus and its involvement in the response to oxidative stress.
No full textIntroduction
To protect against toxic Reactive oxygen species (ROS), aerobic organisms are equipped with a full array of defence mechanisms. In recent years, much attention has been given to peroxiredoxins (Prxs) [1], a new family of thiol-specific antioxidant proteins. Prxs use a redox-active cysteine to reduce peroxides. In the aerobic hyperthermophilic archaeon Sulfolobus solfataricus the investigation of the mechanisms governing ROS protection is at initial stage. Recent analyses of the genomic sequence of S. solfataricus [2] have revealed the presence of four putative Prxs (Bcp1, Bcp2, Bcp3, Bcp4).
We report the involvement of the Bcp2 in oxidative stress in S. solfataricus and the characterization of the recombinant protein (rBcp2) in order to shed light on its role in the detoxification process and on its catalytic mechanism.
Material and Methods
Purification of rBcp2 by affinity chromatography (HisTrap HP Amersham) and size-exclusion chromatography (HiLoad Superdex 75; Amersham).
DNA cleavage assay by the metal ion catalyzed oxidation (MCO) system and assay of peroxidase activity were according to Lim et al. [3].
The mutant rBcp2 C49S was obtained by QuickChange II site directed mutagenesis kit (Stratagene).
Results
To understand the function of Bcp2 in oxidative stress, we provided evidence of its involvement in response to various oxidant agents. The transcriptional and the western blot analysis have showed the increased level of specific mRNA and Bcp2 respectively in response to Paraquat, tert-butyl hydroperoxide and H2O2.
rBcp2, expressed in E.coli, was purified and functionally characterized: rBcp2 removes the H2O2 in a DTT-dependent manner and protects plasmidic DNA against the MCO system (DTT/ Fe3+/O2). Lastly the loss of activity in the Bcp2 mutant (C49S) obtained shows that Cys49 must necessarily be involved in the catalysis
Structural and functional studies of Stf76 from the Sulfolobus islandicus plasmid-virus pSSVx: A novel peculiar member of the winged helix-turn-helix transcription factor family
No full textThe hybrid plasmid-virus pSSVx from Sulfolobus islandicus presents an open reading frame encoding a 76 amino acid protein, namely Stf76, that does not show significant sequence homology with any protein with known 3D structure. The recombinant protein recognizes specifically two DNA-binding sites located in its own promoter, thus suggesting an auto-regulated role of its expression. Circular dichroism, spectrofluorimetric, light scattering and isothermal titration calorimetry experiments indicated a 2:1 molar ratio (protein:DNA) upon binding to the DNA target containing a single site. Furthermore, the solution structure of Stf76, determined by nuclear magnetic resonance (NMR) using chemical shift Rosetta software, has shown that the protein assumes a winged helix-turn-helix fold. NMR chemical shift perturbation analysis has been performed for the identification of the residues responsible for DNA interaction. In addition, a model of the Stf76-DNA complex has been built using as template a structurally related homolog. © 2014 The Author(s) 2014
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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