1,720,976 research outputs found
Functional characterization of the biofilm exopolysaccharide produced by Burkholderia multivorans C1576
Full text linkL’attività di ricerca è stata focalizzata sulla delucidazione del ruolo strutturale e funzionale giocato dall’esopolisaccaride EpolC1576 sintetizzato e secreto nella matrice del biofilm da Burkholderia multivorans C1576, un patogeno opportunista isolato da malati di fibrosi cistica. La formazione del biofilm potrebbe essere una delle cause del cronicizzarsi delle infezioni nei malati di fibrosi cistica anche perché i biofilm sono considerati dei fattori di virulenza che conferiscono tolleranza e resistenza agli agenti antimicrobici. I biofilm sono aggregati polimicrobici costituiti da cellule batteriche immerse in una matrice altamente idratata di biopolimeri da loro prodotti e in cui gli esopolisaccaridi sono generalmente la componente preponderante. A differenza della gran parte degli esopolisaccaridi batterici caratterizzati finora, che risultano essere polimeri altamente idrofilici, l’EpolC1576 mostra un interessante carattere anfifilico. Esso risulta costituito da una unità tetrasaccaridica contenente mannosio e ramnosio in quantità equimolari. L’assenza di un idrossile al carbonio 6 del ramnosio insieme alla presenza di un metossile al carbonio 3 del 50% dei ramnosi legati in posizione 2, conferisce un carattere anfipatico all’EpolC1576 che potrebbe essere cruciale per la formazione ed il mantenimento del biofilm, ma anche per la diffusione di piccole molecole apolari come le molecole segnale del quorum sensing (QS), attraverso l’ambiente acquoso della matrice. La capacità dell’EpolC1576 di interagire con sonde fluorescenti idrofobiche è stata dimostrata attraverso analisi di spettroscopia di fluorescenza e di risonanza magnetica nucleare (NMR). Mediante quest’ultima è stato anche possibile dimostrare che l’EpolC1576 è in grado di aumentare la solubilità di una molecola segnale del QS conosciuta come Fattore Diffusibile del Segnale (DSF). Simulazioni di dinamica molecolare hanno rivelato che l’EpolC1576 è una molecola molto flessibile in grado di ripiegarsi ed allungarsi rapidamente, ma hanno anche confermato la presenza di interazioni significative tra l’EpolC1576 e il DSF. Analisi di spettroscopia di risonanza plasmonica di superficie (SPR) hanno mostrato che l’EpolC1576 è in grado di legare con buona affinità catene alifatiche immobilizzate su un supporto d’oro in funzione della concentrazione di esopolisaccaride utilizzata. Analisi di trasferimento di magnetizzazione (STD NMR) hanno provato che l’EpolC1576 interagisce con l’antibiotico Kanamicina. La conformazione dell’EpolC1576 è stata studiata mediante microscopia a forza atomica (AFM) ed ha rivelato che l’esopolisaccaride dà origine a degli aggregati tridimensionali densamente popolati grazie all’adozione di una conformazione compatta da parte delle catene glucidiche. Parallelamente, l’analisi al microscopio confocale a scansione laser (CLSM) ha prodotto ulteriori informazioni riguardo la morfologia ed la composizione del biofilm di B. multivorans C1576 formatosi in tre terreni diversi. L’analisi della matrice del biofilm al microscopio a trasmissione elettronica ha evidenziato la presenza di vescicole di membrana esterna (OMVs), mentre l’identità delle proteine associate alla matrice del biofilm e alle OMVs è stata svelata mediante analisi di spettrometria di massa. Infine, una libreria fagica di sequenze di DNA genomico di B. multivorans C1576 è stata analizzata per individuare proteine in grado di legare l’EpolC1576.The research is focused on the elucidation of the structural and functional role played by the exopolysaccharide EpolC1576 produced by the opportunistic pathogen Burkholderia multivorans C1576, a cystic fibrosis isolate, and excreted in the biofilm matrix. Biofilm formation might be the cause of chronic infections in cystic fibrosis subjects as biofilms are recognized virulence factors conferring tolerance and resistance to antimicrobials. Biofilms are poly-microbial aggregates in which cells are encased in a self-produced matrix of highly hydrated biopolymers with exopolysaccharides (Epols) being usually the most abundant component. Unlike most of the bacterial Epols characterized so far, which are highly hydrophilic, EpolC1576 shows an interesting amphipathic character. It is made up of a tetrasaccharide repeating unit, containing D-mannose and D-rhamnose.
The lack of the primary alcohol group on carbon 6 of rhamnoses together with the presence of a methoxy substituent on carbon 3 confer to EpolC1576 an amphipathic character that might be necessary for biofilm formation and maintenance, but also for the diffusion of small nonpolar compounds, such as quorum sensing (QS) signal molecules, through the matrix aqueous gel-like structure.
The ability of EpolC1576 to interact with hydrophobic fluorescent probes was demonstrated via both fluorescence and nuclear magnetic resonance (NMR) spectroscopy. NMR analysis also proved the EpolC1576 capability to increase the solubilization of the hydrophobic QS molecule known as Diffusible Signal Factor (DSF). Molecular modelling calculations revealed that EpolC1576 has a very flexible chain that can rapidly bend and straighten, but also confirmed the presence of significant interactions between EpolC1576 and the DSF molecule. Interestingly, surface plasmon resonance spectroscopy analysis showed the EpolC1576 binding to a monolayer of aliphatic chains in a concentration dependent manner. Saturation transfer difference NMR proved EpolC1576 interactions with the aminoglycoside antibiotic Kanamycin. The morphology of EpolC1576 was investigated by atomic force microscopy suggesting that the exopolysaccharide can form three dimensional structures, consisting of packed compact coils. In parallel, confocal laser scanning microscopy imaging of B. multivorans C1576 biofilms brought additional information about biofilm morphology and composition. Transmission electron microscopy analysis revealed that outer membrane vesicles represent a component of the biofilm matrix, whereas a comprehensive proteomic study to identify the nature of proteins dwelling within the biofilm matrix was carried out. Finally, a phage library of genomic DNA sequences obtained from B. multivorans C1576 was screened to seek for proteins possibly interacting with EpolC1576
Liver injury, SARS-COV-2 infection and COVID-19: What physicians should really know?
Full text linkSevere acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is responsible for coronavirus disease 2019 (COVID-19), which in males, especially in advanced age, can sometimes evolve into acute respiratory distress syndrome. In addition, mild to moderate alterations in liver function tests (LFTs) have been reported in the worst affected patients. Our review aims to analyse data on the incidence and prognostic value of LFT alterations, the underlying mechanisms and the management of pre-existing liver disease in COVID-19 affected patients
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
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
Fluorescence and NMR spectroscopy together with molecular simulations reveal amphiphilic characteristics of a Burkholderia biofilm exopolysaccharide
Full text linkBiofilms are a collective mode of bacterial life in which a selfproduced matrix confines cells in close proximity to each other. Biofilms confer many advantages, including protection from chemicals (including antibiotics), entrapment of useful extracellular enzymes and nutrients, as well as opportunities for efficient recycling of molecules from dead cells. Biofilm matrices are aqueous gel-like structures composed of polysaccharides, proteins, and DNA stabilized by intermolecular interactions that may include non-polar connections. Recently, polysaccharides extracted from biofilms produced by species of the Burkholderia cepacia complex were shown to possess clusters of
rhamnose, a 6-deoxy sugar with non-polar characteristics. Molecular dynamics simulations are well suited to characterizing the structure and dynamics of polysaccharides, but only relatively few such studies exist of their interaction with non-polar molecules. Here we report an investigation into the hydrophobic properties of the exopolysaccharide produced by Burkholderia multivorans strain C1576. Fluorescence experiments with two hydrophobic fluorescent probes established that this polysaccharide complexes hydrophobic species, and NMR experiments confirmed these interactions. Molecular simulations to model the hydrodynamics of the polysaccharide and the interaction
with guest species revealed a very flexible, amphiphilic carbohydrate chain that has frequent dynamic interactions with apolar molecules; both hexane and a long-chain fatty acid belonging to the quorum-sensing system of B. multivorans were tested. A possible role of the non-polar domains of the exopolysaccharide in facilitating the diffusion of aliphatic species toward specific targets within the biofilm aqueous
matrix is proposed
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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