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Etude des interactions d’exopolysaccharides de bactéries lactiques avec une bactériocine ou une toxine bactérienne
No full textLes propriétés des polysaccharides conditionnent la texture de nombreux aliments. L’intérêt croissant pour les exopolysaccharides (EPS) des bactéries lactiques (LAB) résulte notamment de la possibilité de les produire in situ dans l’aliment, à la différence des polysaccharides végétaux ou d’algues (ex : pectine, alginate). Avec la tendance du « clean label », les LAB sont des ingrédients (ferments) alors que la pectine ou de l’alginate de sodium sont des additifs alimentaires. Si de nombreuses études portent sur les propriétés techno-fonctionnelles des EPS résultant de leur interaction avec les principaux constituants des aliments, celles sur leurs interactions avec des molécules bioactives restent rares. Ce travail a donc visé à étudier les interactions entre un jeu de polysaccharides, comprenant des EPS, et la nisine Z, un peptide antibactérien produit par Lactococcus lactis subsp. lactis, ou le pentamère de l’entérotoxine B thermolabile d’Escherichia coli (LTB). L’entérotoxine thermolabile d’E. coli est une protéine composée d’une simple sous-unité A avec une activité catalytique et de la sous-unité B (LTB) non toxique, qui interagit avec un récepteur des cellules cibles permettant son internalisation. Le jeu d’EPS comprenait des dextranes de Leuconostoc mesenteroides de poids moléculaire faible (9-11 kDa) ou intermédiaire (60-76 kDa), des EPS de Ln. mesenteroides P35 et 2 kéfiranes (extraits de grains de kéfir de lait commercialisés par Crokfun ou Kefiralia). Les EPS de Ln. mesenteroides P35 sont des dextranes de haut poids moléculaire (Mw estimé à 9,9 × 103 kDa) avec 90 % de liaisons α-(1→6) et 10% de liaisons de branchement α-(1→3) entre molécules de glucose, alors que les deux kéfiranes sont des hétéropolysaccharides de glucose et de galactose. L’étude de l’effet de chacun de ces EPS, de pectine d’agrume hautement méthylée et d’alginate de sodium (à 1g.L-1 dans du bouillon tryptone-soja) sur l’activité antibactérienne de la nisine Z a indiqué que seul ce dernier diminuait son activité (multiplication par 4 des concentrations minimales inhibitrices et bactéricides vis-à-vis de Listeria innocua ATCC 33090 et Kocuria rhizophila ATCC 9341). Les potentiels zeta () à pH 7 de la nisine Z, des 2 souches de bactéries sensibles à la nisine et des polysaccharides ont été déterminés : seule la nisine Z a un potentiel légèrement positif, tandis que ceux des bactéries, de l’alginate de sodium et de la pectine d’agrume étaient tous inférieurs à -20 mV et ceux des EPS tous compris entre 0 et - 10 mV. Il a donc été proposé que l’alginate de sodium, seul polymère anionique à présenter un potentiel plus faible que les 2 bactéries sensibles à la nisine, forme des complexes par interactions électrostatiques avec la nisine Z dont la charge nette est positive, diminuant ainsi la quantité de nisine Z “libre” interagissant avec ces bactéries. Cette hypothèse a été confortée par l’observation à pH 7 de la formation d’agrégats de nisine Z et d’alginate et par l’estimation de l’affinité de l’alginate pour la nisine Z “libre” ou immobilisée (par résonance plasmonique de surface (SPR)). Tout comme la nisine Z, la LTB a été immobilisée sur un capteur à puce d’amino carboxyméthyl dextran, permettant d’évaluer par SPR ses interactions avec les polysaccharides. La constante apparente d’affinité des EPS de Ln. mesenteroides P35 pour la LTB immobilisée (KAapp=(2,05 ± 0.04) ×106 mol.L-1 à 37°C) s’est avérée élevée. L’interaction a été spontanée (ΔG0), et accompagnée d’une augmentation de l’entropie (ΔS>0). L’augmentation avec la température de KAapp suggère des interactions EPS - LTB à dominante hydrophobe. L’analyse in silico par « docking » moléculaire des interactions LTB - EPS de Ln. mesenteroides P35 a permis de proposer des interactions moléculaires putatives impliquées. Ceci suggère que certains EPS de LAB, comme ceux de Ln. mesenteroides P35 EPS, pourraient inhiber l’activité de la toxine thermolabile d’E. coli.Polysaccharides water holding, thickening or gelling properties condition the texture of many foods. During the last decade, exopolysaccharides (EPS) from lactic acid bacteria (LAB) have attracted more interest, since they can be produced in situ in foods, unlike plant or algal polysaccharides (e. g. pectin or sodium alginate, respectively). In the context of the « clean label » trend, LAB can be listed as ferments in the list of food ingredients, unlike pectin or sodium alginate, which are food additives. While many studies dealt with the techno-functional properties of LAB EPS resulting from their interaction with water and the other main food constituents, investigations of LAB EPS interactions with bioactive molecules are scarce. Therefore, the goal of the present study was to investigate interactions between a set of polysaccharides, including LAB EPS, and either nisin Z, an antibacterial peptide produced by Lactococcus lactis subsp. lactis, or Escherichia coli heat-labile enterotoxin B-pentamer (LTB). Indeed, E. coli heat-labile enterotoxin is a protein composed of a single catalytically active A subunit and a non-toxic pentameric B subunit, that mediates receptor interaction and uptake of the toxin by target cells. The set of EPS comprised (i) low (9-11 kDa) and medium (60-76 kDa) molecular weight dextrans from Leuconostoc mesenteroides, EPS from Ln. mesenteroides P35 strain, and 2 kefirans (extracted from milk kefir grains launched by Crokfun or Kefiralia). Elucidation of Ln. mesenteroides P35 EPS structure revealed that it is a high molecular weight dextran (estimated Mw of 9.9 × 103 kDa) with 90 % α-(1→6) linkages and 10% α-(1→3) branch linkages between glucose units, while both kefirans were heteropolysaccharides consisting of glucose and galactose. Investigation of the effect of each EPS and of either highly methoxylated citrus pectin, or sodium alginate (added at a 1g.L-1 concentration in tryptic soy broth) on nisin Z antibacterial activity revealed that only sodium alginate decreased its antibacterial activity (i. e. 4-fold increase of minimal inhibitory and bactericidal concentrations against Listeria innocua ATCC 33090 and Kocuria rhizophila ATCC 9341). Following zeta potential determination at pH 7 of nisin Z, of bacteria and of polysaccharides, only nisin Z had a slightly positive zeta potential, while bacteria, sodium alginate, and citrus pectin zeta potentials were lower than -20 mV, and zeta potentials of EPS were all between 0 and - 10 mV. It is thus proposed that anionic sodium alginate, which is the only polysaccharide having a lower zeta potential than both bacteria, forms complexes stabilized by electrostatic interactions with oppositely charged nisin Z, thereby decreasing the quantity of “free” nisin Z interacting with nisin-susceptible bacteria. This hypothesis was substantiated by the observation of nisin Z - sodium alginate aggregation at pH 7 and estimation of the apparent affinity of sodium alginate for “free” nisin Z and immobilized nisin Z by surface plasmon resonance (SPR). Similarly to nisin Z, LTB was immobilized by amine coupling on an amine carboxymethyl dextran sensor chip, thereby allowing the monitoring of its interactions with polysaccharides by SPR at different temperatures. SPR analysis revealed the high apparent affinity of Ln. mesenteroides P35 EPS for immobilized LTB (KAapp=(2.05 ± 0.04) ×106 mol.L-1 at 37°C). The binding process was spontaneous (ΔG0), and entropy-driven (ΔS>0) with an increase of KAapp with temperature. This suggests that EPS - LTB interaction is dominated by hydrophobic forces. In silico analysis by molecular docking of interactions between LTB and Ln. mesenteroides P35 EPS allowed to precise the putative molecular interactions involved. This suggested that some LAB EPS, such as Ln. mesenteroides P35 EPS are good candidates to inhibit E. coli thermolabile enterotoxin activity. This should now be further investigated
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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