1,721,004 research outputs found
Characterization of Phanerochaete chrysosporium mutants Resistant to wood Extractives (CAREX)
No full textParmi les Basidiomycètes, certains champignons sont spécialisés dans la dégradation du bois. La dégradation du bois par ces champignons conduit à la libération de molécules, appelées extractibles, dont certaines possèdent des propriétés antifongiques. Pour se développer en présence de ces molécules, les champignons dégradeurs de bois ont mis en place des systèmes de détoxication. La majorité des connaissances acquises sur ces mécanismes se restreint au fonctionnement général du Xénome. Cette limitation est principalement dû à un manque d’outils génétiques disponibles chez les Basidiomycètes, dont le champignon dégradeur de bois modèle Phanerochaete chrysosporium. Pour contourner cet obstacle, des collections de mutants résistants à des molécules antifongiques ont été produites chez P. chrysosporium. Ces mutants ont été générés par exposition aux UV et ont été sélectionnés sur leur phénotype de résistance à ces composés. La caractérisation des mutants résistants aux extractibles de bois de Bagassa guianensis a permis de démontrer que la résistance aux extractibles d’un bois confère un avantage au champignon pour le minéraliser. Cette caractérisation a mis en évidence un lien de causalité entre une mutation dans le gène codant pour une protéine DENND6 et le phénotype de résistance acquis par les mutants. La caractérisation des mutants résistants à la rapamycine a permis d’identifier chez P. chrysosporium le mécanisme d’action de cette toxine. Cette molécule inhibe l’activité de la protéine kinase TOR, enzyme impliquée dans une voie de signalisation contrôlant la croissance chez les eucaryotes. Chez les champignons dégradeurs de bois, la régulation de la croissance est intimement liée aux processus contrôlant la production et la sécrétion des enzymes impliquées dans la dégradation du bois. L’utilisation de ces mutants pour étudier la voie de TOR durant ces processus constitue un axe de recherche prometteur.Among the Basidiomycetes, some fungi are specialized in the degradation of wood. The degradation of wood by these fungi leads to the release of molecules, called extractives, some of which have antifungal properties. To grow in the presence of these molecules, wood-degrading fungi possess detoxification systems. Most of the knowledge acquired on these mechanisms is limited to the general functioning of the Xenome. This limitation is mainly due to a lack of genetic tools available in Basidiomycetes, including the model wood-degrading fungus Phanerochaete chrysosporium. To overcome this limit, collections of mutants resistant to antifungal molecules were produced in P. chrysosporium. These mutants were generated by exposure to UV and were selected on their resistance phenotype to these compounds. The characterization of mutants resistant to Bagassa guianensis wood extractives demonstrated that resistance to wood extractives confers an advantage to the fungus to mineralize it. This characterization revealed a causal link between a mutation in the gene coding for a DENND6 protein and the resistance phenotype acquired by the mutants. The characterization of rapamycin resistant mutants allowed to identify the mechanism of action of this toxin in P. chrysosporium. This molecule inhibits the activity of the TOR protein kinase, an enzyme involved in a signalling pathway controlling growth in eukaryotes. In wood-degrading fungi, growth regulation is intimately linked to processes controlling the production and secretion of enzymes involved in wood degradation. The use of these mutants to study the TOR pathway during these processes is a promising line of research
Isolation and characterization of Phanerochaete chrysosporium mutants resistant to antifungal compounds
No full textLes champignons lignivores sont des organismes qui utilisent les composants du bois, la cellulose, les hémicelluloses et la lignine comme sources de carbone et d'énergie. Cependant, les processus oxydatifs utilisés par ces champignons pour décomposer le bois libèrent une myriade de molécules potentiellement toxiques, les extractibles. Ces extractibles sont des composants non structurels du bois. Ils sont responsables des propriétés du bois telles que sa couleur, son odeur et sa durabilité car ils peuvent avoir des propriétés antifongiques. Pour s'adapter à cet environnement toxique, les champignons responsables de la décomposition du bois ont développé diverses stratégies de détoxication des molécules antifongiques. Afin d’étudier cette détoxication, nous avons développé une stratégie de génétique directe chez le champignon modèle Phanerochaete chrysosporium. Après avoir réalisé des mutagènèses aux UV, des mutants résistants à deux molécules, l’itraconazole et la rapamycine, antifongiques aux mécanismes d’action connus ont été sélectionnés et caractérisés. De même, des extractibles provenant de deux essences de bois (Bagassa guianensis et Prunus avium) et présentant des activités antifongiques ont également été utilisés pour produire deux collections de mutants résistants à ces extractibles. Ces mutants ont été partiellement caractérisés ouvrant ainsi la voie à une meilleure compréhension des systèmes impliqués dans la détoxication des extractibles. La possibilité de réaliser de telles études chez les champignons lignivores ouvre de nouvelles perspectives. En effet, ces champignons suscitent un intérêt croissant ces dernières années, principalement en raison de leur utilisation potentielle dans la valorisation de la biomasse afin de produire des biocarburants, de leur fonction importante dans le cycle global du carbone mais également en raison des dommages qu’ils peuvent causer au matériau bois.Ligninolytic fungi are wood-degrading organisms that use cellulose, hemicelluloses, and lignin as sources of carbon and energy. However, the oxidative processes used by these fungi to decompose wood release a myriad of potentially toxic extractable molecules. These extractives are non-structural components of wood. They are involved in wood properties such as color, odor, and natural durability as they have antifungal properties. In order to adapt to this toxic environment, the fungi which are responsible for decomposing wood have developed various strategies to detoxify the antifungal molecules. In order to study this detoxification, we have developed a direct genetic strategy in Phanerochaete chrysosporium known as the wood-decomposing fungus model. After performing UV mutagenesis, screens allowing the identification of fungal strains resistant to different antifungal agents were carried out. Two selected molecules, including itraconazole and rapamycin with known mechanisms of antifungal action, made it possible to obtain two first mutant collections that were characterized. Next, extractives from two wood species (Bagassa guianensis and Prunus avium) with antifungal activities were used to produce two collections of mutants resistant to these extractives. The characterization of these mutants should allow us to understand why these extractives are toxic and how the fungus is able to detoxify them. The possibility of occurring studies on ligninolytic fungi opens new perspectives. Indeed, these fungi have been the subject of growing interest in recent years, mainly because of their potential use in the valorization of biomass to produce biofuels, their important function in the global carbon cycle, and also because of their wood material damage
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
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