1,720,970 research outputs found
Response of 1,2-dichloroethane-adapted microbial communities to ex-situ biostimulation of polluted groundwater
No full textThe microbial community of a groundwater system contaminated by 1,2-dichloroethane (1,2-DCA), a toxic and persistent chlorinated hydrocarbon, has been investigated for its response to biostimulation finalized to 1,2-DCA removal by reductive dehalogenation. The microbial population profile of samples from different wells in the aquifer and from microcosms enriched in the laboratory with different organic electron donors was analyzed by ARISA (Amplified Ribosomal Intergenic Spacer Analysis) and DGGE (Denaturing Gradient Gel Electrophoresis) of 16S rRNA genes. 1,2-DCA was completely removed with release of ethene from most of the microcosms supplemented with lactate, acetate plus formate, while cheese whey supported 1,2-DCA dehalogenation only after a lag period. Microbial species richness deduced from ARISA profiles of the microbial community before and after electron donor amendments indicated that the response of the community to biostimulation was heterogeneous and depended on the well from which groundwater was sampled. Sequencing of 16S rRNA genes separated by DGGE indicated the presence of bacteria previously associated with soils and groundwater polluted by halogenated hydrocarbons or present in consortia active in the removal of these compounds. A PCR assay specific for Desulfitobacterium sp. showed the enrichment of this genus in some of the microcosms. The dehalogenation potential of the microbial community was confirmed by the amplification of dehalogenase-related sequences from the most active microcosms. Cloning and sequencing of PCR products indicated the presence in the metagenome of the bacterial community of a new dehalogenase potentially involved in 1,2-DCA reductive dechlorination
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
Identification of molecular markers to follow up the bioremediation of sites contaminated with chlorinated compounds
No full textThe use of microorganisms to clean up xenobiotics from polluted ecosystems (soil and water) represents an ecosustainable and powerful alternative to traditional remediation processes. Recent developments in molecular-biology-based techniques have led to rapid and sensitive strategies for monitoring and identifying bacteria and catabolic genes involved in the degradation of xenobiotics. This chapter provides a description of recently developed molecular-biology-based techniques, such as PCR with degenerate primers set, real-time quantitative PCR (qPCR), reverse transcription PCR (RT-PCR), southern blot hybridization, and long-range PCR, used to give a picture of the catabolically relevant microorganisms and of the functional genes present in a polluted system. By using a case study of a groundwater aquifer contaminated with 1,2-dichloroethane (1,2-DCA), we describe the identification of microorganisms potentially involved in the 1,2-DCA dehalorespiration (Dehalobacter sp. and Desulfitobacterium sp.) and a complete new gene cluster encoding for a 1,2-DCA reductive dehalogenase. The application of these techniques to bioremediation can improve our understanding of the inner mechanisms to evaluate the feasibility of a given treatment and provide us with a method to follow up bacteria and catabolic genes involved in the degradation of contaminants during the activities in situ
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
Reductive dechlorinating microbiomes in contaminated seawater sediments and groundwaters
No full textHalogenated organic compounds are extensively used in industry and agriculture and are, as a consequence, common contaminants in waters and sediments. Organohalide-respiring bacteria, capable of deriving energy for growth from dehalogenation, belong to several phyla, including Proteobacteria, Firmicutes and Chloroflexi. Reductive dehalogenation has been demonstrated to be a key microbial metabolism for groundwater remediation, and dehalogenase homologous genes have been retrieved both in contaminated groundwater and seawater environments. Aim of this work was to study and compare the phylogenetic and functional diversity of the reductive dechlorinating microbiota in groundwater and seawater sediments from sites with a different contamination context. Sediment slurry microcosms have been set up and spiked with known amounts of 1,2-dichloro ethane (1,2-DCA) as electron acceptor and different sources as electron donors. A series of subsequent culture transfers, where the dehalogenating consortia were inoculated in fresh media supplemented with 1,2-DCA and the proper electron donor, were established with the aim of selecting the best adapted bacterial consortium. Bacterial phylogenetic diversity was monitored by 16S rRNA gene-based PCR-Denaturing Gradient Gel Electrophoresis (DGGE) and barcoded pyrosequencing, while the functional diversity was described by DGGE fingerprinting on conserved domains of the dehalogenase encoding genes. The results indicated that both groundwater and seawater examined have dehalogenating potentials for remediation, showing complete degradation of 1,2-DCA in anaerobic microcosms and the enrichment of different dehalogenase-homologous encoding genes characterized by sequence domains specifically associated to 1,2-DCA metabolism. Despite a conserved 1,2-DCA reductive dechlorinating potential, the different environments and contamination context lead to the selection of specific communities with functional and phylogenetic diversity adapted to the peculiar geo-chemical settings
Integrative approach for characterization of chlorinated benzenes at contaminated sites: laboratory and field study
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