1,720,998 research outputs found
PCB reductive dehalogenation in sediments of venice lagoon: preliminary characterization of the dechlorinating microflora
No full textIt has been documented that PCBs might undergo in situ microbial dechlorination in a wide variety of anaerobic freshwater sediments mostly under methanogenic conditions, although recent studies have shown a possible role of Dehalococcoides-like microrganisms in the process. Recently, we demonstrated the occurrence of microbial-mediated reductive dechlorination processes towards weathered PCBs in marine sediments of the Porto Marghera area of Venice lagoon. The process is a) directed towards meta- and para-chlorines of PCB molecule, b) not primed by the addition of exogenous PCBs, and c) apparently mediated by indigenous sulfate-reducing spore-forming bacteria. To gain deeper insights on the latter finding, native microflora was sub-cultured 5 times in the presence of exogenous PCBs (5 spiked coplanar PCBs and then Aroclor 1254) and decreasing amounts of sterile sediment. Increasing PCB-dechlorination rate along with remarkable increases in sulfate-reduction and a progressive decline in methanogenic activity were observed throughout subculturing. The culture resulting from the last transfer displayed a marked activity towards Aroclor 1254. The addition of H2 and short chain organic acids did not affect the process. However, when the same agents were applied together with vancomycin or ampicillin, higher dechlorination rates and extents were observed. This finding seems to suggest that Dehalococcoides-like bacteria are also involved in PCB dechlorination, even though sulfate-reducing bacteria cannot be excluded. Molecular analysis of the cultures, currently in progress, will allow to have a deeper insight on PCB dechlorinating populations occurring in Venice lagoon sediments
A Dehaloccoides-like bacterium and a new reductive dehalogenase are responsible for PCB dechlorination in marine sediments under in situ biogeochemical conditions
No full textEnrichment of PCB dechlorinators from sediments of the Venice lagoon
No full textReductive dechlorination of polychlorinated biphenyls (PCBs) has been shown to occur in contaminated marine sediments of the Venice Lagoon suspended in water coming from the same site. Aim of this work is to enrich the PCB dechlorinating population under such conditions. Native microflora was sub-cultured 5 times in the presence of exogenous PCBs (5 spiked coplanar PCBs and then Aroclor 1254) and decreasing amounts of sterile sediment. Increasing PCB-dechlorination rates were observed throughout subculturing. The culture resulting from the last transfer displayed a marked activity towards Aroclor 1254. The addition of H2 and short chain organic acids increased sulfate-reducing and methanogenic activities but did not affect the dechlorination process. However, when the same agents were applied together with vancomycin or ampicillin, remarkable and comparable increases in the dechlorination rates were detected. These findings seem to rule out sulfate-reducing and methanogenic bacteria as dechlorinators and suggest that Dehalococcoides-like bacteria, known dehalogenators resistant to the applied antibiotics, could be involved in PCB dechlorination in sediments of the Venice Lagoon
Characteriaztion of microbial consortia from marine sediments of the venice lagoon capable of pcb dechlorination
No full textIn this study we present the characterization of microbial communities supporting PCBs dechlorination, after enrichment from Venice lagoon’s (VL) sediments. The sediment with the native microbiota were sub-cultured in seven successive passages in slurry microcosms spiked with coplanar PCBs or Aroclor 1254, different electron donors and antibiotics. Increasing PCBs-dechlorination rates along with increases in sulfate-reduction and decline in methanogenic activities occurred throughout subculturing. Quantitative real-time PCR and denaturing gradient gel electrophoresis over the 16S rRNA gene of Dehalococcoides-like bacteria, indicated that one bacterial taxon (SF1/M1), strictly related to the genus Dehaloccoides, proliferated in all the microcosms actively dechlorinating PCBs but not in those without the chlorinated compounds. SF1/M1 has been previously reported to actively dechlorinate 3,5-dichlorobiphenyl. A novel reductive dehalogenase gene sequence has been detected only in microcosms enriched with SF1/M1 supporting a dehalorespiring activity by these bacteria
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
PCB reductive dehalogenation in sediments of Venice Lagoon: preliminary characterization of dechlorinating microflora
No full textBacterial symbionts in East African mangrove crabs
No full textMangrove communities are highly productive ecosystems releasing large amounts of organic matter to adjacent coastal waters. Organisms in the mangrove ecosystems have to cope with different stresses like high salinity, periodic tidal flows, anoxic niches in soil and fluctuating thermal regimes. Moreover, mangrove soil and sediments present high contents of lignin-derived tannins and polyphenols that plants produce to preserve the tissues from microbial pathogens. Despite the harsh conditions a large animal biomass characterizes the mangrove ecosystem mainly represented by the true burrowing crabs sesarmids and ocipodids (Crustacea, Brachyura) that play an important role in the ecosystem functioning as ecosystem engineers (Kristensen and Alongi 2006). How the mangrove crabs cope with the harsh conditions of the ecosystem, especially how they manage the high C/N ratio of their diet are intriguing questions. It has been hypothesized that mangrove crabs can take advantage of an associated symbiotic microbiome (Thongtham and Kristensen 2005) that may complement nutritional deficiencies like occurs in other arthorpods (Moran and Dale 2006). The aim of this study was to evaluate the diversity of microbial symbionts associated to two representative mangrove crab species, Uca urvillei (ocipodids) and Perisesarma guttatum (sesarmids), collected from two different populations in a Kenyan and in a South African mangrove forests. The bacterial community associated to different crab organs and tissues such as gill, hindgut, gonads and eggs was characterized by sequencing PCR-amplified 16S rRNA genes following separation by denaturing gradient gel electrophoresis. Rather highly diverse bacterial communities have been associated to all the organs examined. A range of novel taxa showing low sequence identity with previously identified bacteria have been found associated to all crabs organs. rRNA gene sequences related to sulfur- oxidizing bacteria have been identified in the gills suggesting the chemolithoautotrophy may play a role in the maintenance of the crab metacommunity. In hindgut tissues sequences related to nitrifying and denitrifying bacteria were found supporting the hypothesis of a complex nitrogen cycle occurring in the gut
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
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