1,721,025 research outputs found
Identification of two organohalide-respiring Dehalococcoidia associated to different dechlorination activities in PCB-impacted marine sediments
Full text linkAbstract Background Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) plays a major role in detoxifying anoxic contaminated freshwater and marine sediments from PCBs. Known members of the phylum Chloroflexi are typically responsible for this activity in freshwater sediments, whereas less is known about the microorganisms responsible for this activity in marine sediments. PCB-respiring activities were detected in PCB-impacted marine sediments of the Venice Lagoon. The aim of this work was to identify the indigenous organohalide-respiring microorganisms in such environments and assess their dechlorination specificity against spiked Aroclor™ 1254 PCBs under laboratory conditions resembling the in situ biogeochemistry. Results High PCB dechlorination activities (from 150 ± 7 to 380 ± 44 μmol of chlorine removed kg−1 week−1) were detected in three out of six sediments sampled from different locations of the lagoon. An uncultured non-Dehalococcoides phylotype of the class Dehalococcoidia closely related to Dehalobium chlorocoercia DF-1, namely phylotype VLD-1, was detected and enriched up to 109 16S rRNA gene copies per gram of sediment where dechlorination activities were higher and 25-4/24-4 and 25-2/24-2/4-4 chlorobiphenyls (CB) accumulated as the main tri-/dichlorinated products. Conversely, a different phylotype closely related to the SF1/m-1 clade, namely VLD-2, also enriched highly where lower dechlorination activity and the accumulation of 25-3 CB as main tri-chlorinated product occurred, albeit in the simultaneous presence of VLD-1. Both phylotypes showed growth yields higher or comparable to known organohalide respirers and neither phylotypes enriched in sediment cultures not exhibiting dechlorination. Conclusions These findings confirm the presence of different PCB-respiring microorganisms in the indigenous microbial communities of Venice Lagoon sediments and relate two non-Dehalococcoides phylotypes of the class Dehalococcoidia to different PCB dechlorination rates and specificities
Unraveling the Metabolic Potential of Asgardarchaeota in a Sediment from the Mediterranean Hydrocarbon-Contaminated Water Basin Mar Piccolo (Taranto, Italy)
Full text linkIncreasing number of metagenome sequencing studies have proposed a central metabolic role of still understudied Archaeal members in natural and artificial ecosystems. However, their role in hydrocarbon cycling, particularly in the anaerobic biodegradation of aliphatic and aromatic hydrocarbons, is still mostly unknown in both marine and terrestrial environments. In this work, we focused our study on the metagenomic characterization of the archaeal community inhabiting the Mar Piccolo (Taranto, Italy, central Mediterranean) sediments heavily contaminated by petroleum hydrocarbons and polychlorinated biphenyls (PCB). Among metagenomic bins reconstructed from Mar Piccolo microbial community, we have identified members of the Asgardarchaeota superphylum that has been recently proposed to play a central role in hydrocarbon cycling in natural ecosystems under anoxic conditions. In particular, we found members affiliated with Thorarchaeota, Heimdallarchaeota, and Lokiarchaeota phyla and analyzed their genomic potential involved in central metabolism and hydrocarbon biodegradation. Metabolic prediction based on metagenomic analysis identified the malonyl-CoA and benzoyl-CoA routes as the pathways involved in aliphatic and aromatic biodegradation in these Asgardarchaeota members. This is the first study to give insight into the archaeal community functionality and connection to hydrocarbon degradation in marine sediment historically contaminated by hydrocarbons
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
Bacterial colonization dynamics of different microplastic types in an anoxic salt marsh sediment and impact of adsorbed polychlorinated biphenyls on the plastisphere
Full text linkPlastic debris dispersed into the environment provide a substrate for microbial colonization, constituting a new human-made ecosystem called "plastisphere", and altering the microbial species distribution in aquatic, coastal and benthic ecosystems. The study aims at exploring the interaction among microplastics (MPs) made of different polymers, a persistent organic contaminant (polychlorinated biphenyls, PCBs), and the environmental microbial communities, in an anoxic marine sediment. Plastic pellets were incubated in the field in a salt marsh anoxic sediment, to observe the stages of plastisphere formation, by quantitative PCR and 16S rRNA gene sequencing, and PCB dechlorination activity on the MPs surface. Microbes from the sediment rapidly colonized the different microplastics types, with PVC recruiting a peculiar community enriched in sulfate-reducing bacteria. The composition of the plastisphere varied along the 1-year incubation possibly in response either to warmer temperatures in spring-summer or to microhabitat's changes due to the progressive plastic surface weathering. Even if PCB contaminated MPs were able to recruit potentially dehalogenating taxa, actual dechlorination was not detectable after 1 year. This suggests that the concentration of potentially dehalorespiring bacteria in the natural environment could be too low for the onset of the dechlorination process on MP-sorbed contaminants. Our study, which is among very few available longitudinally exploring the plastisphere composition in an anoxic sediment context, is the first exploring the fate and possible biodegradation of persistent organic pollutants sorbed on MPs reaching the seafloor
Repeated batch approach as a feasible procedure for the acclimatization of anaerobic consortia capable of an effective biomethanization of mechanically-sorted organic fraction of municipal solid waste
No full textThe acclimatization of anaerobic consortia capable of an effective biomethanization of a mechanically sorted-organic fraction of municipal solid waste (MS-OFMSW) was achieved in this study by following a repeated batch co-digestion approach. Mixtures of MS-OFMSW and cattle manure were processed in successive batch anaerobic digestion processes. Such an approach generally allowed a significantly increasing of the methane production when the MS-OFMSW represented the 30 and 40 % (v/v) of the initial mixture. On the other hand, the acclimated inocula did not adapt efficiently to higher concentration of the target waste MS-OFMSW. The acclimatization of the anaerobic consortia was demonstrated by means of molecular biology tools, by which a high diversity among populations occurring in the experimental matrices and after anaerobic processes was observed
Obtainment of a microbial consortium able to perform an effective biomethanization of a mechanically-sorted Organic fraction of municipal solid waste through a semicontinuous culture enrichment procedure
No full textMethane production yields achieved through the anaerobic digestion of mechanically sorted-organic fractions of municipal solid waste (MS-OFMSW) are generally lower than those obtained with source sorted-fractions (Hartmann and Ahring, 2006), but MS-OFMSW biomethanization can be enhanced through the acclimatization of a microbial population.
An anaerobic consortium capable of efficiently converting the organic fraction of MS-OFMSW into methane was obtained through a dedicated enrichment procedure in a 0.36 L up-flow anaerobic recirculated reactor. The system was initially filled with cattle manure (2.2% VSS, 6.2 g L-1 COD), an effective co-substrate for biomethanization of MS-OFMSW (Bertin et al., 2008); after a short batch working period, it was fed with MS-OFMSW according to a semi-continuous scheme, i.e. through successive short-time batch processes. In particular, at the beginning of each 56 hours batch cycle, 11mL of the processed waste were collected from the reactor, an equal volume of the waste (2.1% w/w VSS, 57.5 g L-1 COD) was then added by replacing part of the manure with MS-OFMSW which after 5 months theoretically constituted more than 99% of the reaction volume. The COD measured at the end of each period slowly decreased from 7.1 to 4.4 g L-1 and more than 90% of the overall COD fed during the experiment was depleted. Methanogenesis yield gradually increased up to 0.35 L g-1 depleted COD throughout the process. Molecular analysis of the microbial consortium indicated that while Archeal population was unaffected by sequencing fed-batch enrichment on MS-OFMSW, several hydrolytic and acidogenic Firmicutes and Bacteroidetes were enriched concomitantly to the observed increase of the biomethanization. The abovementioned bacterial species are probably essential for the effective biomethanization of MS-OFMSW carried out by the acclimated microbial community obtained in this study.
Hartmann H. and Ahring B.K. (2006). Wat. Sci. Technol. 53(8):7-22.
Bertin et al. (2008). Wat. Sci. Technol. 58(9):1735-174
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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