1,720,957 research outputs found
Detection and monitoring of arsenate respiring bacteria in soil
No full textThe capacity to couple growth to arsenate [As(V)] reduction may be widespread in soil bacteria. Microrganisms involved in arsenate reduction can be classified as either arsenic resistant bacteria (ARB) or dissimilatory arsenate respiring bacteria (DARB). In ARBs the cytoplasmic arsenate reductase is encoded by an arsC gene that is part of an arsenic resistance system. Differently, DARBs use As(V) as electron acceptor in respiration and the reduction is catalyzed by a periplasmic arsenate respiratory reductase (encoded by arrAB gene). DARBs are able to reduce both sorbed and dissolved As(V) (Oremland and Stolz, 2006) in environment with redox potential below +135mV. ArrA genes have been identified in several Proteobacteria and Gram-positive bacteria (Malasarn et al., 2004; Pérez-Jiménez et al., 2005). We investigated the occurrence of DARBs in an As polluted soil when it was spiked with glucose under flooding condition by real-time PCR quantification (qPCR) of the functional gene arrA. As(V) reduction was also monitored during the incubation time. The presence of DARBs was confirmed by using enrichment cultures established by mixing 0.5 g of soil in 45 ml of a modified Niggemyer enrichment medium containing sodium lactate (10 mM) and sodium arsenate (10 mM) (Niggemyer et al, 2001). Anaerobic conditions were achieved by flushing the vials, sealed with rubber stoppers, with N2. Four transplants were performed, in which As(V) reduction and arrA quantification were determined. Cloning and sequencing of arrA amplified in soil microcosms and in enrichment cultures were also performed.
In glucose amended soil As(V) reduction occurred in the first 15 days of incubation, when reducing conditions occurred; copy numbers of arrA gene were detected only at 15 days of incubation at levels of 10 copy number g-1 soil, close to the detection limit.
After the fourth transplant of the enrichment culture, As(V) reduction was 85% within 3 days and the qPCR analysis revealed an increase of copy numbers of arrA gene in concomitance of As(V) reduction, thus demonstrating the presence of DARBs in this polluted soil and a their potential activity in As solubilization
The microbial arsenic cycle in groundwater of Lombardia (Italy)
No full textArsenic in contaminated groundwater occurs largely as arsenite [As(III)], while As(V) is more prevalent in surface water. As the presence of arsenic species in drinking water, even in low concentrations, is a threat to human health, the World Health Organization recommends 10μgL-1 as the maximum arsenic concentration in drinking water. Groundwater of several Italian regions, has been found to contain As concentrations higher than 10μg L-1, due to the complexity of geological history and to substratum rock types of the regions. Within a project, financed by Fondazione Cariplo (Italy), aimed to study the indigenous microbial communities of As-rich groundwater from
Lombardia, we isolated bacteria involved in biogenic As cycle, i.e., in the reduction of As(V) and in the oxidation of As(III). Microbial species with arsenic biotransforming capability had so far not been studied in groundwater in Italy. The objectives of this study were to study the diversity and distribution of culturable As(V)-reducing and As(III)–oxidizing bacteria in groundwater with different Ascontaminated levels. Bacteria transforming As were isolated from all groundwater samples collected from 7 sites around Cremona (Lombardia, Italy). While bacteria able to reduce As(V) were isolated from each site, bacteria involved in the oxidation of reduced As
species were not always retrieved. In one site, the concomitant presence of an arsenate reducer and arsenite oxidizer was detected, indicating the occurrence of a full As cycle. For the first time, we provide evidence for the presence of an arsenite oxidase gene in an Aliihoeflea aestuarii strain and for its As(III)-oxidizing capability. The bacterial oxidation of As(III) to As(V) is being a promising technology for effective removal of As from groundwater as As(V) is more adsorptive to sorbents than As(III). Physico-chemical techniques that are usually used to remove arsenic from contaminated water have however some limitations, such as the use of chemicals
with environmental impact, the production of large amount of sludge, the need of secondary treatment, high costs and in some cases a low efficiency
Characterization of Microbial Communities in Groundwater from Lombardia (Italy) Polluted by Arsenic
No full textHuman exposure to arsenic (As) typically occurs through drinking water and the World Health Organization indicates a maximum threshold of 10 μg L-1 in drinking water. The aims of the work were 1) to investigate the relationships between groundwater microbial populations and water characteristics and 2) to envisage an origin of As contamination.
Water samples were collected from ten sites (six wells and four piezometers, Cremona, Italy), chosen from ARPA Lombardia (Regional Agency for Health Prevention and Environmental Protection) dataset, based on their different levels of As pollution. Samples from piezometers showed neutral pH value, significantly higher concentrations of total dissolved iron (Fe) and manganese (Mn) and significantly higher values of electrical conductivity (EC) than samples from wells. These latter samples had a mean pH value of 7.8. The total As concentration in groundwater samples ranged from 0.7 to 171 μg L-1. Samples from eight out of 10 sites exceeded the 10 μg L-1 As threshold (D.Lgs. 31/2001). AsIII was dominant in all the samples and AsIII/AsV ratio ranged from 3.6 to 6.7.
Denaturing gradient gel electrophoresis (DGGE) and Pyrotag sequence were used to characterize six microbial groundwater communities by analysing 16S rRNA genes amplified from environmental DNA. Sequence of dominant DGGE bands showed significant similarities with those of uncultured bacteria related to chemolithoautotrophic denitrifying, nitrite-oxidizing, sulfur-oxidising, sulfate-reducers and methylophilic strains. A Nitrospira-related sequence was found in three out of six groundwater samples reflecting the widespread of these nitrifiers in natural ecosystems. No sequence was directly related to known As strains, possibly because their number was below the detection limit. By Pyrotag sequence analysis Betaproteobacteria (retrieved in five samples), Delta and Epsilonproteobacteria (in four samples), and Alphaproteobacteria (in three samples) were found as the mostly represented classes. Pyrotag sequence analysis allowed the detection of Fe (Gallionella sp.) and of Mn (Hyphomicrobium sp.) oxidizers and Fe reducers (Geobacter sp.). In addition to the 16S rRNA genes, genes related to the AsV respiratory reductase (ArrA) and the AsV reductase (ArsC) were found in some groundwater samples.
Dissimilatory AsV respiring, AsV reducing and Fe reducing bacteria could be responsible for As mobilization in groundwaters from Lombardia, although the presence of AsV in reducing environment suggests also activity of AsIII-oxidizing bacteria.
Acknowledgment
The research is supported by CARIPLO Foundation, project 2010-2221
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
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
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