1,720,983 research outputs found
Selenite biotransformation and detoxification by Stenotrophomonas maltophilia SeITE02: Novel clues on the route to bacterial biogenesis of selenium nanoparticles
No full textA putative biosynthetic mechanism for selenium nanoparticles (SeNPs) and efficient reduction of selenite (SeO32-) in the bacterial strain Stenotrophomonas maltophilia SeITE02 are addressed here on the basis of information gained by a combined approach relying on a set of physiological, chemical/biochemical, microscopy, and proteomic analyses. S. maltophilia SeITE02 is demonstrated to efficiently transform selenite into elemental selenium (Se°) by reducing 100% of 0.5mM of this toxic oxyanion to Se° nanoparticles within 48h growth, in liquid medium. Since the selenite reducing activity was detected in the cytoplasmic protein fraction, while biogenic SeNPs showed mainly extracellular localization, a releasing mechanism of SeNPs from the intracellular environment is hypothesized. SeNPs appeared spherical in shape and with size ranging from 160nm to 250nm, depending on the age of the cultures. Proteomic analysis carried out on the cytoplasmic fraction identified an alcohol dehydrogenase homolog, conceivably correlated with the biogenesis of SeNPs. Finally, by Fourier Transformed Infrared Spectrometry, protein and lipid residues were detected on the surface of biogenic SeNPs. Eventually, this strain might be efficaciously exploited for the remediation of selenite-contaminated environmental matrices due to its high SeO32- reducing efficiency. Biogenic SeNPs may also be considered for technological applications in different fields
Resolving electron transport in the selenate respiring bacterium Thauera selenatis
No full textThe Gram negative bacterium Thauera selenatis is able to respire with selenate as the sole terminal electron acceptor, utilising a periplasmic selenate reductase enzyme to reduce selenate to selenite. Previous characterisation of this enzyme has shown that it is a heterotrimeric molybdo-enzyme (SerABC) of the dimethylsulfoxide reductase family, containing a Mo-bis molybdopterin guanine dinucleotide co-factor, Fe-S clusters and a b-type haem (Schroder et al., 1997, J Biol Chem, 272: 23765-68, Dridge et al., 2007, Biochem J, 408: 19-28). In order to elucidate the electron transport pathway to selenate reductase, and how it can generate a proton motive force, detailed study was required. Firstly, the redox potential of the b-haem of SerC was determined by optical redox titration to be +234 mV. The serC gene was cloned and expressed heterologously in E. coli, but the protein was incorrectly folded into inclusion bodies, and attempts to refold and reconstitute SerC with haem were unsuccessful. A profile of c-type cytochromes in T. selenatis was undertaken, and characterisation of a number of cytochromes was carried out. Two cytochromes were purified, cytc7 and cytc4, and cytc4 was shown to be able to donate electrons to SerABC in vitro. Protein sequence was obtained by N-terminal sequencing and LC-MS/MS, and assigned cytc4 to the cytochrome c4 family of dihaem cytochromes. Redox potentiometry combined with UV-visible and electron paramagnetic spectroscopy showed that cytc4 is a dihaem cytochrome with a redox potential of +282 mV and both haems are predicted to have His-Met ligation. To investigate the role of membrane bound cytochromes in selenate respiration, PCR with degenerate primers amplified a partial gene coding for quinol: cytochrome c oxidoreductase (QCR). A microplate growth method was developed to monitor growth of T. selenatis under reproducible conditions, and used to analyse the effect of respiratory chain inhibitors on growth under different conditions. Aerobic metabolism was unaffected by QCR inhibitors, while nitrite reduction was totally inhibited, linking nitrite reduction to the generation of a proton motive force by the QCR. The QCR inhibitor myxothiazol partially inhibited selenate respiration, showing that some electron flux is via the QCR, but total inhibition of selenate respiration was achieved by combining myxothiazol with the more general inhibitor 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO). These data suggest that electron transfer to selenate reductase occurs via a branched pathway, in which one route is inhibited by myxothiazol and the other by HQNO. Electron transfer via a QCR and a dihaem cytochrome c4 is a novel route for a member of the dimethylsulfoxide reductase family of molybdo-enzymes
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
Purification and characterisation of cytochrome c’ from Neisseria meningitidis
No full textCytochrome c', a c-type cytochrome with unique spectroscopic and magnetic properties, has been characterized in a variety of denitrifying and photosynthetic bacteria. Cytochrome c' has a role in defence and/or removal of NO but the mechanism of action is not clear. To examine the function of cytochrome c' from Neisseria meningitidis, the protein was purified after heterologous overexpression in Escherichia coli. The electronic spectra of the oxidized c' demonstrated a pH-dependent transition (over the pH range of 6-10) typical of known c'-type cytochromes. Interestingly, the form in which NO is supplied determines the redox state of the resultant haem-nitrosyl complex. Fe(III)-NO complexes were formed when Fe(II) or Fe(III) cytochrome c' was sparged with NO gas, whereas an Fe(II)-NO complex was generated when NO was supplied using DEA NONOate (diazeniumdiolate)
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
Understanding the Role of Anaerobic Respiration in Burkholderia Thailandensis and B. pseudomallei Survival and Virulence
No full textBurkholderia pseudomallei is the causative agent of melioidosis, a disease endemic in Northern Australia and Southeast Asia. Melioidosis can present with acute, chronic and latent infections and can relapse several months or years after initial presentation. Currently not much is known about the ways in which B. pseudomallei can persist within the host, although it has been speculated that the ability to survive within an anaerobic environment will play some role. B. pseudomallei is able to survive anaerobically for extended periods of time but little is known about the molecular basis of anaerobic respiration in this pathogenic species.
Bioinformatic analysis was used to determine the respiratory flexibility of both B. pseudomallei and B. thailandensis, identifying multiple genes required for aerobic and anaerobic respiration, and molybdopterin biosynthesis. Using B. thailandensis as a model organism a transposon mutant library was created in order to identify genes required for anaerobic respiration. From this library one transposon mutant was identified to have disrupted moeA, a gene required for the molybdopterin biosynthetic pathway. This B. thailandensis transposon mutant (CA01) was unable to respire anaerobically on nitrate, exhibiting a significant reduction in nitrate reductase activity, altered motility and biofilm formation, but did not affect virulence in Galleria mellonella.
It was hypothesised that the reduction in nitrate reductase activity was contributing to the phenotypes exhibited by the B. thailandensis moeA transposon mutant. To determine whether this was true an in-frame narG deletion mutant was created in B. pseudomallei. Deletion of B. pseudomallei narG (ΔnarG) resulted in a significant reduction in nitrate reductase activity, anaerobic growth, motility and altered persister cell formation, and but did not affect virulence in G. mellonella or intracellular survival within J774A.1 murine macrophages. This study has highlighted the importance of anaerobic respiration in the survival of B. thailandensis and B. pseudomallei.BBSR
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