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Ramos I.B.,University of Georgia | Ramos I.B.,Federal University of Rio de Janeiro | Miranda K.,Federal University of Rio de Janeiro | Miranda K.,Instituto Nacional Of Metrologia Normalizacao E Qualidade Industrial | And 9 more authors.
Biochemical Journal | Year: 2010

Acidocalcisomes are acidic calcium-storage compartments described from bacteria to humans and characterized by their high content in poly P (polyphosphate), a linear polymer of many tens to hundreds of Pi residues linked by high-energy phosphoanhydride bonds. In the present paper we report that millimolar levels of short-chain poly P (in terms of Pi residues) and inorganic PPi are present in sea urchin extracts as detected using 31P-NMR, enzymatic determinations and agarose gel electrophoresis. Poly P was localized to granules randomly distributed in the sea urchin eggs, as shown by labelling with the poly-P-binding domain of Escherichia coli exopolyphosphatase. These granules were enriched using iodixanol centrifugation and shown to be acidic and to contain poly P, as determined by Acridine Orange and DAPI (4′,6′-diamidino-2- phenylindole) staining respectively. These granules also contained large amounts of calcium, sodium, magnesium, potassium and zinc, as detected by X-ray microanalysis, and bafilomycin A1-sensitive ATPase, pyrophosphatase and exopolyphosphatase activities, as well as Ca2+/H+ and Na+/H+ exchange activities, being therefore similar to acidocalcisomes described in other organisms. Calcium release from these granules induced by nigericin was associated with poly P hydrolysis. Although NAADP (nicotinic acid-adenine dinucleotide phosphate) released calcium from the granule fraction, this activity was not significantly enriched as compared with the NAADP-stimulated calcium release from homogenates and was not accompanied by poly P hydrolysis. GPN (glycyl-L-phenylalanine-naphthylamide) released calcium when added to sea urchin homogenates, but was unable to release calcium from acidocalcisome-enriched fractions, suggesting that these acidic stores are not the targets for NAADP. © 2010 The Author(s).

Salem-Sugui S.,Federal University of Rio de Janeiro | Ghivelder L.,Federal University of Rio de Janeiro | Alvarenga A.D.,Instituto Nacional Of Metrologia Normalizacao E Qualidade Industrial | Cohen L.F.,Imperial College London | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We study the vortex dynamics of a BaFe1.82Ni 0.18As2 crystal with Tc=8 K by measuring flux creep over the second magnetization (or fishtail) peak for both H c axis and H ab planes. Magnetic relaxation data show an anomalously long initial stage of relaxation, lasting ∼10 min for the H c axis and 2-3 min for H ab, resembling a transient effect with a lower relaxation rate, which is followed by the usual log(time) relaxation. Interestingly, study of the relaxation rate R vs H for both stages of relaxation and for both field directions are featureless over the field range associated with the fishtail. The same trend was confirmed by plotting R vs T obtained from flux-creep data measured as a function of temperature for a fixed field (H c axis). A plot of the activation energy U(M,T) calculated from the time of relaxation of the magnetization at a fixed field also shows a smooth behavior, further supporting the view that the fishtail peak is not associated with a crossover in a vortex pinning regime within the collective pinning scenario. © 2011 American Physical Society.

Mosqueira J.,University of Santiago de Compostela | Dancausa J.D.,University of Santiago de Compostela | Vidal F.,University of Santiago de Compostela | Salem-Sugui S.,Federal University of Rio de Janeiro | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

High-resolution magnetization measurements performed in a high-quality Ba1-xKxFe2As2 single crystal allowed to determine the diamagnetism induced above the superconducting transition by thermally activated Cooper pairs. These data, obtained with magnetic fields applied along and transverse to the crystal ab layers, demonstrate experimentally that the superconducting transition of iron pnictides may be explained at a phenomenological level in terms of the Gaussian Ginzburg-Landau approach for three-dimensional anisotropic superconductors. © 2011 American Physical Society.

Turque A.S.,Federal University of Rio de Janeiro | Batista D.,Pontifical Catholic University of Rio de Janeiro | Silveira C.B.,Federal University of Rio de Janeiro | Cardoso A.M.,Instituto Nacional Of Metrologia Normalizacao E Qualidade Industrial | And 7 more authors.
PLoS ONE | Year: 2010

Background: Archaea are ubiquitous symbionts of marine sponges but their ecological roles and the influence of environmental factors on these associations are still poorly understood. Methodology/Principal Findings: We compared the diversity and composition of archaea associated with seawater and with the sponges Hymeniacidon heliophila, Paraleucilla magna and Petromica citrina in two distinct environments: Guanabara Bay, a highly impacted estuary in Rio de Janeiro, Brazil, and the nearby Cagarras Archipelago. For this we used metagenomic analyses of 16S rRNA and ammonia monooxygenase (amoA) gene libraries. Hymeniacidon heliophila was more abundant inside the bay, while P. magna was more abundant outside and P. citrina was only recorded at the Cagarras Archipelago. Principal Component Analysis plots (PCA) generated using pairwise unweighted UniFrac distances showed that the archaeal community structure of inner bay seawater and sponges was different from that of coastal Cagarras Archipelago. Rarefaction analyses showed that inner bay archaeaoplankton were more diverse than those from the Cagarras Archipelago. Only members of Crenarchaeota were found in sponge libraries, while in seawater both Crenarchaeota and Euryarchaeota were observed. Although most amoA archaeal genes detected in this study seem to be novel, some clones were affiliated to known ammonia oxidizers such as Nitrosopumilus maritimus and Cenarchaeum symbiosum. Conclusion/Significance: The composition and diversity of archaeal communities associated with pollution-tolerant sponge species can change in a range of few kilometers, probably influenced by eutrophication. The presence of archaeal amoA genes in Porifera suggests that Archaea are involved in the nitrogen cycle within the sponge holobiont, possibly increasing its resistance to anthropogenic impacts. The higher diversity of Crenarchaeota in the polluted area suggests that some marine sponges are able to change the composition of their associated archaeal communities, thereby improving their fitness in impacted environments. © 2010 Turque et al.

Salem-Sugui Jr. S.,Federal University of Rio de Janeiro | Ghivelder L.,Federal University of Rio de Janeiro | Alvarenga A.D.,Instituto Nacional Of Metrologia Normalizacao E Qualidade Industrial | Cohen L.F.,Imperial College London | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We report on isofield magnetic relaxation data on a single crystal of Ba1-xKxFe2As2 with superconducting transition temperature Tc =32.7 K which exhibit the so-called fish-tail effect. A surface map of the superconducting transition temperature shows that the superconducting properties are close to homogeneous across the sample. Magnetic relaxation data, M (t), was used to obtain the activation energy U (M) in order to study different vortex-dynamics regimes. Results of this analysis along with time-dependent measurements as a function of field and temperature extended to the reversible region of some M (H) curves demonstrate that the irreversibility as well the second magnetization peak position, H p (T), are time dependent and controlled by plastic motion of the vortex state. In the region delimited by a characteristic field Hon (well below Hp), and Hp, the vortex dynamics is controlled by collective pinning. For fields below Hon the activation energy, U0, increases with field as expected for collective pinning, but the pinning mechanism is likely to be in the single vortex limit. © 2010 The American Physical Society.

De Jesus T.C.L.,University of Sao Paulo | De Jesus T.C.L.,University of Georgia | Tonelli R.R.,University of Sao Paulo | Nardelli S.C.,University of Sao Paulo | And 11 more authors.
Journal of Biological Chemistry | Year: 2010

Target of rapamycin (TOR) kinases are highly conserved protein kinases that integrate signals from nutrients and growth factors to coordinate cell growth and cell cycle progression. It has been previously described that two TOR kinases control cell growth in the protozoan parasite Trypanosoma brucei, the causative agent of African trypanosomiasis. Here we studied an unusual TOR-like protein named TbTOR-like 1 containing a PDZ domain and found exclusively in kinetoplastids. TbTOR-like 1 localizes to unique cytosolic granules. After hyperosmotic stress, the localization of the protein shifts to the cell periphery, different from other organelle markers. Ablation of TbTOR-like 1 causes a progressive inhibition of cell proliferation, producing parasites accumulating in the S/G2 phase of the cell cycle. TbTOR-like 1 knocked down cells have an increased area occupied by acidic vacuoles, known as acidocalcisomes, and are enriched in polyphosphate and pyrophosphate. These results suggest that TbTOR-like 1 might be involved in the control of acidocalcisome and polyphosphate metabolism in T. brucei. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.

Silveira C.B.,Federal University of Rio de Janeiro | Vieira R.P.,Federal University of Rio de Janeiro | Cardoso A.M.,Instituto Nacional Of Metrologia Normalizacao E Qualidade Industrial | Paranhos R.,Federal University of Rio de Janeiro | And 2 more authors.
PLoS ONE | Year: 2011

Background: Planktonic bacteria are recognized as important drivers of biogeochemical processes in all aquatic ecosystems, however, the taxa that make up these communities are poorly known. The aim of this study was to investigate bacterial communities in aquatic ecosystems at Ilha Grande, Rio de Janeiro, Brazil, a preserved insular environment of the Atlantic rain forest and how they correlate with a salinity gradient going from terrestrial aquatic habitats to the coastal Atlantic Ocean. Methodology/Principal Findings: We analyzed chemical and microbiological parameters of water samples and constructed 16S rRNA gene libraries of free living bacteria obtained at three marine (two coastal and one offshore) and three freshwater (water spring, river, and mangrove) environments. A total of 836 sequences were analyzed by MOTHUR, yielding 269 freshwater and 219 marine operational taxonomic units (OTUs) grouped at 97% stringency. Richness and diversity indexes indicated that freshwater environments were the most diverse, especially the water spring. The main bacterial group in freshwater environments was Betaproteobacteria (43.5%), whereas Cyanobacteria (30.5%), Alphaproteobacteria (25.5%), and Gammaproteobacteria (26.3%) dominated the marine ones. Venn diagram showed no overlap between marine and freshwater OTUs at 97% stringency. LIBSHUFF statistics and PCA analysis revealed marked differences between the freshwater and marine libraries suggesting the importance of salinity as a driver of community composition in this habitat. The phylogenetic analysis of marine and freshwater libraries showed that the differences in community composition are consistent. Conclusions/Significance: Our data supports the notion that a divergent evolutionary scenario is driving community composition in the studied habitats. This work also improves the comprehension of microbial community dynamics in tropical waters and how they are structured in relation to physicochemical parameters. Furthermore, this paper reveals for the first time the pristine bacterioplankton communities in a tropical island at the South Atlantic Ocean. © 2011 Silveira et al.

Machado R.C.S.,Federal University of Rio de Janeiro | Machado R.C.S.,Instituto Nacional Of Metrologia Normalizacao E Qualidade Industrial | de Figueiredo C.M.H.,Federal University of Rio de Janeiro | Vuskovic K.,University of Leeds
Theoretical Computer Science | Year: 2010

The class C of graphs that do not contain a cycle with a unique chord was recently studied by Trotignon and Vušković (in press) [23], who proved for these graphs strong structure results which led to solving the recognition and vertex-colouring problems in polynomial time. In the present paper, we investigate how these structure results can be applied to solve the edge-colouring problem in the class. We give computational complexity results for the edge-colouring problem restricted to C and to the subclass C′ composed of the graphs of C that do not have a 4-hole. We show that it is NP-complete to determine whether the chromatic index of a graph is equal to its maximum degree when the input is restricted to regular graphs of C with fixed degree Δ ≥ 3. For the subclass C′, we establish a dichotomy: if the maximum degree is Δ = 3, the edge-colouring problem is NP-complete, whereas, if Δ ≠ 3, the only graphs for which the chromatic index exceeds the maximum degree are the odd holes and the odd order complete graphs, a characterization that solves edge-colouring problem in polynomial time. We determine two subclasses of graphs in C′ of maximum degree 3 for which edge-colouring is polynomial. Finally, we remark that a consequence of one of our proofs is that edge-colouring in NP-complete for r-regular tripartite graphs of degree Δ ≥ 3, for r ≥ 3. © 2009 Elsevier B.V. All rights reserved.

PubMed | Federal University of Rio de Janeiro, Instituto Nacional Of Metrologia Normalizacao E Qualidade Industrial and Microbiologia
Type: Journal Article | Journal: Pathogens and disease | Year: 2016

The obligate intracellular protozoan parasite Toxoplasma gondii actively invades virtually all warm-blooded nucleated cells. This process results in a non-fusogenic vacuole, inside which the parasites replicate continuously until egress signaling is triggered. In this work, we investigated the role of the large GTPase dynamin in the interaction of T. gondii with the host cell by using laser and electron microscopy during three key stages: invasion, development and egress. The detection of dynamin during invasion indicates the occurrence of endocytosis, while T. gondii egress appeared to be independent of dynamin participation. However, the presence of dynamin during T. gondii development suggests that this molecule plays undescribed roles in the tachyzoites cell cycle.

Badica P.,National Institute of Materials Physics Bucharest | Salem-Sugui Jr. S.,Federal University of Rio de Janeiro | Alvarenga A.D.,Instituto Nacional Of Metrologia Normalizacao E Qualidade Industrial | Jakob G.,Mainz University
Superconductor Science and Technology | Year: 2010

We report on magnetization data obtained as a function of temperature and magnetic field in Li2(Pd0.82Pt0.2)3B and Li2Pd3B non-centro-symmetric superconductors. Reversible magnetization curves were plotted as M1/2 versus T . This allows study of the asymptotic behavior of the averaged order parameter amplitude (gap) near the superconducting transition. Results of the analysis show, as expected, a mean field superconducting transition for Li2Pd3B. By contrast, a large deviation from the mean field behavior is revealed for Li 2(Pd0.8Pt0.2)3B. This is interpreted as due to the strength of the non-s-wave spin-triplet pairing in this Pt-containing compound which produces nodes in the order parameter and, consequently, phase fluctuations. The diamagnetic signal above Tc(H) in Li2Pd3B is well explained by superconducting Gaussian fluctuations and agrees with the observed mean field transition. For Li2(Pd0.8Pt 0.2)3B the diamagnetic signal above Tc(H) is much higher than the expected Gaussian values and appears to be well explained by three-dimensional critical fluctuations of the lowest-Landau-level type, which somehow agrees with the scenario of a phase mediated transition. © 2010 IOP Publishing Ltd.

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