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Search Results: 1 - 10 of 576 matches for " Delphine Capela "
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Como as aringas de Mo?ambique se transformaram em quilombos
Capela, José;
Tempo , 2006, DOI: 10.1590/S1413-77042006000100005
Abstract: runaway slaves in mozambique gathered in several communities located in stronghold points named aringas. these aringas became maroon communities where armed slaves called achicunda became the most serious opponents to the portuguese conquests between the late 19th century and the early 20th century.
Queuosine Biosynthesis Is Required for Sinorhizobium meliloti-Induced Cytoskeletal Modifications on HeLa Cells and Symbiosis with Medicago truncatula
Marta Marchetti, Delphine Capela, Renaud Poincloux, Nacer Benmeradi, Marie-Christine Auriac, Aurélie Le Ru, Isabelle Maridonneau-Parini, Jacques Batut, Catherine Masson-Boivin
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0056043
Abstract: Rhizobia are symbiotic soil bacteria able to intracellularly colonize legume nodule cells and form nitrogen-fixing symbiosomes therein. How the plant cell cytoskeleton reorganizes in response to rhizobium colonization has remained poorly understood especially because of the lack of an in vitro infection assay. Here, we report on the use of the heterologous HeLa cell model to experimentally tackle this question. We observed that the model rhizobium Sinorhizobium meliloti, and other rhizobia as well, were able to trigger a major reorganization of actin cytoskeleton of cultured HeLa cells in vitro. Cell deformation was associated with an inhibition of the three major small RhoGTPases Cdc42, RhoA and Rac1. Bacterial entry, cytoskeleton rearrangements and modulation of RhoGTPase activity required an intact S. meliloti biosynthetic pathway for queuosine, a hypermodifed nucleoside regulating protein translation through tRNA, and possibly mRNA, modification. We showed that an intact bacterial queuosine biosynthetic pathway was also required for effective nitrogen-fixing symbiosis of S. meliloti with its host plant Medicago truncatula, thus indicating that one or several key symbiotic functions of S. meliloti are under queuosine control. We discuss whether the symbiotic defect of que mutants may originate, at least in part, from an altered capacity to modify plant cell actin cytoskeleton.
Transient Hypermutagenesis Accelerates the Evolution of Legume Endosymbionts following Horizontal Gene Transfer
Philippe Remigi,Delphine Capela,Camille Clerissi,Léna Tasse,Rachel Torchet,Olivier Bouchez,Jacques Batut,Stéphane Cruveiller,Eduardo P. C. Rocha,Catherine Masson-Boivin
PLOS Biology , 2014, DOI: 10.1371/journal.pbio.1001942
Abstract: Horizontal gene transfer (HGT) is an important mode of adaptation and diversification of prokaryotes and eukaryotes and a major event underlying the emergence of bacterial pathogens and mutualists. Yet it remains unclear how complex phenotypic traits such as the ability to fix nitrogen with legumes have successfully spread over large phylogenetic distances. Here we show, using experimental evolution coupled with whole genome sequencing, that co-transfer of imuABC error-prone DNA polymerase genes with key symbiotic genes accelerates the evolution of a soil bacterium into a legume symbiont. Following introduction of the symbiotic plasmid of Cupriavidus taiwanensis, the Mimosa symbiont, into pathogenic Ralstonia solanacearum we challenged transconjugants to become Mimosa symbionts through serial plant-bacteria co-cultures. We demonstrate that a mutagenesis imuABC cassette encoded on the C. taiwanensis symbiotic plasmid triggered a transient hypermutability stage in R. solanacearum transconjugants that occurred before the cells entered the plant. The generated burst in genetic diversity accelerated symbiotic adaptation of the recipient genome under plant selection pressure, presumably by improving the exploration of the fitness landscape. Finally, we show that plasmid imuABC cassettes are over-represented in rhizobial lineages harboring symbiotic plasmids. Our findings shed light on a mechanism that may have facilitated the dissemination of symbiotic competency among α- and β-proteobacteria in natura and provide evidence for the positive role of environment-induced mutagenesis in the acquisition of a complex lifestyle trait. We speculate that co-transfer of complex phenotypic traits with mutagenesis determinants might frequently enhance the ecological success of HGT.
Experimental Evolution of a Plant Pathogen into a Legume Symbiont
Marta Marchetti,Delphine Capela,Michelle Glew,Stéphane Cruveiller,Béatrice Chane-Woon-Ming,Carine Gris,Ton Timmers,Véréna Poinsot,Luz B. Gilbert,Philipp Heeb,Claudine Médigue,Jacques Batut,Catherine Masson-Boivin
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1000280
Abstract: Rhizobia are phylogenetically disparate α- and β-proteobacteria that have achieved the environmentally essential function of fixing atmospheric nitrogen in symbiosis with legumes. Ample evidence indicates that horizontal transfer of symbiotic plasmids/islands has played a crucial role in rhizobia evolution. However, adaptive mechanisms that allow the recipient genomes to express symbiotic traits are unknown. Here, we report on the experimental evolution of a pathogenic Ralstonia solanacearum chimera carrying the symbiotic plasmid of the rhizobium Cupriavidus taiwanensis into Mimosa nodulating and infecting symbionts. Two types of adaptive mutations in the hrpG-controlled virulence pathway of R. solanacearum were identified that are crucial for the transition from pathogenicity towards mutualism. Inactivation of the hrcV structural gene of the type III secretion system allowed nodulation and early infection to take place, whereas inactivation of the master virulence regulator hrpG allowed intracellular infection of nodule cells. Our findings predict that natural selection of adaptive changes in the legume environment following horizontal transfer has been a major driving force in rhizobia evolution and diversification and show the potential of experimental evolution to decipher the mechanisms leading to symbiosis.
Hairy Black Holes in Massive Gravity: Thermodynamics and Phase Structure
Fabio Capela,Germano Nardini
Physics , 2012, DOI: 10.1103/PhysRevD.86.024030
Abstract: The thermodynamic properties of a static and spherically symmetric hairy black hole solution arising in massive gravity with spontaneous Lorentz breaking are investigated. The analysis is carried out by enclosing the black hole in a spherical cavity whose surface is maintained at a fixed temperature $T$. It turns out that the ensemble is well-defined only if the "hair" parameter $Q$ characterizing the solution is conserved. Under this condition we compute some relevant thermodynamic quantities, such as the thermal energy and entropy, and we study the stability and phase structure of the ensemble. In particular, for negative values of the hair parameter, the phase structure is isomorphic to the one of Reissner-Nordstrom black holes in the canonical ensemble. Moreover, the phase-diagram in the plan ($Q,T$) has a line of first-order phase transition that at a critical value of $Q$ terminates in a second-order phase transition. Below this line the dominant phase consists of small, cold black holes that are long-lived and may thus contribute much more to the energy density of the Universe than what is observationally allowed for radiating black holes.
Vertical Heterogeneity of Genotypic Structure and Toxic Potential within Populations of the Harmful Cyanobacterium Microcystis aeruginosa  [PDF]
Benjamin Misson, Delphine Latour
Advances in Microbiology (AiM) , 2013, DOI: 10.4236/aim.2013.36A004
Abstract: We investigated the vertical variability of toxic potential (i.e. proportions of cells containing microcystin genes) and genotypic structure within different populations of Microcystis aeruginosa that developed in deep artificial reservoirs on the Loire River (France). We demonstrated that a great qualitative vertical heterogeneity could exist within a single bloom of this cyanobacterium in deep lakes. Indeed, we observed important vertical shifts of both toxic potential and genotypic structure, whatever the bloom magnitude. These variations occurred mainly within the euphotic zone and proved to occur independently from abundance vertical shifts. One of the most striking results of this study is that the genotypic structure of a population of M. aeruginosa was more variable between different depths sampled at a single site than between different sites of the same reservoir sampled on top of the water column. In the same way the proportion of potentially toxic cells was sometimes more variable vertically than horizontally. The occurrence of such vertical heterogeneity in three different blooms suggests that this could be a frequent pattern within populations of M. aeruginosa.
Generaliza??o de um modelo linear de impedancia eletroquímica
Capela, J. M. V.;Capela, M. V.;Magnani, R.;
Eclética Química , 2003, DOI: 10.1590/S0100-46702003000100008
Abstract: the function of impedance for processes of simple electrode is generally deduced from the randles equivalent electric circuit. in this work the generalization of this function was studied, by the introduction of a parameter related to the flexibility of its phase angle and magnitude. the function was fitted to the impedance experimental measures from the ti-10wt.%al alloy in sodium chloride solution 0.9% and varying the amplitude of perturbation. the results showed that the generalized function reduces the distortions between the experimental and the theoretical curve with the best results obtained for signals with amplitude of 10 mv.
Dynamic model simulations as a tool for evaluating the stability of an anaerobic process
C Azeiteiro, IF Capela, AC Duarte
Water SA , 2001,
Abstract: The association of a wall growth factor with a dynamic model based on Andrews' work (1969), without pH restrictions, is used herein to study the inhibition of methanogenesis by high concentrations of volatile acids. The model considers the methanogenic bacteria as being representative of the biological phase of the anaerobic digestion, and assumes a continuous feed of acetic acid to the continuously stirred anaerobic reactor. The model can be used for simulations on transient conditions, namely the effect of initial conditions on the start-up of a digester, as well as for studying the significant improvements in stability when wall growth occurs in the reactor. The effect of changing the feed characteristics to a digester was studied in two situations: with and without wall growth. The presence of wall growth allows a better behaviour of an anaerobic process in any case, namely when a step increase in the feeding substrate concentration or in flow rate is performed. WaterSA Vol.27(1) 2001: 109-114
Black Hole Thermodynamics and Massive Gravity
Fabio Capela,Peter G. Tinyakov
Physics , 2011, DOI: 10.1007/JHEP04(2011)042
Abstract: We consider the generalized laws of thermodynamics in massive gravity. Making use of explicit black hole solutions, we devise black hole merger processes in which i) total entropy of the system decreases ii) the zero-temperature extremal black hole is created. Thus, both second and third laws of thermodynamics are violated. In both cases, the violation can be traced back to the presence of negative-mass black holes, which, in turn, is related to the violation of the null energy condition. The violation of the third law of thermodynamics implies, in particular, that a naked singularity may be created as a result of the evolution of a singularity-free state. This may signal a problem in the model, unless the creation of the negative-mass black holes from positive-mass states can be forbidden dynamically or the naked singularity may somehow be resolved in a full quantum theory.
Palynological and Physicochemical Characterization of Honey in the Sudano-Guinean Zone of Cameroon  [PDF]
Dongock Nguemo Delphine, Tchoumboue Joseph
Food and Nutrition Sciences (FNS) , 2015, DOI: 10.4236/fns.2015.615140
Abstract: The palynological and physico-chemical characterization of honey was investigated in the Sudano- Guinean zone of Cameroon through the melissopalynology analysis. Results showed that honey with the dark amber color was the most represented. Sweet honey with less odour considered as pleasant highly predominate. The pH of honey is low and varies from 3.95 to 5.00; this ranking confirms the hypothesis that honey is from plant through visit of honeybees. The sugar content is very high ranging from 77.93% to 83.13%; the mean value is 78.90% and this value confirms that the honey is floral honey. The density value ranges from 1.39 to 1.43 and does not exceed the average standard (1.39 to 1.44 at 20). Water contents correspond to the standards norms. For free acidity, the highest value is 48.68 ± 0.28. There is a low positive correlation (r = 0.2) between free acidity and the pH of honey. Pollen analysis of honeys led to the identification of 41 pollen species belonging to 25 families. The highly represented families are Asteraceae and Myrtaceae. Two thirds of honey is monofloral and characteristics of three dominant species: Nymphaea maculata, Terminalia avicennioides and Syzygium guineense. The pollens of Syzygium guineense are present in all honey samples analysed.
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