Helium star donor channel for the progenitors of type Ia supernovae

Type Ia supernovae (SNe Ia) play an important role in astrophysics, especially in the study of cosmic evolution. There are several progenitor models for SNe Ia proposed in the past years. In this paper, we have carried out a detailed study of the He star donor channel, in which a carbon-oxygen white dwarf (CO WD) accretes material from a He main sequence star or a He subgiant to increase its mass to the Chandrasekhar mass. Employing Eggleton's stellar evolution code with an optically thick wind assumption, and adopting the prescription of Kato & Hachisu (2004) for the mass accumulation efficiency of the He-shell flashes onto the WDs, we performed binary evolution calculations for about 2600 close WD binary systems. According to these calculations, we mapped out the initial parameters for SNe Ia in the orbital period--secondary mass ($\log P^{\rm i}-M^{\rm i}_2$) plane for various WD masses from this channel. The study shows that the He star donor channel is noteworthy for producing SNe Ia (i.e. $\sim 1.2\times10^{-3} {\rm yr}^{-1}$ in the Galaxy), and that the progenitors from this channel may appear as supersoft X-ray sources. Importantly, this channel can explain SNe Ia with short delay times (\la 10^{8} yr), which is consistent with recent observational implications of young populations of SN Ia progenitors.Comment: 9 pages, 8 figure, accepted by MNRA

Transcriptomic response of the red tide dinoflagellate, Karenia brevis, to nitrogen and phosphorus depletion and addition

<p>Abstract</p> <p>Background</p> <p>The role of coastal nutrient sources in the persistence of <it>Karenia brevis </it>red tides in coastal waters of Florida is a contentious issue that warrants investigation into the regulation of nutrient responses in this dinoflagellate. In other phytoplankton studied, nutrient status is reflected by the expression levels of N- and P-responsive gene transcripts. In dinoflagellates, however, many processes are regulated post-transcriptionally. All nuclear encoded gene transcripts studied to date possess a 5' <it>trans</it>-spliced leader (SL) sequence suggestive, based on the trypanosome model, of post-transcriptional regulation. The current study therefore sought to determine if the transcriptome of <it>K. brevis </it>is responsive to nitrogen and phosphorus and is informative of nutrient status.</p> <p>Results</p> <p>Microarray analysis of N-depleted <it>K. brevis </it>cultures revealed an increase in the expression of transcripts involved in N-assimilation (nitrate and ammonium transporters, glutamine synthetases) relative to nutrient replete cells. In contrast, a transcriptional signal of P-starvation was not apparent despite evidence of P-starvation based on their rapid growth response to P-addition. To study transcriptome responses to nutrient addition, the limiting nutrient was added to depleted cells and changes in global gene expression were assessed over the first 48 hours following nutrient addition. Both N- and P-addition resulted in significant changes in approximately 4% of genes on the microarray, using a significance cutoff of 1.7-fold and p ≤ 10^-4. By far, the earliest responding genes were dominated in both nutrient treatments by pentatricopeptide repeat (PPR) proteins, which increased in expression up to 3-fold by 1 h following nutrient addition. PPR proteins are nuclear encoded proteins involved in chloroplast and mitochondria RNA processing. Correspondingly, other functions enriched in response to both nutrients were photosystem and ribosomal genes.</p> <p>Conclusions</p> <p>Microarray analysis provided transcriptomic evidence for N- but not P-limitation in <it>K. brevis</it>. Transcriptomic responses to the addition of either N or P suggest a concerted program leading to the reactivation of chloroplast functions. Even the earliest responding PPR protein transcripts possess a 5' SL sequence that suggests post-transcriptional control. Given the current state of knowledge of dinoflagellate gene regulation, it is currently unclear how these rapid changes in such transcript levels are achieved.</p

Etude des facteurs d'opportunisme chez Staphyloccocus lugdunensis

My PhD project on the study of opportunistic factors in Staphylococcus lugdunensis aimed to better un- derstand how this commensal bacterium can be responsible for serious infections. The first part of our work was the construction of the ΔagrA and ΔRNAIII mutants of S. lugdunensis, encoding regulators potentially involved in virulence, to phenotypically characterize them and to identify the members of the regulons by global transcriptomic and proteomic analyzes. Our results have shown that AgrA is the major regulator of the Agr system in S. lugdunensis and that it controls the expression of genes allowing it to be more virulent, to adapt to environmental stresses (especially osmotic and oxidative stresses), to induce the formation of biofilm as well as the synthesis of carotenoid pigments. The second part of our work con- sisted in evaluating the impact of iron limitation, which represents a stress encountered by bacteria during infection, on the expression of the pathogenicity of S. lugdunensis. Phenotypic, transcriptomic and pro- teomic approaches were undertaken and the method for evaluating the pathogenicity of S. lugdunensis in a model of infection of Galleria mellonella larvae was developed. Our data revealed that iron deficiency in S. lugdunensis is a stress that promotes its ability to form biofilm while decreasing its resistance to oxidative stress as well as its virulence. Moreover, in response to this condition, S. lugdunensis is able to set up several mechanisms of iron acquisition, which probably provides it an advantage during infection and may partly explain the opportunistic behavior of this pathogen.Mon projet de thèse portant sur l’étude des facteurs d’opportunisme chez Staphylococcus lugdunensis avait pour but de mieux comprendre comment cette bactérie commensale peut être responsable d’in- fections graves. La première partie de nos travaux a consisté en la construction chez S. lugdunensis de mutants ΔagrA et ΔARNIII, codant des régulateurs potentiellement impliqués dans la virulence, afin de les caractériser phénotypiquement et d’identifier les membres des régulons par des analyses transcripto- mique et protéomique globales. Nos résultats ont mis en évidence que AgrA est le régulateur majeur du système Agr chez S. lugdunensis et qu’il contrôle l’expression de gènes lui permettant d’être plus virulent, de s’adapter aux stress environnementaux (notamment les stress osmotique et oxydatif), d’induire la formation de biofilm ainsi que la synthèse des pigments caroténoïdes. La seconde partie de nos travaux a consisté à évaluer l’impact de la limitation en fer, qui représente un stress rencontré par les bactéries pendant l’infection, sur l’expression de la pathogénicité de S. lugdunensis. Des approches phénotypique, transcriptomique et protéomique ont été entreprises et la méthode d’évaluation de la pathogénicité de S. lugdunensis en modèle d’infection de larves de Galleria mellonella a été mise au point. Nos données ont révélé que la carence en fer chez S. lugdunensis est un stress qui favorise sa capacité à former du biofilm tandis qu’il diminue sa résistance au stress oxydatif ainsi que sa virulence. De plus, en réponse à la condition de limitation en fer, S. lugdunensis est capable de mettre en place plusieurs mécanismes d’acquisition du fer, ce qui lui apporte vraisemblablement un avantage lors de l’infection et peut expliquer en partie le caractère opportuniste de ce pathogène

Study of opportunism factors in Staphylococcus lugdunensis

Mon projet de thèse portant sur l’étude des facteurs d’opportunisme chez Staphylococcus lugdunensis avait pour but de mieux comprendre comment cette bactérie commensale peut être responsable d’in- fections graves. La première partie de nos travaux a consisté en la construction chez S. lugdunensis de mutants ΔagrA et ΔARNIII, codant des régulateurs potentiellement impliqués dans la virulence, afin de les caractériser phénotypiquement et d’identifier les membres des régulons par des analyses transcripto- mique et protéomique globales. Nos résultats ont mis en évidence que AgrA est le régulateur majeur du système Agr chez S. lugdunensis et qu’il contrôle l’expression de gènes lui permettant d’être plus virulent, de s’adapter aux stress environnementaux (notamment les stress osmotique et oxydatif), d’induire la formation de biofilm ainsi que la synthèse des pigments caroténoïdes. La seconde partie de nos travaux a consisté à évaluer l’impact de la limitation en fer, qui représente un stress rencontré par les bactéries pendant l’infection, sur l’expression de la pathogénicité de S. lugdunensis. Des approches phénotypique, transcriptomique et protéomique ont été entreprises et la méthode d’évaluation de la pathogénicité de S. lugdunensis en modèle d’infection de larves de Galleria mellonella a été mise au point. Nos données ont révélé que la carence en fer chez S. lugdunensis est un stress qui favorise sa capacité à former du biofilm tandis qu’il diminue sa résistance au stress oxydatif ainsi que sa virulence. De plus, en réponse à la condition de limitation en fer, S. lugdunensis est capable de mettre en place plusieurs mécanismes d’acquisition du fer, ce qui lui apporte vraisemblablement un avantage lors de l’infection et peut expliquer en partie le caractère opportuniste de ce pathogène.My PhD project on the study of opportunistic factors in Staphylococcus lugdunensis aimed to better un- derstand how this commensal bacterium can be responsible for serious infections. The first part of our work was the construction of the ΔagrA and ΔRNAIII mutants of S. lugdunensis, encoding regulators potentially involved in virulence, to phenotypically characterize them and to identify the members of the regulons by global transcriptomic and proteomic analyzes. Our results have shown that AgrA is the major regulator of the Agr system in S. lugdunensis and that it controls the expression of genes allowing it to be more virulent, to adapt to environmental stresses (especially osmotic and oxidative stresses), to induce the formation of biofilm as well as the synthesis of carotenoid pigments. The second part of our work con- sisted in evaluating the impact of iron limitation, which represents a stress encountered by bacteria during infection, on the expression of the pathogenicity of S. lugdunensis. Phenotypic, transcriptomic and pro- teomic approaches were undertaken and the method for evaluating the pathogenicity of S. lugdunensis in a model of infection of Galleria mellonella larvae was developed. Our data revealed that iron deficiency in S. lugdunensis is a stress that promotes its ability to form biofilm while decreasing its resistance to oxidative stress as well as its virulence. Moreover, in response to this condition, S. lugdunensis is able to set up several mechanisms of iron acquisition, which probably provides it an advantage during infection and may partly explain the opportunistic behavior of this pathogen

Etude des facteurs d'opportunisme chez Staphyloccocus lugdunensis

My PhD project on the study of opportunistic factors in Staphylococcus lugdunensis aimed to better un- derstand how this commensal bacterium can be responsible for serious infections. The first part of our work was the construction of the ΔagrA and ΔRNAIII mutants of S. lugdunensis, encoding regulators potentially involved in virulence, to phenotypically characterize them and to identify the members of the regulons by global transcriptomic and proteomic analyzes. Our results have shown that AgrA is the major regulator of the Agr system in S. lugdunensis and that it controls the expression of genes allowing it to be more virulent, to adapt to environmental stresses (especially osmotic and oxidative stresses), to induce the formation of biofilm as well as the synthesis of carotenoid pigments. The second part of our work con- sisted in evaluating the impact of iron limitation, which represents a stress encountered by bacteria during infection, on the expression of the pathogenicity of S. lugdunensis. Phenotypic, transcriptomic and pro- teomic approaches were undertaken and the method for evaluating the pathogenicity of S. lugdunensis in a model of infection of Galleria mellonella larvae was developed. Our data revealed that iron deficiency in S. lugdunensis is a stress that promotes its ability to form biofilm while decreasing its resistance to oxidative stress as well as its virulence. Moreover, in response to this condition, S. lugdunensis is able to set up several mechanisms of iron acquisition, which probably provides it an advantage during infection and may partly explain the opportunistic behavior of this pathogen.Mon projet de thèse portant sur l’étude des facteurs d’opportunisme chez Staphylococcus lugdunensis avait pour but de mieux comprendre comment cette bactérie commensale peut être responsable d’in- fections graves. La première partie de nos travaux a consisté en la construction chez S. lugdunensis de mutants ΔagrA et ΔARNIII, codant des régulateurs potentiellement impliqués dans la virulence, afin de les caractériser phénotypiquement et d’identifier les membres des régulons par des analyses transcripto- mique et protéomique globales. Nos résultats ont mis en évidence que AgrA est le régulateur majeur du système Agr chez S. lugdunensis et qu’il contrôle l’expression de gènes lui permettant d’être plus virulent, de s’adapter aux stress environnementaux (notamment les stress osmotique et oxydatif), d’induire la formation de biofilm ainsi que la synthèse des pigments caroténoïdes. La seconde partie de nos travaux a consisté à évaluer l’impact de la limitation en fer, qui représente un stress rencontré par les bactéries pendant l’infection, sur l’expression de la pathogénicité de S. lugdunensis. Des approches phénotypique, transcriptomique et protéomique ont été entreprises et la méthode d’évaluation de la pathogénicité de S. lugdunensis en modèle d’infection de larves de Galleria mellonella a été mise au point. Nos données ont révélé que la carence en fer chez S. lugdunensis est un stress qui favorise sa capacité à former du biofilm tandis qu’il diminue sa résistance au stress oxydatif ainsi que sa virulence. De plus, en réponse à la condition de limitation en fer, S. lugdunensis est capable de mettre en place plusieurs mécanismes d’acquisition du fer, ce qui lui apporte vraisemblablement un avantage lors de l’infection et peut expliquer en partie le caractère opportuniste de ce pathogène

Etude de la prévalence du syndrome métabolique dans un service de chirurgie vasculaire

TOURS-BU Médecine (372612103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Characterization of the gen locus involved in β‐1,6‐oligosaccharide utilization by Enterococcus faecalis

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The transcriptional repressor SmvR is important for chlorhexidine decreased susceptibility in Enterobacter cloacae complex

International audienceMajor Facilitator Superfamily (MFS) efflux pumps have been shown to be important for bacterial cells to cope with biocides such as chlorhexidine (CHX), a widely used molecule in hospital settings. In this work, we evaluated the role of two genes smvA and smvR in CHX resistance in Enterobacter cloacae complex (ECC). smvA encodes an MFS pump whereas smvR, located upstream of smvA, codes for a TetR-type transcriptional repressor. To this aim, we constructed corresponding deletion mutants from the ATCC 13047 strain (MIC = 2 mg/L) as well as strains overexpressing smvA or smvR both in ATCC 13047 and three clinical isolates exhibiting elevated MICs of CHX (16-32 mg/L). Determination of MICs revealed that smvA played a modest role in CHX resistance, contrarily to smvR that modulated the ability of ECC to survive in the presence of CHX. In clinical isolates, the overexpression of smvR significantly reduced MICs of CHX (2-8 mg/L). Sequences analyses of smvR and promotor regions pointed out substitutions in conserved regions. Moreover, transcriptional studies revealed that SmvR acted as a repressor of smvA expression even if no quantitative correlation between the level of smvA mRNA and MICs of CHX could be observed. On the other hand, overproduction of smvA was able to complement the lack of the major resistance-nodulation-cell division (RND) superfamily efflux pump AcrB and restored resistance to ethidium bromide and acriflavine. Although SmvA could efflux biocides such as CHX, other actors, of which the expression is under SmvR control, should play critical role in ECC

Phenotypic and proteomic approaches of the response to iron-limited condition in Staphylococcus lugdunensis

International audienceBackground: Staphylococcus lugdunensis is a coagulase-negative Staphylococcus part of the commensal skin flora but emerge as an important opportunistic pathogen. Because iron limitation is a crucial stress during infectious process, we performed phenotypic study and compared proteomic profiles of this species incubated in absence and in presence of the iron chelator 2,2′-dipyridyl (DIP). Results: No modification of cell morphology nor cell wall thickness were observed in presence of DIP. However iron-limitation condition promoted biofilm formation and reduced the ability to cope with oxidative stress (1 mM H 2 O 2). In addition, S. lugdunensis N920143 cultured with DIP was significantly less virulent in the larvae of Galleria mellonella model of infection than that grown under standard conditions. We verified that these phenotypes were due to an iron limitation by complementation experiments with FeSO 4. By mass spectrometry after trypsin digestion, we characterized the first iron-limitation stress proteome in S. lugdunensis. Among 1426 proteins identified, 349 polypeptides were differentially expressed. 222 were more and 127 less abundant in S. lugdunensis incubated in iron-limitation condition, and by RT-qPCR, some of the corresponding genes have been shown to be transcriptionally regulated. Our data revealed that proteins involved in iron metabolism and carriers were over-expressed, as well as several ABC transporters and polypeptides linked to cell wall metabolism. Conversely, enzymes playing a role in the oxidative stress response (especially catalase) were repressed. Conclusions: This phenotypic and global proteomic study allowed characterization of the response of S. lugdunensis to iron-limitation. We showed that iron-limitation promoted biofilm formation, but decrease the oxidative stress resistance that may, at least in part, explained the reduced virulence of S. lugdunensis observed under low iron condition

Characterization of Arabidopsis thaliana mismatch specific endonucleases: application to mutation discovery by TILLING in pea

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