11 research outputs found

    Hosting the Unwanted: Stethoscope Contamination Threat

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    Aims: Stethoscopes represent a vehicle of bacteria and other microorganisms and may play a role in the spread of health-care associated infections (HAIs). We aimed to evaluate the contamination levels of stethoscopes before and after use of a disinfecting technique (DT). Study Design: Matched cross-over study. Place and Duration of Study: The study was conducted in July 2012 and involved three hospitals in Siena Province (Italy). Two were public hospitals with about 750 and 140 beds, and the other was private with 40 beds. Methodology: We evaluated: i) contamination on 74 shared and non shared stethoscopes; ii) bacterial load before and after use of a DT. Total bacterial count (TBC) at 36ÂșC and 22ÂșC, Staphylococcus spp., molds, Enterococcus spp., Pseudomonas spp., Escherichia coli and total coliforms bacteria were evaluated. Mann Whitney and Wilcoxon tests were used for comparisons (p<0.05). Results: Before DT, 49 stethoscopes were positive for TBC at 36ÂșC, 48 for TBC at 22ÂșC, 40 for Staphylococcus spp., 18 for methicillin-resistant Staphylococcus aureus, 33 for coliforms (9 for Escherichia coli), 5 for Enterococcus spp. and 2 for molds. After cleaning, the percentage reduction in CFUs was close at 100% in most comparisons. Shared stethoscopes proved to be less contaminated than non shared ones (p<0.05). Conclusion: Our results suggest that stethoscopes may be potential vehicles of HAIs. The DT was effective in reducing bacterial contamination

    Multisignal control of expression of the LHCX protein family in the marine diatom Phaeodactylum tricornutum

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    Diatoms are phytoplanktonic organisms that grow successfully in the ocean where light conditions are highly variable. Studies of the molecular mechanisms of light acclimation in the marine diatom Phaeodactylum tricornutum show that carotenoid de-epoxidation enzymes and LHCX1, a member of the light-harvesting protein family, both contribute to dissipate excess light energy through non-photochemical quenching (NPQ). In this study, we investigate the role of the other members of the LHCX family in diatom stress responses. Our analysis of available genomic data shows that the presence of multiple LHCX genes is a conserved feature of diatom species living in different ecological niches. Moreover, an analysis of the levels of four P. tricornutum LHCX transcripts in relation to protein expression and photosynthetic activity indicates that LHCXs are differentially regulated under different light intensities and nutrient starvation, mostly modulating NPQ capacity. We conclude that multiple abiotic stress signals converge to regulate the LHCX content of cells, providing a way to fine-tune light harvesting and photoprotection. Moreover, our data indicate that the expansion of the LHCX gene family reflects functional diversification of its members which could benefit cells responding to highly variable ocean environments

    The DivJ, CbrA and PleC system controls DivK phosphorylation and symbiosis in Sinorhizobium meliloti

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    Sinorhizobium meliloti is a soil bacterium that invades the root nodules it induces on Medicago sativa, whereupon it undergoes an alteration of its cell cycle and differentiates into nitrogen-fixing, elongated and polyploid bacteroid with higher membrane permeability. In Caulobacter crescentus, a related alphaproteobacterium, the principal cell cycle regulator, CtrA, is inhibited by the phosphorylated response regulator DivK. The phosphorylation of DivK depends on the histidine kinase DivJ, while PleC is the principal phosphatase for DivK. Despite the importance of the DivJ in C. crescentus, the mechanistic role of this kinase has never been elucidated in other Alphaproteobacteria. We show here that the histidine kinases DivJ together with CbrA and PleC participate in a complex phosphorylation system of the essential response regulator DivK in S. meliloti. In particular, DivJ and CbrA are involved in DivK phosphorylation and in turn CtrA inactivation, thereby controlling correct cell cycle progression and the integrity of the cell envelope. In contrast, the essential PleC presumably acts as a phosphatase of DivK. Interestingly, we found that a DivJ mutant is able to elicit nodules and enter plant cells, but fails to establish an effective symbiosis suggesting that proper envelope and/or low CtrA levels are required for symbiosis.National Institutes of Health (U.S.) (Grant GM31010

    A systems-wide understanding of photosynthetic acclimation in algae and higher plants

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    The ability of phototrophs to colonise different environments relied on the robust protection against oxidative stress in phototrophs, a critical requirement for the successful evolutionary transition from water to land. Photosynthetic organisms have developed numerous strategies to adapt their photosynthetic apparatus to changing light conditions in order to optimise their photosynthetic yield, crucial for life to exist on Earth. Photosynthetic acclimation is an excellent example of the complexity of biological systems, in which highly diverse processes, ranging from electron excitation over protein protonation to enzymatic processes coupling ion gradients with biosynthetic activity interact on drastically different timescales, ranging from picoseconds to hours. An efficient functioning of the photosynthetic apparatus and its protection is paramount for efficient downstream processes including metabolism and growth. Modern experimental techniques can be successfully integrated with theoretical and mathematical models to promote our understanding of underlying mechanisms and principles. This Review aims to provide a retrospective analysis of multidisciplinary photosynthetic acclimation research carried out by members of the Marie Curie Initial Training Project “AccliPhot”, placing the results in a wider context. The Review also highlights the applicability of photosynthetic organisms for industry, particularly with regards to the cultivation of microalgae. It aims to demonstrate how theoretical concepts can successfully complement experimental studies broadening our knowledge of common principles in acclimation processes in photosynthetic organisms, as well as in the field of applied microalgal biotechnology

    RÎle des protéines de la famille des antennes collectrices de lumiÚre, LHCX, dans la photoprotection chez les diatomées

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    Diatoms dominate phytoplanktonic communities in contemporary oceans, contributing to 20% of global primary productivity. In their extremely variable environment, diatoms are especially efficient in adjusting their photosynthetic activity by dissipating as heat the light energy absorbed in excess, through a process called “Non-Photochemical Quenching of chlorophyll fluorescence”, (NPQ). In the model diatom Phaeodactylum tricornutum, it has been shown that LHCX1, a photosynthetic antenna-related gene, is involved in the NPQ process. Through integrated approaches of genetics, molecular biology, biochemistry, study of the kinetics of chlorophyll fluorescence yields and ultrafast spectroscopy, I studied the role of the LHCX family in the photoprotection activity of P. tricornutum. I first correlated a differential regulation of the 4 P. tricornutum LHCX genes with different dynamics of NPQ and photosynthetic activity, in different light and nutrient conditions. By localizing the LHCXs in fractioned photosynthetic complexes and the different sites of energy dissipation, I was able to propose a model of dynamic regulation of NPQ capacity involving mainly the LHCX1 in the reaction centers, during short-term high light responses. During prolonged high light stress, the quenching occurs mainly in the antennas, potentially mediated by the LHCX3 isoform. Finally, using photosynthetic parameters, I screened a series of transgenic lines putatively deregulated in their LHCX amount, and I identified lines with altered NPQ, which could represent novel investigation tools. Altogether, this work highlighted the functional diversification and the importance of the LHCX protein family in the fine-tuning of light harvesting and photoprotection capacity, possibly contributing to explain diatoms success in their highly fluctuating environment.Les diatomĂ©es constituent le principal groupe du phytoplancton dans les ocĂ©ans, contribuant Ă  prĂšs de 20% de la production primaire globale. Dans leur environnement trĂšs variable, les diatomĂ©es sont particuliĂšrement efficaces dans leur capacitĂ© Ă  ajuster leur activitĂ© photosynthĂ©tique en dissipant sous forme de chaleur l’énergie lumineuse absorbĂ©e en excĂšs, par un processus appelĂ© le « Non-Photochemical Quenching of chlorophyll fluorescence », (NPQ). Chez la diatomĂ©e modĂšle, Phaeodactylum tricornutum, il a Ă©tĂ© montrĂ© que LHCX1, une protĂ©ine proche des antennes photosynthĂ©tiques, est impliquĂ©e dans le NPQ. Par des approches intrĂ©grĂ©es de gĂ©nĂ©tique, biologie molĂ©culaire, biochimie, imagerie des cinĂ©tiques de fluorescence et spectroscopie ultrarapide, j’ai Ă©tudiĂ© le rĂŽle de la famille des LHCX chez P. tricornutum. J’ai tout d’abord pu corrĂ©ler une expression diffĂ©rentielle des 4 gĂšnes LHCX de P. tricornutum avec diffĂ©rentes dynamiques de NPQ et activitĂ©s photosynthĂ©tiques, dans diffĂ©rentes conditions de lumiĂ©re et nutriments. En localisant les LHCX dans les differents complexes photosynthĂ©tiques et les diffĂ©rents sites de dissipation d’énergie, j’ai pu proposer un modĂšle de rĂ©gulation dynamique du NPQ impliquant Ă  court terme principalement LHCX1 au niveau des centres rĂ©actionnels, et une autre isoforme, possiblement LHCX3, au niveau des antennes lors d’un stress lumineux prolongĂ©. Enfin, par le criblage d’une sĂ©rie de mutants potentiellement dĂ©rĂ©gulĂ©s dans leur contenu en LHCXs, j’ai pu identifier des lignĂ©es avec un NPQ altĂ©rĂ© qui pourront constituer des nouveaux outils de recherche. Dans l’ensemble ce travail de thĂšse a permis de mettre en Ă©vidence la diversification fonctionnelle et l’importance de la famille des LHCX dans la fine modulation des capacitĂ©s de collecte de lumiĂšre et de photoprotection, expliquant sans doute en partie le succĂšs des diatomĂ©es dans leur environnement trĂšs fluctuant

    Dynamic Changes between Two LHCX-Related Energy Quenching Sites Control Diatom Photoacclimation

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    International audienceMarine diatoms are prominent phytoplankton organisms that perform photosynthesis in extremely variable environments. Diatoms possess a strong ability to dissipate excess absorbed energy as heat via nonphotochemical quenching (NPQ). This process relies on changes in carotenoid pigment composition (xanthophyll cycle) and on specific members of the light-harvesting complex family specialized in photoprotection (LHCXs), which potentially act as NPQ effectors. However, the link between light stress, NPQ, and the existence of different LHCX isoforms is not understood in these organisms. Using picosecond fluorescence analysis, we observed two types of NPQ in the pennate diatom Phaeodactylum tricornutum that were dependent on light conditions. Short exposure of low-light-acclimated cells to high light triggers the onset of energy quenching close to the core of photosystem II, while prolonged light stress activates NPQ in the antenna. Biochemical analysis indicated a link between the changes in the NPQ site/mechanism and the induction of different LHCX isoforms, which accumulate either in the antenna complexes or in the core complex. By comparing the responses of wild-type cells and transgenic lines with a reduced expression of the major LHCX isoform, LHCX1, we conclude that core complex-associated NPQ is more effective in photoprotection than is the antenna complex. Overall, our data clarify the complex molecular scenario of light responses in diatoms and provide a rationale for the existence of a degenerate family of LHCX proteins in these algae

    Evolution of internal stresses and substructure during creep at intermediate temperatures

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    [EN] Secondary creep has most generally been associated with a rather steady structure. Many models have been suggested to explain the constant strain rate in terms of the effective stress which is determined by the structurally-dependent internal stresses. The internal stresses deduced macroscopically have been of the order of half the applied stress. In this article, by pinning the dislocations under load in an Al-Zn alloy, the evolution of the structure and local effective stresses with strain has been identified by electron microscopy. Values of local effective stresses at the subgrain boundaries ranging between 10-20 times the applied stress have been measured. The emission of dislocations from these boundaries and the evolution of substructure within the subgrain interior indicate that the controlling mechanism during the creep process is the relaxation of internal stresses by this emission. At the same time, the subboundary stress-fields existing in different subgrains determine their different behaviour as a function of time. Hard and soft subgrains alternate in the deformation process to produce overall uniform strain.[FR] Le fluage secondaire a Ă©tĂ© le plus souvent associĂ© Ă  une structure plutĂŽt constante. De nombreux modĂšles ont Ă©tĂ© proposĂ©s pour expliquer la vitesse de dĂ©formation constante Ă  partir de la contrainte effective dĂ©terminĂ©e par les contraintes internes dĂ©pendant de la structure. Les contraintes internes dĂ©duites macroscopiquement Ă©taient de l'ordre de la moitiĂ© de la contrainte appliquĂ©e. Dans cet article, nous avons prĂ©cisĂ© par microscopie Ă©lectronique l'Ă©volution de la structure et des contraintes effectives locales en fonction de la dĂ©formation, en ancrant les dislocations sous charge dans un alliage Al-Zn. Nous avons mesurĂ© des valeurs des contraintes effectives locales aux sous-joints de grains comprises entre 10 et 20 fois la contrainte appliquĂ©e. L'Ă©mission de dislocations hors de ces sous-joints et l'Ă©volution de la sous-structure Ă  l'intĂ©rieur des sous-grains montrent que le mĂ©canisme qui contrĂŽle le phĂ©nomĂšne de fluage est la relaxation des contraintes internes par cette Ă©mission. En mĂȘme temps, les champs de contrainte des sous-joints qui existent dans diffĂ©rents sous-grains dĂ©terminent leur comportement diffĂ©rent en fonction du temps. Au cours de la dĂ©formation, on a des sous-grains alternativement durs et mous qui donnent une dĂ©formation globale uniforme
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