Characterization of an fdxN mutant of Rhodobacter capsulatus indicates that ferredoxin I serves as electron donor to nitrogenase

AbstractA mutant of Rhodobacter capsulatus, carrying an insertion into the fdxN gene encoding ferredoxin I (FdI), has been studied by biochemical analysis and genetic complementation experiments. When compared to the wild-type strain, the fdxN mutant exhibited altered nitrogen fixing ability and 20-fold lower levels of nitrogenase activity as assayed in vivo. When assayed in vitro with an artificial reductant, nitrogenase activity was only 3- to 4-fold lower than in the wild type. These results suggested that the FdI-deleted mutant had impaired electron transport to nitrogenase. Immunochemical assay of both nitrogenase components showed that the fdxN mutant contained about 4-fold less enzyme than wild-type cells. Results of pulse-chase labeling experiments using [35S]methionine indicated that nitrogenase was significantly less stable in the FdI-deleted mutant. When a copy of fdxN was introduced in the mutant in trans, the resulting strain appeared to be fully complemented with respect to both diazotrophic growth and nitrogenase activity. Depending on whether fdxN expression was driven by a nif promoter or a fructose-inducible promoter. FdI was synthesized either at wild-type level or in 10-fold lower amounts. The strain producing 10-fold less FdI did, however, display normal N2-fixing ability. Analysis of cytosolic proteins by bidimensional electrophoresis revealed that the fdxN mutant produced a 14 kDa polypeptide in amounts about 3-fold greater than wild-type cells. This protein was identified by N-terminal microsequencing as a recently purified [2Fe-2S] ferredoxin, called FdV, which cannot reduce nitrogenase. It is concluded that FdI serves as the main electron donor to nitrogenase in R. capsulatus and that an ancillary electron carrier, distinct of FdV, is responsible for the residual nitrogenase activity observed in the FdI-deleted mutant

Mesures d'air ambiant en conditions de trafic : évolution des COV sur 3 ans

International audienceInfluence of traffic emission on air quality in European cities has widely been studied. Nevertheless, measurement campaigns are usually limited. We present here a set of VOC measurements which has been collected during 5 to 6 campaigns each year over three years. Ambient air is sampled outside vehicles, inside the traffic. Evolution of the concentrations both in urban and rural air over the 3 years are discussed, compound by compound, and compared to data from literature. Influence of traffic on concentrations is obvious. The major fînding is that the concentrations of pollutants related to traffic have been decreasing between 2003 and 2005, specially in urban atmospheres, and in a lesser way, in rural areas.L'influence des émissions liées au trafic automobile sur la qualité de l'air a largement été étudiée. Cependant, les campagnes de mesures sont généralement limitées, dans la durée et le nombre de composés étudiés. Nous présentons ici les résultats d'un ensemble de campagnes réalisées sur une durée de 3 ans, sur plusieurs composés organiques volatils. Le prélèvement est réalisé à l'extérieur de véhicules en roulage, dans la Région Parisienne, en milieux urbain et semi-rural. L'évolution des concentrations au cours du temps est discutée, et les teneurs sont comparées aux données de la littérature. Le fait marquant est la diminution très importante entre 2003 et 2005 des teneurs pour une majorité des polluants, surtout en milieu urbain, et dans une moindre mesure en milieu rural. La diminution de la teneur en benzène des essences, ainsi que l'amélioration des moteurs et le développement des pots catalytiques, explique largement cette tendance

Preferred antiretroviral drugs for the next decade of scale up

Global commitments aim to provide antiretroviral therapy (ART) to 15 million people living with HIV by 2015, and recent studies have demonstrated the potential for widespread ART to prevent HIV transmission. Increasingly, countries are adapting their national guidelines to start ART earlier, for both clinical and preventive benefits. To maximize the benefits of ART in resource-limited settings, six key principles need to guide ART choice: simplicity, tolerability and safety, durability, universal applicability, affordability and heat stability. Currently available drugs, combined with those in late-stage clinical development, hold great promise to simplify treatment in the short term. Over the longer-term, newer technologies, such as long-acting formulations and nanotechnology, could radically alter the treatment paradigm. This commentary reviews recommendations made in an expert consultation on treatment scale up in resource-limited settings

Inverser la classe : effets sur la formation de futurs enseignants

Dans le cadre d’une formation universitaire initiale en enseignement secondaire, un dispositif de classe inversée a été expérimenté dans un cours portant sur l’évaluation des apprentissages. Structuré selon un mode plutôt traditionnel, le temps de classe était, dans ce cours, principalement consacré aux apprentissages conceptuels tandis que les apprentissages pratiques étaient réalisés en dehors de la classe. À partir de l’hypothèse qu’une pédagogie active et différenciée serait souhaitable pour soutenir les apprentissages procéduraux visés par ce cours, nous avons décidé d’intégrer des capsules d’autoformation en ligne portant sur les concepts, afin de pouvoir davantage accompagner les apprentissages procéduraux des étudiants en classe. Le contexte d’enseignement et d’apprentissage initial a donc été « hybridé » par l’introduction de matériel d’autoapprentissage disponible à distance en mode asynchrone. La problématisation de la situation et l’analyse de l’expérimentation réalisées s’inscrivent dans l’approche Scholarship of Teaching and Learning (SoTL) et le partage d’expertises requises pour le développement du nouveau dispositif de formation s’appuie sur le modèle Technological Pedagogical and Content Knowledge (TPaCK). En vue de bénéficier de cette expérimentation pour enrichir notre enseignement, et considérant la nécessité de recueillir des données probantes et scientifiquement valides pour la viabilité du dispositif de formation du type « classe inversée », notre démarche pédagogique était accompagnée d’une démarche de recherche visant à décrire les modalités d’appropriation des ressources technopédagogiques par les étudiants et à caractériser la dynamique présentielle du point de vue de la formatrice qui a mis à l’essai le dispositif.As part of a university teacher training program in secondary education, a flipped classroom design was tested in a course on assessment of learning. Structured in a rather traditional way, class time was, in this course, mainly devoted to conceptual learning while practical learning were done outside of the classroom. From the hypothesis that active pedagogy and differentiation would be appropriate to support the procedural learning targeted in this course, we decided to integrate online self-learning clips about the concepts, in order to further support students procedural learning in the classroom. The initial teaching and learning context has been « hybridized » with the introduction of self-learning materials available remotely asynchronously. The problematization of the situation and the analysis of the experiment carried out are part of the Scholarship of Teaching and Learning approach (SoTL) and the sharing of expertise required for the development of this new training approach is based on the Technological Pedagogical and Content Knowledge (TPACK) model. In order to benefit from this experiment to enrich our teaching, and considering the need to gather scientifically valid evidence for the sustainability of a training approach such as « flipped classroom », our pedagogical engineering was accompanied by a research approach that aimed to describe the appropriation of the resources by students and to characterize the learning dynamics in class from the trainer’s point of view

Review of the safety, efficacy, and pharmacokinetics of elvitegravir with an emphasis on resource-limited settings

Integrase inhibitors represent an important new class of antiretroviral drugs. Elvitegravir, the second available integrase inhibitor to be submitted for regulatory approval appears to be a promising once-daily agent when combined with other antiretroviral drugs. Elvitegravir has demonstrated good efficacy and safety, with minimal side effects and no specific requirements in terms of laboratory monitoring. In addition, elvitegravir is available as a fixed-dose combination. However, the drug requires boosting and this leads to a number of drug–drug interactions and necessary dose adjustment when dosing with certain drugs, including dose reduction in the presence of atazanavir, lopinavir, rifabutin, and ketoconazole, and dose increase for ethinyl estradiol when co-administered with boosted elvitegravir. The main advantage of elvitegravir lies in its potential to be administered as a once-daily, single pill. Limitations include dose adjustment requirements, a relatively low genetic barrier to resistance, high price, and lack of data for use in children. Clinical trials addressing specific challenges encountered in resources-limited settings should be encouraged

Formation and structure of slightly anionically charged nanoemulsions obtained by the phase inversion concentration (PIC) method

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.While nanoemulsions (10–200 nm) are not thermodynamically stable systems they can exhibit quite long term stability. In this paper oil/surfactant mixtures, containing diethylhexyl carbonate/phenoxyethanol/parabens as oil and polyglyceryl-4 laurate/dilauryl citrate as surfactant, form nanoemulsions simply by dilution with water, i.e. by means of the phase inversion concentration (PIC) method. In order to study this highly interesting phenomenon an investigation at constant oil-to-surfactant (O/S) ratio was done by means of viscosity, conductivity, and UV/Vis-transmittance measurements. This phase study as a function of the dilution by water shows that at an intermediate water content a two-phase system of bicontinuous structure is formed, which exhibits a very pronounced viscosity and conductivity maximum shortly before the homogeneous nanoemulsion phase is reached. In the same region SANS shows a high degree of ordering of this bicontinuous structure. SANS and cryo-TEM investigations of the nanoemulsion regime show an increasing average size with dilution and, more interestingly, the presence of two populations with different average particle sizes around 10–15 nm and 25–40 nm. The relative proportion of each population depends on the amount of added water, leading to an average growth of the particle size with increasing dilution