Benefits of a positive intervention for chronic pain patients on their health and well-Being: The french ABCD program

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Simultaneous determination of mercury methylation and demethylation capacities of various sulfate-reducing bacteria using species-specific isotopic tracers

International audienceThe use of species-specific isotopic tracers for inorganic and methyl mercury has allowed the simultaneous determination of the methylation and demethylation potentials of pure culture of isolated sulfate-reducing (SR) bacterial strains using low Hg species concentration levels (7 μg/L 199Hg(II), 1 μg/L Me 201Hg). A major advantage of the method reported here is that it can be used to follow simultaneously both the degradation of the species added but also the formation of their degradation products and thus the determination during the same incubation of the specific methylation/demethylation yields and rate constants. Methylation/demethylation capacities and extents have been found to differ between the tested strains and the tested conditions. The methylating/demethylating capacities of bacteria appear to be strain specific. All the methylating strains were found to demethylate methylmercury (MeHg). The active mechanism responsible for Hg methylation appears directly dependent on the bacterial activity but is not dependent on the metabolism used by the tested bacteria (sulfate reduction, fermentation, or nitrate respiration). The results provide confirmation that SR strains contribute to MeHg demethylation under anoxic conditions, leading to Hg(II) as the end product, consistent with the oxidative degradation pathway. Kinetic experiments have allowed specific transformation rate constants to be addressed for the two reversible processes and the reactivity of each isotopic tracer to be compared. The differential reactivity highlighted the different steps involved in the two apparent processes (i.e., uptake plus internal transformation of mercury species). Methylation appears as the slowest process, mainly controlled by the assimilation of Hg(II), whereas demethylation is faster and not dependent on the MeHg concentration

Transformation, localization, and biomolecular binding of Hg species at subcellular level in methylating and nonmethylating sulfate-reducing bacteria

International audienceMicrobial activity is recognized to play an important role on Hg methylation in aquatic ecosystems. However, the mechanism at the cellular level is still poorly understood. In this work subcellular partitioning and transformation of Hg species in two strains: Desulfovibrio sp. BerOc1 and Desulfovibrio desulfuricans G200 (which exhibit different Hg methylation potential) are studied as an approach to the elucidation of Hg methylation/demethylation processes. The incubation with isotopically labeled Hg species (199Hgi and Me201Hg) not only allows the determination of methylation and demethylation rates simultaneously, but also the comparison of the localization of the originally added and resulting species of such metabolic processes. A dissimilar Hg species distribution was observed. In general terms, monomethylmercury (MeHg) is preferentially localized in the extracellular fraction; meanwhile inorganic mercury (Hgi) is associated to the cells. The investigation of Hg binding biomolecules on the cytoplasmatic and extracellular fractions (size exclusion chromatography coupled to ICP-MS) revealed noticeable differences in the pattern corresponding to the Hg methylating and nonmethylating strains

Identical Hg isotope mass dependent fractionation signature during methylation by sulfate-reducing bacteria in sulfate and sulfate-free environment

International audienceInorganic mercury (iHg) methylation in aquatic environments is the first step leading to monomethylmercury (MMHg) bioaccumulation in food webs and might play a role in the Hg isotopic composition measured in sediments and organisms. Methylation by sulfate reducing bacteria (SRB) under sulfate-reducing conditions is probably one of the most important sources of MMHg in natural aquatic environments, but its influence on natural Hg isotopic composition remains to be ascertained. In this context, the methylating SRB Desulfovibrio dechloracetivorans (strain BerOc1) was incubated under sulfate reducing and fumarate respiration conditions (SR and FR, respectively) to determine Hg species specific (MMHg and IHg) isotopic composition associated with methylation and demethylation kinetics. Our results clearly establish Hg isotope mass-dependent fractionation (MDF) during biotic methylation (-1.20 to +0.58‰ for δ202Hg), but insignificant mass-independent fractionation (MIF) (-0.12 to +0.15‰ for Δ201Hg). During the 24h of the time-course experiments Hg isotopic composition in the produced MMHg becomes significantly lighter than the residual IHg after 1.5h and shows similar δ202Hg values under both FR and SR conditions at the end of the experiments. This suggests a unique pathway responsible for the MDF of Hg isotopes during methylation by this strain regardless the metabolism of the cells. After 9 h of experiment, significant simultaneous demethylation is occurring in the culture and demethylates preferentially the lighter Hg isotopes of MMHg. Therefore, depending on their methylation/demethylation capacities, SRB communities in natural sulfate reducing conditions likely have a significant and specific influence on the Hg isotope composition of MMHg (MDF) in sediments and aquatic organisms

Species-specific stable isotope fractionation of mercury during Hg(II) methylation by an anaerobic bacteria (Desulfobulbus propionicus) under dark conditions

International audienceThis work reports the first results on the stable isotope fractionation of Hg during methylation by anaerobic bacteria under dark conditions.TheGC-MC- ICPMSmethodologyemployed is capable of simultaneously measuring the species-specific isotopic composition of different Hg species within the same sample. We have studied Hg isotopic fractionation caused by methylation of Hg(II) standard reference material NIST-3133 in the presence of the pure bacterial strain Desulfobulbus propionicus MUD10 (DSM 6523) under fermentative conditions. We have measured the isotopic composition of Hg(II) and monomethyl mercury (MMHg) in these cultures as a function of time and calculated delta-values for both species versus the starting material (NIST-3133) as a delta-zero standard. Two differentstrategiesfortheincubationwereapplied: singlesampling cultures and a continuous sampling culture. The results obtained have shown that under the conditions employed in this work the methylation of Hg(II) causes mass-dependent fractionation of the Hg isotopes for both Hg(II) substrate and producedMMHg.Suchaprocess occurred under the exponential growth of the bacteria which preferentially methylate the lighter isotopes of Hg. After 96 h for the continuous culture and 140 h for the single sampling cultures,weobserved a change in the fractionation trend in the samples at a similar cell density value (ca. 6.0 × 107 cells mL -1) which suggests the increasing contribution of a simultaneous process balancing methylation extent such as demethylation.Assumingthat Rayleigh type fractionation conditions are met before such suppression, we have obtained a α202/198 fractionation factor of 1.0026 ± 0.0004 for the single sampling cultures

Overview of mercury methylation capacities among anaerobic bacteria including representatives of the sulphate-reducers: Implications for environmental studies

International audienceMercury methylation has been extensively reported in the literature among "Firmicutes" and "Proteobacteria." Nevertheless, results are hardly comparable because of differences in initial inorganic mercury concentrations used. The use of stable isotopic tracers now permits to study mercury transformations at concentrations close to environmental levels. Here, several strains, including strict fermentative and sulphate-reducing bacteria, were tested for their mercury methylation capacities and the results were compared with data available to date. Under such conditions, mercury methylation only occurs among the delta-Proteobacteria. The absence of relation between taxonomic/phylogenetic affiliation and mercury methylation capacities was pointed out and discussed for environmental studies

Miroirs multicouches apériodiques à large bande passante (2–10 keV) pour les diagnostics d’imagerie X à haute résolution spatiale

Les miroirs multicouches interférentiels, constitués d’un empilement alternant des couches minces de matériaux lourds et légers, permettent, par un phénomène d’addition en phase des rayons réfléchis à chaque interface, d’obtenir des pouvoirs réflecteurs élevés dans le domaine des rayons X. Malheureusement les largeurs spectrales accessibles avec des multicouches périodiques sont peu étendues, de l’ordre de quelques centaines d’eV aux énergies de photons de quelques keV et sont incompatibles avec le fonctionnement large bande envisagé pour certains microscopes X que nous développons. Les supermiroirs ou en anglais « Depth – graded X ray mirrors »  sont une alternative intéressante pour accroître la bande passante du miroir par « superposition»  de la contribution des différentes périodes présentes dans l’empilement. Cet article précise les résultats expérimentaux qui ont permis la mise au point d’un supermiroir de qualité exceptionnelle travaillant entre 2 et 10 keV sous une incidence rasante de 0,7°

Investigations into the differential reactivity of endogenous and exogenous mercury species in coastal sediments

International audienceStable isotopic tracer methodologies now allow the evaluation of the reactivity of the endogenous (ambient) and exogenous (added) Hg to further predict the potential effect of Hg inputs in ecosystems. The differential reactivity of endogenous and exogenous Hg was compared in superficial sediments collected in a coastal lagoon (Arcachon Bay) and in an estuary (Adour River) from the Bay of Biscay (SW France). All Hg species (gaseous, aqueous, and solid fraction) and ancillary data were measured during time course slurry experiments under variable redox conditions. The average endogenous methylation yield was higher in the estuarine (1. 2 %) than in the lagoonal sediment (0. 5 %), although both methylation and demethylation rates were higher in the lagoonal sediment in relation with a higher sulfate-reducing activity. Demethylation was overall more consistent than methylation in both sediments. The endogenous and exogenous Hg behaviors were always correlated but the exogenous inorganic Hg (IHg) partitioning into water was 2. 0-4. 3 times higher than the endogenous one. Its methylation was just slightly higher (1. 4) in the estuarine sediment while the difference in the lagoonal sediment was much larger (3. 6). The relative endogenous and exogenous methylation yields were not correlated to IHg partitioning, demonstrating that the bioavailable species distributions were different for the two IHg pools. In both sediments, the exogenous IHg partitioning equaled the endogenous one within a week, while its higher methylation lasted for months. Such results provide an original assessment approach to compare coastal sediment response to Hg inputs