Contact metamorphic reactions and fluid–rock interactions related to magmatic sill intrusion in the Guaymas Basin

Igneous basaltic intrusions into young organic-rich sedimentary basins have a major impact not only on the carbon cycle but also on major and trace element transfers between deep and superficial geological reservoirs. The actively rifting Guaymas Basin in the Gulf of California, which was drilled by the International Ocean Discovery Program during Expedition 385, represents the nascent stage of an ocean characterized by siliceous organic-rich sediments (diatom ooze) intruded by a very dense network of basaltic sills. This study focuses on Site U1546 where the relatively high geothermal gradient (over 200 ∘C km−1) induces early diagenetic transformations in both pore waters and sediments, involving sulfide, carbonate and silica. Geochemical and mineralogical characterizations of the sediment at sill contacts indicate that sulfides and silica polymorphs are the main phases impacted by contact metamorphism, being evident by a transition from opal-CT to quartz and pyrite to pyrrhotite, respectively. Mass balance calculations have been used to estimate mass transfers in metamorphic aureoles. In the top contact aureole, predominantly isochemical metamorphism is reflected by the presence of authigenic quartz and disseminated 20–50 µm sized pyrrhotite crystals, filling primary interstitial space, and partial dissolution of detrital feldspar grains. In the bottom contact aureole, quartz and euhedral pyrrhotite crystals occur, which are up to 4 times larger than those at the top contact. Significant metamorphism of sediments is observed in the lower contact aureole, where plagioclase recrystallizes around the detrital feldspars and locally euhedral pyroxenes are included in patches of carbonate cement; this suggests precipitation from carbon-rich fluids at temperatures (T) higher than 300 ∘C. The lower contact aureole also is more enriched in CaO, Na2O, Fe2O3 and trace elements (Cu, As, Zn, etc.) compared to the upper contact. Based on these petrological investigations, a conceptual model of magma–sediment–fluid interaction is proposed distinguishing top and bottom contact processes. Initial contact metamorphism due to sill emplacement is characterized by dehydration reactions in sediments and crystallization of new minerals. It was followed by carbonate precipitation from the released fluids. At a final stage, the temperature re-equilibrated with the geothermal gradient and the rocks were further altered by hydrothermal fluids.</p

Observatoire régional du pneumocoque en région Pays de la Loire : résistance de Streptococcus pneumoniae aux antibiotiques en 2007

But de l’étudeEntre le 1er janvier et le 31 décembre 2007, les 20 laboratoires participant à l’observatoire régional du pneumocoque (ORP) Pays de la Loire ont collecté 331 souches invasives de Streptococcus pneumoniae afin d’étudier leur sensibilité aux antibiotiques et la répartition des sérogroupes/sérotypes. Méthode Les concentrations minimales inhibitrices (CMI) de la pénicilline G, de l’amoxicilline et du céfotaxime ont été déterminées par le centre coordinateur, par la méthode de référence de diffusion en milieu gélosé. Les résultats ont été interprétés selon les recommandations du CA-SFM. Les sensibilités à d’autres antibiotiques ont été étudiées et les typages des souches réalisées par le centre coordinateur. Résultats Trois cent trente et une souches ont été isolées en 2007. Elles provenaient de 30 liquides céphalorachidiens, 239 hémocultures, 53 pus d’otites moyennes aiguës et neuf liquides pleuraux. Le pourcentage de pneumocoques de sensibilité diminuée à la pénicilline G (PSDP) était de 39 % et restait plus élevé chez l’enfant (51 %) que chez l’adulte (35 %). Les PSDP étaient souvent multirésistants, avec en particulier un pourcentage élevé de résistance à l’érythromycine (87,6 % contre 8,4 % pour les pneumocoques sensibles à la pénicilline). Enfin, le sérogroupe majoritairement rencontré était le sérogroupe 19 (29,6 % des isolats). Conclusion Une diminution des PSDP a été observée depuis 2001 et les souches de haut niveau de résistance aux β-lactamines restent rares. Le pourcentage de PSDP observés en ORP Pays de la Loire demeure dans la moyenne nationale

Alterations in MicroRNA Expression Contribute to Fatty Acid–Induced Pancreatic β-Cell Dysfunction

OBJECTIVE—Visceral obesity and elevated plasma free fatty acids are predisposing factors for type 2 diabetes. Chronic exposure to these lipids is detrimental for pancreatic β-cells, resulting in reduced insulin content, defective insulin secretion, and apoptosis. We investigated the involvement in this phenomenon of microRNAs (miRNAs), a class of noncoding RNAs regulating gene expression by sequence-specific inhibition of mRNA translation

Analysis of SEC9 Suppression Reveals a Relationship of SNARE Function to Cell Physiology

BACKGROUND:Growth and division of Saccharomyces cerevisiae is dependent on the action of SNARE proteins that are required for membrane fusion. SNAREs are regulated, through a poorly understood mechanism, to ensure membrane fusion at the correct time and place within a cell. Although fusion of secretory vesicles with the plasma membrane is important for yeast cell growth, the relationship between exocytic SNAREs and cell physiology has not been established. METHODOLOGY/PRINCIPAL FINDINGS:Using genetic analysis, we identified several influences on the function of exocytic SNAREs. Genetic disruption of the V-ATPase, but not vacuolar proteolysis, can suppress two different temperature-sensitive mutations in SEC9. Suppression is unlikely due to increased SNARE complex formation because increasing SNARE complex formation, through overexpression of SRO7, does not result in suppression. We also observed suppression of sec9 mutations by growth on alkaline media or on a non-fermentable carbon source, conditions associated with a reduced growth rate of wild-type cells and decreased SNARE complex formation. CONCLUSIONS/SIGNIFICANCE:Three main conclusions arise from our results. First, there is a genetic interaction between SEC9 and the V-ATPase, although it is unlikely that this interaction has functional significance with respect to membrane fusion or SNAREs. Second, Sro7p acts to promote SNARE complex formation. Finally, Sec9p function and SNARE complex formation are tightly coupled to the physiological state of the cell

A Novel Function of Noc2 in Agonist-Induced Intracellular Ca2+ Increase during Zymogen-Granule Exocytosis in Pancreatic Acinar Cells

Noc2, a putative Rab effector, contributes to secretory-granule exocytosis in neuroendocrine and exocrine cells. Here, using two-photon excitation live-cell imaging, we investigated its role in Ca2+-dependent zymogen granule (ZG) exocytosis in pancreatic acinar cells from wild-type (WT) and Noc2-knockout (KO) mice. Imaging of a KO acinar cell revealed an expanded granular area, indicating ZG accumulation. In our spatiotemporal analysis of the ZG exocytosis induced by agonist (cholecystokinin or acetylcholine) stimulation, the location and rate of progress of ZG exocytosis did not differ significantly between the two strains. ZG exocytosis from KO acinar cells was seldom observed at physiological concentrations of agonists, but was normal (vs. WT) at high concentrations. Flash photolysis of a caged calcium compound confirmed the integrity of the fusion step of ZG exocytosis in KO acinar cells. The decreased ZG exocytosis present at physiological concentrations of agonists raised the possibility of impaired elicitation of calcium spikes. When calcium spikes were evoked in KO acinar cells by a high agonist concentration: (a) they always started at the apical portion and traveled to the basal portion, and (b) calcium oscillations over the 10 µM level were observed, as in WT acinar cells. At physiological concentrations of agonists, however, sufficient calcium spikes were not observed, suggesting an impaired [Ca2+]i-increase mechanism in KO acinar cells. We propose that in pancreatic acinar cells, Noc2 is not indispensable for the membrane fusion of ZG per se, but instead performs a novel function favoring agonist-induced physiological [Ca2+]i increases

Observatoire Régional du Pneumocoque en région Pays de la Loire : résistance de Streptococcus pneumoniae (Sp) aux antibiotiques en 2007

Date du colloque&nbsp;: 12/2008</p

Modelling of 60 Co concentrations in the dissolved and particulate phases in the Loire estuary

International audienc

Modelling of

EDF has initiated a program assessing the fate of radionuclides released by nuclear power plants located along the river basin. In order to estimate the behaviour of radionuclides associated with suspended sediment in the Loire estuary, a multivariate transport model has been developed. Several dissolved and particulate constituents can be simultaneously computed, the later being followed in the superficial sediment according to the deposition events. Modelling of salinity and suspended matter was included as having an influence on sorption kinetics, and on radionuclide transport. Indeed, the association of radionuclides with particle can affect their residence time in sedimentation zones of water systems. Partitioning of radionuclides between water and suspended matter is usually expressed as Kd, concentration ratio between particulate and dissolved phases. In the simulations presented, particulate and dissolved 60Co behaviour were considered to interact with suspended solids and salinity trough sorption and desorption kinetics, distribution coefficients being considered as representing equilibrium conditions seldom reached in nature. Simulation was carried out for two river discharges (high river input and low river input). The computed results are compared with observed values for surface levels, salinity and suspended matter as well as 60Co concentrations

Numerical simulation of cohesive sediment transport: intercomparison of several numerical models

Five different numerical models are used to reproduce estuarine cohesive sediment transport and intercomparisons are made of the resulting predictions. Comparison with test cases have shown that the numerical treatment of cohesive sediment is very sensitive to model parameters and formulations, and requires good calibration. Some of the specific processes that have been developed through the MAST.3-COSINUS European project are used here to improve the ability of numerical models to reproduce the sediment behaviour in real estuaries. Despite this progress, it is shown that numerical models results still have many limitations, and their results should always be interpreted with great care