Silicon cycle in the tropical South Pacific: contribution to the global Si cycle and evidence for an active pico-sized siliceous plankton

This article presents data regarding the Si biogeochemical cycle during two oceanographic cruises conducted in the tropical South Pacific (BIOSOPE and OUTPACE cruises) in 2005 and 2015. It involves the first Si stock measurements in this understudied region, encompassing various oceanic systems from New Caledonia to the Chilean upwelling between 8 and 34°&thinsp;S. Some of the lowest levels of biogenic silica standing stocks ever measured were found in this area, notably in the southern Pacific gyre, where Chlorophyll a concentrations are the most depleted worldwide. Integrated biogenic silica stocks are as low as 1.08±0.95&thinsp;mmol&thinsp;m−2 and are the lowest stocks measured in the South Pacific. Size-fractionated biogenic silica concentrations revealed a non-negligible contribution of the pico-sized fraction (&lt;2–3&thinsp;µm) to biogenic silica standing stocks, representing 26% ± 12% of total biogenic silica during the OUTPACE cruise and 11% ± 9% during the BIOSOPE cruise. These results indicate significant accumulation in this size class, which was undocumented for 2005, but has since then been related to Si uptake by Synechococcus cells. Si uptake measurements carried out during BIOSOPE confirmed biological Si uptake by this size fraction. We further present diatoms community structure associated with the stock measurements for a global overview of the Si cycle in the tropical South Pacific.</p

Multi-Particle Collision Dynamics -- a Particle-Based Mesoscale Simulation Approach to the Hydrodynamics of Complex Fluids

In this review, we describe and analyze a mesoscale simulation method for fluid flow, which was introduced by Malevanets and Kapral in 1999, and is now called multi-particle collision dynamics (MPC) or stochastic rotation dynamics (SRD). The method consists of alternating streaming and collision steps in an ensemble of point particles. The multi-particle collisions are performed by grouping particles in collision cells, and mass, momentum, and energy are locally conserved. This simulation technique captures both full hydrodynamic interactions and thermal fluctuations. The first part of the review begins with a description of several widely used MPC algorithms and then discusses important features of the original SRD algorithm and frequently used variations. Two complementary approaches for deriving the hydrodynamic equations and evaluating the transport coefficients are reviewed. It is then shown how MPC algorithms can be generalized to model non-ideal fluids, and binary mixtures with a consolute point. The importance of angular-momentum conservation for systems like phase-separated liquids with different viscosities is discussed. The second part of the review describes a number of recent applications of MPC algorithms to study colloid and polymer dynamics, the behavior of vesicles and cells in hydrodynamic flows, and the dynamics of viscoelastic fluids

Etude prospective sur l'agriculture bretonne

Diffusion du document : INRA Unité d'Economie et Sociologie rurales rue Adolphe Bobierre CS 61103 35011 Rennes Cedex (FRA)Cette étude a été conduite à la demande des autorités régionales dans le cadre de la préparation du contrat de plan Etat-Région. La première partie introductive présente l'objectif de l'étude qui est de proposer une vue prospective de l'agriculture bretonne dans un contexte de réexamen de la politique agricole commune (PAC), lié aux contraintes actuelles et anticipées de l'Organisation mondiale du commerce (OMC), à l'élargissement de l'Europe à l'Est, et aux préoccupations environnementales. La deuxième partie dresse un état des lieux de l'agriculture bretonne. On met d'abord l'accent sur l'importance du complexe agro-alimentaire dans l'économie bretonne. On aborde ensuite les structures de production qui ont connu une évolution classique (baisse des effectifs, concentration et gains de productivité) accompagnée de la spécialisation et de la simplification des systèmes de production. Les conséquences de la concentration et de la spécialisation sur l'environnement sont ensuite analysées ainsi que les politiques environnementales mises en oeuvre. Un bilan des industries agro-alimentaires est également fait. La troisième partie fait le point sur les évolutions fondamentales qui vont affecter l'agriculture et celle de la Bretagne en particulier, notamment l'évolution du comportement du consommateur-citoyen, l'intensification des échanges internationaux, les réglementations sanitaires et phytosanitaires ainsi que les politiques environnementales. La quatrième partie tente de cerner les enjeux de la contribution de l'agriculture bretonne à un développement régional durable, face aux risques externes (montée de la concurrence internationale) et internes (forte spécialisation, effets d'image négatifs liés à la dégradation de l'environnement). Elle donne également des principes pour l'action publique. Les aspects prospectifs sont prolongés par des projections d'impact de la future réforme de la PAC (Agenda 2000) sur les résultats économiques du secteur agricole breton. Compte tenu des aides nouvelles, le revenu brut d'exploitation par actif en termes réels devrait augmenter entre 1996 et 2005. Enfin, des initiatives régionales sont proposées visant le maintien du système productif du complexe agroalimentaire breton, la diversification mais aussi la mise au point de produits à vocation universelle rattachés à l'origine régionale, la mise en place d'un système de suivi crédible des pratiques environnementales et d'un zonage complet de l'espace rural pour atténuer les conflits d'usage, la mise en valeur du potentiel de l'espace rural

Metabolic compartmentalization in the human cortex and hippocampus: evidence for a cell- and region-specific localization of lactate dehydrogenase 5 and pyruvate dehydrogenase

BACKGROUND: For a long time now, glucose has been thought to be the main, if not the sole substrate for brain energy metabolism. Recent data nevertheless suggest that other molecules, such as monocarboxylates (lactate and pyruvate mainly) could be suitable substrates. Although monocarboxylates poorly cross the blood brain barrier (BBB), such substrates could replace glucose if produced locally.The two key enzymatiques systems required for the production of these monocarboxylates are lactate dehydrogenase (LDH; EC1.1.1.27) that catalyses the interconversion of lactate and pyruvate and the pyruvate dehydrogenase complex that irreversibly funnels pyruvate towards the mitochondrial TCA and oxydative phosphorylation. RESULTS: In this article, we show, with monoclonal antibodies applied to post-mortem human brain tissues, that the typically glycolytic isoenzyme of lactate dehydrogenase (LDH-5; also called LDHA or LDHM) is selectively present in astrocytes, and not in neurons, whereas pyruvate dehydrogenase (PDH) is mainly detected in neurons and barely in astrocytes. At the regional level, the distribution of the LDH-5 immunoreactive astrocytes is laminar and corresponds to regions of maximal 2-deoxyglucose uptake in the occipital cortex and hippocampus. In hippocampus, we observed that the distribution of the oxidative enzyme PDH was enriched in the neurons of the stratum pyramidale and stratum granulosum of CA1 through CA4, whereas the glycolytic enzyme LDH-5 was enriched in astrocytes of the stratum moleculare, the alveus and the white matter, revealing not only cellular, but also regional, selective distributions. The fact that LDH-5 immunoreactivity was high in astrocytes and occurred in regions where the highest uptake of 2-deoxyglucose was observed suggests that glucose uptake followed by lactate production may principally occur in these regions. CONCLUSION: These observations reveal a metabolic segregation, not only at the cellular but also at the regional level, that support the notion of metabolic compartmentalization between astrocytes and neurons, whereby lactate produced by astrocytes could be oxidized by neurons

Silica fluxes in the northeast Atlantic frontal zone of Mode Water formation (38 degrees-45 degrees N, 16 degrees-22 degrees W) in 2001-2002

International audience[ 1] The biogenic (BSi) and lithogenic (LSi) silica export fluxes were investigated in the northeast Atlantic (38 degrees - 45 degrees N, 16 degrees - 22 degrees W) as part of the Programme Ocean Multidisciplinaire Meso Echelle (POMME) program in 2001 - 2002. They were measured at four stations located on both sides of a frontal zone (40 degrees - 42 degrees N) by means of permanent moorings of sediment traps deployed at 400 and 1000 m depth. Averaged over the area, the annual BSi fluxes ( corrected from Th-230 trapping efficiencies) ranged between 0.240 mmol m(-2) d(-1) at 400 m to 0.316 mmol m(-2) d(-1) at 1000 m. The bulk annual BSi fluxes are comparable to bulk BSi export fluxes recorded for oligotrophic areas. The annual export flux of LSi ( range 0.029 mmol m(-2) d(-1) at 400 m to 0.054 mmol m(-2) d(-1) at 1000 m) was lower than BSi and accounted for 10% of the total silica export flux. Results show a strong coupling between the two siliceous particulate fractions, which is interpreted as reflecting LSi scavenging by BSi and limitation of BSi production in surface water by lithogenic ( trace metals) inputs. BSi export was maximum at the beginning of the productive season during the spring bloom. However, annual BSi export fluxes in 2001 were quite higher at 400 m in the southern area ( e. g., 0.249 - 0.288 at the southeast station versus 0.211 mmol BSi m(-2) d(-1) at the northeast station) contradictory to the classical south-north surface production increase. We suggest an advective lateral transport within the upper 400 m of siliceous particles from the northern, more productive area to the southern region

Capillary electrophoresis single-strand conformation polymorphism for the monitoring of gastrointestinal microbiota of chicken flocks

International audienceThe objective of the present study was to evaluate the capillary electrophoresis single-strand conformation polymorphism (CE-SSCP) to characterize poultry gut microbiota and the ability of this molecular method to detect modifications related to rearing conditions to be used as an epidemiological tool. The V3 region of the 16S rRNA gene was selected as the PCR target. Our results showed that this method provides reproducible data. The microbiota analysis of individuals showed that variability between individual fingerprints was higher for ileum and cloaca than for ceca. However, pooling the samples decreased this variability. To estimate the variability within and between farms, we compared molecular gut patterns of animals from the same hatchery reared under similar conditions and fed the same diet in 2 separate farms. Total aerobic bacteria, coliforms, and lactic acid bacteria were enumerated using conventional bacteriological methods. A significant difference was observed for coliforms present in the ceca and the cloaca depending on the farm. Ileal contents fingerprints were more closely related to those of cloacal contents than to those of ceca contents. When comparing samples from the 2 farms, a specific microbiota was highlighted for each farm. For each gut compartment, the microbiota fingerprints were joined in clusters according to the farm. Thus, this rapid and potentially high-throughput method to obtain gut flora fingerprints is sensitive enough to detect a "farm effect" on the balance of poultry gut microbiota despite the birds being fed the same regimens and reared under similar conditions

Etude prospective sur l'agriculture bretonne

Cette étude a été conduite à la demande des autorités régionales dans le cadre de la préparation du contrat de plan Etat-Région. La première partie introductive présente l'objectif de l'étude qui est de proposer une vue prospective de l'agriculture bretonne dans un contexte de réexamen de la politique agricole commune (PAC), lié aux contraintes actuelles et anticipées de l'Organisation mondiale du commerce (OMC), à l'élargissement de l'Europe à l'Est, et aux préoccupations environnementales. La deuxième partie dresse un état des lieux de l'agriculture bretonne. On met d'abord l'accent sur l'importance du complexe agro-alimentaire dans l'économie bretonne. On aborde ensuite les structures de production qui ont connu une évolution classique (baisse des effectifs, concentration et gains de productivité) accompagnée de la spécialisation et de la simplification des systèmes de production. Les conséquences de la concentration et de la spécialisation sur l'environnement sont ensuite analysées ainsi que les politiques environnementales mises en oeuvre. Un bilan des industries agro-alimentaires est également fait. La troisième partie fait le point sur les évolutions fondamentales qui vont affecter l'agriculture et celle de la Bretagne en particulier, notamment l'évolution du comportement du consommateur-citoyen, l'intensification des échanges internationaux, les réglementations sanitaires et phytosanitaires ainsi que les politiques environnementales. La quatrième partie tente de cerner les enjeux de la contribution de l'agriculture bretonne à un développement régional durable, face aux risques externes (montée de la concurrence internationale) et internes (forte spécialisation, effets d'image négatifs liés à la dégradation de l'environnement). Elle donne également des principes pour l'action publique. Les aspects prospectifs sont prolongés par des projections d'impact de la future réforme de la PAC (Agenda 2000) sur les résultats économiques du secteur agricole breton. Compte tenu des aides nouvelles, le revenu brut d'exploitation par actif en termes réels devrait augmenter entre 1996 et 2005. Enfin, des initiatives régionales sont proposées visant le maintien du système productif du complexe agroalimentaire breton, la diversification mais aussi la mise au point de produits à vocation universelle rattachés à l'origine régionale, la mise en place d'un système de suivi crédible des pratiques environnementales et d'un zonage complet de l'espace rural pour atténuer les conflits d'usage, la mise en valeur du potentiel de l'espace rural