Production primaire et activité bactérienne hétérotrophe potentielle au sein d'un lac eutrophe (lac d'Aydat, Puy-de-Dôme)

La production primaire phytoplanctenique et l'activité hétérotrophe bactérienne ont été étudiées parallèlement sur le lac d'AYDAT en 1985. L'activité photosynthétique, mesurée au alentours du midi solaire évolue entre 10 et 141 mg C m-2h-1, le maximum étant atteint en juillet. La vitesse maximale, V max, d'assimilation de glucose par les bactéries, (en présence de concentrations de traceur non limitantes) se situe entre 0,06 - 1,26 mg C m-2h-1. Le compartiment phytoplanctonique, de par sa production, semble être l'un des éléments régulateurs de l'activité hétérotrophe bactérienne en zone épilimnique.The seasonal distributions of phytoptanktonic primary production and bacterial heterotrophicpotentials (using respectivey 14C and 14Glucose incorporations) were studied in a eutrophic lake (Lake Aydat, Massif Central, France).Primary production and bacterial heterotrophic potentials vary respectively from 10 to 141 mg.C.m-2h-1 and from 0,06 to 1,26 mg.C.m-2h-1.The comparative evolution of these two activities in relation to the temperature shows that the general idea about "the temperature - bacterial development" model seems to be insufficient when the investigation takes place in a complex ecosystem such as Lake Aydat. Indeed, the phytoplanktonic compartment, apart from its production, seems to be one of the regulating elements of the heterotrophic bacterial activity whose variations cannot be explained by changes in temperature alone.In spite of the significant correlation obtained between bacterial activity and temperature, we should consider that the influence of this abiotic parameter on the bacterial development is an indirect one

Sumoylation of the THO complex regulates the biogenesis of a subset of mRNPs

International audienceAssembly of messenger ribonucleoparticles (mRNPs) is a pivotal step in gene expression, but only a few molecular mechanisms contributing to its regulation have been described. Here, through a comprehensive proteomic survey of mRNP assembly, we demonstrate that the SUMO pathway specifically controls the association of the THO complex with mRNPs. We further show that the THO complex, a key player in the interplay between gene expression, mRNA export and genetic stability, is sumoylated on its Hpr1 subunit and that this modification regulates its association with mRNPs. Altered recruitment of the THO complex onto mRNPs in sumoylation-defective mutants does not affect bulk mRNA export or genetic stability, but impairs the expression of acidic stress-induced genes and, consistently, compromises viability in acidic stress conditions. Importantly, inactivation of the nuclear exosome suppresses the phenotypes of the hpr1 non-sumoylatable mutant, showing that SUMO-dependent mRNP assembly is critical to allow a specific subset of mRNPs to escape degradation. This article thus provides the first example of a SUMO-dependent mRNP-assembly event allowing a refined tuning of gene expression, in particular under specific stress conditions

Variations à court terme des compartiments planctoniques d'un lac humique du Bouclier canadien

Les variations spatio-temporelles à court terme des compartiments planctoniques ont été étudiées simultanément du 30 juillet au 5 août 1986 dans un lac humique du Bouclier canadien. L'abondance du bactérioplancton fluctue de 1,4 à 1,7.106 cell. ml.-1 (coloration DAPI) ou de 2,7 à 7,7.106 cell. ml-1; (coloration Acridine Orange). La production du bactérioplancton estimée par incorporation de 3H méthyl thimidine, varie de 4 à 24.106 cell. l-1 h-1. Les valeurs d'activité hétérotrophe potentielle bactérienne estimée par assimilation de 14C glucose, s'échelonnent de 0,007 à 0,065 µg C.l-1. h-1. La biomasse pigmentaire (chlore. a et pheopigments) varie de 6,8 à 21,7 mg.m-3 . La production primaire est très faible (max. : 10 mg C. m-3 .h-1; 20 mg C.m-2 .h-1 ) et décroît très rapidement avec la profondeur (25 % à 82 % dans le premier mètre). Le microzooplancton (Rotifères, Bosmina, nauplies) représente plus de 90 % du peuplement zooplanctonique et les taux de broutage global du macrozooplancton sont faibles (25 % j-1). Les compartiments hétérotrophes prédominent dans le métabolisme du lac par rapport au compartiment autotrophe. Les patrons de variation spatiale reflètent la stratification verticale des compartiments et des processus autotrophes et hétérotrophes. Les maxima de photosynthèse, d'ATP et de production bactérienne se situent dans les eaux épilimnétiques tandis que les maxima d'abondance du bactérioptancton et des pigments se rencontrent dans l'hypolimnion. Le zooplancton est plus dense et broute d'avantage dans la strate 1-3 m. Ces variations spatiales semblent influencer l'activité hétérotrophe potentielle du bactérioptancton. Nos résultats montrent aussi des variations temporelles à court terme de la production primaire, de l'assimilation hétérotrophe et du broutage du macrozooplancton. Cette étude préliminaire met en lumière la nécessité de tenir compte des variations à court terme lors des études des relations trophodynamiques dans les écosystèmes planctoniques.Short term spatial and temporal variations in planktonic compartments were studied simultaneously, from July 30th to August 5th, 1986, in a humic lake on the Canadian Shield. Abundance of bacterioplankton ranged from 1,4 to 1,7 106 cell. ml-1 (DAP1) or from 2,7 to 7,7 106 cell. ml-1 (Acridine Orange). Bacterial production, as measured by incorporation of 3H methyl-thimidine, was estimated at 4-24 106 cells. l-1. h-1 and potential heterotrophic bacterial activity ranged from 0,007 to 0,065 µg C.l-1. h-1, as estimated by 14C glucose incorporation. Pigments biomass (chloro. a and phaeopigments) varied from 6,8 to 21,7 mg m-3. Primary production was low (max. : 10 mg C.m-3. h-1; 20 mg C.m-2. h-1) and decreased rapidly with depth (25-82 % in 1 m depth). Microzooplankton (rotifera, Bosmina, nauplii) accounted for more than 90 % of total numbers and macrozooplankton global grazing rates were low (25 % d-1). The heterotrophic compartments play a greater rate in the lake metabolism than the autotrophic compartment. Spatial variations reflect the stratification of the heterotrophic and autotrophic organisms and processes with depth. Maximum levels in primary production, ATP and bacterial production occur in epilimnetic waters, while maxima in bacterial numbers and algal pigments occur in the hypolimnion. Zooplancton density and macrozooplankton grazing rates were higher in the 1-3 m strata. These spatial patterns seem to influence the vertical profiles of the bacterial potential heterotrophic activity. Our results also show short term temporal variations in primary production, potential heterotrophic activity of bacterioplankton and macrozooplankton grazing rates. This preliminary study stresses the importance of short term variations in the assessment of the trophodynamics of the planktonic food wed

Quantum Imaging

We provide a brief overview of the newly born field of quantum imaging, and discuss some concepts that lie at the root of this field.Comment: 8 pages, 19 figure

Detection of sub-shot-noise spatial correlation in high-gain parametric down-conversion

Using a 1GW-1ps pump laser pulse in high gain parametric down-conversion allows us to detect sub-shot-noise spatial quantum correlation with up to one hundred photoelectrons per mode, by means of a high efficiency CCD. The statistics is performed in single-shot over independent spatial replica of the system. The paper highlights the evidence of quantum correlation between symmetrical signal and idler spatial areas in the far field, in the high gain regime. In accordance with the predictions of numerical calculations the observed transition from the quantum to the classical regime is interpreted as a consequence of the narrowing of the down-converted beams in the very high gain regime.Comment: 4,2 pages, 4 figure

Prospects for K+→π+ννˉK^+ \to \pi^+ \nu \bar{ \nu } at CERN in NA62

The NA62 experiment will begin taking data in 2015. Its primary purpose is a 10% measurement of the branching ratio of the ultrarare kaon decay $K^+ \to \pi^+ \nu \bar{ \nu }$, using the decay in flight of kaons in an unseparated beam with momentum 75 GeV/c.The detector and analysis technique are described here.Comment: 8 pages for proceedings of 50 Years of CP

Recent NA48/2 and NA62 results

The NA48/2 Collaboration at CERN has accumulated and analysed unprecedented statistics of rare kaon decays in the $K_{e4}$ modes: $K_{e4}(+-)$ ($K^\pm \to \pi^+ \pi^- e^\pm \nu$) and $K_{e4}(00)$ ($K^\pm \to \pi^0 \pi^0 e^\pm \nu$) with nearly one percent background contamination. It leads to the improved measurement of branching fractions and detailed form factor studies. New final results from the analysis of 381 $K^\pm \to \pi^\pm \gamma \gamma$ rare decay candidates collected by the NA48/2 and NA62 experiments at CERN are presented. The results include a decay rate measurement and fits to Chiral Perturbation Theory (ChPT) description.Comment: Prepared for the Proceedings of "Moriond QCD and High Energy Interactions. March 22-29 2014." conferenc

Influence of the annealing treatments on the luminescence properties of SiO∕SiO2 multilayers

International audienceThe formation of silicon nanocrystals ͑Si-ncs͒ and their room temperature photoluminescence ͑PL͒ properties were investigated in samples elaborated by the evaporation method. Silicon oxide ͑SiO͒ single layer and SiO / SiO 2 multilayers with different SiO layer thicknesses from 1 to 5 nm were prepared and annealed at different temperatures up to 1050°C. The structure and the formation of Si-nc were studied by transmission electron microscopy ͑TEM͒ and by Fourier transform infrared ͑FTIR͒ absorption spectroscopy. It is demonstrated that the Si-ncs appear by the phase separation process from SiO due to the annealing treatments. Contrary to the SiO single layer, the multilayers are a powerful system to obtain highly luminescent Si-nc and to control the Si-nc size for SiO layer thicknesses lower than or equal to 4 nm. It is clearly shown that, in agreement with the quantum confinement theory, the PL energy is a decreasing function of the Si-nc size. However, thanks to the correlation between FTIR, TEM, and PL results, it is demonstrated that the PL energy is also strongly dependent on the quality of the matrix in which the Si-nc are embedded. A model based on the existence of a SiO x shell surrounding the Si-nc is proposed to explain the PL results

A new measurement of J/psi suppression in Pb-Pb collisions at 158 GeV per nucleon

We present a new measurement of J/psi production in Pb-Pb collisions at 158 GeV/nucleon, from the data sample collected in year 2000 by the NA50 Collaboration, under improved experimental conditions with respect to previous years. With the target system placed in vacuum, the setup was better adapted to study, in particular, the most peripheral nuclear collisions with unprecedented accuracy. The analysis of this data sample shows that the (J/psi)/Drell-Yan cross-sections ratio measured in the most peripheral Pb-Pb interactions is in good agreement with the nuclear absorption pattern extrapolated from the studies of proton-nucleus collisions. Furthermore, this new measurement confirms our previous observation that the (J/psi)/Drell-Yan cross-sections ratio departs from the normal nuclear absorption pattern for semi-central Pb-Pb collisions and that this ratio persistently decreases up to the most central collisions.Comment: 19 pages, 10 figures. Submitted to Eur. Phys. J.