Virus, bactéries et protistes pathogènes du phytoplancton, le rôle insoupçonné des parasites dans le fonctionnement des écosystèmes aquatiques

International audienceMicroscopiques, les parasites sont la plupart du temps invisibles, mais présents partout. Ils infectent tous les organismes du monde vivant. La dernière décennie a révélé une incroyable diversité chez les parasites viraux, bactériens et eucaryotes. Ceux infectant le phytoplancton pourraient avoir une importance capitale dans la dynamique des populations algales et dans le fonctionnement des écosystèmes aquatiques, mais leur rôle est encore très largement méconnu à ce jour (Brussaard, 2004). Sur ces questions, la recherche ne fait que commencer

Diet of Elagatis bipinnulata (Guoy & Gaimard, 1824) in Côte d’Ivoire (Gulf of Guinea)

The rainbow runner, Elagatis bipinnulata, which belongs to the Carangidae family, is regularly encountered in the landing of artisanal fishing in Abobo-Doumé (Republic of Côte d’Ivoire). The object of this work is to study the diet of Elagatis bipinnulata according to the marine seasons and the size of the various specimens (immature and mature). About 900 fish measuring between 43 and 93 cm (fork length - FL) were examined from September 2015 to August 2017. On the 900 examined stomachs, 541 were empty, which is giving a vacuity coefficient of 60.11%. A feeding index (IRI: index of relative importance of food item) combining three methods percentage occurrence, numerical method and weight method) was used. The identification of the items found in the stomach contents revealed that the principals food items were fish (%IRI=48.85) and crustaceans (%IRI=45.78). Cephalopods (%IRI=4.17), fish detritus (%IRI=1.2) and crustaceans (Portunus puber) (%IRI=0.55) are accidental food. The diet of the species does not change according to the seasons and the size of fish

The NLRP3 inflammasome is activated by nanoparticles through ATP, ADP and adenosine.

International audienceThe NLR pyrin domain containing 3 (NLRP3) inflammasome is a major component of the innate immune system, but its mechanism of activation by a wide range of molecules remains largely unknown. Widely used nano-sized inorganic metal oxides such as silica dioxide (nano-SiO2) and titanium dioxide (nano-TiO2) activate the NLRP3 inflammasome in macrophages similarly to silica or asbestos micro-sized particles. By investigating towards the molecular mechanisms of inflammasome activation in response to nanoparticles, we show here that active adenosine triphosphate (ATP) release and subsequent ATP, adenosine diphosphate (ADP) and adenosine receptor signalling are required for inflammasome activation. Nano-SiO2 or nano-TiO2 caused a significant increase in P2Y1, P2Y2, A2A and/or A2B receptor expression, whereas the P2X7 receptor was downregulated. Interestingly, IL-1β secretion in response to nanoparticles is increased by enhanced ATP and ADP hydrolysis, whereas it is decreased by adenosine degradation or selective A2A or A2B receptor inhibition. Downstream of these receptors, our results show that nanoparticles activate the NLRP3 inflammasome via activation of PLC-InsP3 and/or inhibition of adenylate cyclase (ADCY)-cAMP pathways. Finally, a high dose of adenosine triggers inflammasome activation and IL-1β secretion through adenosine cellular uptake by nucleotide transporters and by its subsequent transformation in ATP by adenosine kinase. In summary, we show for the first time that extracellular adenosine activates the NLRP3 inflammasome by two ways: by interacting with adenosine receptors at nanomolar/micromolar concentrations and through cellular uptake by equilibrative nucleoside transporters at millimolar concentrations. These findings provide new molecular insights on the mechanisms of NLRP3 inflammasome activation and new therapeutic strategies to control inflammation

Marine protist diversity in European coastal waters and sediments as revealed by high-throughput sequencing

International audienceAlthough protists are critical components of marine ecosystems, they are still poorly characterized. Here we analysed the taxonomic diversity of planktonic and benthic protist communities collected in six distant European coastal sites. Environmental deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) from three size fractions (pico-, nano- and micro/mesoplankton), as well as from dissolved DNA and surface sediments were used as templates for tag pyrosequencing of the V4 region of the 18S ribosomal DNA. Beta-diversity analyses split the protist community structure into three main clusters: picoplankton-nanoplankton-dissolved DNA, micro/mesoplankton and sediments. Within each cluster, protist communities from the same site and time clustered together, while communities from the same site but different seasons were unrelated. Both DNA and RNA-based surveys provided similar relative abundances for most class-level taxonomic groups. Yet, particular groups were overrepresented in one of the two templates, such as marine alveolates (MALV)-I and MALV-II that were much more abundant in DNA surveys. Overall, the groups displaying the highest relative contribution were Dinophyceae, Diatomea, Ciliophora and Acantharia. Also, well represented were Mamiellophyceae, Cryptomonadales, marine alveolates and marine stramenopiles in the picoplankton, and Monadofilosa and basal Fungi in sediments. Our extensive and systematic sequencing of geographically separated sites provides the most comprehensive molecular description of coastal marine protist diversity to date

Antiretroviral-naive and -treated HIV-1 patients can harbour more resistant viruses in CSF than in plasma

Objectives The neurological disorders in HIV-1-infected patients remain prevalent. The HIV-1 resistance in plasma and CSF was compared in patients with neurological disorders in a multicentre study. Methods Blood and CSF samples were collected at time of neurological disorders for 244 patients. The viral loads were >50 copies/mL in both compartments and bulk genotypic tests were realized. Results On 244 patients, 89 and 155 were antiretroviral (ARV) naive and ARV treated, respectively. In ARV-naive patients, detection of mutations in CSF and not in plasma were reported for the reverse transcriptase (RT) gene in 2/89 patients (2.2%) and for the protease gene in 1/89 patients (1.1%). In ARV-treated patients, 19/152 (12.5%) patients had HIV-1 mutations only in the CSF for the RT gene and 30/151 (19.8%) for the protease gene. Two mutations appeared statistically more prevalent in the CSF than in plasma: M41L (P = 0.0455) and T215Y (P = 0.0455). Conclusions In most cases, resistance mutations were present and similar in both studied compartments. However, in 3.4% of ARV-naive and 8.8% of ARV-treated patients, the virus was more resistant in CSF than in plasma. These results support the need for genotypic resistance testing when lumbar puncture is performe

Les amoebophryidae (Syndiniales) parasitoïdes de dinoflagellés (cycle de vie, dynamique et spécificité in situ )

Les Syndiniales sont des parasitoïdes marins capables d infecter un très grand nombre d organismes planctoniques ou non. Parmi ces pathogènes, les Amoebophryidae, infectent tout particulièrement les dinoflagellés. En rivière de Penzé (Nord Bretagne, France), ces parasitoïdes infectent toutes les espèces présentes, y compris l espèce toxique Alexandrium minutum. La spécificité de ces interactions est grande : une espèce hôte est infectée par un parasitoïde génétiquement distinct, le même pathogène infectant la même espèce d une année sur l autre (entre 2004 et 2006). Ces pathogènes spécifiques sont donc capables de réguler les populations hôtes entraînant une succession rapide des espèces de dinoflagellés. Le nombre croissant de marées rouges (ou efflorescences de dinoflagellés) pourrait ainsi être une conséquence du le découplage entre le dinoflagellé hôte et son pathogène naturel.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocROSCOFF-Observ.Océanol. (292393008) / SudocSudocFranceF

Méthodes d’étude du traductome régulé par les récepteurs couplés aux protéines G

National audienceWith the advent of next-generation sequencing technologies, identifying the translatome, which includes genome-wide ribosome-associated mRNAs, provides new opportunities to define faithfully the protein repertoire of a cell, as opposed to transcriptomic approaches. In addition, the role that extracellular signals such as hormonal modulations could play on the translatome remains to be deciphered. In particular, the regulation of the translatome by G protein-coupled receptors (GPCR) is still poorly described, albeit the trophic role that many receptors of this family play in their target cells. Here, we provide an overview of the current methods that are used to study the translatome, applied to the GPCR receptor family.Depuis l’avènement des méthodes de séquençage à haut débit, l’identification du traductome, qui comprend l’ensemble des ARNm associés aux ribosomes, ouvre de nouvelles perspectives pour définir le répertoire des protéines réellement exprimées dans une cellule, contrairement au séquençage du transcriptome correspondant. De plus, l’impact que les signaux extracellulaires tels que des modulations hormonales peuvent avoir sur le traductome reste méconnu. En particulier, la régulation du traductome par les récepteurs couplés aux protéines G (RCPG) est un domaine encore peu exploré, alors que de nombreux récepteurs de cette famille jouent un rôle trophique très important dans leur cellule cible. L’objectif de cette revue est de présenter les méthodes les plus utilisées pour étudier le traductome, en les appliquant aux RCPG

Advances in field noble gasmeasurements towards operationalhydrology

International audienceIn natural waters, noble gas concentrations are governedby a diversity of relatively simple and well-studied physicalprocesses. As a result, noble gas measurements provideimportant information on various phenomena such asgroundwater residence time distribution (4He, 21Ne, 37Ar, 39Ar,40Ar, 85Kr, 81Kr), aquifer recharge conditions (temperature,elevation …) or aquifer-river exchange (222Rn).However, despite their interest, noble gas data remainrelatively scarce and punctual owing to the complexity andcosts of their production. In view of the spatial and temporalvariety and variability of the Hydrosphere dynamics a newinvestigation method is needed.This study approaches the concept of “operationalhydrology” aiming to enhance both the spatio-temporaldistribution and the quality of environmental data for athorough exploration of the Hydrosphere.In this perspective, we developed a new analytical toolbased on membrane inlet mass spectrometry (MIMS)allowing the continuous measurement of dissolved gases(Chatton et al., 2017).To illustrate our approach, we present atmospheric andradiogenic noble gas data (He, Ne, Ar, Kr, Xe) measured insitu with a CF-MIMS (Chatton et al, 2017) installed in amobile laboratory arranged in an all-terrain truck (CRITEXLab).This ongoing work focuses on groundwater and thefield investigation of residence time distribution, rechargeprocesses, water flow paths and mixing

Concentration de sédiment en suspension près de la surface en Manche : modélisation numérique vs observation satellite

International audienceLa présente étude vise à analyser la variabilité spatio-temporelle de la concentration de sédiment en suspension (CSS) en surface en Manche par une approche conjointe d'observation satellite et de modélisation numérique. Les prédictions numériques sont comparées à trois images satellite claires représentant différentes conditions hydrodynamiques de marée et de houle. Le modèle reproduit globalement les structures de CSS observées en surface sur les images satellite autour de l'ile de Wight et dans le golfe normano-breton. Le modèle permet d'analyser la composition granulométrique de la CSS et indique que les particules fines (<50 µm) sont majoritaires en surface. Les classes de taille supérieure (entre 100 et 500 µm) ont un impact en surface principalement autour de l'ile de Wight et dans le golfe normano-breton. Une sensibilité au temps d'initialisation (spin up) est mise en avant. Mots-clés : Modélisation-Satellite-Sédiment en suspension-Marée-Houl

Modeling vs. satellite remote-sensing of near-surface non-algal suspended particulate matter in the English Channel.

International audienceConcentration of near-surface suspended particulate matter (SPM) is a key parameter for the characterization of sediment dynamics and the quantification of light in the water column for hydrological and biological modeling in coastal seas. The influences of tides and wind-generated surface-gravity waves on non-algal near-surface SPM in the English Channel have recently been identified by Rivier et al. (2012) on the basis of statistical models applied to a large satellite dataset. The present study extends this analysis by comparing satellite images and numerical model predictions of non-algal near-surface SPM. Satellite images are MODIS and MERIS remote-sensing reflectance processed by the IFREMER semi-analytical algorithm (Gohin et al., 2011). These data have been provided through the MyOcean/GMES project. The numerical modeling approach is based on the three-dimensional (3D) hydro-sedimentary model ROMS (“Regional Ocean Model System”) (e.g., Warner et al., 2008). It considers realistic heterogeneous bottom sediments (Guillou and Chapalain, 2010), tidal forcing along open boundaries, wind stress at the sea-surface and wave-current interactions in the bottom boundary layer. Numerical results are compared with a series of “clear” satellite images gathered in 2008 under various tide and waves conditions. Modeling provides further insights of the spatio-temporal variability of non-algal surface SPM in the English Channel by resolving small-scale vertical transport processes and much shorter time-scales than daily satellite observation does. The granulometric distribution of non-algal near-surface SPM is examined. Finally, the focus is placed on two particular features: (i) the formation of a turbidity maximum zone around the Isle of Wight (English coastline) and (ii) the near-surface SPM variability in the Norman-Breton Gulf (French coastline)