Estimating sharka dispersal function by stochastic spatiotemporal modelling

Plant viral diseases, and especially the ones transmitted by aerial vectors, can cause considerable yield losses. A good knowledge of the distances of spread is key to the understanding of disease dynamics. Exploratory approaches aiming at characterizing the spatiotemporal distribution of diseased plants are often used to get an insight into the distances of spread. A more powerful approach is based on stochastic spatiotemporal modelling in order to estimate the dispersal function of the disease (probability density function describing the probability for an infectious plant to infect a healthy plant at distance d). In this study, we implemented a method for estimating the dispersal function of the sharka disease. Sharka is one of the most serious diseases of stone fruit trees (Prunus sp.). It is caused by Plum pox virus (PPV, genus Potyvirus), transmitted by at least twenty different aphid species in a non persistent manner. Due to the inefficiency of insecticides and the very rare sources of resistance against the virus available in the host species, prophylactic disease control is based on the removal of the diseased trees in the orchards. Thus, a very good knowledge of the dispersal function of sharka is crucial for building epidemiological models and optimizing the strategies of surveillance and control. We adapted the methodology published by Gibson (1997) based on a Markov chain Monte Carlo (MCMC) algorithm in order to estimate sharka dispersal function from the maps of 157 contiguous peach orchards reporting the exact location and the sanitary status (asymptomatic/symptomatic) of each of the trees during six consecutive years. An estimation method based on the Gibbs sampling algorithm was developed taking into account the specificities of the dataset (more than two dates of observation, annual removal of diseased trees). This estimation algorithm was validated on simulated data and was proved to be more powerful and better adapted to large datasets than the one proposed by Gibson. Moreover, the influence of latency on the estimation of the dispersal function was quantified. This methodology was then used to estimate the dispersal function of the disease from a subset of the real dataset. The methods developed in this study are generic enough to be used and adapted for the estimation of dispersal functions of any disease transmitted in a non persistent manner, and even for diseases with similar characteristics. (Texte intégral

Mapping Regions of the Cauliflower Mosaic Virus ORF III Product Required for Infectivity

AbstractThe open reading frame (ORF) III product (PIII) of the pararetrovirus cauliflower mosaic virus (CaMV) has nucleic acid-binding propertiesin vitro,but its biological role is not yet determined. ORF III is closely linked to ORF II and overlaps ORF IV out of frame in the CaMV genome. A new CaMV-derived vector (CaΔ) devoid of ORF III and containing unique restriction sites between ORFs II and IV was designed. Introduction of the wild-type CaMV ORF III into CaΔ results in a clone (Ca3) infectious in turnip plants. Truncated or point-mutated versions of ORF III were then inserted into CaΔ and testedin vivo.Inoculation of the different mutants into turnip revealed that the four C-terminal amino acid residues of PIII are dispensable for infectivity as well as an internal domain (amino acids 61 to 80). Taken together the results show that PIII possesses a functional two-domain organization. Moreover, the CaMV PIII function(s) cannot be replaced either by the PIII protein of another caulimovirus, the figwort mosaic virus, or by the P2 protein of the cacao swollen shoot badnavirus, a member of the second plant pararetrovirus group

Conditions and mechanism for the formation of iron-rich Montmorillonite in deep sea sediments (Costa Rica margin): Coupling high resolution mineralogical characterization and geochemical modeling

International audienceIron-rich smectite is commonly described in the diagenetic fraction of deep-sea sediment, as millimeter to centimeter aggregates dispersed in the sediment, or as a coating on sedimentary particles or nodules. This study examines several factors to elucidate formation mechanisms of a particular iron-rich smectite and its potential transformation to glauconite. The study combines a detailed mineralogical investigation on natural samples and a chemical modeling approach to assess mineralogical reactions and pathways. Transmission electron microscopy (TEM) observations and analytical electron microscopy (TEM-AEM) analyses were conducted on microtomed samples of millimeter- to centimeter-long green grains. These grains are widespread in pelagic calcareous sediment from the Costa Rica margin. They are composed of pyrites that are partially dissolved and are surrounded by amorphous or very poorly crystallized iron-rich particles. Iron-rich montmorillonite grows from an amorphous precursor and its formation requires the input of Si, O, Mg, K, Na and Ca; our results suggest that these inputs are supported by the dissolution of sedimentary phases such as volcanic glasses, siliceous fossils and silicates. Thermodynamic modeling of fluid-sediment interactions was conducted with the geochemical computer code PhreeqC, using mineralogical and pore fluid compositions from sediment samples and calculated estimates for thermodynamic constants of smectites that are not maintained by the computer code. Simulations confirm the possibility that the green grains are the product of pyrite alteration by seawater under oxidizing conditions. The extent of smectite production is controlled by the kinetics of pyrite dissolution and fluid migration. The absence of aluminum in the Costa Rica margin system explains the formation of an iron-rich montmorillonite instead of glauconite, whereas the presence of calcite that buffers the system explains the formation of an iron-rich montmorillonite instead of iron oxides

Investigation of dioctahedral smectite hydration properties by modeling of X-ray diffraction profiles: Influence of layer charge and charge location

International audienceHydration of the <1 μm size fraction of a high-charge montmorillonite (Clay Minerals Society Source Clay SAz-1), and of low- and high-charge beidellites (Source Clays SbId-1 and SbCa-1, respectively) was studied by modeling of X-ray diffraction patterns recorded under controlled relative humidity (RH) for Sr- and/or Ca-saturated specimens. The influence of layer charge and charge location on smectite hydration was studied. Distribution of layers with different hydration states (dehydrated – 0W, monohydrated – 1W, bi-hydrated – 2W, or tri-hydrated – 3W) within smectite crystals often leads to two distinct contributions to the X-ray diffraction pattern, each contribution having different layer types randomly interstratified. Structure models are more heterogeneous for beidellite than for montmorillonite. For beidellite, two distinct populations of particles with different coherent scattering domain sizes account for the heterogeneity. Increased hydration heterogeneity in beidellite originates also from the presence of 0W (non-expandable) and of 1W layers under high relative humidity (RH) conditions. Similarly, after ethylene-glycol (EG) solvation, some beidellite layers incorporate only one plane of EG molecules whereas homogeneous swelling was observed for montmorillonite with the systematic presence of two planes of EG molecules. For montmorillonite and beidellite, the increase of layer charge shifts the 2W-to-1W and the 1W-to-0W transitions towards lower RH values. For all samples, layer thickness of 0W, 1W, and 2W layer types was similar to that determined for low-charge SWy-1 montmorillonite (Source Clay SWy-1), and no change of layer thickness was observed as a function of the amount or of the location of layer charge. Layer thickness however increased with increasing RH conditions

"Thermal Spike" model applied to thin targets irradiated with swift heavy ion beams at few MeV/u

International audienceHigh electronic excitations in radiation of metallic targets with swift heavy ion beams at the coulomb barrier play a dominant role in the damaging processes of some metals. The inelastic thermal spike model was developed to describe tracks in materials and is applied in this paper to some systems beams/targets employed recently in some nuclear physics experiments. Taking into account the experimental conditions and the approved electron-phonon coupling factors, the results of the calculation enable to interpret the observation of the fast deformation of some targets

Impact of kefir derived lactobacillus kefiri on the mucosal immune response and gut microbiota

The evaluation of the impact of probiotics on host health could help to understand how they can be used in the prevention of diseases. On the basis of our previous studies and in vitro assays on PBMC and Caco-2 ccl20:luc reporter system presented in this work, the strain Lactobacillus kefiri CIDCA 8348 was selected and administrated to healthy Swiss mice daily for 21 days. The probiotic treatment increased IgA in feces and reduced expression of proinflammatory mediators in Peyer Patches and mesenteric lymph nodes, where it also increased IL-10. In ileum IL-10, CXCL-1 and mucin 6 genes were upregulated; meanwhile in colon mucin 4 was induced whereas IFN-γ, GM-CSF, and IL-1β genes were downregulated. Moreover, ileum and colon explants showed the anti-inflammatory effect of L. kefiri since the LPS-induced increment of IL-6 and GM-CSF levels in control mice was significantly attenuated in L. kefiri treated mice. Regarding fecal microbiota, DGGE profiles allowed differentiation of experimental groups in two separated clusters. Quantitative PCR analysis of different bacterial groups revealed only significant changes in Lactobacillus population. In conclusion, L. kefiri is a good candidate to be used in gut inflammatory disorders.Facultad de Ciencias ExactasInstituto de Estudios Inmunológicos y Fisiopatológico

Etude du comportement superélastique d'un stent en alliage à mémoire de forme. Investigations expérimentales et numériques

Les alliages à mémoire de forme (AMF) sont classiquement utilisés en biomécanique. On s'intéresse ici à prédire le comportement superélastique d'un stent AMF (nickel titane) présentant une géométrie particulière à fils enchevêtrés. Le modèle CAO tridimensionnel réalisé avec Catia V5 est importé dans Abaqus, et une loi de comportement phénoménologique implémentée via la routine UMAT permet de prendre en compte le comportement superélastique. Des tests de compression et de gonflement sont simulés et les résultats comparés avec les investigations expérimentales correspondantes