Search

International audience; Minerals excavated during industrial activities are stored on the soil surface, exposed to weathering, which leads to the initial development of soil. Plants contribute to soil mineral weathering, mainly by producing acidic or complexing root exudates. In addition, many plants produce antioxidant compounds and phenolic substances that could also contribute to mineral transformation processes, but have rarely been considered in relation to mineral weathering. An incubation experiment was carried out for 2 months under controlled conditions to assess the effects of antioxidant plant metabolites on the weathering processes of a clay mineral. A freshly excavated, sulphur‐rich Callovo‐Oxfordian argillite (COx) sample was artificially leached with three concentrations of three antioxidant compounds (linalool, thymol and carvacrol) or water as a control. The weathering of COx was followed by the analysis of amounts of anions and cations in the leachates. Chlorine, sulphate, nitrate, phosphate, calcium, magnesium and potassium were found in the leachates, whereas iron and aluminium were close to the detection limits. Sulphate leaching reflected oxidation of the pyritic matter contained in COx (mainly fine pyrite particles) by air. Water alone was enough to cause notable leaching of elements such as S and P, but the percentage of leached sulphate increased in the presence of two antioxidant compounds, carvacrol and thymol, and increased to 38% with thymol at 2 mg l−1 compared with the antioxidant‐free control. Thus, antioxidant compounds could contribute to the leaching of elements from COx, depending on their nature and concentration.

International audience

International audience; The wide collection of currently available fluorescent proteins (FPs) offers new possibilities for multicolor reporter gene-based studies of bacterial functions. However, the simultaneous use of multiple FPs is often limited by the bleed-through of their emission spectra. Here we introduce an original approach for detection and separation of multiple overlapping fluorescent signals from mixtures of bioreporters strains. The proposed method relies on the coupling of synchronous fluorescent spectroscopy (SFS) with blind spectral decomposition achieved by the Canonical Polyadic (CP) decomposition (also known as Candecomp/Parafac) of three-dimensional data arrays. Due to the substantial narrowing of FP emission spectra and sensitive detection of multiple FPs in a one-step scan, SFS reduced spectral overlap and improved the selectivity of the CP unmixing procedure. When tested on mixtures of labeled E. coli strains, the SFS/CP approach could easily extract the contribution of at least four overlapping FPs. Furthermore, it allowed to simultaneously monitor the expression of three iron responsive genes and pyoverdine production in P. aeruginosa. Implemented in a convenient microplate format, this multiplex fluorescent reporter method provides a useful tool to study complex processes with different variables in bacterial systems.

Hybrid silica gels (HSGs) were prepared according to an acid-catalyzed sol–gel method using tetraethoxysilane (TEOS) as silica precursors and colloidal suspension of nontronite clay mineral. The silica surfaces were hydrophilic in relation to silanol groups and it was of interest to increase hydrophobicity by substituting silanol by methylated groups through addition of methyltrimethoxysilane (MTMS) in a molar ratio TEOS: MTMS equaled to 1:0.4. The aim of the present paper was to predict effects of water content in soil on HSG hydration by characterizing HSG water desorption and sorption with dynamic vapor sorption device. From desorption kinetics, TEOS HSGs showed higher ability to water surface evaporation and diffusion compared to the TEOS–MTMS HSGs. After complete dehydration, water sorption isotherms Type II were obtained for HSGs. Isotherms were fitted with Brunauer-Emmett-Tellet (BET) and Guggenheim, Andersen, de Boer (GAB) models. The higher monolayer values of water adsorbed for HSGs containing nontronite suggested a major influence of clay minerals on overall hydration. However, the water binding energy depended upon the nature of silica matrix indicating weaker bonds with methylated groups at solid surface in MTMS–TEOS HSGs. Apparent water sorption diffusivities, Dapp were calculated according to Fick’s diffusion model. Maximal Dapp values were obtained in the range 0.2–0.3 aw after which the Dapp decreased in relation with capillary condensation.

International audience; In this paper we address the problem of estimating the interaction matrices of Paralind decomposition. In general, this is an ill-posed problem admitting an infinite number of solutions. First we study the gain of imposing sparsity constraints on the interaction matrices, in terms of model identifiability. Then, we propose a new algorithm (S-Paralind) for fitting the Paralind model, using a l2-l1 optimization step for estimating the interaction matrix. This new approach provides more accurate and robust estimates of the constraint matrices than ALS-Paralind, thus improving the interpretability of the Paralind decomposition.

National audience

Ion exchange polymers doped with a suitable electroactive mediator (i.e., Cu2+ or Fe(CN)63-) have been used to modify carbon paste electrodes that have been further applied to the indirect amperometric detection of non-redox cations or anions in flow injection analysis. The detection mechanism involves ion exchange between the non-redox ionic analyte and the electroactive mediator, in the polymer particles located at the electrode surface, followed by the electrochemical transformation of the mediator species leached out of the polymer at the electrode/solution interface. Operating in the absence of added supporting electrolyte led to peak currents made of a major faradic component that is added to a capacitive contribution due to the conductivity jump occurring upon the analyte passing the electrode surface. The method can be applied to the detection of non-electroactive mineral cations and anions, as well as poorly-dissociated organic acids, which are usually involved in mineral weathering. After having characterized and discussed the main parameters affecting the sensitivity of the detection (with respect to analyte charge, size and degree of dissociation), the electrochemical device was evaluated as a possible test to monitor mineral weathering in a simple case (zeolite dissolution in acidic medium) and in a more sophisticated one (biomediated olivine dissolution by fungi).

International audience; We address the problem of complexity reduction in hyperspectral image unmixing. When the hyperspectral images are highly resoluted, we propose to select a limited number of pixels, therefore reducing dramatically the size of the data. Then, the related mixtures are used as inputs to a positive source separation algorithm. Our pixel selection procedure is based on a convex cone analysis of the data mixtures; indeed, positive mixtures of sources are embedded in a convex cone whose boundary contains complete available information regarding the sources. We search for the least number of mixtures embedding the convex cone and then store the corresponding pixel indices as the selected pixels. We apply this method to the analysis of hyperspectral images of bacterial cells obtained on a confocal microscope. The bacterial cells, acting as whole-cell biosensors, display great potential as living transducers in sensing applications.