Acid-base activity of live bacteria: Implications for quantifying cell wall charge     

Jacqueline Claessens  Yvonne van Lith  Philippe Van Cappellen 《Geochimica et cosmochimica acta》2006,70(2):267-276

To distinguish the buffering capacity associated with functional groups in the cell wall from that resulting from metabolic processes, base or acid consumption by live and dead cells of the Gram-negative bacterium Shewanella putrefaciens was measured in a pH stat system. Live cells exhibited fast consumption of acid (pH 4) or base (pH 7, 8, 9, and 10) during the first few minutes of the experiments. At pH 5.5, no acid or base was required to maintain the initial pH constant. The initial amounts of acid or base consumed by the live cells at pH 4, 8, and 10 were of comparable magnitudes as those neutralized at the same pHs by intact cells killed by exposure to gamma radiation or ethanol. Cells disrupted in a French press required higher amounts of acid or base, due to additional buffering by intracellular constituents. At pH 4, acid neutralization by suspensions of live cells stopped after 50 min, because of loss of viability. In contrast, under neutral and alkaline conditions, base consumption continued for the entire duration of the experiments (5 h). This long-term base neutralization was, at least partly, due to active respiration by the cells, as indicated by the build-up of succinate in solution. Qualitatively, the acid-base activity of live cells of the Gram-positive bacterium Bacillus subtilis resembled that of S. putrefaciens. The pH-dependent charging of ionizable functional groups in the cell walls of the live bacteria was estimated from the initial amounts of acid or base consumed in the pH stat experiments. From pH 4 to 10, the cell wall charge increased from near-zero values to about −4 × 10⁻¹⁶ mol cell⁻¹ and −6.5 × 10⁻¹⁶ mol cell⁻¹ for S. putrefaciens and B. subtilis, respectively. The similar cell wall charging of the two bacterial strains is consistent with the inferred low contribution of lipopolysaccharides to the buffering capacity of the Gram-negative cell wall (of the order of 10%).  相似文献   

Acid–base activity of microorganisms     

Jacqueline Claessens  Yvonne van Lith  Anniet Laverman  Philippe Van Cappellen 《Journal of Geochemical Exploration》2006,88(1-3):181

In order to distinguish the buffering capacity associated with functional groups in the cell wall from that resulting from metabolic processes, the base or acid consumption of live and dead cells of the Gram-negative bacterium Shewanella putrefaciens was measured as a function of time in a pH stat system. Under neutral (pH 7) to basic (pH 8 and 10) conditions, base neutralization by suspensions of live bacteria beyond 1 h was clearly due to respiratory activity. At pH 4, however, proton neutralization ceased after 50 min due to cell death. Dead cells only produced or consumed protons during the very first minutes after exposure to pH 4, 8 or 10. From the time-dependent acid and base consumption curves of live cells, and the comparison of the acid–base activity of live and dead cells, the charging of ionizable groups in the cell wall was derived. From pH 4 to 10, cell wall charge increases from 0 to about − 4 × 10^− 16 mol cell^− 1.  相似文献   

Quaternary faulting in the Upper Rhine Graben revealed by high-resolution multi-channel reflection seismic     

Guillaume Bertrand  Philippe Elsass  Gunther Wirsing  Alex Luz 《Comptes Rendus Geoscience》2006,338(8):574-580

A high-resolution multichannel seismic reflection river profiling campaign was completed in July 2002 in the southern Upper Rhine graben (URG), along the River Rhine. Preliminary results show apparent Quaternary vertical slip rates, on intra-graben faults that are relatively slow, of the order of a few thousandths to a few hundredths of mm/yr. Moreover, kinematical data from the Ludwigshafen area show decreasing vertical slip rates since the Middle Pleistocene and/or a migration of tectonic activity. While still preliminary, these data show inhomogeneous and relatively slow tectonic activity in the URG that could probably not alone have shaped the Quaternary graben morphology. To cite this article: G. Bertrand et al., C. R. Geoscience 338 (2006).  相似文献   

Mechanical modelling of oblique convergence in the Zagros, Iran     

Philippe Vernant  Jean Chéry 《Geophysical Journal International》2006,165(3):991-1002

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Archaeomagnetism in Italy: a compilation of data including new results and a preliminary Italian secular variation curve     

Evdokia Tema  Ian Hedley  Philippe Lanos 《Geophysical Journal International》2006,167(3):1160-1171

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Effects of Drying on the Low-Frequency Electrical Properties of Tournemire Argillites   总被引：1，自引：0，他引：1  

Philippe Cosenza  Ahmad Ghorbani  Nicolas Florsch  André Revil 《Pure and Applied Geophysics》2007,164(10):2043-2066

Nearly water-saturated argillite samples (initial water content near 3.4 wt%) were cored from an undisturbed area of an underground facility of the French Institute for Radioprotection and Nuclear Safety (IRSN), located at Tournemire (Aveyron, France). These samples were subjected to the following desiccation path: (a) A desaturation phase during which the samples were dried at ambient temperature conditions, relative humidity equal to 43% in average and (b) a heating phase during which the same samples were heated at four temperature levels from 70°C up to 105°C. During both phases, the low-frequency complex resistivity (0.18Hz–12 kHz) was recorded by a four-electrode device. The amplitude of the complex resistivity was extremely sensitive to water content change. At the end of the isotherm desaturation phase, it was multiplied by a factor of 3 to 5. During the heating phase, the resistivity increased by more than two orders of magnitude compared to the initial state. The percentage of Frequency Effect shows a low sensitivity to water content changes during the desaturation stage while it increased by two orders of magnitude during the heating phase. This result confirms that low-frequency spectral signature is extremely sensitive to textural changes (i.e., thermal-induced microcracking in this case) that occurred during heating. Moreover, the complex resistivity of the samples shows a strong anisotropy (a ratio of 10 between both amplitudes measured in the perpendicular directions). The classical Cole-Cole model cannot be used to fit the experimental data obtained in the heating phase. A generalized formulation of this model is required and was successfully applied to represent the complex resistivity data.  相似文献   

Observational Evidence And Modelling Of An Internal Hydraulic Jump At The Atmospheric Boundary-Layer Top During A Tramontane Event     

Philippe Drobinski  Cyrille Flamant  Jan Dusek  Pierre H. Flamant  Jacques Pelon 《Boundary-Layer Meteorology》2001,98(3):497-515

A hydraulic jump has been observed with the airborne backscatter lidar LEANDRE 1 (Lidar embarqué pour l'Etude des Aérosols, des Nuages, des interactions Dynamique-Rayonnement etdu cycle de l'Eau) at the top of the atmospheric boundary layer (ABL) during a Tramontane event in the framework of the Pyréneés experiment. An analytical fluid mechanics model is used to interpret lidar observations in connection with in situ measurements andto study the sensitivity of the hydraulic jump triggering to the boundary conditions. This model, which generalizes the reduced-gravity shallow-water theory for two-dimensional stratified flows over a topograpy, is diagnostic (i.e., the reduced gravity g' = g _{v v} is prescribed) and uses boundary conditions defined in terms of Riemann invariants. Using inflow and outflow boundary conditions as well as the reduced gravity prescribed from in situ measurements, the model is able to diagnose the presence of a hydraulic jump at the location suspected from the lidar observations. The wind speed, ABL height and Froude number derived from the model are in good agreement with the observations (within about 20–30%).  相似文献   

Extraction of water and solutes from argillaceous rocks for geochemical characterisation: Methods, processes and current understanding     

Elisa Sacchi  Jean-Luc Michelot  Helmut Pitsch  Philippe Lalieux  Jean-François Aranyossy 《Hydrogeology Journal》2001,9(1):17-33

This paper summarises the results of a comprehensive critical review, initiated by the OECD/NEA "Clay Club," of the extraction techniques available to obtain water and solutes from argillaceous rocks. The paper focuses on the mechanisms involved in the extraction processes, the consequences on the isotopic and chemical composition of the extracted pore water and the attempts made to reconstruct its original composition. Finally, it provides some examples of reliable techniques and information, as a function of the purpose of the geochemical study. Electronic Publication  相似文献   

Stochastic forecasts of seawater intrusion towards sustainable groundwater management: application to the Korba aquifer (Tunisia)     

Jaouher Kerrou  Philippe Renard  Fabien Cornaton  Pierre Perrochet 《Hydrogeology Journal》2013,21(2):425-440

A stochastic study of long-term forecasts of seawater intrusion with an application to the Korba aquifer (Tunisia) is presented. Firstly, a geostatistical model of the exploitation rates was constructed, based on a multi-linear regression model combining incomplete direct data and exhaustive secondary information. Then, a new method was designed and used to construct a geostatistical model of the hydraulic conductivity field by combining lithological information and data from hydraulic tests. Secondly, the effects of the uncertainties associated with the pumping rates and the hydraulic conductivity field on the 3D density-dependent transient model were analysed separately and then jointly. The forecasts of the impacts of two different management scenarios on seawater intrusion in the year 2048 were performed by means of Monte Carlo simulations, accounting for uncertainties in the input parameters as well as possible changes of the boundary conditions. Combining primary and secondary data allowed maps of pumping rates and the hydraulic conductivity field to be constructed, despite a lack of direct data. The results of the stochastic long-term forecasts showed that, most probably, the Korba aquifer will be subject to important losses in terms of regional groundwater resources.  相似文献   

Coupled modeling of thermics and hydrogeology with the Cast3M code: application to the Rainbow hydrothermal field (Mid-Atlantic Ridge, 36°14′N)     

Florian Perez  Claude Mügler  Philippe Jean-Baptiste  Jean Luc Charlou 《Computational Geosciences》2013,17(2):217-237

We present a new numerical tool developed in the Cast3M software framework to model hydrothermal circulation. Thermodynamic properties of one-phase pure water are calculated from the International Association for the Properties of Water and Steam formulation. This new numerical tool is validated on several test cases of convection in closed-top and open-top boxes. Simulations of hydrothermal circulation in a homogeneous-permeability porous medium also give results in good agreement with already published simulations. This new numerical tool is used to construct a geometric and physical conceptual model of the Rainbow vent site at 36°14^′N on the Mid-Atlantic Ridge. Several configurations are discussed, showing that high temperatures and high mass fluxes measured at the Rainbow site cannot be modeled with hydrothermal circulation in a homogeneous-permeability porous medium. These high values require the presence of a fault or a preferential pathway right below the venting site. We propose and discuss a two-dimensional single-pass model that allows us to simulate both high temperatures and high mass fluxes. This modeling of the hydrothermal circulation at the Rainbow site constitutes the first but necessary step to understand the origin of high concentrations of hydrogen issued from this ultramafic-hosted vent field.  相似文献