Sedimentological imprint on subseafloor microbial communities in Western Mediterranean Sea Quaternary sediments

An interdisciplinary study was conducted to evaluate the relationship between geological and paleoenvironmental parameters and the bacterial and archaeal community structure of two contrasting subseafloor sites in the Western Mediterranean Sea (Ligurian Sea and Gulf of Lion). Both depositional environments in this area are well-documented from paleoclimatic and paleooceanographic point of views. Available data sets allowed us to calibrate the investigated cores with reference and dated cores previously collected in the same area, and notably correlated to Quaternary climate variations. DNA-based fingerprints showed that the archaeal diversity was composed by one group, Miscellaneous Crenarchaeotic Group (MCG), within the Gulf of Lion sediments and of nine different lineages (dominated by MCG, South African Gold Mine Euryarchaeotal Group (SAGMEG) and <i>Halobacteria</i>) within the Ligurian Sea sediments. Bacterial molecular diversity at both sites revealed mostly the presence of the classes <i>Alphaproteobacteria</i>, <i>Betaproteobacteria</i> and <i>Gammaproteobacteria</i> within <i>Proteobacteria</i> phylum, and also members of <i>Bacteroidetes</i> phylum. The second most abundant lineages were <i>Actinobacteria</i> and <i>Firmicutes</i> at the Gulf of Lion site and <i>Chloroflexi</i> at the Ligurian Sea site. Various substrates and cultivation conditions allowed us to isolate 75 strains belonging to four lineages: <i>Alpha-</i>, <i>Gammaproteobacteria</i>, <i>Firmicutes</i> and <i>Actinobacteria</i>. In molecular surveys, the <i>Betaproteobacteria</i> group was consistently detected in the Ligurian Sea sediments, characterized by a heterolithic facies with numerous turbidites from a deep-sea <i>levee</i>. Analysis of relative betaproteobacterial abundances and turbidite frequency suggested that the microbial diversity was a result of main climatic changes occurring during the last 20 ka. Statistical direct multivariate canonical correspondence analyses (CCA) showed that the availability of electron acceptors and the quality of electron donors (indicated by age) strongly influenced the community structure. In contrast, within the Gulf of Lion core, characterized by a homogeneous lithological structure of upper-slope environment, most detected groups were <i>Bacteroidetes</i> and, to a lesser extent, <i>Betaproteobacteria</i>. At both site, the detection of <i>Betaproteobacteria</i> coincided with increased terrestrial inputs, as confirmed by the geochemical measurements (Si, Sr, Ti and Ca). In the Gulf of Lion, geochemical parameters were also found to drive microbial community composition. Taken together, our data suggest that the palaeoenvironmental history of erosion and deposition recorded in the Western Mediterranean Sea sediments has left its imprint on the sedimentological context for microbial habitability, and then indirectly on structure and composition of the microbial communities during the late Quaternary

Computational Fluid Dynamics Applied to Chemical Reaction Engineering

Computational Fluid Dynamics (CFD) and its applications have developed quite rapidly during the last ten years. This fast growing hybrid branch of Mechanics and Mathematics is certainly to be considered as a potentially useful and efficient tool in the field of Chemical Engineering and more specifically in the area of Chemical Reaction Engineering (CRE). The difficulties in this new approach stems from the consequence of the complexity of the mechanims to be simulated simultaneously : fluid dynamics, chemical reactions and physical aspects of each system considered. Another difficulty comes from the numerical treatment of the equations for the final model, resulting in very sophisticated and diversified mathematical treatments. The types of chemical reactors to be considered for potential performance improvements when applying CFD as a new tool for their design are numerous ; two broad classes of problem have be identified as relevant to this new approach :(a) Systems involving fast chemical reactions, with characteristic times of the same order of magnitude as the characteristic time scales of turbulence. In-line mixing equipment should preferably be studied for this type of reactions. (b) Multiphase systems, whose scaling-up still has to be performed with great difficulty and, more often than not, according to empirical procedures based on very simplified models. When looking at the various types of systems found in practice, it appears that gas-liquid and fluid-solid systems should be considered first. However, basic knowledge is still missing concerning the physical behaviour of these systems, especially for the coalescence of bubbles and the momentum transfer between gas and solid. Specific research should be done in order to get this missing information. Presently there are a certain number of existing CFD software packages available commercially or developed by various research laboratories. This is certainly an interesting starting point, but we can never be sure that the numerical results given by any of these software packages are applicable to a practical industrial case, without checking these results in one way or another. There is quite general agreement on the necessity of obtaining experimental data concerning problem examples, in order to check and compare the computation results of the various software packages proposed for dealing with these specific problems. On the experimental side, there are a great deal of measurement methods able to give local values of temperature, pressure, velocities, concentrations of chemical species, phases ratio, size of bubbles, drops or particles, as well as to produce an overall visualization of flows. We have mentioned the difficulties linked to the mathematical treatment of the equations written for simulating reactive flows. As usually done in CFD, for most problems encountered, a first useful solution can be obtained by limitingthe modelto oneortwospace dimensions (1D or 2D). However, very often it will be necessary not only to solve the 3D simulation set of equations, but also to achieve the unstationary solution of the same equations in order to really represent the true behaviour of the physical system. This last objective means much more complicated research, especially from the mathematical point of view

Distillation principes de calcul et de contrôle

Cet article présente les principes de base utilisés lors de la conception et de la conduite des colonnes à distiller continues ou discontinues. Dans cet exposé d'initiation le cas des mélanges binaires est seul considéré de manière à ne pas compliquer inutilement la présentation. Par contre pour conserver à cette étude un aspect pratique, la dernière partie est consacrée aux problèmes technologiques et aux principales solutions mises en oeuvre

Méthodologie de l'extrapolation des réacteurs chimiques

Après un exposé général relatif à la méthodologie du développement des procédés, applicable à l'extrapolation des réacteurs, est présenté un rapide examen critique des deux principales techniques mises en oeuvre, à savoir : - la théorie de la similitude ; - l'élaboration de modèles mathématiques. Deux exemples pratiques, relatifs aux réacteurs homogènes et aux réacteurs catalytiques à lit fixe et deux phases fluides, sont ensuite examinés à la lumière des considérations générales précédentes

Procédé de détection et de quantification de molécules immobilisés sur support solide

Invention reposant sur une nouvelle méthodologie de caractérisation dans le domaine des matériaux aminés. Procédé colorimétrique innovant reposant sur une intéraction spécifique NH2 - colorant et une étape de décoloration de performance inégalée à ce jour