Thermophilic Sulfate Reduction in Hydrothermal Sediment of Lake Tanganyika, East Africa

In environments with temperatures above 60 degrees C, thermophilic prokaryotes are the only metabolically active life-forms. By using the (SO42-)-S-35 tracer technique, we studied the activity of sulfate-reducing microorganisms (SRM) in hot sediment from a hydrothermal vent site in the northern part of freshwater Lake Tanganyika (East Africa). Incubation of slurry samples at 8 to 90 degrees C demonstrated meso- and thermophilic sulfate reduction with optimum temperatures of 34 to 45 degrees C and 56 to 65 degrees C, respectively, and with an upper temperature limit of 80 degrees C. Sulfate reduction was stimulated at all temperatures by the addition of short-chain fatty acids and benzoate or complex substrates (yeast extract and peptone). A time course experiment showed that linear thermophilic sulfate consumption occurred after a lag phase (12 h) and indicated the presence of a large population of SRM in the hydrothermal sediment. Thermophilic sulfate reduction had a pH optimum of about 7 and was completely inhibited at pH 8.8 to 9.2. SRM could be enriched from hydrothermal chimney and sediment samples at 60 and 75 degrees C. In lactate-grown enrichments, sulfide production occurred at up to 70 and 75 degrees C, with optima at 63 and 71 degrees C, respectively. Several sporulating thermophilic enrichments were morphologically similar to Desulfotomaculum spp. Dissimilatory sulfate reduction in the studied hydrothermal area of Lake Tanganyika apparently has an upper temperature limit of 80 degrees C

GMSB SUSY Models with Non Pointing Photons Signatures in ATLAS at the LHC

The reconstruction of non pointing photons is a key feature for studying Gauge Mediated Supersymmetry Breaking (GMSB) models at the LHC. In this note the photon angular resolution of the ATLAS electromagnetic calorimeter is characterized from a detailed simulation of the detector. Resulting performance are used to reconstruct GMSB events with a fast simulation program, taking into account reconstruction effects. Finally, the sensitivity in extracting the sparticles masses and the lightest neutralino lifetime is estimated

Reconstruction de photons non pointants avec ATLAS dans le cadre de théories SUSY GMSB

La reconstruction des photons non pointants est un point essentiel pour étudier les modèles de brisure de supersymmétrie par médiation de jauge au LHC. Dans cet article la résolution angulaire sur la mesure de la direction de photons non pointants, avec le calorimètre électromagnétique du détecteur ATLAS, est étudié

Experimental studies of trophic relationships between marine bacteria and bivalve molluscs

The importance of bacteria in the feeding of marine bivalves has been demonstrated by several authors. Some examples of good growth of molluscs were noted on a bacterial diet only. But, while the intense filtration of bacteria by molluscs has been observed, the exact role of bacteria in the nutrition of bivalves was not completely known. The filtered particles were sometimes eliminated as pseudofaeces, without any intestinal transit. On the other hand, live cells could also pass through the gut without being degested. To study in detail the fate of bacterial cells distributed as food to young bivalves, we used a new method which combines histology and scanning electron microscopy. This made it possible to observe, on serial histological sections of whole animals, the gut content and the condition of the ingested cells at the different levels of the intestinal tract. The ingestion and digestion by young mussels (Mytilus edulis) of some marine bacterial strains belonging to different taxonomic groups were studied by this method. Thus, partially digested bacterial cells were observed in the stomach, when the hind gut contained undamaged cells, three hours after food distribution. The results obtained for all the strains we tested are presented and discussed in this paper

Imaging of the Shell Galaxies NGC 474 and NGC 7600, and Implications for their Formation

We present photometric observations of two shell galaxies, NGC 474 and NGC 7600. We examine the photometric colours and surface brightnesses of the shells and their host galaxies, and the isophotal parameters of each galaxy. In the case of NGC 474, we find that the shell formation is consistent with a merger origin although it is possible that the close companion NGC 470 is contributing to the shell system via mass transfer. NGC 7600 exhibits shell geometry and colours which also favour a merger origin.Comment: Accepted by MNRA

Experimental silicification of the extremophilic Archaea Pyrococcus abyssi and Methanocaldococcus jannaschii: applications in the search for evidence of life in early Earth and extraterrestrial rocks

International audienceHydrothermal activity was common on the early Earth and associated micro-organisms would most likely have included thermophilic to hyperthermophilic species. 3.5–3.3 billion-year-old, hydrothermally influenced rocks contain silicified microbial mats and colonies that must have been bathed in warm to hot hydrothermal emanations. Could they represent thermophilic or hyperthermophilic micro-organisms and if so, how were they preserved? We present the results of an experiment to silicify anaerobic, hyperthermophilic micro-organisms from the Archaea Domain Pyrococcus abyssi and Methanocaldococcus jannaschii, that could have lived on the early Earth. The micro-organisms were placed in a silica-saturated medium for periods up to 1 year. Pyrococcus abyssi cells were fossilized but the M. jannaschii cells lysed naturally after the exponential growth phase, apart from a few cells and cell remains, and were not silicified although their extracellular polymeric substances were. In this first simulated fossilization of archaeal strains, our results suggest that differences between species have a strong influence on the potential for different micro-organisms to be preserved by fossilization and that those found in the fossil record represent probably only a part of the original diversity. Our results have important consequences for biosignatures in hydrothermal or hydrothermally influenced deposits on Earth, as well as on early Mars, as environmental conditions were similar on the young terrestrial planets and traces of early Martian life may have been similarly preserved as silicified microfossils

Adaptive density estimation for stationary processes

We propose an algorithm to estimate the common density $s$ of a stationary process $X_1,...,X_n$. We suppose that the process is either $\beta$ or $\tau$-mixing. We provide a model selection procedure based on a generalization of Mallows' $C_p$ and we prove oracle inequalities for the selected estimator under a few prior assumptions on the collection of models and on the mixing coefficients. We prove that our estimator is adaptive over a class of Besov spaces, namely, we prove that it achieves the same rates of convergence as in the i.i.d framework