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Orange F.,CNRS Center for Molecular Biophysics | Orange F.,Observatoire Des Science Of Lunivers En Region Center | Chabin A.,CNRS Center for Molecular Biophysics | Gorlas A.,University of Western Brittany | And 7 more authors.
Biogeosciences | Year: 2011

The role of viruses at different stages of the origin of life has recently been reconsidered. It appears that viruses may have accompanied the earliest forms of life, allowing the transition from an RNA to a DNA world and possibly being involved in the shaping of tree of life in the three domains that we know presently. In addition, a large variety of viruses has been recently identified in extreme environments, hosted by extremophilic microorganisms, in ecosystems considered as analogues to those of the early Earth. Traces of life on the early Earth were preserved by the precipitation of silica on the organic structures. We present the results of the first experimental fossilisation by silica of viruses from extremophilic Archaea (SIRV2 - Sulfolobus islandicus rod-shaped virus 2, TPV1 - Thermococcus prieurii virus 1, and PAV1 - Pyrococcus abyssi virus 1). Our results confirm that viruses can be fossilised, with silica precipitating on the different viral structures (proteins, envelope) over several months in a manner similar to that of other experimentally and naturally fossilised microorganisms. This study thus suggests that viral remains or traces could be preserved in the rock record although their identification may be challenging due to the small size of the viral particles. © Author(s) 2011.


Dudok de Wit T.,Observatoire Des Science Of Lunivers En Region Center
Contributions to Plasma Physics | Year: 2011

Multipoint or multichannel observations in plasmas can frequently be modelled as an instantaneous mixture of contributions (waves, emissions, ...) of different origins. Recovering the individual sources from their mixture then becomes one of the key objectives. However, unless the underlying mixing processes are well known, these situations lead to heavily underdetermined problems. Blind source separation aims at disentangling such mixtures with the least possible prior information on the sources and their mixing processes. Several powerful approaches have recently been developed, which can often provide new or deeper insight into the underlying physics. This tutorial paper briefly discusses some possible applications of blind source separation to the field of plasma physics, in which this concept is still barely known. Two examples are given. The first shows how concurrent processes in the dynamical response of the electron temperature in a tokamak can be separated. The second example deals with solar spectral imaging in the Extreme UV and shows how empirical temperature maps can be built. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zocatelli R.,CNRS Earth Sciences Institute of Orléans | Zocatelli R.,Federal University of Fluminense | Moreira-Turcq P.,CIRAD - Agricultural Research for Development | Bernardes M.,Federal University of Fluminense | And 6 more authors.
Organic Geochemistry | Year: 2013

A multi-proxy study has been performed on a sediment core from the Curuai floodplain, Central Amazonia. The combination of elemental, isotopic and molecular analysis of a 110. cm core (a record of ca. the last 100. yr) allowed reconstruction of the hydrological conditions of organic matter (OM) deposition. Two units could be delineated. The first (UI) was composed of three sub-units: UIa (0-15. cm), composed of highly degraded organic particles originating from the surrounding soil and indicative of restricted transport; UIb (15-48. cm), during which the region was permanently flooded and the material stored came from soil runoff, mainly from alluvial forest; and UIc (48-88. cm) composed of material from Amazon River suspended sediment, itself originating from OM degradation in forest soil. In UII (88-111. cm), the OM originated mainly from the forest soil and other plant remains in the floodplain. The data reveal that, during the four distinct depositional periods, the sedimentary OM alternated between land derived soil and alluvial vegetation due to changes in hydrodynamics. © 2013 Elsevier Ltd.


Orange F.,CNRS Center for Molecular Biophysics | Orange F.,Observatoire Des Science Of Lunivers En Region Center | Orange F.,University of Orléans | Orange F.,French National Center for Scientific Research | And 10 more authors.
Geomicrobiology Journal | Year: 2014

Recent experiments to fossilize microorganisms using silica have shown that the fossilization process is far more complex than originally thought; microorganisms not only play an active role in silica precipitation but may also remain alive while silica is precipitating on their cell wall. To better understand the mechanisms that lead to the preservation of fossilized microbes in recent and ancient rocks, we experimentally silicified a Gram-positive bacterium, Geobacillus SP7A, over a period of five years. The microbial response to experimental fossilization was monitored with the use of LIVE/DEAD staining to assess the structural integrity of the cells during fossilization. It documented the crucial role of silicification on the preservation of the cells and of their structural integrity after several years. Electron microscopy observations showed that initial fossilization of Gram-positive bacteria was extremely rapid, thus allowing very good preservation of Geobacillus SP7A cells. A thick layer of silica was deposited on the outer surface of cell walls in the earliest phase of silicification before invading the cytoplasmic space. Eventually, the cell wall was the only recognizable feature. Heavily mineralized cells thus showed morphological similarities with natural microfossils found in the rock record. © 2014 Copyright © Taylor & Francis Group, LLC.

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