Habitability on Mars from a Microbial Point of View

International audienceExtraterrestrial habitability is a complex notion. We briefly review what is known about the origin of life on Earth, that is, life based on carbon chemistry and water. We then discuss habitable conditions (past and present) for established life and for the survival of microorganisms. Based on these elements, we propose to use the term habitable only for conditions necessary for the origin of life, the proliferation of life, and the survival of life. Not covered by this term would be conditions necessary for prebiotic chemistry and conditions that would allow the recognition of extinct or hibernating life. Finally, we apply this concept to the potential emergence of life on Mars where suitable conditions for life to start, proliferate, and survive have been heterogeneous throughout its history. These considerations have a profound impact on the nature and distribution of eventual traces of martian life, or any precursor, and must therefore inform our search-for-life strategies. Key Words: Mars-- Microbial life--Punctuated habitabilit

Exogenic origin of prebiotic amino acids

Cette étude vise à conforter l’apport de matière organique extraterrestre via les météorites et les micrométéorites. Elle permet de mieux cerner les conditions dans lesquelles les molécules organiques, synthétisées dans l’espace, ont contribué à l’émergence de la vie sur Terre il y a environ quatre milliards d’années. Pour cela, des molécules organiques ont été exposées aux conditions de l’espace à bord de la station spatiale internationale et également irradiées en laboratoire lors d’expériences au sol. Par ailleurs, des molécules organiques associées à une argile, ont été soumises à des chocs mécaniques pour simuler des impacts météoritiques. Des acides aminés et des dipeptides ont été choisis pour ces études en raison de leur intérêt prébiotique et de la diversité des groupements fonctionnels qu’ils offrent. Des méthodes de fonctionnalisation pour l’analyse chirale ou non chirale de ces molécules par chromatographie gazeuse couplée à un spectromètre de masse ont été développées. Les expériences démontrent que la résistance des molécules à l’irradiation et à l’impact est fonction de la nature chimique des composés. De ce fait, le transport dans l’espace et l’impact météoritique pourraient servir de filtres moléculaires en favorisant certaines molécules au détriment d’autres.This study concerns the transport to Earth of exogenic organic matter by meteorites or micrometeorites in order to better determine the conditions under which organic molecules synthesized in space contributed to the emergence of the life on Earth four billion years ago or more. Organic molecules were exposed to space conditions on board the international space station as well as in laboratory experiments. Moreover, simulated meteorite impacts on organic molecules associated with a clay were carried out to determine the survival of the organic components. Amino-acids and dipeptides were selected for these studies because of their prebiotic interest and for the diversity of their functional groups. Methods of derivatization for chiral and not chiral analysis of these molecules by gas chromatography coupled to a mass spectrometer were developed. The results of the experiments show that the resistance of the molecules to irradiation and to impact is a function of their chemical nature, and that transport in the space environment as well meteoritic impact could be used as molecular filters by favouring the survival of certain molecules rather than others

Conformational Transition of Acidic Peptides Exposed to Minerals in Suspension

International audienceMineral surfaces probably participated in the chemical processes which led to life in the primitive oceans. The ordered conformations of simple acidic peptides exposed to insoluble minerals are described. Alternating poly(Glu-Leu) adopts a random coil conformation in water due to charge repulsion. The polypeptide extracts cations from insoluble crystalline CdS or molybdenum and adopts an ordered conformation. CdS leads to the formation of beta-sheets whereas molybdenum leads to alpha-helices. Peptides with at least 10-amino acids are necessary to exhibit a significative adsorption onto the surface. Under the same conditions, montmorillonite adsorbs the polypeptide but does not induce any conformational change

Origine exogène des acides aminés prébiotiques

Cette étude vise à conforter l apport de matière organique extraterrestre via les météorites et les micrométéorites. Elle permet de mieux cerner les conditions dans lesquelles les molécules organiques, synthétisées dans l espace, ont contribué à l émergence de la vie sur Terre il y a environ quatre milliards d années. Pour cela, des molécules organiques ont été exposées aux conditions de l espace à bord de la station spatiale internationale et également irradiées en laboratoire lors d expériences au sol. Par ailleurs, des molécules organiques associées à une argile, ont été soumises à des chocs mécaniques pour simuler des impacts météoritiques. Des acides aminés et des dipeptides ont été choisis pour ces études en raison de leur intérêt prébiotique et de la diversité des groupements fonctionnels qu ils offrent. Des méthodes de fonctionnalisation pour l analyse chirale ou non chirale de ces molécules par chromatographie gazeuse couplée à un spectromètre de masse ont été développées. Les expériences démontrent que la résistance des molécules à l irradiation et à l impact est fonction de la nature chimique des composés. De ce fait, le transport dans l espace et l impact météoritique pourraient servir de filtres moléculaires en favorisant certaines molécules au détriment d autres.This study concerns the transport to Earth of exogenic organic matter by meteorites or micrometeorites in order to better determine the conditions under which organic molecules synthesized in space contributed to the emergence of the life on Earth four billion years ago or more. Organic molecules were exposed to space conditions on board the international space station as well as in laboratory experiments. Moreover, simulated meteorite impacts on organic molecules associated with a clay were carried out to determine the survival of the organic components. Amino-acids and dipeptides were selected for these studies because of their prebiotic interest and for the diversity of their functional groups. Methods of derivatization for chiral and not chiral analysis of these molecules by gas chromatography coupled to a mass spectrometer were developed. The results of the experiments show that the resistance of the molecules to irradiation and to impact is a function of their chemical nature, and that transport in the space environment as well meteoritic impact could be used as molecular filters by favouring the survival of certain molecules rather than others.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF

Preferential beta-sheet structuration of multiconformational poly(Glu-Leu) by metallic ions

International audienc

Conformational variety of polyanionic peptides at low salt concentrations.

International audienceSequential oligo- and polypeptides based on glutamic acid and leucine residues have been synthesized. In pure water, they exhibit a random coil conformation. Addition of very small amounts of divalent metallic cations induces the formation of ordered structure in the peptides which remain in solution. Higher salt concentrations precipitate the peptides. Polypeptides with alternating glutamic acid and leucine residues undergo a coil to beta-sheet transition in the presence of Ca2+, Ba2+, Mn2+, Co2+, Zn2+ and Hg2+. Addition of Cu2+ or Fe3+ induces the formation of an alpha-helix. Solid amorphous CdS generates water soluble beta-sheets, as well. Sequential poly(Leu-Glu-Glu-Leu) adopts an alpha-helix in the presence of divalent cations. The sequence-dependent conformational diversity was extended to poly(Asp-Leu) and poly(Leu-Asp-Asp-Leu)

Salt-dependent conformational diversity of alternating poly (Glu-Leu)

International audienc

Separation of amino acid enantiomers via chiral derivatization and non chiral column by gas chromatography

Two GC-MS methods for the enantioselective separation of the 20 proteinogenic amino acids are compared. Ethyl chloroformate and 2-chloropropanol were used to derivatize amino acid enantiomers. The diastereomers formed were separated on a non-chiral column by capillary gas chromatography. The separation performances were compared to those obtained when using non-chiral derivatization on a chiral column

La RMN, un outil pour la métabolomique

International audienc

Prediction of Huntingon's Disease by Metabolomic NMR Analyzes: Studies in Drosophila Model

International audienc