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Limites moléculaires de la vie en conditions extraterrestres : biosystèmes extrêmophiles sous haute pression et haute salinité

Abstract : Astrobiology is an interdisciplinary field studying life in the Universe. Among its subjects, it questions the limits of life and the habitability of extraterrestrial environments. Close to these limits, terrestrial extremophiles thriving in extreme environments such as hydrothermal vents and the Dead Sea indicate that liquid water remains a sine qua non condition for life. Hence, its research within the Solar System and beyond is of particular astrobiological importance, rising interest in the subglacial oceans of icy moons as well as Martian brines.Subglacial oceans contain, by far, most of the liquid water in the Solar System and several such as Enceladus could also have abyssal hydrothermal vents. On Earth, hydrothermal vents are autonomous, complex and productive biotopes in spite of their characteristic extreme pressure and temperature conditions. Hence, they represent essential model of putative life on the icy moons. However, such analogy is limited by differences of physical and chemical conditions. In particular, pressure in the abysses of Europa could exceed those encountered in the terrestrial abyssal hydrothermal vents. Is life compatible with such conditions?With a first project, we studied effects of high pressure (HP) at a molecular scale using the B DNA polymerase (DNApol) of hyperthermophilic abyssal archaeon Pyrococcus abyssi as a main model. By using various fluorescent probes and a fluorimeter coupled with a HP-cell, we monitored effects of pressure ranging from 0.1 to 100MPa on the activity of this enzyme and we compared its sensitivity to HP to other thermostable DNApols. We demonstrate that HP directly inhibits activity of DNApols and that this inhibition can be largely compensated by an increase of temperature. The implications for astrobiology and pressure-adaptation of deep-sea organisms are discussedAnother environment of the Solar System closer to the Earth could have liquid water: Martian brines. Whether transitory on the surface or more perennial in the subsurface, these brines are characterized by high salinity and abundancy of chaotropic ions such as Mg2+, Ca2+ and ClO42-. On Earth, hypersaline environments such as the Dead Sea or abyssal brine basins are inhabited by specialized halophilic microorganisms. The most extreme halophiles are archaea from the Halobacteria class displaying specific traits, such as intracellular accumulation of KCl and protein acidification, and represent essential astrobiological models.In this second project, we compared properties of the whole proteomes, rather than model isolated proteins, between five strains of hyperhalophilic archaea isolated from various environments. This comparison was made using various methods, such as statistical analysis of protein sequences, quantification of intracellular ions or neutron scattering, and allowed the development of a method for characterizing salt-dependency of proteome. We revealed significative differences in intrinsic properties of proteomes and intracellular environment related to the link between environmental and molecular adaptations in halophiles. Proteome response to salts that are abundant in Martian brines also presented astrobiological implications for the search of biomarkers on Mars.
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Submitted on : Wednesday, May 25, 2022 - 10:30:31 AM
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  • HAL Id : tel-03678038, version 1

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Lorenzo Carré. Limites moléculaires de la vie en conditions extraterrestres : biosystèmes extrêmophiles sous haute pression et haute salinité. Biologie structurale [q-bio.BM]. Université Grenoble Alpes [2020-..], 2022. Français. ⟨NNT : 2022GRALV006⟩. ⟨tel-03678038⟩

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