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International audience; Sur de nombreux sites miniers, la stabilisation de résidus par des végétaux permettrait de réduire les risques associés aux transfert des métaux et métalloïdes potentiellement toxiques. Le projet Phytoselect (Région Centre-Val-de-Loire 2016-00108485) a pour objectif de développer une stratégie de re-fonctionnalisation d'un technosol minier par le développement d'un couvert végétal. Le site choisi est une ancienne mine d'argent et plomb (Pontgibaud) présentant des résidus acides (pH ~ 4) et riches en plomb (25 000 mg/kg), arsenic et baryum (environ 1000 mg/kg). Des microcosmes ont été préparés sous conditions contrôlées avec le résidu et deux amendements: du fumier de vache (source de nutriments pour les plantes), et une boue riche en oxy-hydroxydes de fer, susceptible de fixer l'arsenic et les métaux. Les conditions testées étaient les suivantes : résidu sans amendement; résidu + 5% de boue; résidu + 5% boue + 0,15% fumier; résidu + 5% boue + 1% fumier; résidu + 5% boue + 2% fumier. Parallèlement au suivi de la mobilité des polluants, l'effet des amendements sur les activités métaboliques potentielles du résidu a été évalué avec des microplaques Ecolog®. La croissance du raygrass a été testée sur les sols amendés et incubés pendant 1 mois. Tous les amendements ont accru et modifié l'activité métabolique présentant une valeur maximale après 1 mois d'incubation avec 2% de fumier. Les polymères sont les substrats les plus utilisés, suggérant la présence d'une communauté microbienne spécialisée. La croissance du raygrass a modifié le profil métabolique de la microflore, qui consomme davantage des substrats simples. En présence de plantes, la microflore la plus active est celle du résidu amendé avec la boue et 1% de fumier. Ces amendements représentent des perspectives intéressantes pour stabiliser la pollution en fixant les contaminants métalliques et métalloïdes tout en favorisant la croissance de plantes et l'activité microbienne.

International audience; In mining sites, the dispersion of solid particles of tailings, induces a risk of dispersion of toxic elements, in addition with potential pollution of groundwater and surface water through leaching. The development of a vegetal cover is one of the potential options to decrease the risks. However, the growth of plants on mine tailings is generally hampered by several parameters: acidity, lack of nutrients, poor texture and toxicity of metals and metalloids. Thus, amendments are necessary to overcome these limitations. A mine tailing material was sampled on a former silver and lead mining site. Chemical analysis indicated the following concentrations in pollutants: 26 432 mg.kg-1 Pb, 265 mg.kg-1 Zn, 1 063 mg.kg-1 Ba, 1134 mg.kg-1 As. The tailing is acidic, siliceous and coarse (76% of particles with size in the range of 315 µm - 2 mm). A cow manure and some ochre (iron oxide-hydroxide) material produced in the water treatment plant of a coal mine were tested, alone or in combination, to stabilize the most mobile toxic pollutant, Pb, while avoiding the mobilization of other toxic elements. Leaching and microcosm experiments were performed and showed that the Pb concentration in water, that was higher than 10 mg.L-1 with the not-amended tailing, was decreased by a factor ×100, while As, Zn and Ba concentration did not increase significantly. Ochre (added at 5% in weight/weight) allowed increasing pH and could adsorb some metals and metalloïds. The metabolic microbial diversity, evaluated using Ecolog® plates, was improved by all amendements after one month of incubation. Polymers were the most used substrates in the non-planted microcosms, after one month of incubation, suggesting a specialized microbial community. Planted microcosms revealed that the growth of ryegrass was significantly improved by the addition of ochre and manure : the biomass of ryegrass is 3.5 X (with 5% ochre and 2% manure) to 4.8 X (with 5% ochre and 0.15%) greater than in the condition of plants growing on unamended soil. The next experimental step will include the monitoring of phytostabilization at metric scale, in mesocosm, with a vegetal specie naturally present on Pontgibaud mine site, belonging to the Agrostis genus.

International audience; In mining sites, the dispersion of solid particles of tailings, induces a risk of dispersion of toxic elements, in addition with potential pollution of groundwater and surface water through leaching. The development of a vegetal cover is one of the potential options to decrease the risks. However, the growth of plants on mine tailings is generally hampered by several parameters: acidity, lack of nutrients, poor texture and toxicity of metals and metalloids. Thus, amendments are necessary to overcome these limitations. A mine tailing material was sampled on a former silver and lead mining site. Chemical analysis indicated the following concentrations in pollutants: 26 432 mg.kg-1 Pb, 265 mg.kg-1 Zn, 1 063 mg.kg-1 Ba, 1134 mg.kg-1 As. The tailing is acidic, siliceous and coarse (76% of particles with size in the range of 315 µm - 2 mm). A cow manure and some ochre (iron oxide-hydroxide) material produced in the water treatment plant of a coal mine were tested, alone or in combination, to stabilize the most mobile toxic pollutant, Pb, while avoiding the mobilization of other toxic elements. Leaching and microcosm experiments were performed and showed that the Pb concentration in water, that was higher than 10 mg.L-1 with the not-amended tailing, was decreased by a factor ×100, while As, Zn and Ba concentration did not increase significantly. Ochre (added at 5% in weight/weight) allowed increasing pH and could adsorb some metals and metalloïds. The metabolic microbial diversity, evaluated using Ecolog® plates, was improved by all amendements after one month of incubation. Polymers were the most used substrates in the non-planted microcosms, after one month of incubation, suggesting a specialized microbial community. Planted microcosms revealed that the growth of ryegrass was significantly improved by the addition of ochre and manure : the biomass of ryegrass is 3.5 X (with 5% ochre and 2% manure) to 4.8 X (with 5% ochre and 0.15%) greater than in the condition of plants growing on unamended soil. The next experimental step will include the monitoring of phytostabilization at metric scale, in mesocosm, with a vegetal specie naturally present on Pontgibaud mine site, belonging to the Agrostis genus.

International audience

Critical to the origin of life are the ingredients of life, of course, but also the physical and chemical conditions in which prebiotic chemical reactions can take place. These factors place constraints on the types of Hadean environment in which life could have emerged. Many locations, ranging from hydrothermal vents and pumice rafts, through volcanic-hosted splash pools to continental springs and rivers, have been proposed for the emergence of life on Earth, each with respective advantages and certain disadvantages. However, there is another, hitherto unrecognized environment that, on the Hadean Earth (4.5–4.0 Ga), would have been more important than any other in terms of spatial and temporal scale: the sedimentary layer between oceanic crust and seawater. Using as an example sediments from the 3.5–3.33 Ga Barberton Greenstone Belt, South Africa, analogous at least on a local scale to those of the Hadean eon, we document constant permeation of the porous, carbonaceous, and reactive sedimentary layer by hydrothermal fluids emanating from the crust. This partially UV-protected, subaqueous sedimentary environment, characterized by physical and chemical gradients, represented a widespread system of miniature chemical reactors in which the production and complexification of prebiotic molecules could have led to the origin of life. Key Words: Origin of life—Hadean environment—Mineral surface reactions—Hydrothermal fluids—Archean volcanic sediments. Astrobiology 18, 259–293.

International audience; Arsenic is one of the more widespread toxic trace elements, whose presence in environment is linked either to geological background or human activities. The fate of arsenic in environmental compartments is closely linked to the microbial transformations of the inorganic species AsIII and AsV. In order to monitor the evolution of microbial As-related global activities, a simple batch test has been designed and applied. The principle of the test is based on the monitoring of oxidation of 1 mM AsIII in a basal medium inoculated with environmental samples. Results are interpreted considering of oxidation rate or rate constant, and lapse time. Several phenomena are likely to influence the global oxidation rate, such as the relative activity of diverse oxidizing microbes and the competition between oxidizing and reducing processes, in relation to organic matter bioavailability. AsIII oxidizing activities of microorganisms in eight surface soils from polluted sites were quantified with and without addition of organic substrates to the basal medium. Results suggested that AsIII oxidation rate constant was limited by the low concentration of organic substrate, this limitation being removed by supplying 0.08 g/L of organic carbon. Higher organic carbon input negatively affected AsIII oxidation rate constant. Then, the AsIII oxidizing test was applied to a soil highly polluted by the destruction of chemical weapons, simultaneously with the enumeration of AsIII-oxidizing microbes using the Most Probable Number method. Results suggested that the concentration of AsIII-oxidizing microbes was correlated with the lapse time and not with the oxidation rate. Experiments performed with a pure AsIII oxidizing bacterium confirmed a correlation between the lapse time and initial concentration of active cells, AsIII oxidation being detected when the bacterial concentration was close to 107 cells ml-1. In these conditions, the oxidation rate was independent from bacterial concentration. In a next step, the influence of microbial AsV reduction parameters will be considered.

International audience; At the end of the Great War, a large amount of unfired chemical ammunitions were burned near the former westernfrontline. This destruction resulted in locally intense soil contamination by arsenic and heavy metals. This soil was affected for 80 years by water saturation episodes and input of forest litter. To study the As behavior in this specific polluted material submitted to environmental changes, an 8-months experiment was conducted with an 1 m3 instrumented mesocosm including unsaturated, alternatively saturated and saturated levels. Arsenic speciation in water and solid compartiment was analyzed all along the experiment. Microbial characterization including bacterial identification and the determination of As(III)-oxidizing and As(V) reducing activities was performed.Figure 1: Microbial As(III)-oxidizing activity for four sample levels at the beginning and the end of the experiment.Arsenic concentration reached 132.44 ± 3.66 g.kg-1 in soil and 20-110 µM in soil solution. As(V) was the major species of soluble arsenic. Immobilization of As was observed in the saturated soil caused by As(V) adsorption onto iron oxide-hydroxides and by the precipitation of secondary arsenates. As(III)-oxidizing activity (Fig.1) and bacterial communauty structure were strongly impacted by soil saturation and the addition of organic litter. Results showed a decrease of the As III-oxidizing activity of bacteria together with a stimulation of the As V-reducing activity inducing an increase of As(III) mobility in saturated soil.

In the context of astrobiological missions to Mars, the key question is what biosignatures to search for and how? lndigenous Martian organisms, if they existed or still exist, can be classified as extremophile per se. Following this precept the FP7-funded European MASE project (Mars Analogues for Space Exploration} is investigating various aspects of anaerobic life under Mars' extreme envrionmental conditions, including the potential for preservation over long geological time periods of certain strains. In this contribution, we report on the mineralisation and preservation of Yersinia sp. in silica and gypsum, two minerals that have been reported on Mars, in cold and anaerobic conditions, similar to Martian conditions. The organism, polyextremotolerant bacterium Yersinia sp. MASE-LG-1 (hereafter named Yersinia. sp.) was isolated from the lcelandic Graenavatn Lake, an acidic (pH3), cold and oligotrophic volcanic crater lake. These organisms have a strong tolerance to diverse Mars-like stresses (Rettberg et al., 2015). We also studied the effect of physiological status on mineralisation by exposing Yersinia to two common stresses thought to have increased du ring Mars history, desiccation and radiation. The mineralisation process has been studied using microbiological (microbial viability), morphological (scanning and transmission electron microscopy), biochemical (GC-MS, Rock-Eval) and spectroscopic (FTIR and RAMAN spectroscopy) methodologies. Based on these approaches, the potential of mineralised Yersinia sp. cells to be preserved over geological time scales is also discussed. Salient results include the fact that fossilisation in gypsum solutions is slower than in silica; not all cells were mineralised, even after 6-months in the fossilising solutions, although the FTIR, Raman and SOLID biomarker signatures were lost by this time period; Rock-Eval analysis suggests that the kerogen in the fossilised strain may not survive preservation over long geological periods, although carbon molecules preserved in fossil microbial traces up to ~3.45 Ga have been detected in the rock record.

Introduction: Several decades dedicated to the study of Mars has enabled scientists to understand that, during its history, environmental conditions on early Mars strongly contrasted with the present-day conditions, hostile for life. Indeed, previous (Mars Express, Viking…) and more recent (MSL) missions confirmed that liquid water, heat (volcan-ism, hydrothermalism), organic matter, and redox conditions probably occurred on the planet, thus enabling scientists to seriously consider early Mars as being habitable ans suitable for the emergence of Martian life [1]. However, the detection of past life on Mars, if it existed, also requires that biomarkers (i) be preserved over geological time scales and that (ii) they remained detectable. Therefore, as terrestrial analogues for Mars, astrobiologists are addressing questions related to microbial adaptation, lifestyles and survival in extraterrestrial environments [2]. In this context, the European MASE project (Mars Ana-logues for Space Exploration) aims at better understand-ing habitability, microbial lifestyles and biomarker preservation in such environmental analogues. To do this, one of the goals of MASE is to better characterize the evolution and preservation of diverse biomarkers during the microbial fossilization process [3].

International audience; The search for traces of life is one of the principal objectives of Mars exploration. Central to this objective is theconcept of habitability, the set of conditions that allows the appearance of life and successful establishment ofmicroorganisms in any one location. While environmental conditions may have been conducive to the appearanceof life early in martian history, habitable conditions were always heterogeneous on a spatial scale andin a geological time frame. This ‘‘punctuated’’ scenario of habitability would have had important consequencesfor the evolution of martian life, as well as for the presence and preservation of traces of life at a specificlanding site. We hypothesize that, given the lack of long-term, continuous habitability, if martian life developed,it was (and may still be) chemotrophic and anaerobic. Obtaining nutrition from the same kinds of sourcesas early terrestrial chemotrophic life and living in the same kinds of environments, the fossilized traces of thelatter serve as useful proxies for understanding the potential distribution of martian chemotrophs and theirfossilized traces. Thus, comparison with analog, anaerobic, volcanic terrestrial environments (Early Archean>3.5–3.33 Ga) shows that the fossil remains of chemotrophs in such environments were common, althoughsparsely distributed, except in the vicinity of hydrothermal activity where nutrients were readily available.Moreover, the traces of these kinds of microorganisms can be well preserved, provided that they are rapidlymineralized and that the sediments in which they occur are rapidly cemented. We evaluate the biogenicity ofthese signatures by comparing them to possible abiotic features. Finally, we discuss the implications of differentscenarios for life on Mars for detection by in situ exploration, ranging from its non-appearance, throughpreserved traces of life, to the presence of living microorganisms. Key Words: Mars—Early Earth—Anaerobicchemotrophs—Biosignatures—Astrobiology missions to Mars. Astrobiology 15, 998–1029.

International audience; During the period from 1920 to 1928, 200,000 unfired German chemical ammunitions from World War I were broken down and open-burned near the former western Frontline. This destruction resulted in locally severe top-soil contamination by arsenic, heavy metals and dioxins and furans. The main type of shell, called “blue cross shell” were loaded high explosives coating a glass bottle containing solid diphenylchloroarsine (CLARK 1) and diphenylcyanoarsine (CLARK 2) which have released considerable amounts of arsenic oxides during their combustion. The biogeochemical behavior of arsenic is poorly documented in this type of environment. The aim of this study was to explore the arsenic speciation in relation to mineral and microbial compartments in this particular context.. Four soils were sampled presenting different levels of contamination. The concentrations of major and trace elements were analyzed by ICP-MS. In the samples, the concentration range of arsenic was 1937-72,820 mg/kg. Zinc, copper and lead reached concentrations up to 90,190 mg/kg, 9113 mg/kg and 5777 mg/kg, respectively. SEM observations and EDS analyses were performed on different grains. Results showed that the polluted material was composed of inherited minerals (silicates), charcoal and secondary phases, carrier of metals. In metal rich grains, two phases were identified : a crystalline phase, where arsenic was associated with copper and zinc, and an amorphous phase rich in iron, zinc, copper, and arsenic. Four secondary arsenate minerals were identified by X-ray diffraction: adamite and olivenite (zinc and copper arsenates, respectively) and two pharmacosiderites. Arsenic speciation displayed by SEM-EDS and XRD was proven to be directly linked to the thermal treatments of shells. Indeed, the two main As-carriers were identified as vitreous phases, composed of a blend of metals, and secondary arsenates minerals, which were formed in the material’s porosity during its cooling. AsIII and AsV concentrations were 1577 mg/kg and 70,178 mg/kg, respectively : whereas AsV was the major species, AsIII concentration was high. Microbial activities may influence the speciation and mobility of the bioavailable fraction of As, in relation with redox conditions and organic matter. Microbial characterization included total cell counts, respiration, and determination of AsIII-oxidizing and AsV reducing activities. Results showed the presence of microorganisms actively contributing to carbon and arsenic metabolims, even in the most polluted soil, thus potentially driving cycle of biovailable As on the site.

International audience; La restauration des propriétés physico-chimiques et des fonctions biologiquesd’un sol contaminé par des polluants inorganiques nécessitele plus souvent des amendements de matière organique. Cependant, lesinteractions entre la matière organique et l’activité bactérienne des solspeuvent conduire à des réactions biogéochimiques influençant la mobilitédes métaux. Quatre sols pollués, contenant d’importantes concentrationsen As et en métaux, ont été échantillonnés sur des sites industrielset miniers. Ces sols ont été incubés en condition aérobie dans del’eau, avec ou sans addition d’un mélange complexes de composés organiques.Des témoins abiotiques ont été préparés en autoclavant les sols.Les concentrations en As total, As (III), Fe, ainsi que Pb et Sb pour lesdeux sols présentant des concentrations importantes de ces éléments,ont été déterminées au début et à la fin de l’incubation. La biomasse etla diversité bactérienne ont également été évaluées en début et en find’expérience. Les résultats ont montré que, sans ajout de matière organique,les micro-organismes contribuent à diminuer les concentrationsde métaux en solution. En revanche, l’ajout de matière organique dansles incubations biotiques augmente fortement la mobilité de l’As et duPb. Dans ces conditions, seules les concentrations de Fe n’augmententpas, suggérant que la mobilisation de l’As et du Pb n’est pas liée à la bioréductiondes oxydes de fer mais à d’autres processus biogéochimiques.L’ajout de matière organique peut avoir plusieurs effets : (1) augmenterla solubilité des métaux par chélation avec des ligands organiques ;(2) influencer les métabolismes bactériens qui agissent sur la spéciationet la mobilité des métaux. Ces processus ont besoin d’être mieux comprisafin de prédire la mobilisation d’éléments toxiques dans les solspendant leur re-fonctionnalisation. Des expériences en grand volume,dans une colonne instrumentalisée, permettront de vérifier ces résultatset d’étudier le comportement d’un sol pollué dans un environnementcontrôlé. Ce travail a été réalisé dans le cadre du Labex VOLTAIREANR,10,LABX,100,01.

National audience; La restauration des propriétés physico-chimiques et des fonctions biologiques d'un sol contaminé par des polluants inorganiques nécessite le plus souvent des amendements de matière organique. Cependant, les interactions entre la matière organique et l'activité bactérienne des sols peuvent conduire à des réactions biogéochimiques influençant la mobilité des métaux. Quatre sols pollués, contenant d'importantes concentrations en As et en métaux, ont été échantillonnés sur des sites industriels et miniers. Ces sols ont été incubés en condition aérobie dans de l'eau, avec ou sans addition d'un mélange complexe de composés organiques. Des témoins abiotiques ont été préparés en autoclavant les sols. Les concentrations en As total, As (III), Fe, Pb et Sb ont été déterminées au début et à la fin de l'incubation, ainsi que la biomasse et la diversité bactérienne. Les résultats ont montré que, sans ajout de matière organique, les micro-organismes contribuent à diminuer les concentrations de métaux en solution. En revanche, l'ajout de matière organique dans les incubations biotiques augmente fortement la mobilité de l'As et du Pb. Dans ces conditions, seules les concentrations de Fe n'augmentent pas, suggérant que la mobilisation de l'As et du Pb n'est pas liée à la bioréduction des oxydes de fer mais à d'autres processus biogéochimiques. L'ajout de matière organique peut avoir plusieurs effets : (1) augmenter la solubilité des métaux par chélation avec des ligands organiques ; (2) influencer les métabolismes bactériens qui agissent sur la spéciation et la mobilité des métaux. Ces processus ont besoin d'être mieux compris afin de prédire la mobilisation d'éléments toxiques dans les sols pendant leur re-fonctionnalisation. Des expériences en grand volume, dans une colonne instrumentalisée, permettront de vérifier ces résultats et d'étudier le comportement d'un sol pollué dans un environnement contrôlé. Ce travail a été réalisé dans le cadre du Labex VOLTAIRE ANR,10,LABX,100,01.

International audience; Processes of remediation on anthropogenic polluted sites often involve the addition of organic amendments to restore soils biological functions and physic-chemical properties. However, interactions between organic matter and bacterial activities with inorganic pollutants drive many biogeochemical reactions influencing metal(loids) mobility. Incubation experiments were performed with four polluted soils sampled on industrial and mining sites all, containing high concentration of arsenic, iron, together with lead and antimony on one site. Soils were incubated in aerobic slurries, with or without addition of a complex mixture of organic substances. Abiotic controls were prepared with autoclaved soils. Arsenic speciation and concentrations of total arsenic and metals were determined at the beginning and at the end of incubation together with bacterial biomass and diversity. Results showed that without organic matter addition, micro-organisms contribute to reduce As and metal concentrations in the aqueous phase. In contrast, when organic matter was added, micro-organisms enhanced As(III), total arsenic and lead concentrations in the liquid phase. Only iron concentration was not increased by microbial activity when organic matter was added, suggesting that As and lead mobilization were not linked to bioreduction of iron oxides, but involved other biogeochemical mechanisms. The addition of organic matter may (i) enhance the solubilization by chelation of metal(loids), and/or (ii) influence bacterial activities directly influencing metal(loids) speciation and mobility. These processes need to be better understood in order to avoid mobilization of toxic elements from soils that may be enriched in organic matter, through amendment or growth of vegetal cover. This work was performed in the frame of Labex VOLTAIRE ANR,10,LABX,100,01.

International audience; La Salada de Chiprana' (NE Spain) is a permanent athalassic saline lake, and as such unique in Western Europe. More than 20 years ago, it was recognized that this lake should be protected; particularly, because it supported extensive microbial mat communities built by the cyanobacterium Coleofasciculus (Microcoleus) chthonoplastes and submerged aquatic vegetation of an endemic form of the foxtail stonewort (Lamprothamnium papulosum var. papulosum f. aragonense). For centuries, the lake hydrology, salinity and water levels have been driven by the combined effects of anthropogenic activities (e.g. irrigation in the watershed) and climatic factors. In the early 1990s, the water level increased and salinity dropped as a consequence of excessive freshwater inputs from direct overflow via irrigation canals. As a result, the microbial mats and aquatic vegetation perished and water column turbidity increased. Based on these observations, since 1994 management measures were introduced aimed at reducing the freshwater input by stopping the direct overflow from irrigation canals. This resulted in a rapid recovery of the hypersaline features of the lake, particularly of the microbial mat communities and the aquatic vegetation. Since 2000, there has been a persistent trend of decreasing lake level and increasing salinity. The population of the endemic foxtail stonewort collapsed in 2006 and the area occupied by C. chthonoplastes mats has drastically decreased. This raises the important question on how to manage athalassic saline lakes in their agrocultural context and calls for a review of the management option taken in the early 1990s. While it could be argued that the current situation is closer to natural hydrological functioning than 20 years ago, we propose that management should seek to conserve the original microbial and aquatic vegetation communities.