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International audienceInteractions between cementitious materials and claystone are driven by chemical gradients in pore water and might lead to mineralogical modifications in both materials. In the context of a radioactive waste repository, this alteration might influence safety-relevant clay properties like swelling pressure, permeability, or specific retention. In this study, interfaces of Opalinus Clay, a potential host-rock in Switzerland, and three concrete formulations emplaced in the Cement-Clay Interaction (CI) Experiment at the Mont Terri Underground Laboratory (St. Ursanne, Switzerland) were analysed after 2.2 years of interaction. Sampling techniques with interface stabilisation followed by inclined intersection drilling were developed. Element distribution maps of the concrete-clay interfaces show complex zonations like sulphur enrichment, zones depleted in Ca but enriched in Mg, strong Mg enrichment adjacent to the interface, or carbonation. Consistently, the carbonated zone shows a reduced porosity. Properties of the complex zonation strongly depend on cement properties like water content and pH (ordinary Portland cement vs. low-pH cement). An increased Ca or Mg content in the first 100 lm next to the interface is observed in Opalinus Clay. The cation occupancy of clay exchanger phases next to the ordinary Portland cement interface is depleted in Mg, but enriched in Na, whereas porosity shows no changes at all. The current data suggests migration of CO2=HCO 3 , SO2 4 , and Mg species from clay into cement. pH decrease in the cement next to the interface leads to instability of ettringite, and the sulphate liberated diffuses towards higher pH regions (away from the interface), where additional ettringite can form

The Opalinus Clay formation will host geological nuclear waste repositories in Switzerland. It is expected that gas pressure will build-up due to hydrogen production from steel corrosion, jeopardizing the integrity of the engineered barriers. In an in situ experiment located in the Mont Terri Underground Rock Laboratory, we demonstrate that hydrogen is consumed by microorganisms, fuelling a microbial community. Metagenomic binning and metaproteomic analysis of this deep subsurface community reveals a carbon cycle driven by autotrophic hydrogen oxidizers belonging to novel genera. Necromass is then processed by fermenters, followed by complete oxidation to carbon dioxide by heterotrophic sulfate-reducing bacteria, which closes the cycle. This microbial metabolic web can be integrated in the design of geological repositories to reduce pressure build-up. This study shows that Opalinus Clay harbours the potential for chemolithoautotrophic-based system, and provides a model of microbial carbon cycle in deep subsurface environments where hydrogen and sulfate are present.

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Rhizobactin 1021, a novel siderophore from the nitrogen-fixing alfalfa symbiont Rhizobium meliloti 1021, was isolated and structurally characterized by a combination of chemical and spectroscopic techniques. The compound is a citrate derivative in which the distal carboxyl groups of the molecule are amide linked to two different side chains.One of these is 1 -amino-3-(N-hydroxy-N-acetylamino)propane, and the other is l-amino-3-(N-hydroxy-N-(E)-2-deceny1amino)propane. The structure of rhizobactin 1021 was determined as (E)-4-[ [3-(acetylhydroxyamino)propyl]amino]-2-hydroxy-2-[2-[ 3-[hydroxy( 1-oxo-2-decenyl)amino]propyl]amino]-2-oxoethyl]-4-oxobutanoic acid. Ferric rhizobactin 1021 exists in solution predominantly in the A configuration, in an apparent equilibrium between a monomeric and a dimeric species.Iron is essential for virtually all forms of life, and microorganisms have evolved elaborate and tightly regulated systems for its uptake. These systems are compatible with the extremely low solubility of polymeric ferric oxyhydroxides at neutral pH in an oxidizing atmosphere (Ks = 10-38, [Fe3+] = I W 7 M) and the ability of iron ions to catalyze radical-producing reactions.1.2 The extracellular components of these high-affinity iron acquisition systems are known as siderophores, Fe(II1)-specific ligands that are excreted and, upon chelation, diffuse back to the cell surface and reenter the cell via outer membrane ferric siderophore receptor^.^ In host-dependent environments, microorganisms face the additional obstacle of iron-withholding mechanisms$ for endosymbiontic rhizobia, part of the life cycle involves invasion, growth, and differentiation within plant tissue.5Rhizobium meliloti is an endosymbiont of Medicago sativa (alfalfa) and, like other rhizobia, induces nodule formation in the root cortex of its legume host.5 Dinitrogen fixation is catalyzed by bacteroids in the nodules, and since both nitrogenase and leghemoglobin,s as well as regulatory proteins related to nitrogen fixation: contain iron, a satisfactory supply of this element is essential.'The hexadentate siderophore rhizobactin, a complexone type compound from R . meliloti DM-4, has been structurally char-' Present address: