Influence of Uranium on Bacterial Communities: A Comparison of Natural Uranium-Rich Soils with Controls

This study investigated the influence of uranium on the indigenous bacterial community structure in natural soils with high uranium content. Radioactive soil samples exhibiting 0.26% - 25.5% U in mass were analyzed and compared with nearby control soils containing trace uranium. EXAFS and XRD analyses of soils revealed the presence of U(VI) and uranium-phosphate mineral phases, identified as sabugalite and meta-autunite. A comparative analysis of bacterial community fingerprints using denaturing gradient gel electrophoresis (DGGE) revealed the presence of a complex population in both control and uranium-rich samples. However, bacterial communities inhabiting uraniferous soils exhibited specific fingerprints that were remarkably stable over time, in contrast to populations from nearby control samples. Representatives of Acidobacteria, Proteobacteria, and seven others phyla were detected in DGGE bands specific to uraniferous samples. In particular, sequences related to iron-reducing bacteria such as Geobacter and Geothrix were identified concomitantly with iron-oxidizing species such as Gallionella and Sideroxydans. All together, our results demonstrate that uranium exerts a permanent high pressure on soil bacterial communities and suggest the existence of a uranium redox cycle mediated by bacteria in the soil

Etude par spectroscopie vibrationnelle infrarouge a transformee de Fourier du transfert d'electron dans le photosysteme II des plantes

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 79007 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Histidine oxidation in the S2 to S3 transition probed by FTIR difference spectroscopy in the Ca2+-depleted photosystem II: comparison with histidine radicals generated by UV irradiation

International audienceFTIR difference and EPR spectroscopies were used to identify the organic radical species formed during the Sz to S3 transition in Ca2+-depleted, EGTA-treated, and polypeptide-reconstituted photosystem II membranes (denoted Sz' and 83', respectively). Ferricyanide was added to the samples to act as an exogenous electron acceptor. Using EPR spectroscopy, it was shown that, under the experimental conditions used, only the species oxidized in the S3' state was detected during the time required for theacquisition of the FTIR difference spectra. No contributions from the electron acceptor side were observed. The corresponding Ss'/Sz' FTIR difference spectra were recorded at 10 °C in HzO, DzO, and with 15Nlabeled photosystem II membranes. Spectra were compared with radical-minus-neutral FTIR difference spectra of amino acid model compounds generated by UV irradiation at low temperature. Under our experimental conditions, we did not observe FTIR difference signals consistent with tyrosine oxidation in the S2' to S3' transition. The infrared signals characteristic of radical formation with 4-methylimidazole and histidine obtained by UV irradiation of 4-methylimidazolium at pH 6 and of a His-Tyr dipeptide at pH 7 are presented. The analogy found between these spectra and the Ss'/Sz' spectmm obtained in situ supports the oxidation of a histidinium in the Sz' to S3' transition

Etude des interactions protéine-métal par spectroscopie infrarouge dans le domaine des basses fréquences

L'analyse de complexes d'une hémoprotéine (MP8) par spectroscopie infrarouge (IR-TF) de différence couplée à l'électrochimie a permis d'identifier dans l'IR moyen (1800-1000 cm-1) des bandes IR sensibles à l'état redox du fer, spécifiques de l'hème, du peptide et des deux ligands axiaux imidazole et histidine. L'adaptation de l'appareillage optique a permis d'obtenir pour la première fois des spectres IR-TF de différence pour des métalloprotéines en solution dans le domaine de l'IR lointain (1000-50 cm 1), où sont détecte es les vibrations métal-ligands. L'étude dans l'IR lointain de la superoxyde dismutase et des complexes de la MP8 a permis d'attribuer les premiers modes de vibrations métal-ligands IR pour une métalloprotéine redox. Les fréquences IR de ces modes sont directement corrélées à la force des liaisons et offrent un outil expérimental fin pour l'analyse des propriétés des sites métalliques qui contrôlent la réactivité de nombreuses métalloprotéines.Structural changes accompanying the change in the redox state of the iron in various complexes of MP8, a model for hemoproteins, were studied by FT-IR difference spectroscopy coupled to electrochemistry in the mid-IR (1800-1000 cm-1). We identified IR redox heme markers, sensitive to the electronic or coordination state of the iron. The specific IR bands of the two axial ligands imidazole and histidine allowed us to provide the first direct determination of their pKa. We also modified the IR set-up to record spectra with redox metalloproteins in the far IR domain (1000-50 cm-1), wherein metal-ligand vibrations are expected to contribute. For the first time, we identified metal-ligand vibration in hemoproteins and in superoxide dismutase. The IR bands frequencies are highly dependent on the bond strength and offer a useful experimental tool to study the properties of metallic active sites that control the reactivity of various metalloproteins.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Iron Coordination in Photosystem II: Interaction between Bicarbonate and the Q B Pocket Studied by Fourier Transform Infrared Spectroscopy

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Bicarbonate binding to the non-heme iron of photosystem II, investigated by Fourier transform infrared difference spectroscopy and 13C-labeled bicarbonate.

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FTIR and EPR study of radicals of aromatic amino acids 4-methylimidazole and phenol generated by UV irradiation

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Fourier transform infrared (FTIR) spectroscopy

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Molecular Analysis by Vibrational Spectroscopy

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