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Verrecchia, Eric

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Verrecchia, Eric
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https://libra.unine.ch/handle/123456789/143

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  • Publication
    Accès libre
    Use of an isothermal microcalorimetry assay to characterize microbial oxalotrophic activity
    (2011)
    Bravo, Daniel 
    ;
    Braissant, Olivier
    ;
    Solokhina, Anna
    ;
    Clerc, Martin
    ;
    Daniels, Alma U.
    ;
    Verrecchia, Eric 
    ;
    Junier, Pilar 
    Isothermal microcalorimetry (IMC) has been used in the past to monitor metabolic activities in living systems. A few studies have used it on ecological research. In this study, IMC was used to monitor oxalotrophic activity, a widespread bacterial metabolism found in the environment, and particularly in soils. Six model strains were inoculated in solid angle media with K-oxalate as the sole carbon source. Cupriavidus oxalaticus, Cupriavidus necator, and Streptomyces violaceoruber presented the highest activity (91, 40, and 55 μW, respectively) and a maximum growth rate (μmax h−1) of 0.264, 0.185, and 0.199, respectively, among the strains tested. These three strains were selected to test the incidence of different oxalate sources (Ca, Cu, and Fe-oxalate salts) in the metabolic activity. The highest activity was obtained in Ca-oxalate for C. oxalaticus. Similar experiments were carried out with a model soil to test whether this approach can be used to measure oxalotrophic activity in field samples. Although measuring oxalotrophic activity in a soil was challenging, there was a clear effect of the amendment with oxalate on the metabolic activity measured in soil. The correlation between heat flow and growth suggests that IMC analysis is a powerful method to monitor bacterial oxalotrophic activity.
  • Publication
    Accès libre
    Evidence for an organic origin of pedogenic calcitic nanofibres
    (2009)
    Dadras, Massoud
    ;
    Abolhassani-Dadras, Sousan
    ;
    Braissant, Olivier
    ;
    Verrecchia, Eric 
    Calcium carbonate nanofibres are found in numerous terrestrial environments, often associated with needle fibre calcite. This study attempts to mimic the natural system and generate comparable crystalline structures. A comparison of natural and synthesized nanofibre structures, using HRTEM as well as electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), has demonstrated that this type of nanocrystal can result from precipitation on organic templates, most likely cellulose nanofibres. This study emphasizes the fundamental role of organic templates in the precipitation of calcium carbonate in vadose environments, even at the nanoscale.
  • Publication
    Accès libre
    Roles of bacteria and fungi in carbonate-oxalate biomineralization
    (2006)
    Verrecchia, Eric 
    ;
    Braissant, Olivier
    ;
    Cailleau Guillaume
  • Publication
    Métadonnées seulement
    Carbonatogénèse bactérienne liée au cycle biogéochimique oxalate-carbonate
    (2005)
    Braissant, Olivier
    ;
    Verrecchia, Eric 
    L'influence des micro-organismes sur la précipitation et la dissolution des minéraux est connue depuis longtemps. Dans ce contexte, le cas particulier de l'oxalate de calcium est particulièrement intéressant car l'oxalate est présent dans de nombreux systèmes biologiques tels que chez les plantes et chez les champignons. L'oxalate joue aussi un rôle important dans certains cycles biogéochimiques ainsi que dans certaines pathologies humaines telles que les calculs rénaux. Malgré la faible solubilité des complexes métaux-oxalates et le degré d'oxydation élevé de l'anion oxalate, un nombre limité de bactéries sont capables d'utiliser l'acide oxalique et l'oxalate de calcium comme sources de carbone et d'énergie. La dégradation de l'oxalate par des bactéries aérobies mène à une augmentation du pH qui permet la précipitation de minéraux carbonatés. L'étude de ce processus dans les sols autour de l'iroko (Milicia excelsa), de cactus, et de plants de vigne montre que les pools d'oxalates sont très variables et que leur dégradation dans le sol et la rhizosphère est assurée principalement par les streptomycètes et les protéobacteries, respectivement. Dans tous les cas, on observe une alcalinisation des sols et une précipitation de carbonate de calcium. De plus les carbonates observés dans les différents sols peuvent être reproduits en laboratoire en utilisant les bactéries oxalotrophes isolées. L'étude de la morphologie et de la minéralogie des carbonates produits en laboratoire montre que les exopolysaccharides et les polymères pariétaux ont une grande influence sur la nature des carbonates produits. De même la cristallisation abiotique de différents polymorphes du carbonate de calcium dans un EPS commercial souligne l'importance de celui-ci dans la formation de phases métastables et des morphologies particulières du carbonate de calcium. Considérant ces éléments, cette étude propose le modèle suivant pour résumer le fonctionnement du cycle oxalate-carbonate dans les sols. Les plantes produisent un premier reservoir d'oxalate. Lors de la dégradation des tissus ligneux et de la litière, les champignons saprophytes produisent un second pool d'oxalate. De plus ils favorisent la libération des cristaux d'oxalate de calcium enchâssés dans les tissus végétaux. Ces deux pools d'oxalate sont ensuite consommés par les bactéries oxalotrophes. Il en résulte une augmentation du pH et une précipitation concomitante de carbonate de calcium., The influence of microbes on the precipitation and dissolution of minerals is known for a long time. In this context the case of calcium oxalate is particularly interesting because calcium oxalate is present in many biological systems such as plant and fungi. Oxalate also plays an important role in biogeochemical cycles and human diseases such as kidney stones. Despite the poor solubility of metal oxalate complexes and the high oxidation state of oxalate, a limited number of bacteria are able to use oxalate and calcium oxalate as carbon and energy sources. Bacterial aerobic degradation of oxalates leads to a pH increase that allows the precipitation of carbonate minerals. The investigation of such processes in soils around an African tree (iroko, Milicia excelsa), cacti, and grape plants shows that oxalate pools are highly variable. In the soil and the rhizosphere, oxalic acid and oxalate crystals are mainly degraded by streptomycetes and proteobacteria respectively. In each case, an alcalinization of soil solution is observed and precipitation of calcium carbonate can occur. Moreover, calcium carbonate crystals observed in soils can be reproduced in the laboratory using isolated oxalotrophic bacteria. The study of the different morphologies and mineralogies produced by oxalotrophic bacteria in the laboratory shows that exopolysaccharides (EPS) and parietal polymers have a great influence on the nature of calcium carbonate crystal produced. In addition, abiotic crystallization of different polymorphs of calcium carbonate in an industrial EPS emphasizes EPS role in the formation of metastable phases and specific morphologies of calcium carbonate. Considering these points, this study proposes the following model for the oxalate-carbonate cycle in soils. Plants produce a first pool of oxalate. During wood and litter degradation, saprophytic fungi produces a second pool of oxalate, increasing the release of oxalate crystals encased in plant tissues. These two pools of oxalates are consumed by oxalotrophic bacteria resulting in a pH increase and a concomitant calcium carbonate precipitation
  • Publication
    Accès libre
    Biologically induced accumulations of CaCO3 in orthox soils of Biga, Ivory Coast
    (2005)
    Cailleau, Guillaume 
    ;
    Braissant, Olivier
    ;
    Dupraz, Christophe
    ;
    Aragno, Michel 
    ;
    Verrecchia, Eric 
    Biologically induced accumulations of calcium carbonate have been found inside orthox soils, under and around the native iroko tree Milicia excelsa (Moraceae) in Biga (Ivory Coast). The nature of these accumulations and their origin were studied in two soil profiles, directly under the tree and at a distance of 30 cm from the trunk. Microscale forms of CaCO3 include: (1) wood pseudomorphic structures such as parenchyma cells, cellulose fibers, and calcitic vessel infillings; (2) three types of rhombohedra; and (3) needle fiber calcite (NFC). In addition, large scale blocks exhibit three types of textures: (1) micritic calcite, which seems to be the original material; (2) light-colored sparite in moldic voids; and (3) asymmetrical radiaxial laminated fibrous cement. Some micritic aggregates and hemi-spherulites (vaterite) were found in the sap on the trunk as well as in soils on silica grains and the wood itself. The mineralogy of all these carbonate forms is mainly a stoichiometric calcite or a moderately enriched Mg calcite. However, some samples contain monohydrocalcite, as well as two polymorphs of calcium oxalate (weddellite and whewellite). Calcite precipitation is facilitated by the oxidation of oxalate by soil bacteria that contributes to the increase in pH in Biga soils. This is in contrast to conventional orthox soils. Therefore, three conditions are necessary for biologically induced precipitation of calcium carbonate in orthox soils associated with iroko trees: the presence of a large amount of oxalate (originating from the tree and fungi), the existence of an oxalotrophic flora for oxalate oxidation into carbonate, and a dry season.
  • Publication
    Accès libre
    Biologically induced mineralization in the tree Milicia excelsa (Moraceae) : its causes and consequences to the environment
    (2004)
    Braissant, Olivier
    ;
    Cailleau, Guillaume 
    ;
    Aragno, Michel 
    ;
    Verrecchia, Eric 
    Iroko trees (Milicia excelsa) in Ivory Coast and Cameroon are unusual because of their highly biomineralized tissues, which can virtually transform the trunk into stone. Oxalic acid (C2O4H2) and metal-oxalate play important roles in their ecosystems. In this study, the various forms of oxalate and carbonate mineralization reactions are investigated by using scanning electron microscopy and X-ray diffraction. Calcium oxalate monohydrate is associated with stem, bark and root tissues, whereas calcium oxalate dihydrate is found with wood rot fungi in soils, as well as in decaying wood. Laboratory cultures show that many soil bacteria are able to oxidize calcium oxalate rapidly, resulting in an increase in solution pH. In terms of M. excelsa, these transformations lead to the precipitation of calcium carbonate, not only within the wood tissue, but also within the litter and soil. We calculate that c. 500 kg of inorganic carbon is accumulated inside an 80-year-old tree, and c. 1000 kg is associated with its surrounding soil. Crucially, the fixation of atmospheric CO2 during tree photosynthesis, and its ultimate transformation into calcite, potentially represents a long-term carbon sink, because inorganic carbon has a longer residence time than organic carbon. Considering that calcium oxalate biosynthesis is widespread in the plant and fungal kingdoms, the biomineralization displayed by M. excelsa may be an extremely common phenomena.
  • Publication
    Accès libre
    Bacterially Induced Mineralization of Calcium Carbonate in Terrestrial Environments: The Role of Exopolysaccharides and Amino Acids
    (2003)
    Braissant, Olivier
    ;
    Cailleau, Guillaume 
    ;
    Dupraz, Christophe
    ;
    Verrecchia, Eric 
    This study stresses the role of specific bacterial outer structures (such as glycocalix and parietal polymers) on calcium carbonate crystallization in terrestrial environments. The aim is to compare calcium carbonate crystals obtained in bacterial cultures with those obtained during abiotically mediated synthesis to show implications of exopolysaccharides and amino acids in the mineralogy and morphology of calcium carbonate crystals produced by living bacteria. This is done using various amounts of purified exopolysaccharide (xanthan EPS) and L-amino acids with a range of acidities. Amino acids and increasing xanthan content enhance sphere formation in calcite and vaterite. Regarding calcite, the morphology of crystals evolves from rhombohedral to needle shape. This evolution is characterized by stretching along the c axis as the amino acid changes from glutamine to aspartic acid and as the medium is progressively enriched in EPS. Regarding vaterite, the spherulitic habit is preserved throughout the morphological sequence and starts with spheres formed by the agglomeration of short needles, which are produced in a xanthan-free medium with glutamine. Monocrystals forming spheres increase in size as xanthan is added and the acidity of amino acids (glutamic and aspartic acids) is increased. At high xanthan concentrations, amino acids, and mainly aspartic and glutamic acids, induce vaterite precipitation. The role of the carboxyl group is also probably critical because bacterial outer structures associated with peptidoglycan commonly contain carboxyl groups. This role, combined with the results presented here, clearly demonstrate the influence of bacterial outer structure composition on the morphology and mineralogy of bacterially induced calcium carbonate. This point should not be neglected in the interpretation of calcite cements and carbonate accumulations in terrestrial environments.
  • Publication
    Accès libre
    Is the contribution of bacteria to terrestrial carbon budget greatly underestimated ?
    (2002)
    Braissant, Olivier
    ;
    Verrecchia, Eric 
    ;
    Aragno, Michel 
    Some commonly found species of soil bacteria use low molecular weight organic acids as their sole source of carbon and energy. This study shows that acids such as citrate and oxalate (produced in large amounts by fungi and plants) can rapidly be consumed by these bacteria. Two strains, Ralstonia eutropha and Xanthobacter autotrophicus, were cultured on acetate- and citrate-rich media. The resulting CO2 and/or HCO3- reacted with calcium ions to precipitate two polymorphs of calcium carbonate (CaCO3), calcite and vaterite, depending on the quantity of slime produced by the strains. This production of primary calcium carbonate crystals by oxalate- and citrate-degrading bacteria from soil organic carbon sources highlights the existence of an important and underestimated potential carbon sink.