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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
    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 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
    Isolation and characterization of oxalotrophic bacteria from tropical soils
    Bravo, Daniel 
    ;
    Braissant, Olivier
    ;
    Cailleau, Guillaume 
    ;
    Verrecchia, Eric 
    ;
    Junier, Pilar 
    The oxalate–carbonate pathway (OCP) is a biogeochemical set of reactions that involves the conversion of atmospheric CO2 fixed by plants into biomass and, after the biological recycling of calcium oxalate by fungi and bacteria, into calcium carbonate in terrestrial environments. Oxalotrophic bacteria are a key element of this process because of their ability to oxidize calcium oxalate. However, the diversity and alternative carbon sources of oxalotrophs participating to this pathway are unknown. Therefore, the aim of this study was to characterize oxalotrophic bacteria in tropical OCP systems from Bolivia, India, and Cameroon. Ninety-five oxalotrophic strains were isolated and identified by sequencing of the 16S rRNA gene. Four genera corresponded to newly reported oxalotrophs (Afipia, Polaromonas, Humihabitans, and Psychrobacillus). Ten strains were selected to perform a more detailed characterization. Kinetic curves and microcalorimetry analyses showed that Variovorax soli C18 has the highest oxalate consumption rate with 0.240 μM h-1. Moreover, Streptomyces achromogenes A9 displays the highest metabolic plasticity. This study highlights the phylogenetic and physiological diversity of oxalotrophic bacteria in tropical soils under the influence of the oxalate–carbonate pathway.