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Verrecchia, Eric
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Verrecchia, Eric
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- PublicationMétadonnées seulementUse of the frc gene as a molecular marker to characterize oxalate-oxidizing bacterial abundance and diversity structure in soil(2009)
; ; Oxalate catabolism, which can have both medical and environmental implications, is performed by phylogenetically diverse bacteria. The formyl-CoA-transferase gene was chosen as a molecular marker of the oxalotrophic function. Degenerated primers were deduced from an alignment of frc gene sequences available in databases. The specificity of primers was tested on a variety of frc-containing and frc-lacking bacteria. The frc-primers were then used to develop PCR-DGGE and real-time SybrGreen PCR assays in soils containing various amounts of oxalate. Some PCR products from pure cultures and from soil samples were cloned and sequenced. Data were used to generate a phylogenetic tree showing that environmental PCR products belonged to the target physiological group. The extent of diversity visualised on DGGE pattern was higher for soil samples containing carbonate resulting from oxalate catabolism. Moreover, the amount of frc gene copies in the investigated soils was detected in the range of 1.64x10(7) to 1.75x10(8)/g of dry soil under oxalogenic tree (representing 0.5 to 1.2% of total 16S rRNA gene copies), whereas the number of frc gene copies in the reference soil was 6.4x10(6) (or 0.2% of 16S rRNA gene copies). This indicates that oxalotrophic bacteria are numerous and widespread in soils and that a relationship exists between the presence of the oxalogenic trees Milicia excelsa and Afzelia africana and the relative abundance of oxalotrophic guilds in the total bacterial communities. This is obviously related to the accomplishment of the oxalate-carbonate pathway, which explains the alkalinization and calcium carbonate accumulation occurring below these trees in an otherwise acidic soil. The molecular tools developed in this study will allow in-depth understanding of the functional implication of these bacteria on carbonate accumulation as a way of atmospheric CO2 sequestration. (c) 2008 Elsevier B.V. All rights reserved. - PublicationMétadonnées seulement
- PublicationMétadonnées seulementCarbonatogénèse bactérienne liée au cycle biogéochimique oxalate-carbonate(2005)
- PublicationMétadonnées seulementCycle du carbone et biominéralisation carbonatée en milieu continental: la diagénèse des phases oxalate-carbonate(2005)
; In terrestrial environments, the carbon sequestration pool in the global carbon cycle is almost entirely attributed to soil and plant organic carbon storage while soil mineral carbon is generally neglected. Nevertheless, significant biologically induced accumulations of carbonate have been observed in soils under the tropical tree "iroko" (Milicia excelsa). Without an input of calcium from carbonate sources in the system, these accumulations constitute a carbon sink by definition. Approximately 1.2. 10-4 to 2.3.10-3 PgC are not sequestered each year due to deforestation of irokos. This calculation is based on an average of 5.76 kg/yr of carbon sequestration by one tree and extrapolated for to the iroko population in Africa. This proposed quantification suggests that the iroko carbon sink is about one or two orders of magnitude less than some environments such as coral reefs or continental shelfes. Furthermore, this carbon sink is highly significant because the residence time of mineral carbon in carbonate-enriched soils associated with the irokos is 102 - 106 years, i.e. 100,000 times longer than soil organic matter residence time. These accumulations of carbonate are the result of the oxalate-carbonate transformation by oxalotrophic bacteria. The iroko tree provides a large amount of oxalate (a photosynthetic by-product), which once released in the soil, can be consumed by soil oxalotrophic bacteria. There are two consequences of this consumption: (i) carbonate ions are produced and available in the soil solution, (ii) and soil pH increases leading to favorable conditions for carbonate precipitation (in a primary acid soil with a pH around 5, the induced pH can reach 9). In the iroko ecosystem, biological agents are present and active at various scales. Termites and saprophytic fungi are involved in the release of oxalate crystals in the soil. Soil oxalotrophic bacteria are able to consume oxalate leading to CO32- production. Carbonate ions can be pumped by iroko roots, circulating into wood vessels in which they can form calcium carbonate crystals in the presence of calcium, when conditions are favorable. They can also precipitate as calcium carbonate in soil pores, depending on local conditions. Soil bacteria and fungi obviously influence precipitation of carbonate inside the soil. Moreover, regarding carbon isotopic signatures and crystallographic properties of needle fiber calcite (NFC) observed in surficial environments, including African soils, they result from a direct biogenic influence. The nomenclature of the various types of NFC has been reinterpreted regarding diagenesis and geochemical fingerprints. The possible biogenic origin of nanorods usually found in the presence of NFC is also discussed from new observations and experiments. In conclusion, this study has demonstrated the potential importance of the oxalate-carbonate pathway in the global carbon cycle, emphasizing the crucial interrelations between geological and biological processes. - PublicationMétadonnées seulementTranslation of energy into morphology: Simulation of stromatolite morphospace using a stochastic modelStromatolites are examples of ail iterative system involving radiate accretive growth of microbial mats, biofilm and/or minerals that result from interaction between intrinsic and extrinsic factors, which progressively shape the final morphology. These interactions call neither be easily described by simple mathematical equations, nor by simple physical laws or chemical reactions. Therefore, a holistic approach that will reduce the system to a set of variables (which are combinations of natural variables) is proposed in order to create virtual morphologies which will be compared with their natural counterparts. The combination of both Diffusion Limited Aggregation (DLA) and cellular automata (CA) allows the exploration of the stromatolite morphological space and a representation of the intrinsic and extrinsic factors responsible for natural stromatolite morphogenesis. The holistic approach provides a translation in simple parameters of (I) the way that energy, nutrients and sedimentary particles reach the active surface of a future build-up, (2) flow these elements are distributed and used in order to create morphology, and (3) how simple environmental parameters, such as sedimentation, can disturb morphogenesis. In addition, most Precambrian stromatolite morphologies that are impossible to produce with numerical modeling such as the Kardar-Parisi-Zhan (KPZ) equation can be simulated with the DLA-CA model and this, with a minimum set of variables. (c) 2005 Elsevier B.V. All rights reserved.
- PublicationMétadonnées seulementBacterially induced mineralization of calcium carbonate in terrestrial environments: the role of exopolysaccharides and amino acids(2003)
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