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Interlayer structures and binding
Carbonate ooid formation in a
conformations in the interaction of a
modern freshwater lake:
tetracycline antibiotic with a smectite
How determinant is the
biological role?
Section of Earth and Environmental Sciences, University of 1Environmental Geochemistry Group, LGIT, Grenoble, France Geneva, 13 rues des Maraichers, 1205 Geneva, (*correspondence: ludmilla@nature.berkeley.edu) Switzerland (*correspondence: daniel ariztegui@unige.ch) 2Mineralogy Group, LGCA, Grenoble, France 3Computing for Science, Institut Laue-Langevin, Grenoble, Shallow water sediments in western Lake Geneva, Switzerland, are composed of more than 90% of ooidal sands. The presence of biofilms lining depressions on ooid surfaces Interactions of antibiotics with soil particles can influence has been previously appointed as starting sites for low Mg their environmental fate and the extent of their potential calcite cortex formation [1]. Field- and laboratory-based effects on soil and aquatic sensitive organisms. Of specific experimental results indicate a dominant role of biological interest are their sorption mechanisms within smectite clay versus purely physicochemical processes in the early stages of interlayers [1]. We employed a combination of experimental and modeling techniques to investigate the molecular A special device was placed in the ooid-rich bank of the interactions of Oxyteracycline (Oxy) with montmorillonite. lake. It contained frosted glass (SiO2) slides, while quartz Sorption experiments were conducted with a synthetic Fe-free (SiO2) is the most abundant mineral composition of ooid Na-montmorillonite [2] at pH 4, pH 6, and pH 8. The pH- nuclei that acted as artificial substrates to favour microbial dependent changes in the clay interlayer structures as a colonization [2]. Microscopic inspection of the slides function of adsorbed Oxy was revealed through X-ray despicted a seasonal pattern of carbonate precipitates, which diffraction pattern analyses of the Oxy-clay systems. These were always closely associated with biofilms that developed XRD results in conjunction with molecular modeling Monte on the surface of the frosted slides. They contain EPS, Carlo simulations were used to probe for the binding cyanobacteria, diatoms and heterotrophic bacteria. Carbonate conformations of the different Oxy species within the clay precipitation peaks during early spring and late summer, and interlayer. This study provides for a mechanistic depiction of low-Mg calcite crystals mostly occur in close association with the sequestration of antibiotics within soil clay particles. filamentous and coccoid cyanobacteria. Further SEM inspection of the samples revealed low-Mg calcite with crystal forms varying from anhedral to euhedral rhombohedra, depending on the seasons. In situ biofilms communities were harvested and cultivated under laboratory conditions. Liquid and solid cultures corroborate the field observations and demonstrate that under the same physicochemical conditions the absence of biofilms prevents low-Mg calcite precipitation. The lack of evidence for the presence of sulphate-reducers further indicate that photosynthetic activity through increasing pH in EPS is the main factor triggering the early precipitation of low-Mg calcite. Hence, these results support the hypothesis of external microbial precipitation of low-Mg calcite as the main mechanism involved in the early stage of ooid formation in freshwater Lake Geneva. Total DNA extractions on natural Figure 1: Selected X-ray Diffractograms: Interstratification at
pH 4 (left) versus segregation at pH 6 (right). Amount of
ooids, biofilms harvested from the in situ glass slides, and adsorbed Oxy (mmol Oxy/kg of clay) from top to bottom: 0.0, cultured biofilms in the laboratory indicate a comparable 40.7, 78.4, 284.2 at pH 4 and 0.0, 80.5, 99.6, and 221.7 at pH microbial diversity supporting this model. [1] Davaud & Girardclos (2001) Journal of Sedimentary [1] Kulshrestha et al. (2004) Environ. Sci. Technol. 38, 4097-
Research 71, 423-429. [2] Plee et al. (2008) Geobiology 6,
4105. [2] Reinholdt et al. (2001) Clay Minerals 40, 147-190.

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