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Etude de la résistance de Cupriavidus metallidurans CH34 aux oxyanions sélénite et séléniate : accumulation, localisation et transformation du sélénium.

Abstract : Selenium is an essential trace element for the living organisms but it is very toxic at high concentration. Selenite and selenate oxides, soluble forms, highly toxic and bio-assimilable, are the most prevalent forms in the environment. Some soil micro-organisms play a dominant role and contribute to the natural cycle of selenium. Our study model, Cupriavidus (formerly Ralstonia) metallidurans CH34, a telluric bacterium characteristic of metal-contaminated biotopes, is known to resist selenite by reducing it into elemental selenium, an insoluble and less toxic form of selenium. In order to better understand the mechanisms of selenium reduction in the bacteria, three methods of speciation were combined (XAS (XANES and EXAFS), HPLC-ICP-MS and SDS-PAGE-PIXE). They were completed by the direct quantification of selenium accumulated in the bacteria. Speciation analyses highlighted the existence of two mechanisms of reduction of selenium oxides in C. metallidurans CH34. Assimilation transforms selenite and selenate into organic selenium, identified as selenomethionine and leads to its non-specific incorporation into bacterial proteins (presence of selenious proteins). Detoxication precipitates selenite in nanoparticules of elemental selenium. This way of detoxication is not set up after an exposure to selenate although it is nevertheless possible to detect elemental selenium but in very small amount compared to the exposure of selenite. Selenodiglutathion is detected in bacteria stressed by an exposure to selenate in medium limited in sulphate. Bacteria exposed to selenite accumulate 25 times more selenium than when they are exposed to selenate. The study of mutants resistant to selenite, which do not express the membrane protein DedA, showed that the accumulation of selenium after exposure to selenite is decreased compared with the wild strain meaning probable link between the transport of selenite and the DedA protein. Finally, selenate would use the sulphate permease pathway for entering C. metallidurans CH34.
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https://tel.archives-ouvertes.fr/tel-00162019
Contributor : Laure Avoscan <>
Submitted on : Monday, November 26, 2007 - 1:17:38 PM
Last modification on : Thursday, February 1, 2018 - 1:37:21 AM
Long-term archiving on: : Thursday, September 23, 2010 - 4:49:31 PM

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  • HAL Id : tel-00162019, version 3

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Laure Avoscan. Etude de la résistance de Cupriavidus metallidurans CH34 aux oxyanions sélénite et séléniate : accumulation, localisation et transformation du sélénium.. Physique [physics]. Université Joseph-Fourier - Grenoble I, 2007. Français. ⟨tel-00162019v3⟩

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