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Revision as of 08:16, 7 July 2011

English version

L'activité du centrale nucléaire moderne à réacteur à eau pressurisée génèrent des effluents radioactifs. Ceux-ci contiennent entre autre du cobalt radioactif. Les tuyaux du circuit de refroidissement sont fait d'un alliage d'acier riche en cobalt. Ce cobalt est stable (59Co). Sous le bombardement de neutrons provenant du réacteur, le cobalt stable se transforme en un isotope radioactif, le cobalt 60 (60Co).

La capture de ce métal est intéressante d'un point de vue sanitaire car celui-ci présente un danger sous ses deux formes : sous la forme radioactive et sous sa forme stable (cancérigène). La capture du cobalt présente également un enjeu environnemental afin d'éviter des contaminations des eaux, des sols et des eaux souterraines. Même si le cobalt 60 possède une demi-vie courte, il émet cependant des rayons gamma de forte intensité et se décompose en nickel stable mais polluant.

Controlled immobilization of radioactive cobalt is both an important sanitary and environmental issue, which we intend to solve with an innovative and economical response. A researcher from the Lyon INSA-ENS team, Agnès Rodrigues, has recently constructed a E.coli strain able to eliminate 85% of radioactive cobalt (60Co), initially present as traces in a simulated nuclear effluent made up of a mix of heavy metals, in only twice one-hour incubation (Appl Microbio Biotechnol 2009 81:571- 578).

The process that was developed by Agnès Rodrigues’ team ensures the decontamination of cobalt up to 0,5 ppm (8 nM in 100 000L) with only 4kg of bacteria as against 50kg with an unmodified bacterium or 8,000kg of an ion-exchange polymer. This kind of process with modified bacteria will be a good value because the production of bacteria in a bioreactor is rather economical. However, one issue remained unsolved at the end of this study, that is the separation of cobalt-fixing bacteria.

The first objective of our project is, with the most recent genetic engineering techniques, to induce the fixation of optimized bacteria for the cobalt capture and retention in response to the presence of contaminants in the effluent to be treated.

A second objective aims to develop a system to construct custom-built “biofilm inducible” strains. Our goal is to construct captors able to launch the formation of biofilm in response to the presence of various radioactive or not pollutants, and to offer more efficient and cheaper bioremediation processes.

To conclude, our objective is to deposit a part able to make any strains inducible to cobalt. In presence of this element, strains will become adherent and will form biofilm thanks to their curli.