Team:Lyon-INSA-ENS/Project/Context

Overproduction of curli via a synthetic operon controled by a cobalt-inducible promoter Prcn-csgBAEFG

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Overexpression of curli genes via the superactivator OmpR234

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A project anchored at the heart of current concerns

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The activity of modern nuclear power plants with pressurized water reactors generates radioactive effluents that contain among other things radioactive cobalt . The tubing of the cooling circuit is made of a steel alloy rich in stable cobalt (⁵⁹Co). Undergoing neutron bombardment coming from the reactor, this stable cobalt changes into its radioactive isotope, cobalt 60 (⁶⁰Co).

The capture of this metal is interesting on a sanitary point of view, because it represents a danger under both its radioactive and stable forms (carcinogenic). It also represents an advantage on an environmental point of view, in order to avoid contamination of waters, soil and groundwater. Even with a short half life, cobalt 60 emits high intensity gamma rays, and decays to nickel, which is stable but polluting.

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 Rodrigue, 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 Rodrigue’s 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 capture and retention of cobalt 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 regular 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.