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Revision as of 13:25, 16 September 2011
Rcn-csgBAEFG : placing the curli secretion under control of the cobalt-inducible promoter
A project anchored at the heart of current concerns
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.
