To Go further

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• Story of Radioactivity


• Story of living Sciences


• What about the future ?


• What is Radioactivity ?


• Neutronic nuclear fission for energy production


• Radiocobalt


• To remove cobalt…


• Cobalt Buster


• Why using a biofilm rather than free cells ?

Story of Radioactivity

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Many scientific discoveries in physics, biology and computer science happened during the 19th and 20th centuries

The understanding of the structure of matter and in particular atom allowed the discovery and explanation of radioactivity ( observed by H. Becquerel and the Curies ). This natural or artificial property of some elements has been used in several domains like medicine and production of electric energy. The second half of the 20th century will see its industrialization.

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Story of living sciences

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In living sciences, progress was slower. The first significant discoveries date from the 16th century.

Then, microbiology rose during the second half of the 19th century with L. Pasteur and other scientists' work.

During the 20th century, discoveries about DNA ( structure, regulation of gene expression, sequencing ) allowed the birth of a new domain : molecular biology.

Then, works on restriction enzymes and Polymerase Chain Reaction (PCR) allow the building of new DNA molecules.

Progress in computer science, increased computing power, new modeling and sequence alignment softwares has now paved the way for synthetic biology.

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What about the future ?

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Any industrialization phase has a generally favorable social and economic impact, but also an environmental impact, unfortunately often negative.

Nuclear technology allowed huge progress but at the cost of several consequences : use as weapon, nuclear accidents (Tchernobyl (1986), Fukushima (2011)…) and nuclear waste, with the associated risks of pollution.

We have to consider those same questions with synthetic biology, but we can also go further : by learning from the past, limit our impact by respecting some "good practice" rules, and propose innovative solutions to the problems aroused during the previous century.

After the great discoveries in nuclear physics ( end of 19th c), after the industrialiation phase (20th c),we hope the 21st century will be a century of solutions thanks to synthetic biology, iGEM and, maybe, our Cobalt Buster project.

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What is Radioactivity ?

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Some atomic nucleus of an unstable atom lose energy by emitting ionizing particles (α, β+ or β-). The emission is spontaneous. This is natural radioactivity. Researchers have used α particle to react with another atom such as Beryllium. The result is a Carbon nucleus and a neutron. This is artificial radioactivity or induced radioactivity. Researchers then used neutrons to react with atoms (for example ²³⁵ Uranium). The result is a bigger nucleus with an exces of neutron leading to an increase of the unstability and the new nucleus can split into 2 smaller nuclei. This phenomenon is the neutronic fission.

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Neutronic nuclear fission for energy production

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Nuclear Power Plants use neutronic fission to produce energy. In France, reactors are pressurized water reactors (PWR). 235 U, the most desirable isotope of uranium absorbs neutron and then split into 2 smaller nuclei and release a lot of energy + new neutrons able to react with other 235U (nuclear chain reaction). A nuclear reactor coolant (water in PWR) is circulated past the reactor core to absorb the heat that it generates. The reactor, pipes and steam generator are in steel that contains Carbon, Iron but also Nickel and Cobalt. These atoms (C, Fe, Ni, Co…) are submitted to neutronic activation leading to activation products.

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Radiocobalt

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59Co is a stable isotope. It can absorb a neutron and become 60Co. This isotope is unstable (half life : 5.272 years). Its disintegration leads to the emission of β particle and γ radiations.

These electromagnetic radiations pass through the matter very easily. To attenuate these rays, lead/concrete shields are necessary. Protective clothing and respirators can protect from internal contact with or ingestion of α or β particles, but provide no protection from γ radiation. To allow human intervention in the Nuclear Power Plant for maintenance, control…, water is filtered continually to remove radioactive atoms.

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To remove cobalt…

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At present, all waters on nuclear sites (Nuclear Power Plant of course but also all the other industries related to nuclear (nuclear fuel production, radioactive waste treatment…) are filtered on Ion-exchange resins.

The resins are effective but not selective and after use, the resins are a voluminous waste (no possibility of incineration or other treatment). Nowadays, the main challenge in nuclear waste management is the reduction of the quantity (volume).

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Cobalt Buster

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Cobaltbuster is a biofiltre using modified bacteria able to adsorb more cobalt than wild strain and with the ability to stick on surfaces in the presence of Cobalt.

• the pollution is concentrated on the bacterial biofilm (volume reduction)


• the pollution could be screened, using different modified bacteria (for Co, for Ni …) and radioactive element could be separated depending the type of radiations. It could be interesting to separate α-generating or γ-rays generating atoms from the others to better answer ANDRA specifications (ANDRA is the agency in charge of nuclear waste storage in France)


• the biofilm, removed after use, could also be incinerated (volume reduction).


• Bacteria cultures are less expensive than ion-exchange resins

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Why using a biofilm rather than free cells ?

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But what is a BIOFILM ??

Antonie van Leeuwenhoek (XVII century) was the first to observe animacules (as he named them) present in his own dental plaque. These animacules are micro-organisms but more precisely a biofilm of micro-organisms . This discovery was outshine by other important researches. Louis Pasteur (XIX century) was the first to realize a pure culture in liquid medium. This culture method became the reference method for all microbiologists and help them to understand physiologic and genetic mechanisms.

A biofilm is a consortium of different species/genus of micro-organisms (bacteria, algae…) fixed onto a surface.

W. J Costerton described in the 80’s the biofilm as a microbial community developing specific structures (proteins, polysaccharides…) to stick on surfaces or on other micro-organisms. Nowadays, biofilm concept is accepted by a large community of scientists which considers that most of micro-organisms live in biofilm in the environment. Biofilm vs free-cell Biofilm can be considered as a cell organization more resistant to environmental “stress” (nutrient depletion, pollutants…). In case of pollutants, the extra-cellular matrix, synthesized by the biofilm, can play the role of a pollution-trap by adsorption. By this way, taking into account that pollutant are less bio-available ( i.e less toxic), cells can live in presence of higher concentrations. And if bacteria have new functions (Co accumulation for example) given by genetic manipulations, the biofilm is more effective.

The dissemination of modified micro-organisms into the environment is not expected especially if their function is removing pollution. If the modified micro-organism is in a biofilm, pollution and modified micro-organisms are confined. And in the case of radioactive substances, it is essential.

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