Résumé
Nuclear activities generate radioactive elements which require processes for their decontamination. Although biological remediation has proved efficient in industrial applications, no biotechnology solution is currently operational for highly radioactive media. Such a solution requires organisms that accumulate radionuclides while withstanding radioactivity. This paper describes the potentialities of an extremophile autotrophic eukaryote, Coccomyxa actinabiotis nov. sp., that we isolated from a nuclear facility and which withstands huge ionizing radiation doses, up to 20,000 Gy. Half the population survives 10,000 Gy, which is comparable to the hyper-radioresistant wellknown prokaryote Deinococcus radiodurans. Cell metabolic profile investigated by nuclear magnetic resonance was hardly affected by radiation doses of up to 10,000 Gy. Cellular functioning completely recovered within a few days. This outstanding microalga also strongly accumulates radionuclides, including 238U, 137Cs, 110mAg, 60Co, 54Mn, 65Zn, and 14C (decontamination above 85% in 24 h, concentration factor, 1,000-450,000 mL g-1 fresh weight). In 1 h, the microalga revealed as effective as the conventional physico-chemical ion-exchangers to purify nuclear effluents. Using this organism, an efficient real-scale radionuclide bio-decontamination process was performed in a nuclear fuel storage pool with an important reduction of waste volume compared to the usual physico-chemical process. The feasibility of new decontamination solutions for the nuclear industry and for environmental clean-up operations is demonstrated.