Characterization of a uranium-tolerant green microalga of the genusCoelastrellawith high potential for the remediation of metal-polluted waters

Uranium (U) pollution of terrestrial and aquatic ecosystems poses a significant threat to the environment and human health because this radionuclide is chemotoxic. Characterization of organisms that tolerate and accumulate U is critical to decipher the mechanisms evolved to cope with the radionuclide and to propose new effective strategies for bioremediation of U-contaminated environments. Here, we isolated a unicellular green microalga of the genus Coelastrella from U-contaminated wastewater. We showed that Coelastrella sp. PCV is much more tolerant to U than Chlamydomonas reinhardtii and Chlorella vulgaris . Coelastrella is able to accumulate U very rapidly, then gradually release it into the medium, behaving as an excluder to limit the toxic effects of U. The ability of Coelastrella to accumulate U is remarkably high, with up to 600 mg U sorbed per g dry biomass. Coelastrella is able to grow and maintain high photosynthesis in natural metal-contaminated waters from a wetland near a reclaimed U mine. Over a single one-week growth cycle, Coelastrella is able to capture 25-55% of U from contaminated waters and demonstrates lipid droplet accumulation. Coelastrella sp. PCV is a very promising microalga for the remediation of polluted waters with valorization of algal biomass that accumulates lipids. Graphical abstract