title: Silver Accumulation in the Green Microalga Coccomyxa actinabiotis: Toxicity, in Situ Speciation, and Localization Investigated Using Synchrotron XAS, XRD, and TEM.
abstract: Microalgae are good candidates for toxic metal remediation biotechnologies. This study explores the cellular processes implemented by the green microalga Coccomyxa actinabiotis to take up and cope with silver over the concentration range of 10(-7) to 10(-2) M Ag(+). Understanding these processes enables us to assess the potential of this microalga for applications for bioremediation. Silver in situ speciation and localization were investigated using X-ray absorption spectroscopy, X-ray diffraction, and transmission electron microscopy. Silver toxicity was evaluated by monitoring microalgal growth and photochemical parameters. Different accumulation mechanisms were brought out depending on silver concentration. At low micromolar concentration, microalgae fixed all silver initially present in solution, trapping it inside the cells into the cytosol, mainly as unreduced Ag(I) bound with molecules containing sulfur. Silver was efficiently detoxified. When concentration increased, silver spread throughout the cell and particularly entered the chloroplast, where it damaged the photosystem. Most silver was reduced to Ag(0) and aggregated to form crystalline silver nanoparticles of face-centered cubic structure with a mean size of 10 nm. An additional minor interaction of silver with molecules containing sulfur indicated the concomitant existence of the mechanism observed at low concentration or nanoparticle capping. Nanoparticles were observed in chloroplasts, in mitochondria, on the plasma membrane, on cytosolic membrane structures, and in vacuoles. Above 10(-4) M Ag(+), damages were irreversible, and photosynthesis and growth were definitely inhibited. However, high silver amounts remained confined inside microalgae, showing their potential for the bioremediation of contaminated water.
authors.affiliation: CEA, DSV, Laboratoire de Physiologie Cellulaire Végétale , 17 rue des Martyrs, 38054 Grenoble, France.|CNRS, UMR5168 , 17 rue des Martyrs, 38054 Grenoble, France.|Université Grenoble Alpes , 17 rue des Martyrs, 38000 Grenoble, France.|INRA , 17 rue des Martyrs, 38054 Grenoble, France.|Institut Laue Langevin , 71 rue des Martyrs, 38042 Grenoble, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Leonardo
authors.affiliation: Institut Laue Langevin , 71 rue des Martyrs, 38042 Grenoble, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Farhi
authors.affiliation: CEA, Institut Nanosciences et Cryogénie , 17 rue des Martyrs, 38054 Grenoble, France.
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Pouget
authors.affiliation: CEA, DRT, LITEN, Laboratoire de Nanocaractérisation et Nanosécurité , 17 rue des Martyrs, 38054 Grenoble, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Motellier
authors.affiliation: CEA, DSV, Laboratoire de Physiologie Cellulaire Végétale , 17 rue des Martyrs, 38054 Grenoble, France.|CNRS, UMR5168 , 17 rue des Martyrs, 38054 Grenoble, France.|Université Grenoble Alpes , 17 rue des Martyrs, 38000 Grenoble, France.|INRA , 17 rue des Martyrs, 38054 Grenoble, France.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Boisson
authors.affiliation: Dutch-Belgian Beamline (DUBBLE), ESRF - European Synchrotron Radiation Facility, CS 40220 , 71 rue des Martyrs, 38043 Grenoble Cedex 9, France.
authors.forename: Dipanjan
authors.initials: D
authors.lastname: Banerjee
authors.affiliation: CEA, DSV, Laboratoire de Physiologie Cellulaire Végétale , 17 rue des Martyrs, 38054 Grenoble, France.|CNRS, UMR5168 , 17 rue des Martyrs, 38054 Grenoble, France.|Université Grenoble Alpes , 17 rue des Martyrs, 38000 Grenoble, France.|INRA , 17 rue des Martyrs, 38054 Grenoble, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rébeillé
authors.affiliation: Institut de Chimie de Nice, UMR7272, Université Nice Sophia Antipolis , 06108 Nice, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: den Auwer
authors.affiliation: CEA, DSV, Laboratoire de Physiologie Cellulaire Végétale , 17 rue des Martyrs, 38054 Grenoble, France.|CNRS, UMR5168 , 17 rue des Martyrs, 38054 Grenoble, France.|Université Grenoble Alpes , 17 rue des Martyrs, 38000 Grenoble, France.|INRA , 17 rue des Martyrs, 38054 Grenoble, France.
authors.forename: Corinne
authors.initials: C
authors.lastname: Rivasseau
mesh_terms: D001673:Biodegradation, Environmental; D000460:Chlorophyta / Q000737:chemistry / Q000378:metabolism; D053768:Metal Nanoparticles / Q000737:chemistry / Q000633:toxicity; D058086:Microalgae / Q000737:chemistry / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D012834:Silver / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D014874:Water Pollutants, Chemical; D012834:Silver