Aquatic Toxicology 80 (2006) 355–361 Thiols in Scenedesmus vacuolatus upon exposure to metals and metalloids S´ everine Le Faucheur ∗ , Fabian Schildknecht, Renata Behra, Laura Sigg EAWAG, Swiss Federal Institute of Aquatic Science and Technology, P.O. Box 611, CH-8600 Duebendorf, Switzerland Received 19 June 2006; received in revised form 6 October 2006; accepted 6 October 2006 Abstract Phytochelatins are intracellular metal ligands produced by algae when exposed to elevated metal concentrations. In freshwater ecosystems, algae are exposed to a wide range of metals and metalloids. The aim of this study was thus to investigate phytochelatin induction in freshwater algae upon metal and metalloid exposure. To that purpose, the unicellular green alga Scenedesmus vacuolatus, was exposed to Cu, Zn, Ni, Pb and Ag, as well as to As(III), As(V), Sb(III) and Sb(V), and examined for its thiol content (gamma-glutamylcysteine, glutathione and phytochelatins). Glutathione content was found to decrease upon the exposure to Zn and to increase upon the exposure to Pb and Ag. Phytochelatins were only induced by Cu (at [Cu 2+ ]=8 × 10 -11 M) and Pb (at [Pb 2+ ]=8 × 10 -11 to 8 × 10 -10 M), where [Cu 2+ ] and [Pb 2+ ] are computed free metal ion concentrations. Glutathione content also decreased upon the exposure to Sb(V) whereas an increase was observed as a result as the exposure to As(III) and As(V). The metalloids As(III), As(V) and Sb(III) in the concentration range from 8 × 10 -6 to 2 × 10 -4 M (total concentrations of oxyanions) were inducing phytochelatins. Glutathione and phytochelatin content in S. vacuolatus do thus sensitively respond to exposure to a number of metals and metalloids. © 2006 Elsevier B.V. All rights reserved. Keywords: Glutathione; Phytochelatins; Detoxification; Metals; Metalloids 1. Introduction Phytochelatins (PC n ) are intracellular metal ligands pro- duced by plants, fungi and algae in response to increased metal exposure (Cobbett, 2000; Rauser, 1995; Robinson, 1989; Steffens, 1990). They are small polypeptides with the amino acid sequence (-Glu-Cys) n Gly where n = 2–11, which are enzy- matically produced from glutathione by phytochelatin synthase. Phytochelatins are believed to play a general role in metal homeostasis and in metal detoxification due to their high metal- binding affinity. Thus, PC n can alleviate the toxicity of metals by decreasing the intracellular free concentration of the accu- mulated metal. In freshwaters, essential and nonessential metals are naturally present at low concentrations. However, human activities have increased metal concentrations up to toxic levels for organisms at contaminated sites. A recent field study in a stream subject to metal increases during rain events, especially Cu and Zn, showed ∗ Corresponding author. Present address: INRS-Eau, Terre et Environnement, Universit´ e du Qu´ ebec, 490 rue de la Couronne, Qu´ ebec, Qc. G1K 9A9, Canada. Tel.: +1 418 654 3765; fax: +1 418 654 2600. E-mail address: severine.lefaucheur@ete.inrs.ca (S. Le Faucheur). that increase of phytochelatin content in periphyton was con- comitant with increase of metals in the biomass (Le Faucheur et al., 2005b). Microcosm experiments carried out under controlled Cu and Zn exposure indicated that Zn rather than Cu induced phytochelatin production in periphyton. However, other met- als present at very low concentrations in the stream may play a role in phytochelatin formation. In particular, lead may con- tribute to phytochelatin induction, as Pb was found to induce PC n in marine algae at low free Pb 2+ concentration (Ahner and Morel, 1995). To understand the occurrence of phytochelatins in periphyton, the induction of phytochelatins in freshwater green algae upon exposure to metals needs to be better understood. In a previous study, induction of phytochelatin by cadmium has been examined in detail in the green algal species Scenedesmus vacuolatus, which can be readily used as a model for freshwa- ter green algae under controlled conditions (Le Faucheur et al., 2005a,b). The present study was performed to investigate the potential of essential metals (Cu, Zn and Ni) and nonessential metals (Pb and Ag) to induce synthesis of PC n in S. vacuolatus. Freshwaters are also subject to pollution with metalloids, such as As and Sb. Both occur in natural waters in inorganic forms, mainly in the oxidation states +III and +V, or in organic forms such as methylated species. At natural pHs, the primary 0166-445X/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2006.10.002