Aquatic Toxicology 126 (2013) 355–364 Contents lists available at SciVerse ScienceDirect Aquatic Toxicology jou rn al h om epa ge: www.elsevier.com/locate/aquatox An omics based assessment of cadmium toxicity in the green alga Chlamydomonas reinhardtii An Jamers a,1 , Ronny Blust a , Wim De Coen a , Julian L. Griffin b , Oliver A.H. Jones c,∗ a Laboratory for Ecophysiology, Biochemistry and Toxicology, Department of Biology, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium b The Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 2QA, United Kingdom c School of Applied Sciences, RMIT University, GPO Box 2476, Melbourne, VIC 3001, Australia a r t i c l e i n f o Article history: Received 30 May 2012 Received in revised form 9 August 2012 Accepted 14 September 2012 Keywords: Cadmium Metabonomics Oxidative stress Systems toxicology a b s t r a c t The effects of cadmium were assessed in the freshwater alga Chlamydomonas reinhardtii. Algae were exposed to concentrations of 0, 8.1 or 114.8 M of cadmium and growth rates, gene transcription and metabolite profiles were examined after 48 and 72 h of exposure. In algae exposed to 8.1 M Cd, several genes were differentially transcribed after 48 h but no adverse growth related effects were detected. A transient effect on both gene transcription patterns and metabolite profiles could be discerned after 48 h of exposure but the majority of these changes disappeared after 72 h. In contrast, all effects were more pronounced at the 114.8 M cadmium exposure. Here growth was clearly reduced and transcription of a large number of genes involved in oxidative stress defense mechanisms was differentially increased. Metabolites involved in the glutathione synthesis pathway (an important antioxidant defense) were also affected but the effects of cadmium were found to be more pronounced at the transcript level than in the metabolome, suggesting that the former exhibits greater sensitivity toward cadmium exposure. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Cadmium (Cd) is a widespread environmental pollutant pri- marily released through anthropogenic activities such as and iron and steel production, the manufacture and disposal of recharge- able nickel–cadmium batteries and phosphate fertilizers (World, 1992). It binds to organic molecules by forming bonds with sulfur and nitrogen, thereby inactivating proteins and is therefore capa- ble of causing a broad range of adverse effects. It is easily absorbed and bio-accumulated by lower organisms and transferred to higher trophic levels in food chain. Cadmium is considered by the US Environmental Protection Agency (EPA) as one of the three contam- inants of greatest threat to the environment (along with mercury and lead). Aquatic microorganisms, in particular microalgae, are very sensitive to the toxic effects of this metal. It has been shown to inhibit growth (Awad and Chu, 2005; Okamoto et al., 1996) and chlorophyll and chloroplast synthesis (Lamai et al., 2005), cause dis- integration of the cell wall and induce a large increase in superoxide dismutase (SOD) activity – indicative of oxidative stress (Okamoto ∗ Corresponding author. Tel.: +61 3 9925 2632; fax: +61 3 9925 3747. E-mail address: oliver.jones@rmit.edu.au (O.A.H. Jones). 1 Present address: Apeiron, Pluyseghemstraat 69, 2550 Kontich, Antwerp, Belgium. et al., 1996). Nevertheless it is often hard to detect the subtle and non-lethal effects of low-level exposure in aquatic systems. The challenge ecotoxicology is faced with today is to help pre- vent damage to sensitive species via the early detection of effects of exposure, even before such effects manifest in the traditional tox- icological endpoints such as growth and reproduction. In recent years, the “omics” technologies have increasingly been used, in a variety of different contexts, in order to form a comprehensive description of nearly all components within a biological entity. The transcriptome, proteome and metabolome refer, respectively, to the pool of RNA transcripts, proteins and metabolites in a cell, tissue biofluid, or indeed whole organisms. The omics technologies and related data processing techniques provide tools which have the potential to be of great value in ecotoxicological research (Spurgeon et al., 2010). The green freshwater alga Chlamydomonas reinhardtii (P.A. Dang), a motile, unicellular green algae commonly found in fresh water and soils, is ideal for omics-based research. The cell contains a single nucleus, chloroplasts, contractile vacuoles, has two anterior flagella and is surrounded by a thin cell wall (composed of glyco- proteins). It is sensitive to environmental perturbations and ubiq- uitously distributed. The ready availability of a sequenced genome means the majority of existing microarray studies in algae have been carried out in this species. Examples include, a study of the expression of light-regulated genes and the involvement of pho- totropin therein (Im et al., 2006), the specificity of a chloroplast RNA 0166-445X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aquatox.2012.09.007