APPLIED MICROBIAL AND CELL PHYSIOLOGY Cátia A. Sousa & Eduardo V. Soares Received: 29 November 2013 /Revised: 12 February 2014 /Accepted: 16 February 2014 /Published online: 21 March 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract The yeast Saccharomyces cerevisiae is a useful model organism for studying lead (Pb) toxicity. Yeast cells of a laboratory S. cerevisiae strain (WT strain) were incubated with Pb concentrations up to 1,000 μmol/l for 3 h. Cells exposed to Pb lost proliferation capacity without damage to the cell membrane, and they accumulated intracellular super- oxide anion (O 2 .- ) and hydrogen peroxide (H 2 O 2 ). The in- volvement of the mitochondrial electron transport chain (ETC) in the generation of reactive oxygen species (ROS) induced by Pb was evaluated. For this purpose, an isogenic derivative ρ 0 strain, lacking mitochondrial DNA, was used. The ρ 0 strain, without respiratory competence, displayed a lower intracellular ROS accumulation and a higher resistance to Pb compared to the WT strain. The kinetic study of ROS generation in yeast cells exposed to Pb showed that the pro- duction of O 2 .- precedes the accumulation of H 2 O 2 , which is compatible with the leakage of electrons from the mitochon- drial ETC. Yeast cells exposed to Pb displayed mutations at the mitochondrial DNA level. This is most likely a conse- quence of oxidative stress. In conclusion, mitochondria are an important source of Pb-induced ROS and, simultaneously, one of the targets of its toxicity. Keywords Lead (Pb) toxicity . Mitochondria . Reactive oxygen species (ROS) . Respiratory-deficient cells . Viability . Yeast Introduction Lead (Pb) is considered a priority pollutant by the US Envi- ronmental Protection Agency (US EPA 2006) and is classified as a probable human carcinogen by the International Agency for Research on Cancer (ATSDR 2007). Lead can enter the environment as a result of various activities such as mining and smelting. It can also enter the environment through the wastewaters from industries that produce lead-acid batteries or lead wire and pipes (ATSDR 2007). Exposure to Pb can occur through different sources such tap water (as a result of Pb leaching from plumbing systems and fixtures containing Pb or with Pb solder), leaded gasoline or contact with household dust from Pb-based paints (Rossi 2008). In the yeast Saccharomyces cerevisiae, Pb impairs the assimilation of nutrients (Chen and Wang 2007) and replica- tion competence (Soares et al. 2002, 2003). Pb affected yeast metabolism because cells exposed to this metal displayed a decreased ability to process the dye FUN-1 [2-chloro-4-(2,3- dihydro-3-methyl-(benzo-1,3-thiazol-2-yl)-methylidene)-1- phenylquinolinium iodide] (Van der Heggen et al. 2010). The exposure of yeast cells to Pb induced a decrease in the intra- cellular level of reduced glutathione (Perez et al. 2013); nu- clear morphological alterations, such as chromatin arranged in half rings (Bussche and Soares 2011) and nuclear DNA dam- age including mutations and telomere length alterations (Yuan and Tang 1999; Cui and Tang 2000; Yu et al. 2009). Pb- induced cell death is an active process, requiring the partici- pation of cellular metabolism, as evidenced by the fact that the addition of cycloheximide, an inhibitor of protein synthesis, attenuated the Pb-induced loss of cell proliferation capacity. It was shown that exposure to Pb resulted in severe oxidative stress, which can be the trigger of programmed cell death by apoptosis (Bussche and Soares 2011). The main role of the mitochondria is the production of ATP. However, mitochondria also participate in other functions C. A. Sousa : E. V. Soares (*) Bioengineering Laboratory-CIETI, Chemical Engineering Department, ISEP-School of Engineering of Polytechnic Institute of Porto, Rua Dr António Bernardino de Almeida, 431, 4200-072 Porto, Portugal e-mail: evs@isep.ipp.pt E. V. Soares CEB-Centre of Biological Engineering, University of Minho, 4710-057 Braga, Portugal Appl Microbiol Biotechnol (2014) 98:5153–5160 DOI 10.1007/s00253-014-5631-9 Mitochondria are the main source and one of the targets of Pb (lead)-induced oxidative stress in the yeast Saccharomyces cerevisiae