Expression of the yggE gene protects Escherichia coli from potassium tellurite-generated oxidative stress
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Expression of the yggE gene protects Escherichia coli from potassium tellurite-generated oxidative stress Lillian G. Acun˜a Æ Iva´n L. Caldero´n Æ Alex O. Elı´as Æ Miguel E. Castro Æ Claudio C. Va´squez
Received: 22 January 2009 / Revised: 5 March 2009 / Accepted: 13 March 2009 / Published online: 28 March 2009 Ó Springer-Verlag 2009
Abstract Potassium tellurite is highly toxic to most forms of life and specific bacterial tellurite defense mechanisms are not fully understood to date. Recent evidence suggests that tellurite would exert its toxic effects, at least in part, through the generation of superoxide anion that occurs concomitantly with intracellular tellurite (Te4?) reduction to elemental tellurium (Teo). In this work the putative antioxidant role of YggE from Escherichia coli, a highly conserved protein in several bacterial species and whose function is still a matter of speculation, was studied. When exposed to tellurite, E. coli lacking yggE exhibited increased activity of superoxide dismutase and fumarase C, augmented levels of reactive oxygen species and high concentration of carbonyl groups in proteins. Upon genetic complementation with the homologous yggE gene these values were restored to those observed in the parental, isogenic, wild type strain, suggesting a direct participation of YggE in E. coli tolerance to tellurite. Keywords YggE Tellurite Oxidative stress Superoxide
Communicated by Jorge Membrillo-Herna´ndez. L. G. Acun˜a I. L. Caldero´n A. O. Elı´as M. E. Castro C. C. Va´squez (&) Departamento de Biologı´a, Laboratorio de Microbiologı´a Molecular, Facultad de Quı´mica y Biologı´a, Universidad de Santiago de Chile, Casilla 40, Correo 33, Santiago, Chile e-mail: [email protected] Present Address: I. L. Caldero´n Facultad de Ciencias de la Salud, Universidad Andre´s Bello, Santiago, Chile
Introduction Oxidative stress occurs when antioxidant mechanisms are overcome by pro-oxidants affecting the redox balance of the cell. These pro-oxidant agents can elicit the generation of intracellular reactive oxygen species (ROS) that may cause metabolic malfunctioning, oxidation of proteins and membrane lipids and/or DNA damage (Imlay 2003). Tellurium (Te) is a metalloid belonging to the Group 16 (VIA) of the periodic table that shares chemical properties with biologically important elements such as oxygen, sulfur and selenium. While elemental tellurium (Teo) is apparently non-hazardous, their soluble oxyanions, tellurite (TeO32-) and tellurate (TeO42-), are highly toxic to most forms of life (Taylor 1999). The specific mechanism underlying tellurite toxicity is not fully understood. Once inside the cell, tellurite (Te4?) is reduced, enzymatically or non-enzymatically, to Teo. Some enzymes as nitrate reductase (Avaze`ri et al. 1997), oxidases from the electron transport chain (Trutko et al. 2000), catalase (Caldero´n et al. 2006) and lately dihydrolipoamide dehydrogenase (Castro et al. 2008) have been shown to be proficient in Te4? to Teo conversion. Superoxide
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