Bacterial Toxicity of Potassium Tellurite: Unveiling an Ancient Enigma

José M Pérez,Alex O Elías,Miguel E Castro,Iván L Calderón,Claudio C Vásquez,Juan M Sandoval,Felipe A Arenas,Gonzalo A Pradenas,Eugenia L Fuentes,Derie E Fuentes,Abraham Sonenshein

doi:10.1371/journal.pone.0000211

Abstract

Biochemical, genetic, enzymatic and molecular approaches were used to demonstrate, for the first time, that tellurite (TeO3 2−) toxicity in E. coli involves superoxide formation. This radical is derived, at least in part, from enzymatic TeO3 2− reduction. This conclusion is supported by the following observations made in K2TeO3-treated E. coli BW25113: i) induction of the ibpA gene encoding for the small heat shock protein IbpA, which has been associated with resistance to superoxide, ii) increase of cytoplasmic reactive oxygen species (ROS) as determined with ROS-specific probe 2′7′-dichlorodihydrofluorescein diacetate (H2DCFDA), iii) increase of carbonyl content in cellular proteins, iv) increase in the generation of thiobarbituric acid-reactive substances (TBARs), v) inactivation of oxidative stress-sensitive [Fe-S] enzymes such as aconitase, vi) increase of superoxide dismutase (SOD) activity, vii) increase of sodA, sodB and soxS mRNA transcription, and viii) generation of superoxide radical during in vitro enzymatic reduction of potassium tellurite.

Highlights

To date, it is not known if elements like Ag, As, Cd, Cr, Hg, Pb, Te, or some of their derivatives play a defined biological function and they are mainly associated with toxicity [1,2].Oxyanions of tellurium, like tellurite (TeO322), are highly toxic for most microorganisms [3]
CspA mRNA is highly transcribed in response to cytoplasmic protein stress [14,15]
We have previously shown that E. coli cells overexpressing G. stearothermophilus V cysteine metabolism-related genes develop a significant increase (,25 fold) in tellurite resistance [9,16,24]

Summary

Introduction

It is not known if elements like Ag, As, Cd, Cr, Hg, Pb, Te, or some of their derivatives play a defined biological function and they are mainly associated with toxicity [1,2].Oxyanions of tellurium, like tellurite (TeO322), are highly toxic for most microorganisms [3]. It is not known if elements like Ag, As, Cd, Cr, Hg, Pb, Te, or some of their derivatives play a defined biological function and they are mainly associated with toxicity [1,2]. Tellurite-resistant bacteria do exist in nature and they often reduce tellurite to its elemental less toxic form Teu that is accumulated as black deposits inside the cell [4,5]. Evidence has accumulated in the last few years suggesting that tellurite could exert its toxicity through intracellular generation of reactive oxygen species (ROS). ROS compounds such as hydrogen peroxide (H2O2), superoxide anion (O22) and hydroxyl radical (OH ) are typical byproducts of the aerobic metabolism that can be formed by exposure of cells to free radical-generating molecules like metals and metalloids [8]

Methods

Results

Conclusion