Involvement of superoxide dismutases in the response of Escherichia coli to selenium oxides.
Selenium can provoke contrasting effects on living organisms. It is an essential trace element, and low concentrations have beneficial effects, such as the reduction of the incidence of cancer. However, higher concentrations of selenium salts can be toxic and mutagenic. The bases for both toxicity and protection are not clearly understood. To provide insights into these mechanisms, we analyzed the proteomic response of Escherichia coli cells to selenate and selenite treatment under aerobic conditions. We identified 23 proteins induced by both oxides and ca. 20 proteins specifically induced by each oxide. A striking result was the selenite induction of 8 enzymes with antioxidant properties, particularly the manganese and iron superoxide dismutases (SodA and SodB). The selenium inductions of sodA and sodB were controlled by the transcriptional regulators SoxRS and Fur, respectively. Strains with decreased superoxide dismutase activities were severely impaired in selenium oxide tolerance. Pretreatment with a sublethal selenite concentration triggered an adaptive response dependent upon SoxRS, conferring increased selenite tolerance. Altogether, our data indicate that superoxide dismutase activity is essential for the cellular defense against selenium salts, suggesting that superoxide production is a major mechanism of selenium toxicity under aerobic conditions.
Bébien
Magali
M
CEN/Cadarache-DSV-DEVM Laboratoire de Bioénergétique Cellulaire, Univ-Méditérranée CEA 1000, 13108 Saint Paul-Lez-Durance Cedex, France.
Lagniel
Gilles
G
Garin
Jérôme
J
Touati
Danièle
D
Verméglio
André
A
Labarre
Jean
J
D000332:Aerobiosis; D001426:Bacterial Proteins / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism; D029968:Escherichia coli Proteins; D005786:Gene Expression Regulation; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics; D064586:Selenic Acid; D018036:Selenium Compounds / Q000494:pharmacology*; D018038:Sodium Selenite / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; D018036:Selenium Compounds; D015534:Trans-Activators; D014157:Transcription Factors; C068477:ferric uptake regulating proteins, bacterial; C070724:SoxR protein, Bacteria; C070725:SoxS protein, E coli; C095500:SodA protein, Bacteria; C087504:SodB protein, Bacteria; D013482:Superoxide Dismutase; D018038:Sodium Selenite; D064586:Selenic Acid