Tellurite-mediated thiol oxidation in Escherichia coli (original) (raw)

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Abstract

The oxyanion of tellurium, tellurite (), is toxic to most micro-organisms, particularly Gram-negative bacteria. The mechanism of tellurite toxicity is presently unknown. Many heavy metals and oxyanions, including tellurite, interact with reduced thiols (RSH). To determine if tellurite interaction with RSH groups is involved in the toxicity mechanism, the RSH content of Escherichia coli cultures was assayed. After exposure to tellurite, cells were harvested and lysed in the presence of the RSH-specific reagent 5,5’-dithiobis(2-nitrobenzoic acid). Upon exposure of tellurite-susceptible cells to , the RSH content decreased markedly. Resistance to potassium tellurite (Ter) in Gram-negative bacteria is encoded by plasmids of incompatibility groups IncFI, IncPα, IncHI2, IncHI3 and IncHII, as well as the tehAtehB operon from the E. coli chromosome. When cells harbouring a Ter determinant were exposed to , only a small fraction of the RSH content became oxidized. In addition to tellurite-dependent thiol oxidation, the resistance of E. coli mutants affected in proteins involved in disulfide-bond formation (dsb) was investigated. Mutant strains of dsbA and dsbB were found to be hypersensitive to tellurite (MIC 0·008–0·015 μg K2TeO3 ml−1 compared to wild-type E. coli with MICs of 1–2 μg K2TeO3 ml−1). In contrast, dsbC and dsbD mutants showed no hypersensitivity. The results suggest that hypersensitivity to tellurite is reliant on the presence of an isomerase activity and not the thiol oxidase activity of the Dsb proteins. The results establish that the Ter determinants play an important role in maintaining homeostasis of the intracellular reducing environment within Gram-negative cells through specific reactions with either or thiol:tellurium products.

• Received: 19/04/1999
• Accepted:24/05/1999
• Published Online:01/09/1999

Keyword(s): Dsb, DTNB, 5,5’-dithiobis(2-nitrobenzoic acid), heavy metal toxicity, resistance, RSH, reduced thiol(s), tellurite, Ter, tellurite resistantand thiol oxidation

© Microbiology Society

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1999-09-01

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