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Media type:
E-Article
Title:
Cadmium Toxicity in Glutathione Mutants ofEscherichia coli
Contributor:
Helbig, Kerstin;
Grosse, Cornelia;
Nies, Dietrich H.
Published:
American Society for Microbiology, 2008
Published in:
Journal of Bacteriology, 190 (2008) 15, Seite 5439-5454
Language:
English
DOI:
10.1128/jb.00272-08
ISSN:
0021-9193;
1098-5530
Origination:
Footnote:
Description:
ABSTRACTThe higher affinity of Cd2+for sulfur compounds than for nitrogen and oxygen led to the theoretical consideration that cadmium toxicity should result mainly from the binding of Cd2+to sulfide, thiol groups, and sulfur-rich complex compounds rather than from Cd2+replacement of transition-metal cations from nitrogen- or oxygen-rich biological compounds. This hypothesis was tested by usingEscherichia colifor a global transcriptome analysis of cells synthesizing glutathione (GSH; wild type), γ-glutamylcysteine (ΔgshBmutant), or neither of the two cellular thiols (ΔgshAmutant). The resulting data, some of which were validated by quantitative reverse transcription-PCR, were sorted using the KEGG (Kyoto Encyclopedia of Genes and Genomes) orthology system, which groups genes hierarchically with respect to the cellular functions of their respective products. The main difference among the three strains concerned tryptophan biosynthesis, which was up-regulated in wild-type cells upon cadmium shock and strongly up-regulated in ΔgshAcells but repressed in ΔgshBcells containing γ-glutamylcysteine instead of GSH. Overall, however, all threeE. colistrains responded to cadmium shock similarly, with the up-regulation of genes involved in protein, disulfide bond, and oxidative damage repair; cysteine and iron-sulfur cluster biosynthesis; the production of proteins containing sensitive iron-sulfur clusters; the storage of iron; and the detoxification of Cd2+by efflux. General energy conservation pathways and iron uptake were down-regulated. These findings indicated that the toxic action of Cd2+indeed results from the binding of the metal cation to sulfur, lending support to the hypothesis tested.