The evaluation of Escherichia coli as a model for oxidant stress in mammalian hepatocytes: Role of glutathione

Among bacteria, Escherichia coli are unique because they contain an amount of glutathione (GSH) comparable to that of mammalian cells. Thus, this bacterium has been suggested as a model for oxidant stress in mammalian systems. Two common strains of E. coli, ATCC 29682, a B strain, and AB 1157, a K-12 strain, were exposed to paraquat (PQ) or t-butyl hydroperoxide (TBH) and the effect on GSH, growth, and lethality was assessed. Exposure of both strains to 5 m m PQ resulted in an 80% decrease in GSH. Exposure to 5 m m TBH resulted in a 31% decrease in GSH in the K-12 strain and an 80% decrease in the B strain. No correlation was found between the GSH decrease in either strain and the PQ or TBH growth inhibitory effects. TBH exposures increased oxidized GSH (GSSG) export. However, no increase in intracellular GSSG or protein-mixed disulfides was found after exposure to either oxidant nor was GSSG secreted following PQ. After failing to inhibit GSH synthesis with buthionine sulfoximine, a B strain GSH-deficient mutant [RCI-1] was constructed. There was no difference in the growth and lethality responses to the oxidants between GSH-deficient and -sufficient strains. GSH supplementation with N-acetylcysteine or l-2-oxothiazolidine decreased the sensitivity of the E. coli B strain to the growth inhibitory but not the lethality effects of TBH. The lack of a correlation of changes in GSH with either oxidant-induced growth inhibitory or lethality effects, the presence of catalase in the cytoplasm not peroxisomes, and the absence of glutathione peroxidase are limitations to the value of this bacterium as a model for mammalian oxidant stress.