The status and the role of glutathione under disturbed ionic balance and pH homeostasis in Escherichia coli

Abstract

The study of glutathione status in aerobically grown Escherichia coli cultures showed that the total intracellular glutathione (GSHin + GSSGin) level falls by 63% in response to a rapid downshift in the extracellular pH from 6.5 to 5.5. The incubation of E. coli cells in the presence of 50 mM acetate or 10 micrograms/ml gramicidin S decreased the total intracellular glutathione level by 50 and 25%, respectively. The fall in the total intracellular glutathione level was accompanied by a significant decrease in the (GSHin:GSSGin) ratio. The most profound effect on the extracellular glutathione level was exerted by gramicidin S, which augmented the total glutathione level by 1.8 times and the (GSHout:GSSGout) ratio by 2.1 times. The gramicidin S treatment and acetate stress inhibited the growth of mutant E. coli cells defective in glutathione synthesis 5 and 2 times more severely than the growth of the parent cells. The pH downshift and the exposure of E. coli cells to gramicidin S and 50 mM acetate enhanced the expression of the sodA gene coding for superoxide dismutase SodA.