Copper and iron overload protect Escherichia coli from exogenous H2O2 by modulating membrane phospholipid composition

Abstract

Development of green technologies for sustainable development requires growth of bacteria in medium containing H2O2 from 50 to 150 mM that may contain millimolar level of copper (Cu) and iron (Fe). However, the mechanism of oxidative stress involving high concentration of exogenous H2O2 in bacteria and the effect of Cu and Fe overload on the same remain controversial. In the present study, we investigated the effect of millimolar concentration of Cu and Fe on H2O2-induced oxidative stress using the enterotoxigenic Escherichia coli 12566 as a model system. Our results indicate that at millimolar concentration, Fe and Cu protect E. coli from H2O2-induced oxidative stress by (1) suppressing H2O2-induced growth inhibition, (2) reducing H2O2-induced lipid peroxidation, (3) decreasing catalase activity and (4) modulating H2O2 -induced release of cytosolic Fe content in a dose-dependent manner. A previous study by our group shows that H2O2 significantly alters the phospholipid (PL) composition in E. coli by a dose-dependent increase in cardiolipin (CL) accompanied by decrease in sum total of phosphatidyl ethanolamine (PE) and phosphatidyl glycerol (PG). In the present study, we show that Cu2+ and Fe3+ at 1 mM reduce H2O2-induced change in PL composition of E. coli leading to stabilization of its membrane components. For the first time, our results show that overloading of E. coli with Cu2+ and Fe3+ activates a protective mechanism against H2O2-induced oxidative damage by modulating its membrane PL composition. Our study reveals a pivotal regulatory role of these metal ions in the sectors of sustainable technologies such as heavy metal bioremediation, sewage treatment and bioelectrochemical reactors that require microbial growth at high concentration of H2O2.