Escherichia coli cytochrome c peroxidase is a respiratory oxidase that enables the use of hydrogen peroxide as a terminal electron acceptor

Significance Hydrogen peroxide has been regarded exclusively as a hazard for bacteria; its sources and concentrations in natural habitats are uncertain. The cytochrome c peroxidase of Escherichia coli exhibits an expression pattern and flux rate that provides surprising insights into these issues. This periplasmic enzyme is induced only when H 2 O 2 is present and molecular oxygen is absent. Intriguingly, it was ineffective as a defensive enzyme, but through its linkage to the quinone pool it did enable E. coli to respire using H 2 O 2 as an anaerobic electron acceptor. We suggest that both chemical and biotic processes generate micromolar H 2 O 2 at oxic/anoxic interfaces and that this scenario is common enough that microbes have evolved strategies to productively exploit the H 2 O 2 .