The impairment of methylmenaquinol:fumarate reductase affects hydrogen peroxide susceptibility and accumulation in Campylobacter jejuni

The methylmenaquinol:fumarate reductase (Mfr) of Campylobacter jejuni is a periplasmic respiratory (redox) protein that contributes to the metabolism of fumarate and displays homology to succinate dehydrogenase (Sdh). Since chemically oxidized redox-enzymes, including fumarate reductase and Sdh, contribute to the generation of oxidative stress in Escherichia coli, we assessed the role of Mfr in C. jejuni after exposure to hydrogen peroxide (H(2)O(2)). Our results show that a Mfr mutant (ΔmfrA) strain was less susceptible to H(2)O(2) as compared to the wildtype (WT). Furthermore, the H(2)O(2) concentration in the ΔmfrA cultures was significantly higher than that of WT after exposure to the oxidant. In the presence of H(2)O(2), catalase (KatA) activity and katA expression were significantly lower in the ΔmfrA strain as compared to the WT. Exposure to H(2)O(2) resulted in a significant decrease in total intracellular iron in the ΔmfrA strain as compared to WT, while the addition of iron to the growth medium mitigated H(2)O(2) susceptibility and accumulation in the mutant. The ΔmfrA strain was significantly more persistent in RAW macrophages as compared to the WT. Scanning electron microscopy showed that infection with the ΔmfrA strain caused prolonged changes to the macrophages’ morphology, mainly resulting in spherical-shaped cells replete with budding structures and craters. Collectively, our results suggest a role for Mfr in maintaining iron homeostasis in H(2)O(2) stressed C. jejuni, probably via affecting the concentrations of intracellular iron.