Fig. 6.

Oxygen and nitrate block both Ccp activity and synthesis. (A) Hpx⁻ (LC106) cells were grown anaerobically, and the rate of H₂O₂ scavenging was measured in absence or presence of oxygen. (B) Hpx⁻ (LC106) cells were both grown and assayed for H₂O₂ scavenging either without an electron acceptor or in the presence of fumarate, nitrate, or oxygen. (C) Expression of the transcriptional ccp′–lacZ⁺ reporter fusion in Hpx⁻ (MK250) cells grown either without an electron acceptor or in the presence of fumarate, nitrate, or oxygen. Cells were incubated with 40 μM H₂O₂ for 1 h before harvesting. Asterisks represent statistical significance compared with anoxic assay in A and no terminal acceptor in B and C (*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001; ns, P > 0.05).