Fig. 4

a Proposed multienzyme complex for ROS detoxification in bacteria (left), G. intestinalis (middle) and S. salmonicida (right). For G. intestinalis and S. salmonicida, Cytochrome p450 reductase (CPR) domain compositions are shown below the panel. In some strict anaerobic bacteria (left), electrons from NADH are transferred to the electron carrier rubredoxin (Rb) via NADH:Rb oxidoreductase (NRO) and ultimately to oxygen or hydrogen peroxide by the concerted action of flavodiiron protein (FDP), superoxide reductase (SOR), or rubrerythrin (RBR). In G. intestinalis, we propose that the CPR protein can funnel electrons from NAD(P)H to FDP or SOR ultimately reducing oxygen. In S. salmonicida, we propose a hybrid of the bacterial and G. intestinalis systems whereby a truncated CPR protein (i.e., the FLD domain; SsFLD) functions as the electron carrier between FDP, SOR, and RBR. This hypothesis is supported by the observed reduction potentials of the proposed reactions shown in the reduction potential graph. b Summary of cellular functions affected by oxygen and antioxidant depletion. Next to each component, the observed gene regulation of OXY (left) and NAO (right) are shown as up arrowheads, down arrowheads, or squares to represent upregulated, downregulated, or unchanged genes expression respectively