FIG. 8.

Model for iron reduction at a distance in S. oneidensis MR-1. Chelated Fe(III) or a redox-active mediator is reduced extracellularly by the OmcB-MtrB complex necessary for iron mineral reduction. In the absence of or in addition to this reduction pathway, chelated Fe(III) or the redox-active mediator is reduced by an alternate pathway that may involve other redox-active outer membrane complexes (such as the mtrDEF complex or the putative outer membrane molybdopterin oxidoreductase complexes encoded by the SO1427-SO1432 and SO4362-SO4357 gene clusters). Alternatively, chelated Fe(III) or the redox-active mediator may be transported into the bacterial periplasm and reduced by periplasmic electron transport components, such as low-potential multiheme c-type cytochromes. OM, outer membrane; MQ, menaquinone; CM, cytoplasmic membrane.