Multi-haem cytochromes from S. oneidensis illustrated schematically to indicate their cellular location and roles. High-resolution structures are presented for proteins from S. oneidensis STC (pdb entry: 2K3V), NrfA (3UBR), OTR (1SP3), FccA (1QJD), MtrF (3PMQ) and OmcA (4LMH) and their homologues NapAB (1OGY), CymA (2J7A), TorC (2J7A) and TorA (1TMO). Cartoons illustrate the OM spanning porin : cytochrome complex for which no structures are available and the IM associated processes that generate ATP and pass electrons to Q in the IM. The arrangement of cofactors in DmsAB is based on that in the homologue NarGH (1R27). Haems (orange), FeS clusters (yellow/green), FAD (cyan) and molybdopterin (purple).