FIG 5.

General scheme for TonB-dependent iron transport systems. The iron complex is recognized by a specific receptor in the outer membrane (OM). Vibrio spp. have receptors for their own endogenously synthesized siderophores and for exogenous siderophores produced by siblings or by members of other species (xenosiderophores). Transport across the outer membrane is dependent on energy provided by the TonB-ExbB-ExbD complex. Following transport, the siderophore or heme is bound to a periplasmic binding protein and is delivered to the ATP-dependent inner membrane (IM) permease.