TtpC is a fourth required protein in the TonB2 energy transduction system in Vibrio anguillarum. TtpC is necessary for iron transport mediated by the TonB2 system and is highly conserved in all pathogenic vibrio species studied to date as well as several marine organisms. We show here that the TtpC proteins from selected pathogenic vibrio species can function with the TonB2 system of V. anguillarum to allow iron transport mediated by a chimeric TonB2 system where the native ExbB2, ExbD2 and TonB2 function with an episomally expressed TtpC in trans from a different species. The discovery that inter-species complementation occurs can be used to identify the functional regions of the TtpC proteins and will lead to an investigation of the mechanism of interaction between the TtpC protein and other members of the TonB2 system.