FeoA and FeoC Are Essential Components of the Vibrio cholerae Ferrous Iron Uptake System, and FeoC Interacts with FeoB

The ferrous iron transport system Feo is widely distributed among bacterial species, yet its physical structure and mechanism of iron transport are poorly understood. In Vibrio cholerae, the feo operon consists of three genes, feoABC. feoB encodes an 83-kDa protein with an amino-terminal GTPase domain and a carboxy-terminal domain predicted to be embedded in the inner membrane. While FeoB is believed to form the pore for iron transport, the roles of FeoA and FeoC are unknown. In this work, we show that FeoA and FeoC, as well as the more highly conserved FeoB, are all required for iron acquisition by V. cholerae Feo. An in-frame deletion of feoA, feoB, or feoC eliminated iron acquisition. The loss of transport activity in the feoA and feoC mutants was not due to reduced transcription of the feo operon, suggesting that these two small proteins are required for activity of the transporter. feoC was found to encode a protein that interacts with the cytoplasmic domain of FeoB, as determined using the BACTH bacterial two-hybrid system. Two conserved amino acids in FeoC were found to be necessary for the interaction with FeoB in the two-hybrid assay, and when either of these amino acids was mutated in the context of the entire feo operon, iron acquisition via Feo was reduced. No interaction of FeoA with FeoB or FeoC was detected in the BACTH two-hybrid assay.