Figure 3.

Iron acquisition, utilization, and storage mechanisms in A. baumannii. the haem scavenger HphA is translocated via the sec-dependent pathway and secreted outside the cell by the haemophilin secretion modulator HsmA (step 1). The haemophilin HphA delivers haem to its receptor, HphR, facilitating haem transport across the outer membrane by the concerted action of an inner membrane TonB complex (step 2). The enzyme HemO causes iron release from haem for use by the cell (step 3). The acinetobactin siderophore binds extracellular ferric iron (Fe[III]) with high affinity, and uses the BauA TonB-dependent outer membrane receptor and an inner membrane ATP-binding cassette (ABC) transporter composed of BauC, BauD, and BauE to deliver iron inside the cell (step 4). Acinetobactin can be recycled by the BarA/BarB siderophore secretion system (step 5). The GTP-dependent FeoAB system located in the cytoplasmic membrane is involved in the import of ferrous iron (Fe[II]) (step 6). NfuA is a cytoplasmic Fe-S cluster protein needed for intracellular iron storage and utilization (step 7). Abbreviations: OM, outer membrane; P, periplasm; IM, inner membrane. Figure created with Biorender.