Genomics of Acinetobacter baumannii iron uptake

Iron is essential for growth in most bacteria due to its redox activity and its role in essential metabolic reactions, being a cofactor for many bacterial enzymes. The bacterium Acinetobacter baumannii is a multidrug-resistant nosocomial pathogen. A. baumannii responds to low iron availability imposed by the host through the exploitation of multiple iron-acquisition strategies, which are likely to deliver iron to the cell under a variety of environmental conditions, including human and animal infection. To date, six different gene clusters for active iron uptake have been described in A. baumannii, encoding protein systems involved in i) ferrous iron uptake (feo); ii) heme-uptake (hemT and hemO), and iii) synthesis and transport of the baumannoferrin(s) (bfn), acinetobactin (bas/bau) and fimsbactin(s) (fbs) siderophores. Here we describe the structure, distribution, and phylogeny of iron uptake gene clusters among > 1,000 genotypically diverse A. baumannii isolates, showing that feo, hemT, bfn and bas/bau clusters are very prevalent across the dataset, whereas the additional heme uptake system hemO is present in only a portion of the dataset, and the fbs gene cluster is very rare. Since the expression of multiple iron uptake clusters can be linked to virulence, the presence of the additional heme uptake system hemO may have contributed to the success of some A. baumannii clones.