from Pierre Cornelis and Simon C. Andrews writing in Bacterial Regulatory Networks:
For the vast majority of bacteria, iron is an essential element that is not readily available due to the poor solubility of the oxidized Fe3+ form that prevails aerobically. Because of this, bacteria inhabiting aerobic niches often suffer deficiencies in iron supply. Pathogenic bacteria experience a particularly acute form of iron-restriction. This arises from the host's 'iron-withdrawal response' to infection, whereby iron availability is constrained by increasing lactoferrin (an iron-chelating, bacteriostatic, extracellular glycoprotein) levels and reducing the degree of iron saturation for the circulating iron-transport protein, transferrin. The importance of iron to bacteria stems from its multiple metabolic roles. Examples of its crucial metabolic involvement include redox-stress resistance (e.g. heme-bearing catalases) and DNA manufacture (di-Fe containing ribonucleotide reductases). Although indispensible, iron is an unfriendly, hazardous metal as the Fe2+-triggered Fenton reaction produces destructive reactive oxygen species (ROS) such as superoxide (O2-), hydrogen peroxide (H2O2) as well as the highly reactive hydroxyl radical (˚OH).
Further reading: Bacterial Regulatory Networks Related publications