Iron Uptake and Homeostasis in Prokaryotic Microorganisms
The vast majority of prokaryotic microorganisms require iron as an essential cofactor involved in many important reactions in the cell. Very little is known about iron uptake mechanisms in Archaea, and most of our knowledge is based on an abundant literature concerning iron uptake and homeostasis in bacteria (Gram-positive and Gram-negative). Multiple strategies are used in iron uptake, depending on whether iron is in the soluble Fe2+ or in the insoluble Fe3+ form. For aerobes, the latter must be chelated by siderophores and the mechanisms of acquisition of ferri-siderophores will be reviewed. Another source of iron is assimilation of the haem group extracted from haemoproteins. Iron accumulation in the cell can be toxic due to the generation of reactive oxygen species caused by the Fenton reaction. Consequently, bacteria have developed regulatory mechanisms to control iron homeostasis and to link their response to oxidative stress to the control of iron levels in the cell.