Iron is required across most forms of life on planet earth, it is involved in many essential processes, in humans it forms a complex with heme and allows for oxygen to be carried around the body by red blood cells. outside of humans, It is also involved in photosynthesis, DNA replication and as a cofactor for enzymes. A lot of it suitability comes from being a redox active metal allowing for electron transfer and energy generation. Life on earth evolved before our aerobic atmosphere and Iron was in its soluble Fe2+ or ferrous form, it was highly soluble and very abundant as the 4th most common element in the earths crust. Cells were easily able to take up Iron through porins, non energetically. Making Iron the ideal metal for life to evolve to rely on. However, life now exists in primarily aerobic environments and as such iron exists mainly its poorly soluble Fe3+ or ferric form (as low as 10$^–$^1$^8$) which is far below the requirement for cells. Fe3+ has a higher propensity to form coordinates with the water surrounding it such as [Fe(H2O)6]3+ making it difficult for cells to take up and use. Furthermore, in the case of bacteria Hosts use what is termed "nutritional immutinity" where host cells secrete iron chelators and deprive infecting cells out of using Iron. additionally in co-cultures where more than one type of bacteria or organism exists they will be competeing for the small ammount of iron available to them. All of this means that it is highly favourable for cells to want to take up iron from their environment. However, it is also not beneficial for cells to become overloaded with iron. Iron is involved in the fenton reaction, which leads to the generation of destructive free radicals that can damage DNA and biomolecules within cells but as outlined above is highly important for many cellular processes so iron levels in cells must remain well regulated, stored away or chelated to protect the very cells its been taken up by. This sharp regulation is carried out mostly by [[Regulation by Fur]] but also [[AraC-Like regulators]], [[ECF sigma factors]], [[Two component signal transduction system]]s and [[IclR-like regulators]] **References** - [Andrews, S.C., Robinson, A.K. and Rodríguez-Quiñones, F. (2003). Bacterial iron homeostasis. _FEMS Microbiology Reviews_, [online] 27(2-3), pp.215–237. doi:https://doi.org/10.1016/S0168-6445(03)00055-X.](https://academic.oup.com/femsre/article/27/2-3/215/614497?login=false) - [Murdoch, C.C. and Skaar, E.P. (2022). Nutritional immunity: the battle for nutrient metals at the host–pathogen interface. _Nature Reviews Microbiology_, 20(11), pp.657–670. doi:https://doi.org/10.1038/s41579-022-00745-6.](https://www.nature.com/articles/s41579-022-00745-6) - [van den Berg, B. (2004). Crystal Structure of the Long-Chain Fatty Acid Transporter FadL. _Science_, 304(5676), pp.1506–1509. doi:https://doi.org/10.1126/science.1097524.](https://www.science.org/doi/10.1126/science.1097524)