Iron and oxidative stress in bacteria

The appearance of oxygen on earth led to two major problems: the production of potentially deleterious reactive oxygen species and a drastic decrease in iron availability, In addition, iron, in its reduced form, potentiates o xygen toxicity by converting, via the Fenton reaction, the less reactive hy drogen peroxide to the more reactive oxygen species, hydroxyl radical and f erryl iron, Conversely superoxide, by releasing iron from iron-containing m olecules, favors the Fenton reaction. It has been assumed that the strict r egulation of iron assimilation prevents an excess of free intracellular iro n that could lead to oxidative stress. Studies in bacteria supporting that view are reviewed. While genetic studies correlate oxidative stress with in crease of intracellular free iron, there are only few and sometimes contrad ictory studies on direct measurements of free intracellular metal. Despite this weakness, the strict regulation of iron metabolism, and its coupling w ith regulation of defenses against oxidative stress, as well as the role pl ayed by iron in regulatory protein in sensing redox change, appear as essen tial factors for life in the presence of oxygen, (C) 2000 Academic Press.