| Iron is the fourth most abundant element in the earth's crust, and it is essential for the growth of nearly all microorganisms. Under aerobic conditions at near neutral pH, such as those that exist in marine environments, iron is, however, only sparingly soluble. In aquatic or marine environments, most iron is complexed by organic ligands. Many microorganisms therefore produce low molecular weight iron-binding compounds, termed siderophores. Microorganisms secrete siderophores, which bind iron(III) with high affinity and are then taken up into the cells as the ferric siderophore, thereby promoting growth.;Some siderophores have been shown to contain alpha-hydroxy carboxylic acid moieties, which are photolabile when bound to iron(III). In open ocean environments, these siderophores are exposed to natural sunlight and are therefore susceptible to photolysis. Iron(III)-aerobactin, one such photolabile siderophore, was shown to produce an oxidized siderophore ligand, iron(II), and carbon dioxide upon photolysis. In aerobic conditions, iron(II) is rapidly oxidized back to iron(III), which can be coordinated by the oxidized siderophore ligand and can continue to play a role in obtaining essential iron.;Photolabile siderophores from marine microorganisms are used for sequestering iron but also play an important role in cycling of iron in open ocean environments. Due to the production of carbon dioxide upon photolysis of iron(III)-bound siderophores, these photoreactive iron chelators are also part of the global carbon cycle taking place in marine environments. |
