text: Ferric iron () is a widespread anaerobic terminal electron acceptor both for autotrophic and heterotrophic organisms.  Electron flow in these organisms is similar to those in electron transport, ending in oxygen or nitrate, except that in ferric iron-reducing organisms the final enzyme in this system is a ferric iron reductase.  Model organisms include Shewanella putrefaciens and Geobacter metallireducens.  Since some ferric iron-reducing bacteria (e.g. G. metallireducens) can use toxic hydrocarbons such as toluene as a carbon source, there is significant interest in using these organisms as bioremediation agents in ferric iron-rich contaminated aquifers.
  Although ferric iron is the most prevalent inorganic electron acceptor, a number of organisms (including the iron-reducing bacteria mentioned above) can use other inorganic ions in anaerobic respiration.  While these processes may often be less significant ecologically, they are of considerable interest for bioremediation, especially when heavy metals or radionuclides are used as electron acceptors.  Examples include:
  * Manganic ion () reduction to manganous ion ()
  * Selenate () reduction to selenite () and selenite reduction to inorganic selenium (Se)
  * Arsenate () reduction to arsenite ()
  * Uranyl ion () reduction to uranium dioxide ()