Iron-Reducing Bacteria (IRB). This group of bacteria reduces ferric iron (Fe3+) into ferrous iron (Fe2+) in anaerobic environments with organic compounds as a main source of energy. They can use the oxide layers formed on the surface of metal, exposing it to more corrosive conditions as well as more corrosive bacteria. They can also directly contribute to external corrosion of pipelines in direct contact with soil. These group of bacteria can be found in a variety of environments from soils, sediments, the subsurface, oil platforms, among others. Members of the Geobacter and Shewanella genera are very common iron reducers.