Many bacteria are capable of using alternative terminal electron acceptors (TEA) for respiration. Iron-reducing bacteria such as Shewanella oneidensis MR-1 are not only able to use soluble Fe(III) but also Fe(III) associated with solid phases such as ferrihydrite, a poorly crystalline Fe oxide and hematite a highly crystalline mineral as terminal electron acceptors for respiration and growth. The mechanism of transporting electrons from this bacterium to hematite involves a respiratory apparatus made up of an assemblage of multi-heme c-type cytrochromes and other proteins distributed across the cytoplasmic membrane, periplasm and outer membrane which . Two cytochromes, OmcA and MtrC appear to play essential roles in the process. MtrC appears to play a role in attachment of the cells to the hematite surface. The reduction of mineral-associated Fe(III) leads to the formation of both soluble and insoluble Fe(II), with at least a portion of the latter remaining associated with the hematite surface as a secondary mineral. Biological respiration of solid phase Fe oxides is likely to be an important mechanism of Fe oxide transformation in anaerobic surface soils and subsurface environments.