Degradation of organic contaminants and steel corrosion by the dissimilatory metal-reducing microorganisms Shewanella and Geobacter spp.

Shewanella and Geobacter are the two genera of dissimilatory metal-reducing microorganisms that can couple intracellular oxidation of organic matter to extracellular reduction of oxidized metal ions, such as solid-phase iron (Fe(III)) and manganese (Mn(IV) (hydr)oxides. To transfer electrons extracellularly, both Shewanella and Geobacter spp. possess pathways that transfer electrons from the quinone/quinol pool in the cytoplasmic membrane, across the cell envelope to the extracellular Fe(III) and Mn(IV) (hydr)oxides. In addition, Geobacter spp. use electrically conductive pili and/or filaments that consist of multiheme c-type cytochromes for long-distance electron transfer to Fe(III) and Mn(IV) (hydr)oxides and other electron acceptors. Furthermore, the Fenton reaction driven by Shewanella oneidensis MR-1 can be used to degrade a variety of organic contaminants. Some Geobacter spp., such as Geobacter metallireducens GS-15, couple oxidative degradation of benzine, phenol and other aromatic contaminants to Fe(III) reduction. Moreover, other Geobacter spp., such as G. loveleyi SZ, also couple oxidation of organic matter to reductive dichlorination of organohalide contaminants. Finally, under anoxic condition, Shewanella and Geobacter spp. corrode carbon steel by direct oxidation. This review focuses on our current understandings of extracellular electron transfer mechanisms of as well as degradation of organic contaminants and steel corrosion by Shewanella and Geobacter spp.