Geobacter is a genus of bacteria. Geobacter species are anaerobic respiration bacterial species which have capabilities that make them useful in bioremediation. Geobacter was found to be the first organism with the ability to oxidize organic compounds and metals, including iron, radioactive metals, and petroleum compounds into environmentally benign carbon dioxide while using iron oxide or other available metals as electron acceptors. Geobacter species are also found to be able to respire upon a graphite electrode. They have been found in anaerobic conditions in soils and aquatic sediment.
History
Geobacter metallireducens was first isolated by Derek Lovley in 1987 in sand sediment from the Potomac River in Washington D.C. The first strain was deemed strain GS-15.
Geobacter spp. and methanotrophs, such as Candidatus Methylomirabilis and Methylobacter, were highly abundant in samples from the 'Bean' and the 'Thorn North' ring, in Ontario, Canada.
Metabolic mechanisms
For quite some time, it was thought that Geobacter species lacked c-cytochromes that can be utilized to reduce metal ions, hence it was assumed that they required direct physical contact in order to use metal ions as terminal electron acceptors (TEAs). The discovery of the highly conductive pili in Geobacter species, and the proposal of using them as biological nano-wires further strengthened this view. Nevertheless, recent discoveries have revealed that many Geobacter species, such as Geobacter uraniireducens, not only do not possess highly conductive pili, but also do not need direct physical contact in order to utilize the metal ions as TEAs, suggesting that there is a great variety of extracellular electron transport mechanisms among the Geobacter species. For example, one other way of transporting electrons is via a quinone-mediated electron shuttle, which is observed in Geobacter sulfurreducens.
Another observed metabolic phenomenon is the cooperation between Geobacter species, in which several species cooperate in metabolizing a mixture of chemicals that neither could process alone. Provided with ethanol and sodium fumarate, G. metallireducens broke down the ethanol, generating an excess of electrons that were passed to G. sulfurreducens via nanowires grown between them, enabling G. sulfurreducens to break down the fumarate ions. The nanowires are made of proteins with metal-like conductivity.
Applications
Biodegradation and bioremediation
Geobacter'''s ability to consume oil-based pollutants and radioactive material with carbon dioxide as waste byproduct has been used in environmental clean-up for underground petroleum spills and for the precipitation of uranium out of groundwater. Geobacter degrade the material by creating electrically conductive pili between itself and the pollutant material, using it as an electron source.