Geobacter is a genus of proteobacteria. Geobacter 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 acceptor. Geobacter are also found to be able to respire upon a graphite electrode. Geobacter have been found in anaerobic conditions in soils and aquatic sediment.
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 metabolize the material by creating electrically conductive pili between itself and the food material.
Multiple Geobacter 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.
The production of electricity during this process (what process) led scientists to theorize that Geobacter could act as a living fuel cell that could convert biomass into electricity. Potential applications exist in the field of nanotechnology for the creation of microbial nanowires in very small circuits and electronic devices. The nanowires could be connected, creating a microscopic power grid.
Biodegradation and bioremediation
Microbial biodegradation of recalcitrant organic pollutants is of great environmental significance and involves intriguing novel biochemical reactions. In particular, hydrocarbons and halogenated compounds have long been doubted to be anaerobically degradable, but the isolation of hitherto unknown anaerobic hydrocarbon-degrading and reductively dehalogenating bacteria documented these processes in nature. Novel biochemical reactions were discovered, enabling the respective metabolic pathways, but progress in the molecular understanding of these bacteria was slowed by the absence of genetic systems for most of them. However, several complete genome sequences later became available for such bacteria. The genome of the hydrocarbon degrading and iron-reducing species G. metallireducens (accession nr. NC_007517) was determined in 2008. The genome revealed the presence of genes for reductive dehalogenases, suggesting a wide dehalogenating spectrum. Moreover, genome sequences provided insights into the evolution of reductive dehalogenation and differing strategies for niche adaptation.
Geobacter species are often the predominant organisms when extracellular electron transfer is an important bioremediation process in subsurface environments. Therefore, a systems biology approach to understanding and optimizing bioremediation with Geobacter species has been initiated with the ultimate goal of developing in silico models that can predict the growth and metabolism of Geobacter species under a diversity of subsurface conditions. The genomes of multiple Geobacter species have been sequenced. Detailed functional genomic/physiological studies on one species, G. sulfurreducens was conducted. Genome-based models of several Geobacter species that are able to predict physiological responses under different environmental conditions are available. Quantitative analysis of gene transcript levels during in situ uranium bioremediation demonstrated that it is possible to track in situ rates of metabolism and the in situ metabolic state of Geobacter in the subsurface.
Geobacter are used as a plot device in the first episode of the third season of ReGenesis. Geobacter has become an icon for teaching about microbial electrogenesis and microbial fuel cells and has appeared in educational kits that are available for students and hobbyists.
- Childers, Susan (2002). "Geobacter metallireducens accesses insoluble Fe (III) oxide by chemotaxis.". Nature 416: 767–769. doi:10.1038/416767a. PMID 11961561. Retrieved 21 August 2015.
- Bond, Daniel (Mar 2003). "Electricity Production by Geobacter sulfurreducens Attached to Electrodes". Applied and Environmental Microbiology 69 (3): 1548–1555. doi:10.1128/AEM.69.3.1548-1555.2003. Retrieved 26 August 2015.
- Lovley DR, Stolz JF, Nord GL, Phillips, EJP (1987). "Anaerobic Production of Magnetite by a Dissimilatory Iron-Reducing Microorganism" (PDF). Nature 350 (6145): 252–254. doi:10.1038/330252a0.
- Anderson RT, Vrionis HA, Ortiz-Bernad I, Resch CT, Long PE, Dayvault R, Karp K, Marutzky S, Metzler DR, Peacock A, White DC, Lowe M, Lovley DR. (2003). "Stimulating the in situ activity of Geobacter species to remove uranium from the groundwater of a uranium-contaminated aquifer". Applied Environmental Microbiology 69 (10): 5884–91. doi:10.1128/aem.69.10.5884-5891.2003. PMC 201226. PMID 14532040.
- Cologgi, Dena (2014). "Enhanced uranium immobilization and reduction by Geobacter sulfurreducens biofilms". Applied and Environmental Microbiology 80 (21): 6638–6646. doi:10.1128/AEM.02289-14. PMC 4249037. PMID 25128347.
- "Experiment and theory unite at last in debate over microbial nanowires". Phys.org. Retrieved 5 January 2016.
- Williams, Caroline (2011). "Who are you calling simple?". New Scientist 211 (2821): 38–41. doi:10.1016/S0262-4079(11)61709-0
- Malvankar, Nikhil; Vargas, Madeline; Nevin, Kelly; Tremblay, Pier-Luc; Evans-Lutterodt, Kenneth; Nykypanchuk, Dmytro; Martz, Eric; Tuominen, Mark T; Lovley, Derek R (2015). "Structural Basis for Metallic-Like Conductivity in Microbial Nanowires". mBio 6 (2).
- Reguera G, McCarthy KD, Mehta T, Nicoll JS, Tuominen MT, Lovley DR (2005). "Extracellular electron transfer via microbial nanowires" (PDF). Nature 435 (7045): 1098–101. doi:10.1038/nature03661.
- Heider J and Rabus R (2008). "Genomic Insights in the Anaerobic Biodegradation of Organic Pollutants". Microbial Biodegradation: Genomics and Molecular Biology. Caister Academic Press. ISBN 978-1-904455-17-2.
- Diaz E (editor). (2008). Microbial Biodegradation: Genomics and Molecular Biology (1st ed.). Caister Academic Press. ISBN 978-1-904455-17-2.
- MudWatt Science Kit
- "Geobacter project". Retrieved August 13, 2005.
- Microbial Biodegradation, Bioremediation and Biotransformation
- An electrifying solution