Geobacter

Geobacter is a genus of proteobacteria. Geobacter are an anaerobic respiration bacterial species which have capabilities that may make them useful in bioremediation. The 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. The Geobacter is under continuing research for a variety of applications, discussed below.

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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 have been found in anaerobic conditions in soils and aquatic sediment.^[1]

Potential and actual applications

Research on the potential of the Geobacter is underway and on-going. The Geobacter's ability to consume oil-based pollutants and radioactive material with carbon dioxide as waste by-product has already been used in environmental clean-up for underground petroleum spills and for the precipitation of uranium out of groundwater. The Geobacter metabolizes the material by creating "pili," columns the width of a 3-5 nanometers that act as conduits to pass electrons between the food material and the Geobacter. This manner of consumption has also lead scientists to theorize that the Geobacter could act as a natural battery. This natural battery could use renewable biomass such as compost materials, or be used to convert human and animal solid waste into electricity.

There are also potential applications in the field of nanotechnology for the creation of nanowires in very small circuits and electronic devices. The miniature wires could also be connected, creating a microscopic power grid.^[2]

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 degradable in the absence of oxygen, but the isolation of hitherto unknown anaerobic hydrocarbon-degrading and reductively dehalogenating bacteria during the last decades provided ultimate proof for these processes in nature. Many novel biochemical reactions were discovered enabling the respective metabolic pathways, but progress in the molecular understanding of these bacteria was rather slow, since genetic systems are not readily applicable for most of them. However, several complete genome sequences are now available for bacteria capable of anaerobic organic pollutant degradation. The genome of the hydrocarbon degrading and iron-reducing species Geobacter metallireducens (accession nr. NC_007517) was determined recently. The genome revealed the presence of genes for reductive dehalogenases, suggesting a wide dehalogenating spectrum of the organisms. Moreover, genome sequences provided unprecedented insights into the evolution of reductive dehalogenation and differing strategies for niche adaptation.^[3]

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. To date, these studies have included sequencing the genomes of multiple Geobacter species and detailed functional genomic/physiological studies on one species, Geobacter sulfurreducens . Genome-based models of several Geobacter species that are able to predict physiological responses under different environmental conditions are now available. Quantitative analysis of gene transcript levels during in situ uranium bioremediation has demonstrated that it is possible to track in situ rates of metabolism and the in situ metabolic state of Geobacter in the subsurface. Initial attempts to link in silico Geobacter models with existing subsurface hydrological and geochemical models are underway. It is expected that this systems approach to bioremediation with Geobacter will provide the opportunity to evaluate multiple Geobacter -catalyzed bioremediation strategies in silico prior to field implementation, thus providing substantial savings when initiating large-scale in situ bioremediation projects for groundwater polluted with uranium and/or organic contaminants.^[4]

Popular culture

Geobacter are used as a plot device in the first episode of the third season of ReGenesis.

References