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Geobacter metallireducens GS-15
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Microorganisms that use insoluble Fe(III)oxides as an electron acceptor can have an important function in the carbon and nutrient cycles of aquatic sediments and in the bioremediation of organic and metal contaminants in groundwater. Geobacter metallireducens strain GS-15, first isolated from freshwater sediment, is able to gain energy through the dissimilatory reduction of iron, manganese, uranium and other metals (Lovley and Phillips 1988). In addition, G. metallireducens can oxidize several short chain fatty acids, alcohols and monoaromatic compounds including toluene and phenol with iron as the sole electron acceptor (Lovley et al 1993). These characteristics, in conjunction with its predominance in many sediment environments, make G. metallireducens a possible agent for bioremediation.

Although Fe(III) oxides are often abundant, Fe(III)-reducing microbes are faced with the problem of how to effectively access an electron acceptor that cannot diffuse to the cell. Geobacter metallireducens specifically expresses flagella and pili, only when grown on insoluble Fe(III) or Mn(IV) oxide, and is chemotactic towards Fe(II) and Mn(II) under these conditions (Childers et al 2002). These results suggest that G. metallireducens senses when soluble electron acceptors are depleted and then synthesizes the appropriate appendages to permit it to search for, and establish contact with, insoluble Fe(III) or Mn(IV) oxide. This approach to the use of an insoluble electron acceptor may explain why Geobacter species predominate over other Fe(III) oxide-reducing microorganisms in a wide variety of sedimentary environments.

Lovley DR, Phillips EJP. Novel mode of microbial energy-metabolism - organic-carbon oxidation coupled to dissimilatory reduction of iron or manganese. Appl Environ. Microb 1988; 54:1472-1480

Lovley DR, Giovannoni SJ, White DC, Champine JE, Phillips EJ, Gorby YA, Goodwin S. Geobacter metallireducens gen. nov. sp. nov., a microorganism capable of coupling the complete oxidation of organic compounds to the reduction of iron and other metals. Arch Microbiol. 1993;159:336-44.

Childers SE, Ciufo S, Lovley DR. Geobacter metallireducens accesses insoluble Fe(III) oxide by chemotaxis. Nature 2002; 416: 767-9.