Journal
BIOCHEMICAL SOCIETY TRANSACTIONS
Volume 40, Issue -, Pages 1227-1232Publisher
PORTLAND PRESS LTD
DOI: 10.1042/BST20120162
Keywords
biological electron transfer; bioremediation; Geobacter; pilus nanowire; uranium reduction
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Funding
- National Institute of Environmental Health Science's Superfund programme [R01 ES017052-03]
- Office of Science (Biological and Environmental Research), U.S. Department of Energy [DE-SC0000795]
- National Science Foundation [MCB 021948]
- Div Of Molecular and Cellular Bioscience
- Direct For Biological Sciences [1021948] Funding Source: National Science Foundation
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The in situ stimulation of Fe(III) oxide reduction in the subsurface stimulates the growth of Geobacter spp. and the precipitation of U(VI) from groundwater. As with Fe(III) oxide reduction, the reduction of uranium by Geobacter spp. requires the expression of their conductive pili. The pili bind the soluble uranium and catalyse its extracellular reductive precipitation along the pili filaments as a mononuclear U(IV) complexed by carbon-containing ligands. Although most of the uranium is immobilized by the pili, some uranium deposits are also observed in discreet regions of the outer membrane, consistent with the participation of redox-active foci, presumably c-type cytochromes, in the extracellular reduction of uranium. It is unlikely that cytochromes released from the outer membrane could associate with the pili and contribute to the catalysis, because scanning tunnelling microscopy spectroscopy did not reveal any haem-specific electronic features in the pili, but, rather, showed topographic and electronic features intrinsic to the pilus shaft. Pili not only enhance the rate and extent of uranium reduction per cell, but also prevent the uranium from traversing the outer membrane and mineralizing the cell envelope. As a result, pili expression preserves the essential respiratory activities of the cell envelope and the cell's viability. Hence the results support a model in which the conductive pili function as the primary mechanism for the reduction of uranium and cellular protection in Geobacter spp.
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