title: A severe reduction in the cytochrome C content of Geobacter sulfurreducens eliminates its capacity for extracellular electron transfer.
abstract: The ability of Geobacter species to transfer electrons outside the cell enables them to play an important role in a number of biogeochemical and bioenergy processes. Gene deletion studies have implicated periplasmic and outer-surface c-type cytochromes in this extracellular electron transfer. However, even when as many as five c-type cytochrome genes have been deleted, some capacity for extracellular electron transfer remains. In order to evaluate the role of c-type cytochromes in extracellular electron transfer, Geobacter sulfurreducens was grown in a low-iron medium that included the iron chelator (2,2'-bipyridine) to further sequester iron. Haem-staining revealed that the cytochrome content of cells grown in this manner was 15-fold lower than in cells exposed to a standard iron-containing medium. The low cytochrome abundance was confirmed by in situ nanoparticle-enhanced Raman spectroscopy (NERS). The cytochrome-depleted cells reduced fumarate to succinate as well as the cytochrome-replete cells do, but were unable to reduce Fe(III) citrate or to exchange electrons with a graphite electrode. These results demonstrate that c-type cytochromes are essential for extracellular electron transfer by G. sulfurreducens. The strategy for growing cytochrome-depleted G. sulfurreducens will also greatly aid future physiological studies of Geobacter species and other microorganisms capable of extracellular electron transfer.
authors.affiliation: Department of Chemical Engineering, University of Alcalá, Alcalá de Henares, Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Estevez-Canales
authors.forename: Akiyoshi
authors.initials: A
authors.lastname: Kuzume
authors.forename: Zulema
authors.initials: Z
authors.lastname: Borjas
authors.forename: Michael
authors.initials: M
authors.lastname: Füeg
authors.forename: Derek
authors.initials: D
authors.lastname: Lovley
authors.forename: Thomas
authors.initials: T
authors.lastname: Wandlowski
authors.forename: Abraham
authors.initials: A
authors.lastname: Esteve-Núñez
mesh_terms: D003470:Culture Media / Q000737:chemistry; D045304:Cytochromes c / Q000378:metabolism*; D004566:Electrodes; D004579:Electron Transport; D005290:Ferric Compounds / Q000378:metabolism; D005650:Fumarates / Q000378:metabolism; D045302:Geobacter / Q000378:metabolism*; D006108:Graphite / Q000378:metabolism; D010084:Oxidation-Reduction; D013059:Spectrum Analysis, Raman; D013194:Staining and Labeling; D019802:Succinic Acid / Q000378:metabolism
chemical_list: D003470:Culture Media; D005290:Ferric Compounds; D005650:Fumarates; C025314:ferric citrate; D006108:Graphite; D045304:Cytochromes c; D019802:Succinic Acid