@article {3137,
	title = {U(VI) reduction by diverse outer surface c-type cytochromes of Geobacter sulfurreducens.},
	journal = {Appl Environ Microbiol},
	volume = {79},
	year = {2013},
	month = {2013 Oct},
	pages = {6369-74},
	abstract = {<p>Early studies with Geobacter sulfurreducens suggested that outer-surface c-type cytochromes might play a role in U(VI) reduction, but it has recently been suggested that there is substantial U(VI) reduction at the surface of the electrically conductive pili known as microbial nanowires. This phenomenon was further investigated. A strain of G. sulfurreducens, known as Aro-5, which produces pili with substantially reduced conductivity reduced U(VI) nearly as well as the wild type, as did a strain in which the gene for PilA, the structural pilin protein, was deleted. In order to reduce rates of U(VI) reduction to levels less than 20\% of the wild-type rates, it was necessary to delete the genes for the five most abundant outer surface c-type cytochromes of G. sulfurreducens. X-ray absorption near-edge structure spectroscopy demonstrated that whereas 83\% {\textpm} 10\% of the uranium associated with wild-type cells correspond to U(IV) after 4 h of incubation, with the quintuple mutant, 89\% {\textpm} 10\% of uranium was U(VI). Transmission electron microscopy and X-ray energy dispersion spectroscopy revealed that wild-type cells did not precipitate uranium along pili as previously reported, but U(IV) was precipitated at the outer cell surface. These findings are consistent with those of previous studies, which have suggested that G. sulfurreducens requires outer-surface c-type cytochromes but not pili for the reduction of soluble extracellular electron acceptors.</p>},
	keywords = {Cytochromes, Fimbriae, Bacterial, Gene Deletion, Geobacter, Microscopy, Electron, Transmission, Oxidation-Reduction, Uranium, X-Ray Absorption Spectroscopy},
	issn = {1098-5336},
	doi = {10.1128/AEM.02551-13},
	author = {Orellana, Roberto and Leavitt, Janet J and Comolli, Luis R and Csencsits, Roseann and Janot, Noemie and Flanagan, Kelly A and Gray, Arianna S and Leang, Ching and Izallalen, Mounir and Mester, T{\"u}nde and Lovley, Derek R}
}
@article {505,
	title = {Importance of c-Type cytochromes for U(VI) reduction by Geobacter sulfurreducens.},
	journal = {BMC Microbiol},
	volume = {7},
	year = {2007},
	month = {2007},
	pages = {16},
	abstract = {BACKGROUND: In order to study the mechanism of U(VI) reduction, the effect of deleting c-type cytochrome genes on the capacity of Geobacter sulfurreducens to reduce U(VI) with acetate serving as the electron donor was investigated.

RESULTS: The ability of several c-type cytochrome deficient mutants to reduce U(VI) was lower than that of the wild type strain. Elimination of two confirmed outer membrane cytochromes and two putative outer membrane cytochromes significantly decreased (ca. 50-60\%) the ability of G. sulfurreducens to reduce U(VI). Involvement in U(VI) reduction did not appear to be a general property of outer membrane cytochromes, as elimination of two other confirmed outer membrane cytochromes, OmcB and OmcC, had very little impact on U(VI) reduction. Among the periplasmic cytochromes, only MacA, proposed to transfer electrons from the inner membrane to the periplasm, appeared to play a significant role in U(VI) reduction. A subpopulation of both wild type and U(VI) reduction-impaired cells, 24-30\%, accumulated amorphous uranium in the periplasm. Comparison of uranium-accumulating cells demonstrated a similar amount of periplasmic uranium accumulation in U(VI) reduction-impaired and wild type G. sulfurreducens. Assessment of the ability of the various suspensions to reduce Fe(III) revealed no correlation between the impact of cytochrome deletion on U(VI) reduction and reduction of Fe(III) hydroxide and chelated Fe(III).

CONCLUSION: This study indicates that c-type cytochromes are involved in U(VI) reduction by Geobacter sulfurreducens. The data provide new evidence for extracellular uranium reduction by G. sulfurreducens but do not rule out the possibility of periplasmic uranium reduction. Occurrence of U(VI) reduction at the cell surface is supported by the significant impact of elimination of outer membrane cytochromes on U(VI) reduction and the lack of correlation between periplasmic uranium accumulation and the capacity for uranium reduction. Periplasmic uranium accumulation may reflect the ability of uranium to penetrate the outer membrane rather than the occurrence of enzymatic U(VI) reduction. Elimination of cytochromes rarely had a similar impact on both Fe(III) and U(VI) reduction, suggesting that there are differences in the routes of electron transfer to U(VI) and Fe(III). Further studies are required to clarify the pathways leading to U(VI) reduction in G. sulfurreducens.},
	keywords = {Biodegradation, Environmental, Cytochrome c Group, Ferric Compounds, Geobacter, Microscopy, Electron, Transmission, Mutation, Oxidation-Reduction, Periplasm, Uranium},
	issn = {1471-2180},
	doi = {10.1186/1471-2180-7-16},
	author = {Shelobolina, Evgenya S and Coppi, Maddalena V and Korenevsky, Anton A and DiDonato, Laurie N and Sullivan, Sara A and Konishi, Hiromi and Xu, Huifang and Leang, Ching and Butler, Jessica E and Kim, Byoung-Chan and Lovley, Derek R}
}
