@article {3090,
	title = {Toward establishing minimum requirements for extracellular electron transfer in Geobacter sulfurreducens.},
	journal = {FEMS Microbiol Lett},
	volume = {364},
	year = {2017},
	month = {2017 May 01},
	abstract = {<p>The highly redundant pathways for extracellular electron transfer in Geobacter sulfurreducens must be simplified for this microorganism to serve as an effective chassis for applications such as the development of sensors and biocomputing. Five homologs of the periplasmic c-type cytochromes, PpcA-E, offer the possibility of multiple routes of electron transfer across the periplasm. The presence of a large number of outer membrane c-type cytochromes allows G. sulfurreducens to adapt to disruption of an electron transfer pathway in the outer membrane. A strain in which genes for all five periplasmic cytochromes, PpcA-E, were deleted did not reduce Fe(III). Introducing ppcA under the control of an IPTG-inducible system in the quintuple deletion strain yielded a strain that reduced Fe(III) only in the presence of IPTG. A strain lacking known major outer membrane cytochromes, OmcB, OmcE, OmcS and OmcT, and putative functional homologs of OmcB, did not reduce Fe(III). Introduction of omcB in this septuple deletion strain restored the ability to reduce Fe(III). These results demonstrate that it is possible to trim redundancy from the extracellular electron transfer pathways in G. sulfurreducens in order to construct strains with defined extracellular electron transfer routes.</p>},
	keywords = {Bacterial Outer Membrane Proteins, Bacterial Proteins, Cytochromes c, Electron Transport, Ferric Compounds, Gene Expression Regulation, Bacterial, Geobacter, Oxidation-Reduction, Periplasm},
	issn = {1574-6968},
	doi = {10.1093/femsle/fnx093},
	author = {Ueki, Toshiyuki and DiDonato, Laurie N and Lovley, Derek R}
}
@article {3114,
	title = {Seeing is believing: novel imaging techniques help clarify microbial nanowire structure and function.},
	journal = {Environ Microbiol},
	volume = {17},
	year = {2015},
	month = {2015 Jul},
	pages = {2209-15},
	abstract = {<p>Novel imaging approaches have recently helped to clarify the properties of {\textquoteright}microbial nanowires{\textquoteright}. Geobacter sulfurreducens pili are actual wires. They possess metallic-like conductivity, which can be attributed to overlapping pi-pi orbitals of key aromatic amino acids. Electrostatic force microscopy recently confirmed charge propagation along the pili, in a manner similar to carbon nanotubes. The pili are essential for long-range electron transport to insoluble electron acceptors and interspecies electron transfer. Previous claims that Shewanella oneidensis also produce conductive pili have recently been recanted, based on novel live-imaging studies. The putative pili are, in fact, long extensions of the cytochrome-rich outer membrane and periplasm that, when dried, collapse to form filaments with dimensions similar to pili. It has yet to be demonstrated whether the cytochrome-to-cytochrome electron hopping documented in the dried membrane extensions takes place in intact hydrated membrane extensions or whether the membrane extensions enhance electron transport to insoluble electron acceptors such as Fe(III) oxides or electrodes. These findings demonstrate that G. sulfurreducens conductive pili and the outer membrane extensions of S. oneidensis are fundamentally different in composition, mechanism of electron transport and physiological role. New methods for evaluating filament conductivity will facilitate screening the microbial world for nanowires and elucidating their function.</p>},
	keywords = {Cytochromes, Electric Conductivity, Electron Transport, Electrons, Ferric Compounds, Fimbriae, Bacterial, Geobacter, Microscopy, Atomic Force, Nanowires, Oxides, Periplasm, Shewanella},
	issn = {1462-2920},
	doi = {10.1111/1462-2920.12708},
	author = {Lovley, Derek R and Malvankar, Nikhil S}
}
@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}
}
@article {576,
	title = {Biochemical and genetic characterization of PpcA, a periplasmic c-type cytochrome in Geobacter sulfurreducens.},
	journal = {Biochem J},
	volume = {369},
	year = {2003},
	month = {2003 Jan 1},
	pages = {153-61},
	abstract = {A 9.6 kDa periplasmic c -type cytochrome, designated PpcA, was purified from the Fe(III)-reducing bacterium Geobacter sulfurreducens and characterized. The purified protein is basic (pI 9.5), contains three haems and has an N-terminal amino acid sequence closely related to those of the previously described trihaem c (7) cytochromes of Geobacter metallireducens and Desulfuromonas acetoxidans. The gene encoding PpcA was identified from the G. sulfurreducens genome using the N-terminal sequence, and encodes a protein of 71 amino acids (molecular mass 9.58 kDa) with 49\% identity to the c (7) cytochrome of D. acetoxidans. In order to determine the physiological role of PpcA, a knockout mutant was prepared with a single-step recombination method. Acetate-dependent Fe(III) reduction was significantly inhibited in both growing cultures and cell suspensions of the mutant. When ppcA was expressed in trans, the full capacity for Fe(III) reduction with acetate was restored. The transfer of electrons from acetate to anthraquinone 2,6-disulphonate (AQDS; a humic acid analogue) and to U(VI) was also compromised in the mutant, but acetate-dependent reduction of fumarate was not altered. The rates of reduction of Fe(III), AQDS, U(VI) and fumarate were also the same in the wild type and ppcA mutant when hydrogen was supplied as the electron donor. When taken together with previous studies on other electron transport proteins in G. sulfurreducens, these results suggest that PpcA serves as an intermediary electron carrier from acetate to terminal Fe(III) reductases in the outer membrane, and is also involved in the transfer of electrons from acetate to U(VI) and humics.},
	keywords = {Amino Acid Sequence, Base Sequence, Cytochrome c Group, DNA, Bacterial, Molecular Sequence Data, Periplasm, Proteobacteria, Sequence Homology, Amino Acid},
	issn = {0264-6021},
	doi = {10.1042/BJ20020597},
	author = {Lloyd, Jon R and Leang, Ching and Hodges Myerson, Allison L and Coppi, Maddalena V and Cuifo, Stacey and Methe, Barb and Sandler, Steven J and Lovley, Derek R}
}
