@article {490,
	title = {PilR, a transcriptional regulator for pilin and other genes required for Fe(III) reduction in Geobacter sulfurreducens.},
	journal = {J Mol Microbiol Biotechnol},
	volume = {16},
	year = {2009},
	month = {2009},
	pages = {146-58},
	abstract = {Growth using Fe(III) as a terminal electron acceptor is a critical physiological process in Geobacter sulfurreducens. However, the mechanisms of electron transfer during Fe(III) reduction are only now being understood. It has been demonstrated that the pili in G. sulfurreducens function as microbial nanowires conducting electrons onto Fe(III) oxides. A number of c-type cytochromes have also been shown to play important roles in Fe(III) reduction. However, the regulatory networks controlling the expression of the genes involved in such processes are not well known. Here we report that the expression of pilA, which encodes the pilistructural protein, is directly regulated by a two-component regulatory system in which PilR functions as an RpoN-dependent enhancer binding protein. Surprisingly, a deletion of the pilR gene affected not only insoluble Fe(III) reduction, which requires pili, but also soluble Fe(III) reduction, which, in contrast, does not require pili. Gene expression profiling using whole-genome DNA microarray and quantitative RT-PCR analyses obtained with a PilR-deficient mutant revealed that the expression of pilA and other pilin-related genes are downregulated, while many c-type cytochromes involved in Fe(III) reduction were differentially regulated. This is the first instance of an enhancer binding protein implicated in regulating genes involved in Fe(III) respiratory functions.},
	keywords = {Bacterial Proteins, Ferric Compounds, Fimbriae Proteins, Gene Expression Regulation, Bacterial, Genes, Regulator, Geobacter, Oxidation-Reduction, Transcription, Genetic},
	issn = {1660-2412},
	doi = {10.1159/000115849},
	author = {Ju{\'a}rez, Katy and Kim, Byoung-Chan and Nevin, Kelly and Olvera, Leticia and Reguera, Gemma and Lovley, Derek R and Meth{\'e}, Barbara A}
}
@article {496,
	title = {Evidence that OmcB and OmpB of Geobacter sulfurreducens are outer membrane surface proteins.},
	journal = {FEMS Microbiol Lett},
	volume = {277},
	year = {2007},
	month = {2007 Dec},
	pages = {21-7},
	abstract = {The c-type cytochrome (OmcB) and the multicopper protein (OmpB) required for Fe(III) oxide reduction by Geobacter sulfurreducens were predicted previously to be outer membrane proteins, but it is not clear whether they are positioned in a manner that permits the interaction with Fe(III). Treatment of whole cells with proteinase K inhibited Fe(III) reduction, but had no impact on the inner membrane-associated fumarate reduction. OmcB was digested by protease, resulting in a smaller peptide. However, immunogold labeling coupled with transmission electron microscopy did not detect OmcB, suggesting that it is only partially exposed on the cell surface. In contrast, OmpB was completely digested with protease. OmpB was loosely associated with the cell surface as a substantial portion of it was recovered in the culture supernatant. Immunogold labeling demonstrated that OmpB associated with the cell was evenly distributed on the cell surface rather than localized to one side of the cell like the conductive pili. Although several proteins required for Fe(III) oxide reduction are shown to be exposed on the outer surface of G. sulfurreducens, the finding that OmcB is also surface exposed is the first report of a protein required for optimal Fe(III) citrate reduction at least partially accessible on the cell surface.},
	keywords = {Bacterial Outer Membrane Proteins, Cell Membrane, Cytochromes c, Ferric Compounds, Geobacter, Microscopy, Electron, Transmission, Oxidation-Reduction, Peptide Hydrolases},
	issn = {0378-1097},
	doi = {10.1111/j.1574-6968.2007.00915.x},
	author = {Qian, Xinlei and Reguera, Gemma and Mester, T{\"u}nde and Lovley, Derek R}
}
@article {510,
	title = {Possible nonconductive role of Geobacter sulfurreducens pilus nanowires in biofilm formation.},
	journal = {J Bacteriol},
	volume = {189},
	year = {2007},
	month = {2007 Mar},
	pages = {2125-7},
	abstract = {Geobacter sulfurreducens required expression of electrically conductive pili to form biofilms on Fe(III) oxide surfaces, but pili were also essential for biofilm development on plain glass when fumarate was the sole electron acceptor. Furthermore, pili were needed for cell aggregation in agglutination studies. These results suggest that the pili of G. sulfurreducens also have a structural role in biofilm formation.},
	keywords = {Agglutination, Biofilms, Electron Transport, Ferric Compounds, Fimbriae, Bacterial, Geobacter},
	issn = {0021-9193},
	doi = {10.1128/JB.01284-06},
	author = {Reguera, Gemma and Pollina, Rachael B and Nicoll, Julie S and Lovley, Derek R}
}
@article {535,
	title = {Extracellular electron transfer via microbial nanowires.},
	journal = {Nature},
	volume = {435},
	year = {2005},
	month = {2005 Jun 23},
	pages = {1098-101},
	abstract = {Microbes that can transfer electrons to extracellular electron acceptors, such as Fe(iii) oxides, are important in organic matter degradation and nutrient cycling in soils and sediments. Previous investigations on electron transfer to Fe(iii) have focused on the role of outer-membrane c-type cytochromes. However, some Fe(iii) reducers lack c-cytochromes. Geobacter species, which are the predominant Fe(iii) reducers in many environments, must directly contact Fe(iii) oxides to reduce them, and produce monolateral pili that were proposed, on the basis of the role of pili in other organisms, to aid in establishing contact with the Fe(iii) oxides. Here we report that a pilus-deficient mutant of Geobacter sulfurreducens could not reduce Fe(iii) oxides but could attach to them. Conducting-probe atomic force microscopy revealed that the pili were highly conductive. These results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(iii) oxides. Electron transfer through pili indicates possibilities for other unique cell-surface and cell-cell interactions, and for bioengineering of novel conductive materials.},
	keywords = {Biotechnology, Electric Conductivity, Electron Transport, Ferric Compounds, Fimbriae Proteins, Fimbriae, Bacterial, Genes, Bacterial, Geobacter, Microscopy, Atomic Force, Microscopy, Electron, Transmission, Mutation, Nanostructures, Phylogeny},
	issn = {1476-4687},
	doi = {10.1038/nature03661},
	author = {Reguera, Gemma and McCarthy, Kevin D and Mehta, Teena and Nicoll, Julie S and Tuominen, Mark T and Lovley, Derek R}
}
@article {534,
	title = {A novel Geobacteraceae-specific outer membrane protein J (OmpJ) is essential for electron transport to Fe(III) and Mn(IV) oxides in Geobacter sulfurreducens.},
	journal = {BMC Microbiol},
	volume = {5},
	year = {2005},
	month = {2005},
	pages = {41},
	abstract = {BACKGROUND: Metal reduction is thought to take place at or near the bacterial outer membrane and, thus, outer membrane proteins in the model dissimilatory metal-reducing organism Geobacter sulfurreducens are of interest to understand the mechanisms of Fe(III) reduction in the Geobacter species that are the predominant Fe(III) reducers in many environments. Previous studies have implicated periplasmic and outer membrane cytochromes in electron transfer to metals. Here we show that the most abundant outer membrane protein of G. sulfurreducens, OmpJ, is not a cytochrome yet it is required for metal respiration.

RESULTS: When outer membrane proteins of G. sulfurreducens were separated via SDS-PAGE, one protein, designated OmpJ (outer membrane protein J), was particularly abundant. The encoding gene, which was identified from mass spectrometry analysis of peptide fragments, is present in other Geobacteraceae, but not in organisms outside this family. The predicted localization and structure of the OmpJ protein suggested that it was a porin. Deletion of the ompJ gene in G. sulfurreducens produced a strain that grew as well as the wild-type strain with fumarate as the electron acceptor but could not grow with metals, such as soluble or insoluble Fe(III) and insoluble Mn(IV) oxide, as the electron acceptor. The heme c content in the mutant strain was ca. 50\% of the wild-type and there was a widespread loss of multiple cytochromes from soluble and membrane fractions. Transmission electron microscopy analyses of mutant cells revealed an unusually enlarged periplasm, which is likely to trigger extracytoplasmic stress response mechanisms leading to the degradation of periplasmic and/or outer membrane proteins, such as cytochromes, required for metal reduction. Thus, the loss of the capacity for extracellular electron transport in the mutant could be due to the missing c-type cytochromes, or some more direct, but as yet unknown, role of OmpJ in metal reduction.

CONCLUSION: OmpJ is a putative porin found in the outer membrane of the model metal reducer G. sulfurreducens that is required for respiration of extracellular electron acceptors such as soluble and insoluble metals. The effect of OmpJ in extracellular electron transfer is indirect, as OmpJ is required to keep the integrity of the periplasmic space necessary for proper folding and functioning of periplasmic and outer membrane electron transport components. The exclusive presence of ompJ in members of the Geobacteraceae family as well as its role in metal reduction suggest that the ompJ sequence may be useful in tracking the growth or activity of Geobacteraceae in sedimentary environments.},
	keywords = {Amino Acid Sequence, Bacterial Outer Membrane Proteins, Base Sequence, Biological Transport, Deltaproteobacteria, DNA Primers, Ferric Compounds, Gene Deletion, Genome, Bacterial, Geobacter, Manganese Compounds, Molecular Sequence Data, Oxides, Peptide Fragments, Phylogeny, Protein Structure, Secondary, Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization},
	issn = {1471-2180},
	doi = {10.1186/1471-2180-5-41},
	author = {Afkar, Eman and Reguera, Gemma and Schiffer, Marianne and Lovley, Derek R}
}
