@article {440,
	title = {Novel regulatory cascades controlling expression of nitrogen-fixation genes in Geobacter sulfurreducens.},
	journal = {Nucleic Acids Res},
	volume = {38},
	year = {2010},
	month = {2010 Nov},
	pages = {7485-99},
	abstract = {Geobacter species often play an important role in bioremediation of environments contaminated with metals or organics and show promise for harvesting electricity from waste organic matter in microbial fuel cells. The ability of Geobacter species to fix atmospheric nitrogen is an important metabolic feature for these applications. We identified novel regulatory cascades controlling nitrogen-fixation gene expression in Geobacter sulfurreducens. Unlike the regulatory mechanisms known in other nitrogen-fixing microorganisms, nitrogen-fixation gene regulation in G. sulfurreducens is controlled by two two-component His-Asp phosphorelay systems. One of these systems appears to be the master regulatory system that activates transcription of the majority of nitrogen-fixation genes and represses a gene encoding glutamate dehydrogenase during nitrogen fixation. The other system whose expression is directly activated by the master regulatory system appears to control by antitermination the expression of a subset of the nitrogen-fixation genes whose transcription is activated by the master regulatory system and whose promoter contains transcription termination signals. This study provides a new paradigm for nitrogen-fixation gene regulation.},
	keywords = {Bacterial Proteins, Binding Sites, DNA-Binding Proteins, Gene Expression Regulation, Bacterial, Geobacter, Nitrogen Fixation, Promoter Regions, Genetic, Protein Kinases, RNA-Binding Proteins, Transcription, Genetic},
	issn = {1362-4962},
	doi = {10.1093/nar/gkq652},
	author = {Ueki, Toshiyuki 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}
}
