title: Evidence that OmcB and OmpB of Geobacter sulfurreducens are outer membrane surface proteins.
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.
authors.affiliation: Department of Microbiology, Morrill IV North, University of Massachusetts, Amherst, MA, USA.
authors.forename: Xinlei
authors.initials: X
authors.lastname: Qian
authors.forename: Gemma
authors.initials: G
authors.lastname: Reguera
authors.forename: Tünde
authors.initials: T
authors.lastname: Mester
authors.forename: Derek R
authors.initials: DR
authors.lastname: Lovley
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure*; D045304:Cytochromes c / Q000378:metabolism; D005290:Ferric Compounds / Q000378:metabolism; D045302:Geobacter / Q000378:metabolism* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D010084:Oxidation-Reduction; D010447:Peptide Hydrolases / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D005290:Ferric Compounds; C436968:OmcB protein, bacteria; C000499:ferric oxide; C025314:ferric citrate; D045304:Cytochromes c; D010447:Peptide Hydrolases