Cell surface exposure of the outer membrane cytochromes of Shewanella oneidensis MR-1

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AimTo determine if the outer membrane (OM) cytochromes of the metal-reducing bacterium Shewanella oneidensis MR-1 are exposed on the cell surface.Methods and ResultsMR-1 cells were incubated with proteinase K or buffer and the resulting degradation of the OM cytochromes was examined by Western blotting. The periplasmic fumarate reductase (control) was not degraded. The OM cytochromes OmcA and OmcB were significantly degraded by proteinase K (71 and 31%, respectively). Immunofluorescence confirmed a prominent cell surface exposure of OmcA and a partial exposure of OmcB and the noncytochrome OM protein MtrB.ConclusionsThe cytochromes OmcA and OmcB are exposed on the outer face of the OM.Significance and Impact of the StudyThe cell surface exposure of these cytochromes could allow them to directly contact extracellular insoluble electron acceptors (e.g. manganese oxides) and is consistent with their in vivo role.

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