ABSTRACT
The Shewanella oneidensis outer membrane ß-barrel protein MtrB is part of a membrane-spanning protein complex (MtrABC) which is necessary for dissimilatory iron reduction. Quantitative PCR, heterologous gene expression, and mutant studies indicated that MtrA is required for periplasmic stability of MtrB. DegP depletion compensated for this MtrA dependence.
Subject(s)
ATP-Binding Cassette Transporters/genetics , ATP-Binding Cassette Transporters/metabolism , Bacterial Outer Membrane Proteins/genetics , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Periplasm/metabolism , Shewanella/genetics , Shewanella/metabolism , Blotting, Western , Electron Transport , Escherichia coli/genetics , Gene Expression , Gene Knockout Techniques , Heat-Shock Proteins/genetics , Heat-Shock Proteins/metabolism , Iron/metabolism , Mutation , Oxidation-Reduction , Periplasm/genetics , Periplasmic Proteins/genetics , Periplasmic Proteins/metabolism , Polymerase Chain Reaction , Protein Stability , Serine Endopeptidases/genetics , Serine Endopeptidases/metabolismABSTRACT
Dissimilatory microbial reduction of insoluble Fe(III) oxides is a geochemically and ecologically important process which involves the transfer of cellular, respiratory electrons from the cytoplasmic membrane to insoluble, extracellular, mineral-phase electron acceptors. In this paper evidence is provided for the function of the periplasmic fumarate reductase FccA and the decaheme c-type cytochrome MtrA in periplasmic electron transfer reactions in the gammaproteobacterium Shewanella oneidensis. Both proteins are abundant in the periplasm of ferric citrate-reducing S. oneidensis cells. In vitro fumarate reductase FccA and c-type cytochrome MtrA were reduced by the cytoplasmic membrane-bound protein CymA. Electron transfer between CymA and MtrA was 1.4-fold faster than the CymA-catalyzed reduction of FccA. Further experiments showing a bidirectional electron transfer between FccA and MtrA provided evidence for an electron transfer network in the periplasmic space of S. oneidensis. Hence, FccA could function in both the electron transport to fumarate and via MtrA to mineral-phase Fe(III). Growth experiments with a DeltafccA deletion mutant suggest a role of FccA as a transient electron storage protein.
