AEM Accepts, published online ahead of print on 16 October 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.01834-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Periplasmic electron transfer via the c-type cytochromes MtrA and FccA of Shewanella oneidensis MR-1.

Bjoern Schuetz, Marcus Schicklberger, Johannes Kuermann, Alfred M. Spormann, and Johannes Gescher^*

Institut für Biologie II, Mikrobiologie, Universität Freiburg, Schänzlestr.1, D-79104 Freiburg; Depts. of Chemical Engineering, and of Civil & Environmental Engineering, Stanford University, Stanford, CA 94305, USA

^* To whom correspondence should be addressed. Email: johannes.gescher{at}biologie.uni-freiburg.de.

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 manuscript 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 y-proteobacterium 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 1.4fold 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 fccA deletion mutant suggest a role of FccA as a transient electron storage.