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Cell-secreted Flavins Bound to Membrane Cytochromes Dictate Electron Transfer Reactions to Surfaces with Diverse Charge and pH

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      The variety of solid surfaces to and from which microbes can deliver electrons by extracellular electron transport (EET) processes via outer-membrane c-type cytochromes (OM c-Cyts) expands the importance of microbial respiration in natural environments and industrial applications. Here, we demonstrate that the bifurcated EET pathway of OM c-Cyts sustains the diversity of the EET surface in Shewanella oneidensis MR-1 via specific binding with cell-secreted flavin mononucleotide (FMN) and riboflavin (RF). Microbial current production and whole-cell differential pulse voltammetry revealed that RF and FMN enhance EET as bound cofactors in a similar manner. Conversely, FMN and RF were clearly differentiated in the EET enhancement by gene-deletion of OM c-Cyts and the dependency of the electrode potential and pH. These results indicate that RF and FMN have specific binding sites in OM c-Cyts and highlight the potential roles of these flavin-cytochrome complexes in controlling the rate of electron transfer to surfaces with diverse potential and pH.

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            Author and article information

            [1 ]Departments of Earth Sciences and Biological Sciences, University of Southern California , Los Angeles, CA 90089
            [2 ]Department of Applied Chemistry, University of Tokyo , Bunkyo-ku, Tokyo, 113-8654
            [3 ]Biofunctional Catalyst Research Team, RIKEN Center for Sustainable Resource Science , Wako, Saitama 351-0198, Japan
            [4 ]J. Craig Venter Institute , San Diego, CA 92121
            Author notes
            Sci Rep
            Sci Rep
            Scientific Reports
            Nature Publishing Group
            11 July 2014
            : 4
            4092373 srep05628 10.1038/srep05628
            Copyright © 2014, Macmillan Publishers Limited. All rights reserved

            This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder in order to reproduce the material. To view a copy of this license, visit




            added an editorial note to Shewanella

            To further elucidate the role of flavins in extracellular electron transfer (EET) in Shewanella, Okamoto et al perform an electrochemical investigation and conclude that rather than randomly mediating EET in their soluble forms, different flavins interact specifically with their respective outer membrane cytochromes in a bifurcated EET mechanism.

            2016-03-21 13:40 UTC

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