Rate enhancement of bacterial extracellular electron transport involves bound flavin semiquinones

Extracellular redox-active compounds, flavins and other quinones, have been hypothesized to play a major role in the delivery of electrons from cellular metabolic systems to extracellular insoluble substrates by a diffusion-based shuttling two-electron-transfer mechanism. Here we show that flavin mo...

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Veröffentlicht in:Proceedings of the National Academy of Sciences - PNAS 2013-05, Vol.110 (19), p.7856-7861
Hauptverfasser: Okamoto, Akihiro, Hashimoto, Kazuhito, Nealson, Kenneth H., Nakamura, Ryuhei
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Sprache:eng
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Zusammenfassung:Extracellular redox-active compounds, flavins and other quinones, have been hypothesized to play a major role in the delivery of electrons from cellular metabolic systems to extracellular insoluble substrates by a diffusion-based shuttling two-electron-transfer mechanism. Here we show that flavin molecules secreted by Shewanella oneidensis MR-1 enhance the ability of its outer-membrane c -type cytochromes (OM c- Cyts) to transport electrons as redox cofactors, but not free-form flavins. Whole-cell differential pulse voltammetry revealed that the redox potential of flavin was reversibly shifted more than 100 mV in a positive direction, in good agreement with increasing microbial current generation. Importantly, this flavin/OM c- Cyts interaction was found to facilitate a one-electron redox reaction via a semiquinone, resulting in a 10 ³- to 10 ⁵-fold faster reaction rate than that of free flavin. These results are not consistent with previously proposed redox-shuttling mechanisms but suggest that the flavin/OM c- Cyts interaction regulates the extent of extracellular electron transport coupled with intracellular metabolic activity.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1220823110