Cyclic voltammetric analysis of the electron transfer of Shewanella oneidensis MR-1 and nanofilament and cytochrome knock-out mutants

Shewanella is frequently used as a model microorganism for microbial bioelectrochemical systems. In this study, we used cyclic voltammetry (CV) to investigate extracellular electron transfer mechanisms from S. oneidensis MR-1 (WT) and five deletion mutants: membrane bound cytochrome (∆mtrC/ΔomcA), transmembrane pili (ΔpilM-Q, ΔmshH-Q, and ΔpilM-Q/ΔmshH-Q) and flagella (∆flg). We demonstrate that the formal potentials of mediated and direct electron transfer sites of the derived biofilms can be gained from CVs of the respective biofilms recorded at bioelectrocatlytic (i.e. turnover) and lactate depleted (i.e. non-turnover) conditions. As the biofilms possess only a limited bioelectrocatalytic activity, an advanced data processing procedure, using the open-source software SOAS, was applied. The obtained results indicate that S. oneidensis mutants used in this study are able to bypass hindered direct electron transfer by alternative redox proteins as well as self-mediated pathways.

Graphical AbstractHow does Shewanella transfer its electrons to solid acceptors? Using cyclic voltammetry direct and mediated electron transfer of S. oneidensis MR-1 and related mutants are investigated. The subsequent analysis, based on an elaborate open source software data -processing, indicates a correlation of the maximum current density (x-axes of the graph) of the respective mutant and its mediated electron-transfer ability (respective CV- peak height on the y-axes).Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► Direct (DET) and mediated (MET) electron transfer of S. Oneidensis. ► Analysis on exemplary knock-out mutants. ► Combining cyclic voltammetry with advanced data analysis. ► Indications for differences in the share of DET and MET between mutants detected.