S147: Water-soluble oligo-electrolytes increase extracellular electron transfer in Shewanella oneidensis MR-1 biofilms

Electroactive biofilms (EABs) are microbial communities capable of conserving energy through extracellular electron transfer (EET) to solid electrodes. EET occurs either directly, through microbially produced soluble electron transfer agents, or through a combination of the previous two mechanisms. EAB-based devices are relevant to biogeochemistry, energy recovery from wastewater (Microbial Fuel Cells (MFCs)), bioremediation, and bioelectrosynthesis. However, the electron transfer at the EAB/electrode interface is the limiting step in the EET chain, thus limiting the full-scale application of EAB-based devices.

The water-soluble oligo-electrolyte distyrylstilbene (DSSN+) can increase transmembrane electron transfer in eukaryotic cells and Escherichia coli grown on carbon electrodes. The use of such conjugated oligo-electrolytes could partially remove the EET limitation at the EAB/electrode interface. To verify this hypothesis, we grow the model electroactive microorganism Shewanella oneidensis MR-1as thin biofilms on carbon felt electrodes in potentiostat-controlled electrochemical cells. Chronoamperometry results show that DSSN+ addition increase current output at 0.2 V vs. Ag/AgCl sat. KCl. Cyclic voltammetry and differential pulse voltammetry prove that the current increase is due to the an additional EET process at 0.1 V. This EET pathway is independent from both the flavins-mediated EET and the cytochrome-mediated processes, whose voltammetry signatures are observed at -0.4 V and -0.1 V. We suggest that this additional EET is due to changes to bacterial membrane porosity following DSSN+ addition. Additionally, DSSN+ does not affect significantly the vitality of the cell. Experiments with outer membrane cytochrome (Mtrc-OmcA) knockout mutants show that DSSN+ requires intact cytochrome chain to facilitate EET process.