Comparison of flavins and a conjugated oligoelectrolyte in stimulating extracellular electron transport from Shewanella oneidensis MR-1

• Conjugated oligoelectrolytes (DSSN+) increase extracellular electron transfer (EET) in Shewanella sp.
• The effect of DSSN+ on the EET rate is potential-dependent.
• Microbially produced flavins are far more effective than DSSN+ in batch experiments.
• DSSN+ addition did not restore the wild-type EET rate in membrane cytochrome knockout mutants.

Slow extracellular electron transfer (EET) rates at the biofilm/electrode interface hinder the application of microbial bioelectronic technology in bioremediation as well as energy recovery from wastewater. Conjugated oligoelectrolytes (COEs) have been shown to increase EET in viable microorganisms. However, confirmation of these results on model electrochemically active microorganisms (EAMs), such as Shewanella oneidensis MR-1, is still lacking. Here, chemical modification of S. oneidensis is achieved through spontaneous intercalation of the amphiphilic water-soluble conjugated oligoelectrolyte, 4,4′-bis(4′-(N,N-bis(6″-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+). Various electrochemical techniques are used to compare the EET enhancement afforded to S. oneidensis by microbially produced flavins and addition of DSSN+. The effect of DSSN+ on the EET rate increases as the working electrode potential increases. However, DSSN+ addition did not fully restore the wild-type EET rate in MtrC–OmcA knockout mutants. These results drive the design of more effective COEs that will serve as an exact molecular surrogate for outer membrane cytochromes.

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