The conjugated oligoelectrolyte DSSN+ enables exceptional coulombic efficiency via direct electron transfer for anode-respiring Shewanella oneidensis MR-1—a mechanistic study

Shewanella oneidensis MR-1 was cultivated on lactate with poised graphite electrode acceptors (E = +0.2 V vs. Ag/AgCl) in order to explore the basis for sustained increases in anodic current output following the addition of the lipid-intercalating conjugated oligoelectrolyte (COE), 4,4'-bis(4'-(N,N-bis(6''-(N,N,N-trimethylammonium)hexyl)amino)-styryl)stilbene tetraiodide (DSSN+). Microbial cultures, which were spiked with DSSN+, exhibit a ∼2.2-fold increase in charge collected, a ∼3.1-fold increase in electrode colonization by S. oneidensis, and a ∼1.7-fold increase in coulombic efficiency from 51 ± 10% to an exceptional 84 ± 7% without obvious toxicity effects. Direct microbial biofilm voltammetry reveals that DSSN+ rapidly and sustainably increases cytochrome-based direct electron transfer and subsequently increases flavin-based mediated electron transfer. Control experiments indicate that DSSN+ does not contribute to the current in the absence of bacteria.