Microbial Phenazine Production Enhances Electron Transfer in Biofuel Cells

TLDR

High‑rate electron transfer to an MFC anode has not been reported for bacteria that produce soluble redox mediators. The study investigates the mechanism of electron transfer in Pseudomonas aeruginosa strain KRP1. Electron transfer was mediated by the bacterial metabolites pyocyanin and phenazine‑1‑carboxamide, whose production was stimulated by the anode. Mutants lacking pyocyanin and phenazine‑1‑carboxamide produced only 5 % of the wild‑type power, while adding pyocyanin restored 50 % of output and also boosted transfer in other bacteria, showing that one species can produce shuttles usable by others—a finding with significant implications for MFC power.

Abstract

High-rate electron transfer toward an anode in microbial fuel cells (MFCs) has thus far not been described for bacteria-producing soluble redox mediators. To study the mechanism of electron transfer, we used a MFC isolate, Pseudomonas aeruginosa strain KRP1. Bacterial electron transfer toward the MFC anode was enabled through pyocyanin and phenazine-1-carboxamide. The presence of the anode stimulated pyocyanin production. Mutant strains, deficient in the synthesis of pyocyanin and phenazine-1-carboxamide, were unable to achieve substantial electron transfer and reached only 5% of the wild type's power output. Upon pyocyanin addition, the power output was restored to 50%. Pyocyanin was not only used by P. aeruginosa to improve electron transfer but as well enhanced electron transfer by other bacterial species. The finding that one bacterium can produce electron shuttles, which can be used also by other bacteria, to enhance electron-transfer rate and growth, has not been shown before. These findings have considerable implications with respect to the power output attainable in MFCs.