Electrochemical and spectroscopic insights into the mechanisms of bidirectional microbe-electrode electron transfer in Geobacter soli biofilms

Abstract

Few electroactive bacteria have shown the capacity of exchanging electrons with electrode in both directions, and the mechanisms of such bidirectional electron transfer remain uncertain hitherto. In this study, we demonstrate that Geobacter soli biofilms could directly donate electrons to and accept electrons from graphite electrode. Under anodic conditions, G. soli oxidizes acetate to generate current, and under cathodic conditions, nitrate is reduced by a truncated denitrification pathway with nitrous oxide as end product. Cyclic voltammetry, differential pulse voltammetry and electrochemical in situ FTIR spectra demonstrate that distinct external membrane redox systems exist in the anode and cathode biofilms, which supports the conclusion that G. soli uses different electron transfer conduits for bidirectional electron transfer. These results expand the horizon of bidirectional electron transfer mechanisms, meanwhile this study represents a first report that Geobacter species might utilize electrode as electron donor for incomplete denitrification.