Anode Biofilms of Geoalkalibacter ferrihydriticus Exhibit Electrochemical Signatures of Multiple Electron Transport Pathways

Thriving under alkaliphilic conditions, Geoalkalibacter ferrihydriticus (Glk. ferrihydriticus) provides new applications in treating alkaline waste streams as well as a possible new model organism for microbial electrochemistry. We investigated the electrochemical response of biofilms of the alkaliphilic anode-respiring bacterium (ARB) Glk. ferrihydriticus voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry. We observed there to be at least four dominant electron transfer pathways, with their contribution to the overall current produced dependent on the set anode potential. These pathways appear to be manifested at midpoint potentials of approximately -0.14 V, -0.2 V, -0.24 V, and -0.27 V vs standard hydrogen electrode. The individual contributions of the pathways change upon equilibration from a set anode potential to another anode potential. Additionally, the contribution of each pathway to the overall current produced is reversible when the anode potential is changed back to the original set potential. The pathways involved in anode respiration in Glk ferrihydriticus biofilms follow a similar, but more complicated, pattern as compared to those in the model ARB, Geobacter sulfurreducens. This greater diversity of electron transport pathways in Glk. ferrihydriticus could be related to its wider metabolic capability (e.g., higher pH and larger set of possible substrates, among others).