Set potential regulation reveals additional oxidation peaks of Geobacter sulfurreducens anodic biofilms

a r t i c l e i n f o Higher current densities produced in microbial fuel cells and other bioelectrochemical systems are associated with the presence of various Geobacter species. A number of electron transfer components are involved in ex-tracellular electron transfer by the model exoelectrogen, Geobacter sulfurreducens. It has previously been shown that 5 main oxidation peaks can be identified in cyclic voltammetry scans. It is shown here that 7 separate oxidation peaks emerged over relatively long periods of time when a larger range of set potentials was used to acclimate electroactive biofilms. The potentials of oxidation peaks obtained with G. sulfurreducens biofilms acclimated at 0.60 V (vs. Ag/AgCl) were different from those that developed at − 0.46 V, and both of their peaks were different from those obtained for biofilms incubated at − 0.30 V, 0 V, and 0.30 V. These results expand the known range of potentials for which G. sulfurreducens produces identifiable oxidation peaks that could be important for extracellular electron transfer. Bioelectrochemical systems (BESs), such as microbial fuel cells (MFCs), microbial electrolysis cells (MECs), and microbial desalination cells (MDCs), have attracted increasing interest as new sustainable techniques for producing bioelectricity, biofuels, and other chemical products. In BESs, the anode is the terminal electron acceptor for microorganisms. Theoretically, more positive anode potentials favor the electron transfer from bacteria to the electrode [1–3], and a number of studies [1–8] have demonstrated that the bacterial activity is significantly affected by the anode potential. Many different Geobacter species have been identified to be predominant in BESs with high current densities [8,9]. Geobacter sulfurreducens is the best known, and most widely studied, exoelectrogenic microorganism in BESs. Genomic analysis of G. sulfurreducens has identified 111 coding sequences of c-type cyto-chromes indicative of heme groups that could potentially be active for cell respiration under different conditions [10]. Microorganisms regulate their electron transfer pathways to tailor them to specific terminal electron acceptors [11], usually to enable them to gain more energy from respiration. However, little direct evidence exists for improved energy capture in BESs, although it is clear that some exoelectrogenic microbes can alter respiratory enzymes used at different electrode potentials. By investigating open-circuit potentials of mixed community biofilms acclimated to different set potentials , it was proposed that exoelectrogenic bacteria could self-regulate the redox potentials of their operative terminal reductases to be slightly more negative than the anode potential [4]. …