Whole Cell Electrochemistry of Electricity-Producing Microorganisms Evidence an Adaptation for Optimal Exocellular Electron Transport

Abstract

The mechanism(s) by which electricity-producing microorganisms interact with an electrode is poorly understood. Outer membrane cytochromes and conductive pili are being considered as possible players, but the available information does not concur to a consensus mechanism yet. In this work we demonstrate that Geobacter sulfurreducens cells are able to change the way in which they exchange electrons with an electrode as a response to changes in the applied electrode potential. After several hours of polarization at 0.1 V Ag/AgCl-KCl (saturated), the voltammetric signature of the attached cells showed a single redox pair with a formal redox potential of about -0.08 V as calculated from chronopotentiometric analysis. A similar signal was obtained from cells adapted to 0.4 V. However, new redox couples were detected after conditioning at 0.6 V. A large oxidation process beyond 0.5 V transferring a higher current than that obtained at 0.1 V was found to be associated with two reduction waves at 0.23 and 0.50 V. The apparent equilibrium potential of these new processes was estimated to be at about 0.48 V from programmed current potentiometric results. Importantly, when polarization was lowered again to 0.1 V for 18 additional hours, the signals obtained at 0.6 V were found to greatly diminish in amplitude, whereas those previously found at the lower conditioning potential were recovered. Results clearly show the reversibility of cell adaptation to the electrode potential and pointto the polarization potential as a key variable to optimize energy production from an electricity producing population.

Microbial Electrolysis of Synthetic Acids for Biohydrogen Production: Influence of Biocatalyst Pretreatment and pH with the Function of Applied Potential

“…Even though low redox slopes were observed at 0.2 V, H 2 production was comparatively less than other applied potentials might be due to the low applied potential. Applied potential upto certain limit will influence the metabolic behavior of the biocatalyst [9,26,27] and the same was noticed in the present work where more substrate degradation was registered at 0.2 V. The resulted protons and electrons generated might have involved in other metabolic activities or the potential difference is not sufficient from 0.2 V to extract more number of protons and electrons from the biocatalyst to make it to H 2 . More protons and electrons are released in the case of 0.6 V and operation with PTr and UTr biocatalyst recorded lower redox slopes and R p with 0.2 V and 0.6 V whereas pH 7 operation recorded lower redox slopes and R p with 1.0 V and 0.6 V operation.…”

“…Almost equal or high consumption of VFA was registered at 0.2 V than 1.0 V particularly at PTr operations than UTr operations. Even though consumption was observed more at 0.2 V but due to the applied potential used, more electrons might have released in the case of 1.0 V to make H 2 [9,25,26] and this might be the reason for the observed high H 2 production at 1.0 V than 0.2 V. Maximum utilization of acetate was visualized during the study indicating that biocatalyst was able to utilize acetate than butyrate and propionate due to its simpler form. At applied potential of 0.6 V, 50% utilization of acetate was noticed which indicated that the system favored electrohydrolysis.…”

“…Maximum H 2 production was observed at 0.6 V irrespective of pH and nature of the biocatalyst studied. Electron discharge pattern of the biocatalyst get enhanced under applied potential conditions [9,25,26]. Application of external potential increases the overall potential difference between anode and microbial cell mobilizing the electron flow to the external environment.…”

Anodic ammonia oxidation to nitrogen gas catalyzed by mixed biofilms in bioelectrochemical systems

“…As seen from Fig. 3, the oxidation-reduction peaks appeared at about 0.6 and 0.3 V (vs. Ag/AgCl), respectively and the peak potentials were similar to that of Geobacter sulfurreducens which was also polarized at 0.6 V (vs. Ag/AgCl) [25]. The electrochemical detection of redox signals in Fig.…”

Performance and recent improvement in microbial fuel cells for simultaneous carbon and nitrogen removal: A review

“…The anode potential regulates the growth and electrochemical activity of the microorganisms in an MFC Busalmen et al, 2008;Kokko et al, 2015). The cathode potential affects the treatment efficiency and intermediate products during nitrate reduction.…”