Rapid and Quantitative Assessment of Redox Conduction Across Electroactive Biofilms by using Double Potential Step Chronoamperometry

Abstract

The mechanism of electron transport across electroactive biofilms (EABs) is of high interest and still a matter of debate. Quantitative assessments of their redox conduction take considerable time and require non-turnover conditions (absence of substrate), which can be detrimental to EABs. Here, we measure the charge-transport parameters of Geobacter spp. dominated EABs with double potential step chronoamperometry (DPSC) with Cottrell analysis. The DPSC measurement is simpler and much faster than usual techniques and allows the determination of the charge-transport parameters even under turnover conditions. The electrochemical responses were well-described by a model of redox conduction driven only by electron diffusion within the EAB. The apparent diffusion coefficient for the electron (D app ) was measured as approximately 3.2 10 À7 cm 2 s À1 , a value similar to those recorded for pure Geobacter sulfurreducens EABs, or for some redox polymers with comparable redox center concentrations. This method will be valuable for assessing the impact of EAB characteristics and environmental factors on the charge-transport ability of the biofilm, and for determining the rate-limiting step(s) for current production.

Reversible Effects of Periodic Polarization on Anodic Electroactive Biofilms

“…Values of j ss were positively correlated with Γ, as previously observed, indicating that the amount (or the average concentration C) of charge carriers is likely a limiting factor for the catalytic current generation of mature EABs under acetate saturation . The charge transport parameter (C×D app 1/2 ) followed a similar trend between EABs than the one of the peak currents (Figure S4), with values ranging from 1.4 to 4.4 ×10 −9 mol cm −2 s −1/2 , as typically observed for Geobacter or Geobacter ‐dominated EABs . The EABs grown under P−C and C−C conditions shared very similar CVs shape as well as Γ and (C×D app 1/2 ) values, further confirming the high degree of reversibility of the electrochemical characteristics of the EABs with the polarization mode.…”

“…Two 8‐electrode reactors were set up as previously described. Eight working electrodes (glassy carbon plates with 4 cm 2 surface area available for growth, HTW, Germany) were successively polished with alumina slurries (0.1 μm, 0.3 μm and 0.05 μm diameter, Buehler, USA).…”

“…Surface coverage in charge carriers (Γ, expressed as nmol of e − per cm 2 ) was obtained by baseline‐subtracted chronocoulometry of full successive charges (−0.6 V) and discharges (−0.1 V) of the EABs under non‐turnover conditions, as previously described (see Figure S11) . The charge transport parameters (C×D app 1/2 ) were obtained by Randles‐Ševčík analysis under non‐turnover conditions as previously described . The parameters C and D app could not be obtained separately because of the difficulty to obtain precise values of biofilm volumes via confocal microscopy (images of EABs provided in Figure S4).…”

Ultrastructure of Shewanella oneidensis MR-1 nanowires revealed by electron cryotomography

“…Paquete et al (74) suggested that OmcA, which interacts with MtrC and is attached only by a lipidated cysteine at the N terminus, is mobile on the surface of Shewanella. Similarly, Zhang et al (75) recently noted the need to consider the molecular motion of ET components in live biofilms, rather than a hypothetical static model of immobilized redox cofactors.…”

Secondary treated domestic wastewater in reverse electrodialysis: What is the best pre-treatment?

“…Membrane pieces were fixed with glutaraldehyde and stained using SYTO9 (green) and propidium iodide (red) (Live/Dead BacLight Bacterial Viability Kits, Life Technologies), as described before [34]. Biofilms were visualized using a Nikon A1R confocal laser scanning microscope (Nikon Instruments Europe B.V., NL), as previously described [35]. Unstained and stained virgin membrane samples were used as controls.…”