A quantitative extracellular electron transfer (EET) kinetics study of Geobacter sulfurreducens enriched microbial community reveals the transition of EET limiting step during biofilm growth

摘要

Extracellular electron transfer (EET) allows exoelectrogens to transfer electrons outside their outer membrane as a unique process to complete respiration. The EET kinetics of Geobacter sulfurreducens is critical to further improving the performance of microbial electrochemical technologies such as microbial fuel cells. However, the EET of Geobacter sulfurreducens is not yet fully understood, and current and power densities of microbial fuel cells meet with a bottleneck. This work addresses this deficit by studying the kinetic parameters of the EET of Geobacter sulfurreducens enriched microbial community for a series of biofilm growth stages through the non-linear fitting of discharging current profiles of micro-scale microbial fuel cells. The quantitative EET rate constants and the amount of redox cofactors associated with individual EET steps are obtained from initial to fullygrown biofilms. This quantitative study reports the rate-limiting step in EET transitions during biofilm growth. In early to mid-stage biofilms, we report current densities of less than 2.2 Am-2 and between 2.2 and 3.1 Am-2, respectively. The rate-limiting step transitions from irreversible acetate turnover to the electron transfer from inside the exoelectrogen to extracellular redox cofactors (ERCs) within the biofilm. We show fully-grown biofilms have a current density of more than 3.1 Am-2, and the rate-limiting step here is instead the electron transfer from ERCs within the biofilm to ERCs at the anode. The results of this study illuminate the mechanisms of the EET of Geobacter sulfurreducens, using quantitative reaction kinetics parameter analysis. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.