Toward Electrosynthesis with Uncoupled Extracellular Electron Uptake and Metabolic Growth: Enhancing Current Uptake with Rhodopseudomonas palustris

Abstract

The production of metabolites from CO2 with microbes at cathodes (i.e., microbial electrosynthesis) is an attractive application of microbial electrochemistry. However, processes for the uptake of electrons from electrodes remain elusive, and microbial conservation of energy does not often occur at the cathode. One mechanism known for the uptake of electrons from electrodes is iron-mediated electron transfer to iron-oxidizing bacteria such as obligate aerobic chemolithotrophs and anaerobic photoautotrophs. However, for photoautotrophs, this requires an illuminated cathode to provide metabolic energy for growth. Here, we increased published iron-mediated electron uptake rates of Rhodopseudomonas palustris TIE-1 by uncoupling the electrochemical from the biological environment in a photobioelectrochemical system consisting of an electrochemical system and a photobioreactor. This uncoupled system resulted in a volumetric iron-mediated electron uptake rate (electric current) 56-fold higher than that in a single photobioelectrochemical system.