The Fate of DIET Consortium exposed to continuous and intermittent electrochemical stimulation

Abstract

AbstractElectromethanogenesis is the electrochemical conversion of carbon dioxide (CO2) to methane (CH4) with microorganisms as catalysts, and it is a promising approach for biogas upgrading. Many studies have shown increased methane production by electrochemical stimulation, allegedly due to the enhancement of direct interspecies electron transfer (DIET) between electrogenic bacteria and methanogens. However, these studies were done with mixed cultures where the interspecies interactions were undefined, so the impact of an electrochemical stimulus on these interactions remains unresolved. Here we report that an electrochemical stimulus diminished the survival and activity of a defined DIET consortium. We investigated the impact of electrochemical stimulation on a co-culture of Geobacter metallireducens and Methanosarcina barkeri, where the two partners interact syntrophically via DIET. The electrochemical stimulus was a cathode poised at - 700 mV (versus the standard hydrogen electrode, SHE). Electrochemical stimulation was provided either continuously or intermittently, and so was the food substrate. Compared to the untreated DIET co-culture, all treatment strategies relying on cathodic current additions resulted in acetate accumulation, lower methane production and lower cell numbers for both partners, indicating a detrimental impact of electrochemical stimulation to a DIET consortium. These findings suggest that future bioelectrochemical technologies must guarantee the survival of the syntrophic partners during current additions.