More efficient enriching of electroactive microorganisms from environmental samples by periodic step polarization.

Advancement of bioelectrochemical technology depends on efficient screening and enriching of electroactive microorganisms. Yet, conventional methods based on microbial fuel cells or microbial electrolysis cell operation suffer from prolonged operation or false negative results. We propose an anode potential control strategy-periodic step (PS) polarization-for application in screening and enriching electroactive microorganisms from environmental samples. Using fixed potential mode as a control, the performance of PS polarization was examined regarding the start-up time, cultivation duration of three fed-batch cycles, Coulombic efficiency, microbial community composition, and electrochemical properties of biofilms. Electrolysis cells were inoculated by either soil microorganisms or activated sludge. Results demonstrated that the PS polarization significantly shortened the start-up time and duration of the first three cultivation cycles (7-70 days depending on the inoculum) while achieving higher apparent current density and Coulombic efficiency. Besides, the enriched microbial communities under PS polarization showed a higher relative abundance of known electroactive microorganisms. Together with the lower open circuit potential and charge transfer resistance of the biofilm enriched by PS polarization, we concluded that the PS polarization can mitigate the inefficiencies caused by conventional enrichment methods, avoiding trial and error, and can be a novel methodology for enriching electroactive microorganisms.