A Four-Channel Millifluidic Electrochemical Flow Reactor for Parallel Screening of Cathodically Active Microbial Communities

This study introduces a four-channel millifluidic microbial electrochemical reactor (mMER) designed for parallel screening of cathodically active microbial communities. This platform integrates electrochemical control with online optical density (OD) monitoring, enabling simultaneous tracking of biomass-associated OD development and current response in four separate culture systems. The system’s performance was initially validated through photometric calibration and biocompatibility tests, leading to the development of a standardized workflow for cathodic enrichment protocols of soil microbial communities. Using this system, a cathode potential of −0.4 V (vs. quasi-reference electrode) was identified as effective and applied to four different soil samples, revealing variations in their electrochemical responses. Based on combined OD and current measurements, a time-resolved ΔOD/ΔQ analysis was introduced to compare biomass-associated electrochemical response behavior during enrichment. This analysis revealed distinct temporal response characteristics among soil microbial communities, including early, delayed, and sustained responses observed under cathodic cultivation conditions. Open-circuit potential measurements, conducted after enrichment, provided additional electrochemical characterization of the enriched systems. Among all samples, the microbial community from a Neolithic earthwork site (Niedersickte, Germany, sample HB51) demonstrated the most stable relationship between cathodic current consumption and OD development during enrichment. The mMER platform offers a valuable tool for the comparative screening of electroactive microbial communities from complex environmental samples.