Closed-circuit bioelectrochemical operation is associated with a higher relative contribution of deterministic...

Microbial fuel cells (MFCs) are increasingly explored for soil remediation, yet the microbial ecological responses associated with conductive-material interfaces and closed-circuit operation remain incompletely understood. Using three experimental setups-a non-electrode anaerobic control (AT), an open-circuit conductive-material treatment (TO), and a closed-circuit treatment (TC)-we examined bacterial community composition, assembly processes, targeted functional-gene profiles, and exploratory co-occurrence patterns. The TO treatment showed a more highly connected exploratory network and slightly lower diversity within the targeted functional-gene panel than AT. The TC treatment showed a higher estimated relative contribution of deterministic processes than TO, although stochastic processes remained dominant in all treatments. TC was also characterized by several electroactive-associated taxa, including Geobacteraceae and Anaeromyxobacter, and by higher 16S-normalized relative abundances of several sulfur-cycling genes. These results suggest that the introduction of conductive materials and closed-circuit operation were associated with different bacterial community and targeted functional-gene responses. Because the TO-AT contrast includes both electrodes and carbon fibers, reactor-level replication was limited, and electrochemical output was not continuously quantified, the findings should be interpreted as exploratory associations rather than direct evidence of current-driven metabolic specialization. This study provides testable hypotheses for future bioelectrochemical soil-remediation experiments with greater reactor replication, electrochemical monitoring, and process-rate measurements.