Interspecies synergism in electroactive biofilms: New directions for advancing and innovating microbial electrochemical technologies

Microbial electrochemical technologies (MET) harness the ability of electroactive microorganisms to exchange electrons with solid electrodes, enabling the conversion of organic matter present in wastes into valuable products, including biofuels, chemicals, and electricity. Early developments in MET have mainly been driven by studies using pure cultures and model organisms. However, practical MET applications use complex, mixed-species biofilms that exhibit enhanced robustness, substrate flexibility, and operational stability. Within electroactive biofilms, interspecies interactions shape biofilm structure, electron transfer efficiency, and overall MET system performance. This review examines recent advances in interspecies synergism within electroactive biofilms, focusing on co-culture studies that have identified and analyzed specific microbial interactions. It highlights how microbial cooperation and communication enhance extracellular electron transfer and improve MET performance. Key mechanisms, including metabolite and redox mediator exchange, as well as the influence of extracellular polymeric substances and biofilm architecture on electroactivity, are discussed. The review also identifies knowledge gaps, particularly in the molecular basis of mutualism in electroactive biofilms, emphasizing the importance of understanding interspecies synergies for the rational design of high-performance, resilient bioelectrochemical platforms to address diverse societal challenges.