Electroactive microbe communication: A crucial aspect for energy generation in bio-electrochemical systems

The rising environmental issues have intensified research in developing microbial fuel cells (MFCs) as a green and sustainable source of energy generation. The discovery of electroactive bacteria (EABs) in the 1980 s and their application in MFCs greatly improved energy generation as they aid in transferring electrons to the anodic surface. EABs can perform extracellular electron transfer (EET), wherein microbes can use the substrate provided for growth and other metabolic processes and transfer the resultant electrons generated to the anode for energy production. EET occurs mainly by two pathways, direct pathways depend on physical contact of bacteria with the anode using outer membrane cytochromes or conductive pili and the indirect pathway using endogenous mediators like flavins and phenazines produced by bacteria or exogenous mediators added to the anolyte like conductive metallic nanoparticles or chemical mediators like methylene blue or neutral red. Also, quorum sensing and outer membrane vesicles are crucial for microbial interaction in a biofilm. A better understanding of EET pathways can help use EABs and MFCs in real-world applications. This review sheds light on the importance of biofilm development, quorum sensing, outer membrane vesicles, direct and mediated electron transfer processes, and prospects and applications in MFCs and other bio electrochemical systems.