Diversity of electroactive and non-electroactive microorganisms and their potential relationships in microbial electrochemical systems: A review

Electroactive microorganisms (EAMs) are the core element of microbial electrochemical technologies (METs) due to their ability to interact with electrodes, allowing wiring of current flow and microbial metabolism. However, EAMs are not the unique microbes in METs, particularly when they are fed with complex substrates. Non-electrochemically-active microorganisms (non-EAMs) often coexist with EAMs in METs, and they can be important not only for electricity generation but also for the treatment of wastewater, the production of hydrogen and methane, among other processes. A systematic review of the diversity of EAMs and non-EAMs and their potential relationships in METs was conducted in this study. The results indicate that EAMs and non-EAMs are highly diverse and present in all three domains of life (Bacteria, Archaea, and Eukarya). Therefore, microbial ecology studies on the diversity of one of these three microbial groups give only a partial characterization of the electromicrobiology in METs. A complex balance between EAMs and non-EAMs appears to be necessary to maintain efficient energy production without detrimental impacts on other treatment processes in METs. Knowledge gaps and areas where future research efforts should be prioritized are discussed. • Diverse electroactive microorganisms were identified in bioelectrochemical systems. • Non-electroactive microorganisms (non-EAMs) are present in bioelectrochemical systems. • Both groups of microorganisms can be important for increasing current generation. • Decreases in energy production may be related to variations in non-EAMs. • A complex balance between electroactive and non-EAMs exists in these systems.