Electroactive (Micro)organisms

Electroactive organisms have the metabolic ability to exchange electrons with solid substrates present in the extracellular environment. This capacity enables them to function as electrogens (electron donors) or electrotrophs (electron acceptors). They accomplish this through two processes of extracellular electron transfer (EET): (i) via direct contact, involving multiheme cytochromes, nanowires, or pili that make it possible for the cell to interact with the extracellular electron acceptor or donor; or (ii) indirectly using soluble redox mediators (e.g., flavins, quinones, humic substances, and phenazines) that mediate electron transfer across the microbe-electrode interface. In this chapter, electroactive organisms found in all three domains of life, bacteria, archaea, and eukarya, are discussed, with an emphasis on electroactive microorganisms, and their microbiological characteristics and the molecular mechanisms that underpin their electroactivity are highlighted. Whereas bacteria and archaea have been separated into groups based on their metabolic mode, eukarya have been separated into fungi and plants. Finally, this chapter touches on current challenges in finding novel electroactive organisms and understanding their modes of EET processes.