Respiration in Electroactive Bacteria: Bioinorganic Aspects

Abstract This article gives an up‐to‐date (2023) account on the bioinorganic basis for extracellular electron transfer (EET) in electroactive bacteria. These microorganisms connect their respiratory metabolism to extracellular solid electron acceptors or donors, typically metal oxides of iron or manganese. Thanks to this peculiar property, electroactive bacteria can develop as biofilms at electrodes, be studied electrochemically, and form the basis of diverse potential applications termed microbial electrochemical systems (MES). The metalloproteins forming the respiratory chain from NADH oxidation to the reduction of the terminal solid electron acceptor are described in detail for the most studied Gram‐negative electroactive strains developed at anodes: Shewanella oneidensis MR‐1 and Geobacter sulfurreducens . Although less efficient than their Gram‐negative counterpart and sometimes referred to as weak electricigens, an example of electroactive anodophile Gram‐positive bacteria, Thermincola sp., is also discussed. The key cytochromes involved in the electron transport chain are discussed such as outer membrane c ‐type cytochromes (Omc) and multiheme cytochromes, forming by self‐assembly up to micrometer‐long electron conductive extracellular pili or nanowires. The case of microorganisms that uptake electrons from solid extracellular electron donors is addressed with a highlight on photoferrotrophs and cathodic denitrifying bacteria. Finally, the common strategy developed by different bacteria to electrically connect different types of respiratory metabolism is stressed together with the apparent ubiquity of EET across life domains including archaea.