Electroactive Microbiomes: Electron Transfer Mechanisms and Environmental Biotechnology Applications

Electroactive microbiomes are mixed microbial communities in which one or more members exchange electrons with extracellular minerals, redox-active compounds, electrodes, or partner organisms and in which community interactions materially influence net electron flow. This review develops a mechanism-interface-function-readiness framework that connects extracellular electron transfer (EET) with biofilm ecology, microbiome-electrode organisation, environmental process performance, and translational maturity. Direct transfer through multiheme cytochromes and conductive structures, mediated transfer through soluble redox shuttles, and interspecies electron transfer are evaluated as system-dependent pathways rather than universally ranked mechanisms. Particular emphasis is placed on wastewater treatment and resource recovery, anaerobic digestion, pollutant and metal transformation, soil and sediment bioelectrochemistry, carbon conversion, microbial fuel cells, microbial electrolysis cells, electro-fermentation, and microbial electrosynthesis. Multi-omics, metabolic modelling, synthetic biology, advanced materials, and artificial intelligence are examined according to the strength of their direct evidence in electroactive systems. Across applications, performance depends strongly on reactor configuration, electrode properties, inoculum, biofilm architecture, mass and charge transport, substrate loading, and normalisation basis, making unqualified cross-study numerical comparison inappropriate. Major barriers are long-term stability, mechanistic attribution in mixed communities, standardisation, scale-up, energy and mass balances, biosafety, techno-economic feasibility, and regulatory compatibility.