Functional genes and microbial interactions governing methanogenesis via direct interspecies electron transfer:...

Direct interspecies electron transfer (DIET) has emerged as an electron-exchange mechanism that enhances methane production in anaerobic digestion (AD) systems. Although the concept of direct electron exchange in syntrophic microbial communities was proposed in the early 2010 s, experimental validation and systematic recognition of methanogenesis via DIET have advanced primarily in the past decade. Significant progress has been made in identifying DIET-active microbial consortia; however, the functional genes and metabolic pathways governing these processes remain unclear. Recent advances in multi-omics approaches, including metagenomics, metatranscriptomics, and proteomics, have provided deeper insights into microbial community organization and gene-level functions underlying electron transfer in AD systems. This review synthesizes current knowledge on functional genes directly mediating DIET (e.g., pilA, omcS), as well as genes that indirectly support DIET, including hydrogenases, extracellular polymeric substance (EPS)-related genes, and methanogenesis-associated enzymes. Understanding of these functional genes is essential for optimizing AD processes and advancing bioenergy production.