Novel electron transport powers archaeal methane metabolism across varied substrates and environments

Methanogens are responsible for producing approximately one billion metric tons of methane each year within Earth’s anaerobic environments as a byproduct of their energy metabolism. They play a vital role in the global carbon cycle. There are three main pathways for methanogenesis: hydrogenotrophic, which uses H 2 and CO 2 to produce methane; methylotrophic, which utilizes methylated compounds like methanol and amines; and aceticlastic, which converts acetate into methane and CO 2 . Instead of substrate-level ATP production, methanogens conserve energy through a membrane-bound electron transport chain and flavin-based electron bifurcation (FBEB). Beyond the canonical modes of growth in methanogens, Methanosarcina acetivorans , a model acetotrophic methanogen, can conserve energy via direct interspecies electron transfer (DIET). Here, we review the metabolic pathways and electron transport processes involved in energy conservation during fermentative, respiratory, and DIET modes. Additionally, we discuss the role of FBEB in energy conservation in gut-associated Methanomassiliicoccus luminyensis . Finally, we discuss the potential roles of heterodisulfide reductase (Hdr) and the process of electron transfer during the reaction mechanism of electron-bifurcating HdrA2B2C2 complex in cytochrome-containing methanogens. Understanding the complex redox control mechanisms in these organisms has broader implications for sustainable energy and environmental management.