Cell surface differences within the genus shape interactions with the extracellular environment.

are metabolically versatile methanogenic archaea that can perform extracellular electron transfer (EET), with important ecological and biotechnological implications. These archaea are broadly classified into two types (Type I and Type II) based on their energy metabolism and also differ in their aggregation-disaggregation behavior, cell surface properties, and electron transfer strategies. Type I typically form large multicellular aggregates within a methanochondroitin extracellular matrix, thrive in organic-rich environments, play a key role in anaerobic digestion during wastewater treatment, and can perform EET. However, their mechanism of EET remains unresolved. In contrast, Type II rely on multiheme c-type cytochromes for EET and are better adapted to low-organic, mineral-rich environments such as deep-sea sediments and aquifers, where they contribute to methane emissions. Despite their significance, the molecular mechanisms behind EET in -particularly for Type I-remain poorly understood. This review highlights what is known and what is unknown regarding the surface biology of , their EET strategies, and biogeochemical and industrial roles, emphasizing the need for further research to unlock their full potential in sustainable methane management.