Fig. 7

Conceptual diagram of primary metabolic processes in the cold seep and the non-seep site. The colors of the arrows represent the metabolic processes. Orange: anaerobic oxidation of methane (AOM). Green: dissimilatory sulfate reduction (DSR). Yellow-green: assimilatory sulfate reduction (ASR). Pink: sulfur-oxidizing X protein system (SOX system). Blue: nitrogen fixation. Light blue: denitrification. The investigated cold seep site exhibits typical sulfate-dependent anaerobic methane oxidation (SAMO), predominantly driven by anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). In the surface layer, SRB exhibits high diversity and evenness, whereas ANME are scarce. In the subsurface layer, the abundance and diversity of ANME increase, leading to the emergence of dominant SRB which can form symbiotic associations with ANME