FIG 1.

Different modes of methanotrophy and different types of syntrophy in methanotrophy. (A) Aerobic methanotrophy. Aerobic methanotrophs require oxygen and can grow as pure cultures; in nature, however, they appear to form consortia with other bacteria. P, Proteobacteria; V, Verrucomicrobia. (B) AOM by ANME archaea (A) linked to sulfate reduction by sulfate-reducing bacteria (S), involving extracellular electron transfer. (C) AOM by ANME archaea linked to anaerobic ammonium oxidation by Kuenenia (K). (D) AOM by ANME archaea via direct electron transfer to insoluble metals. (E) AOM by ANME archaea directly coupled to sulfate reduction. (F) AOM by ANME archaea linked to denitrification, in which NC10 bacteria (N) assist with nitrite removal, linking its reduction to oxygen-dependent methane oxidation. The source of oxygen for the latter is unclear.