Bacterial communities and syntrophic associations involved in anaerobic oxidation of methane process of the Sonora Margin cold seeps, Guaymas Basin.

The Sonora Margin cold seeps present on the seafloor a patchiness pattern of white microbial mats surrounded by polychaete and gastropod beds. These surface assemblages are fuelled by abundant organic inputs sedimenting from the water column and upward-flowing seep fluids. Elevated microbial density was observed in the underlying sediments. A previous study on the same samples identified anaerobic oxidation of methane (AOM) as the potential dominant archaeal process in these Sonora Margin sediments, probably catalysed by three clades of archaeal anaerobic methanotrophs (ANME-1, ANME-2 and ANME-3) associated with bacterial syntrophs. In this study, molecular surveys and microscopic observations investigating the diversity of Bacteria involved in AOM process, as well as the environmental parameters affecting the composition and the morphologies of AOM consortia in the Sonora Margin sediments were carried out. Two groups of Bacteria were identified within the AOM consortia, the Desulfosarcina/Desulfococcus SEEP SRB-1a group and a Desulfobulbus-related group. These bacteria showed different niche distributions, association specificities and consortia architectures, depending on sediment surface communities, geochemical parameters and ANME-associated phylogeny. Therefore, the syntrophic AOM process appears to depend on sulphate-reducing bacteria with different ecological niches and/or metabolisms, in a biofilm-like organic matrix.