title: Methane Seep in Shallow-Water Permeable Sediment Harbors High Diversity of Anaerobic Methanotrophic Communities, Elba, Italy.
abstract: The anaerobic oxidation of methane (AOM) is a key biogeochemical process regulating methane emission from marine sediments into the hydrosphere. AOM is largely mediated by consortia of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB), and has mainly been investigated in deep-sea sediments. Here we studied methane seepage at four spots located at 12 m water depth in coastal, organic carbon depleted permeable sands off the Island of Elba (Italy). We combined biogeochemical measurements, sequencing-based community analyses and in situ hybridization to investigate the microbial communities of this environment. Increased alkalinity, formation of free sulfide and nearly stoichiometric methane oxidation and sulfate reduction rates up to 200 nmol g(-1) day(-1) indicated the predominance of sulfate-coupled AOM. With up to 40 cm thickness the zones of AOM activity were unusually large and occurred in deeper sediment horizons (20-50 cm below seafloor) as compared to diffusion-dominated deep-sea seeps, which is likely caused by advective flow of pore water due to the shallow water depth and permeability of the sands. Hydrodynamic forces also may be responsible for the substantial phylogenetic and unprecedented morphological diversity of AOM consortia inhabiting these sands, including the clades ANME-1a/b, ANME-2a/b/c, ANME-3, and their partner bacteria SEEP-SRB1a and SEEP-SRB2. High microbial dispersal, the availability of diverse energy sources and high habitat heterogeneity might explain that the emission spots shared few microbial taxa, despite their physical proximity. Although the biogeochemistry of this shallow methane seep was very different to that of deep-sea seeps, their key functional taxa were very closely related, which supports the global dispersal of key taxa and underlines strong selection by methane as the predominant energy source. Mesophilic, methane-fueled ecosystems in shallow-water permeable sediments may comprise distinct microbial habitats due to their unique biogeochemical and physical characteristics. To link AOM phylotypes with seep habitats and to enable future meta-analyses we thus propose that seep environment ontology needs to be further specified.
authors.affiliation: Department for Molecular Ecology, Max Planck Institute for Marine MicrobiologyBremen, Germany; HGF MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine MicrobiologyBremen, Germany.
authors.forename: S Emil
authors.initials: SE
authors.lastname: Ruff
authors.affiliation: Department for Molecular Ecology, Max Planck Institute for Marine Microbiology Bremen, Germany.
authors.forename: Hanna
authors.initials: H
authors.lastname: Kuhfuss
authors.affiliation: HGF MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine MicrobiologyBremen, Germany; MARUM Center for Marine Environmental Sciences, University of BremenBremen, Germany.
authors.forename: Gunter
authors.initials: G
authors.lastname: Wegener
authors.affiliation: HYDRA Institute for Marine Sciences, Elba Field Station Campo nell'Elba, Italy.
authors.forename: Christian
authors.initials: C
authors.lastname: Lott
authors.affiliation: HGF MPG Group for Deep Sea Ecology and Technology, Max Planck Institute for Marine Microbiology Bremen, Germany.
authors.forename: Alban
authors.initials: A
authors.lastname: Ramette
authors.affiliation: HYDRA Institute for Marine Sciences, Elba Field StationCampo nell'Elba, Italy; Department of Biogeochemistry, Max Planck Institute for Marine MicrobiologyBremen, Germany.
authors.forename: Johanna
authors.initials: J
authors.lastname: Wiedling
authors.affiliation: Department for Molecular Ecology, Max Planck Institute for Marine Microbiology Bremen, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Knittel
authors.affiliation: HYDRA Institute for Marine Sciences, Elba Field StationCampo nell'Elba, Italy; Department of Biogeochemistry, Max Planck Institute for Marine MicrobiologyBremen, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Weber
keywords: ANME; Mediterranean; advection-driven ecosystem; anaerobic oxidation of methane; environmental selection; habitat heterogeneity; microbial syntrophy; sulfate-methane transition zone