title: Distinct microbial populations are tightly linked to the profile of dissolved iron in the methanic sediments of the Helgoland mud area, North Sea.
abstract: Iron reduction in subseafloor sulfate-depleted and methane-rich marine sediments is currently a subject of interest in subsurface geomicrobiology. While iron reduction and microorganisms involved have been well studied in marine surface sediments, little is known about microorganisms responsible for iron reduction in deep methanic sediments. Here, we used quantitative PCR-based 16S rRNA gene copy numbers and pyrosequencing-based relative abundances of bacteria and archaea to investigate covariance between distinct microbial populations and specific geochemical profiles in the top 5 m of sediment cores from the Helgoland mud area, North Sea. We found that gene copy numbers of bacteria and archaea were specifically higher around the peak of dissolved iron in the methanic zone (250-350 cm). The higher copy numbers at these depths were also reflected by the relative sequence abundances of members of the candidate division JS1, methanogenic and Methanohalobium/ANME-3 related archaea. The distribution of these populations was strongly correlated to the profile of pore-water Fe(2+) while that of Desulfobacteraceae corresponded to the pore-water sulfate profile. Furthermore, specific JS1 populations also strongly co-varied with the distribution of Methanosaetaceae in the methanic zone. Our data suggest that the interplay among JS1 bacteria, methanogenic archaea and Methanohalobium/ANME-3-related archaea may be important for iron reduction and methane cycling in deep methanic sediments of the Helgoland mud area and perhaps in other methane-rich depositional environments.
authors.affiliation: Microbial Ecophysiology Group, Faculty of Biology/Chemistry, University of Bremen Bremen, Germany ; MARUM, Center for Marine Environmental Sciences, University of Bremen Bremen, Germany.
authors.forename: Oluwatobi
authors.initials: O
authors.lastname: Oni
authors.affiliation: Microbial Ecophysiology Group, Faculty of Biology/Chemistry, University of Bremen Bremen, Germany.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Miyatake
authors.affiliation: MARUM, Center for Marine Environmental Sciences, University of Bremen Bremen, Germany ; Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research Bremerhaven, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Kasten
authors.affiliation: Microbial Ecophysiology Group, Faculty of Biology/Chemistry, University of Bremen Bremen, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Richter-Heitmann
authors.affiliation: MARUM, Center for Marine Environmental Sciences, University of Bremen Bremen, Germany ; Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research Bremerhaven, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Fischer
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research Bremerhaven, Germany.
authors.forename: Laura
authors.initials: L
authors.lastname: Wagenknecht
authors.affiliation: Microbial Ecophysiology Group, Faculty of Biology/Chemistry, University of Bremen Bremen, Germany.
authors.forename: Ajinkya
authors.initials: A
authors.lastname: Kulkarni
authors.affiliation: Institute for Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Blumers
authors.affiliation: Institute for Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, Germany ; Department of Chemistry, Taras Shevchenko National University of Kyiv Kyiv, Ukraine.
authors.forename: Sergii I
authors.initials: SI
authors.lastname: Shylin
authors.affiliation: Institute for Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, Germany.
authors.forename: Vadim
authors.initials: V
authors.lastname: Ksenofontov
authors.affiliation: CFisUC, Department of Physics, University of Coimbra, Coimbra Portugal.
authors.forename: Benilde F O
authors.initials: BF
authors.lastname: Costa
authors.affiliation: CFisUC, Department of Physics, University of Coimbra, Coimbra Portugal.
authors.forename: Göstar
authors.initials: G
authors.lastname: Klingelhöfer
authors.affiliation: Microbial Ecophysiology Group, Faculty of Biology/Chemistry, University of Bremen Bremen, Germany ; MARUM, Center for Marine Environmental Sciences, University of Bremen Bremen, Germany.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Friedrich
keywords: ANME; North Sea; SMT; anaerobic oxidation of methane; candidate division JS1; iron reduction; methanogens; subsurface sediments