Anaerobic Oxidation of Methane AOM in marine sediments

Anaerobic Oxidation of Methane (AOM) in marine sediments Contribution 8, by Tina Treude & Antje Boetius

The History of AOM In 1976 William Reeburgh discovered a steep decrease of methane in the anoxic zone of marine sediments. No methane reached the oxygenated sediment layers. The decrease in methane could only be caused by an anaerobic consumption of methane.

The History of AOM In 1985 Marc Alperin and William Reeburgh supplied the evidence that methane is consumed by the oxidation with sulfate under anoxic conditions.

The History of AOM Before that time the only known process of methane oxidation in marine sediments was the oxidation by oxygen: CH 4 methane + 2 O 2 oxygen CO 2 carbon dioxide + 2 H 2 O water But since then a new process, called anaerobic oxidation of methane (AOM) was obvious, by which methane is oxidized by sulfate: CH 4 + SO 42 methane sulfate CO 32 - + H 2 S + H 2 O bicarbonate hydrogen sulfide water

The History of AOM In 1994 Tori Hoehler et al. demonstrated by inhibition experiments that a consortium of methanogenic archaea and sulfate-reducing Bacteria (SRB) could mediate AOM in the sediment (see also next slide): • AOM is stopped when a substrate (BES) is added to the sediment, that is inhibiting methanogenic archaea • AOM is stopped when the sediment is sulfatefree

The History of AOM The inhibition experiments of Tori Hoehler et al.

The History of AOM In 2000 Antje Boetius et al. were able to demonstrate by molecular methods that the syntrophic partners of the AOM consortium occur in structured aggregates. In these aggregates, archaea are located in the center surrounded by the SRB. archaea (stained red) SRB (stained green)

The History of AOM In 2001 Walter Michaelis et al. found out, that such AOM-consortia are able to build up a huge biomass above methane seeps in the anoxic part of the Black Sea. These reef-like structures are up to 1 m in diameter and 4 m high. photos: GHOSTDABS, Jago-Team

The location of the microbial-reef in the Black Sea: methane seeping area

Working platform and sampling equipment that were used for the investigation of the microbial-reef above: Russian research vessel “Prof. Logachev” right: German submersible “Jago” photos: GHOSTDABS

The macroscopic structure of the microbial reef microbial biomass precipitated carbonates 30 cm photos: GHOSTDABS, Jago-Team

Laboratory experiments demonstrate that the microbial reef is fueled by AOM 1: 1 stoichiometry of AOM and SR No SR without methane by T. Treude & K. Nauhaus

Molecular identification reveal that a microbial consortium is responsible for AOM in the reef cells stained blue 30 cm fluorescence in situ hybridization (FISH) GHOSTDABS, Univ. Hamburg by K. Knittel & A. Gieseke

AOM consortia of different shapes aggregate-structure "tissue"-structure Archea SRB AOM consortium above gas hydrates at Hydrate Ridge, Cascadia Margin. AOM consortium above gas seeps in the anoxic Black Sea. by A. Boetius, K. Knittel & A. Gieseke

The AOM symbiosis CH 4 + SO 42 - + Ca 2+ Ca. CO 3 + H 2 S + H 2 O CO 2 2 - SO 4 H 2 S Electrons H 2 S 8 [H] Biomass CH 4 Methanotroph Hydrogen Acetate Formate Electrons …… …… Biomass CO 2 Sulfate reducer Gashydrates / Seeps scheme by K. Nauhaus

Long-term incubations with [14 C]-methane proving microbial induced carbonate precipitation radioactive carbon The colors represent inside mat slice: the activity of 14 C 75%abiomass inside mat slice 25%activity carbonate (high red, lowprecipitation activity blue) by T. Treude & A. Gieseke

AOM all around the world Iversen & Blackburn 1981 Iversen & Joergensen 1985 Reeburgh 1978 Treude et al. (in prep. ) Highest AOM rates are found in sediments bearing gas hydrates. table by Boetius & Hinrichs (2000)

The impact of AOM The major part of methane (>90%) that is produced in ocean sediments is consumed my microbes before it reaches the atmosphere. Therefore AOM has a significant impact on climate regulation as methane is a 30 times stronger greenhouse gas compared to carbon dioxide. picture: : www. solcomhouse. com

References Alperin, M. C. , Reeburgh, W. S. (1985). Inhibition experiments on anaerobic methane oxidation. Appl. Environ. Microbiol. 50 (4), 940 -945. Boetius, A. , Hinrichs, K. -U. (2000). The anaerobic oxidation of methane: new insights in microbial ecology and biogeochemistry. Hanse Workshop "Ocean margin systems", Delmenhorst, Germany. Boetius, A. , Ravenschlag, K. , Schubert, C. J. , Rickert, D. , Widdel, F. , Giesecke, A. , Amann, R. , Joergensen, B. B. , Witte, U. , Pfannkuche, O. (2000). A marine microbial consortium apparently mediating anaerobic oxidation of methane. Nature 407, 623 -626. Hoehler, T. M. , Alperin, M. J. , Albert, D. B. , Martens, C. S. (1994). Field and laboratory studies of methane oxidation in an anoxic marine sediments: evidence for methanogen-sulphate reducer consortium. Global Biochem. Cycles 8 (4), 451 -463. Iversen, N. , Blackburn, T. H. (1981). Seasonal rates of methane oxidation in anoxic marine sediments. Appl. Environ. Microbiol. 41 (6), 1295 -1300. Iversen, N. , Joergensen, B. B. (1985). Anaerobic methane oxidation rates at the sulphate-methane transition in marine sediments from Kattegat and Skagerrak (Denmark). Limnol. Oceanogr. 30 (5), 944 -955. Michaelis, W. , Seifert, R. , Nauhas, K. , Treude, T. , Thiel, V. , Blumenberg, M. , Knittel, K. , Gieseke, A. , Peterknecht, K. , Pape, T. , Boetius, A. , Amann, R. , Joergensen, B. B. , Widdel, F. , Peckmann, J. , Pimenov, N. V. , Gulin, M. B. (2002). Microbial reefs in the Black Sea fueled by anaerobic oxidation of methane. Science 297, 1013 -1015. Reeburgh, W. S. (1976). Methane consumption in Cariaco Trench waters and sediments. Earth Planet. Sci. Lett. 28, 337 -344.

Acknowledgement G HO S D AB T S R/V Prof. Logachev

Contact Tina Treude: Max Planck Institute for Marine Microbiology, Bremen, Germany, ttreude@mpi-bremen. de Antje Boetius: Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, aboetius@awi-bremerhaven. de MUMM-Project: http: //www. mpi-bremen. de/deutsch/biogeo/mumm 2. html