Cluster Project F2

F. Wenzhöfer, M. Zabel
M. Bau, A. Boetius, T. Ferdelmann, S. Kasten, A. Koschinsky, M. Schlüter, G. Wegener

Background
Subseafloor processes of fluid mixing, cooling , and mineral precipitation at sites of hydrothermal venting are associated with redistribution of energy sources for microorganisms. Not only do these processes affect biological communities on the seafloor, they also support microorganims thriving below the seafloor, in zones where fluid mixing and cooling creat favourable habitats for chemosynthesis. Fluid sampling and in-situ measurements of chemical speices together with temperature and pH measurements allows us to trace critical components and define chemical potentials at the interface between litho- and biosphere.

Biogeochemistry of the Hydrothermal Vents in the Guaymas Basin

G.Wegener, M. Y. Kellermann, A. Ramette, D. de Beer, K.-U. Hinrichs, A. Boetius

The Guaymas Basin (Gulf of California) is characterized by strong hydrothermal activity in a high-sedimentation environment. The steep temperature gradients within the sediments cause near-surface, thermogenic formation of crude oil and short-chain hydrocarbons such as methane, which are transported to the sediment-surface. Large and diverse populations of hydrocarbon-degrading aerobic and anaerobic microorganisms inhabit the sediments. Anaerobic hydrocarbon degradation leads to high fluxes of sulfide via sulfate reduction. This attracts many different types of vent organisms which are specialized to consume sulfide, such as bacterial mats (Beggiatoa), symbiont-hosting mussels and giant tube worms. The Guaymas basin vented sediments provide a unique natural laboratory to study thermal-driven organic matter degradation and the accompanied biogeochemical cycles, which usually take place in deeply buried sediments over geological time scales. Furthermore Guaymas vents are a unique habitat for thermophilic microorganisms and chemosynthetic communities associated with hydrocarbon degradation.

In collaboration with Prof. A. Teske, UNC Chapel Hill (link) we joined two research expeditions (AT15-45, link) to the Guaymas basin. Deep sea dives with the research submersible Alvin (WHOI) enabled us to do different in situ experiments. As part of the F2 project we studied the carbon and sulfur cycle in the sediments. We were able to measure biogeochemically important electron acceptor and donor fluxes (oxygen, nitrate, sulfate, methane etc) and determined in situ and in vitro rates of the dominant microbial processes. In heated sediments we observed thermophilic microbial activity based predominantly on the anaerobic oxidation of methane coupled to sulfate reduction carbon fixation. In laboratory experiments we identified a unique, mostly autotrophic community benefiting from the thermophilic oxidation of methane. From the sediments we enriched a novel strain of thermophilic methanotrophic archaea living in direct association with a completely novel strain of deeply branching Deltaproteobacteria (fluorescence micrograph). The discovery of thermophilic AOM at finally explains the widely observed transformation of gypsum to limestone observed in cap rocks of warm hydrocarbon reservoirs.

Currently the syntrophic enrichment cultures and recently retrieved monospecific isolates of the organisms are studied for their physiological properties, and we finally aim to elucidate the yet not understood interaction of archaea and bacteria in methane oxidation. For additional Guaymas Basin projects see Cluster Project F3.

Micrograph of syntrophic methanotrophic consortia cultured from heated sediments of the Guaymas Basin. (Archaea stained in red, partner bacteria stained in green).

Duperron S, Guezi H, Gaudron SM, Pop Ristova P, Wenzhöfer F, Boetius A (2011) Relative abundances of methane- and sulphur-oxidising symbionts in the gills of a cold seep mussel and link to their potential energy sources. Geobiology 9(6), 481-491

Holler T, Widdel F, Knittel K, Amann R, Kellermann MY, Hinrichs K-U, Teske A, Boetius A, Wegener G (2011) Thermophilic anaerobic oxidation of methane by marine microbial consortia. ISME J. 5, 1946–1956.

PopSchauer R, Røy H, Augustin N, Gennerich H-H, Peters M, Wenzhöfer F, Amann R, Meyerdierks A (2011) Bacterial sulfur cycling shapes microbial communities in surface sediments of an ultramafic hydrothermal vent field. Environ. Microbio. 13(10), 2633-2648

Zielinski FU, Borowski C, Gennerich H-H, Wenzhöfer F, Dubilier N (2011) In situ measurements of hydrogen sulfide, oxygen, and temperature in diffuse fluids of the ultramafic-hosted Logatchev hydrothermal vent field (Mid-Atlantic Ridge): implications for chemosymbiotic bathymodiolin mussels. G-Cubed 12(9) doi:10.1029/2011GC003632