Methanogenesis under Extreme Environmental Conditions in Permafrost Soils: A Model for Exobiological Processes? D. Wagner 1 , S. Kobabe 1 , E.-M. Pfeiffer 2 and H.-W. Hubberten 1 1 Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany 2 Institute of Soil Science, University of Hamburg, Hamburg, Germany ARC 915 + DAPI ARC 915 + DAPI ARC 915 + EUB 338 mix ARC 915 + EUB 338 mix ARC 915 ARC 915 The evolution of life on Earth had already started 3.8 Ga ago, when living conditions on Mars were similar to those on early Earth. Assuming that first life on both planets was determined by complex microbial communities, the Martian life must have adapted to drastically changing environmental conditions or become extinct again. One possibility for survival of Martian primitive life might be subsurface lithoautotrophic ecosystems. Comparable environments exist in permafrost regions on Earth. Therefore, terrestrial permafrost, in which microorg-anisms have survived for several million years, is considered to be a model for extraterrestrial analogues. I NTRODUCTION NTRODUCTION METHANOGENIC ETHANOGENIC ARCHAEA RCHAEA Responsible for the microbial methane production (methanogenesis) is a small group of highly specialised microorganisms, called methanogenic archaea. They are regarded as strictly anaerobic microbes, which can grow and survive only under anoxic conditions. They are characterised by lithoautotrophic growth, whereby energy is gained by the oxidation of hydrogen and carbon dioxide can be used as the only carbon source. Because of the specific adaptations of methanogenic archaea to conditions like those on early Earth (e.g. no oxygen, no or little organic substrates) and their phylogenetic origin, they are considered as key-organisms in astrobiological research . METHANOGENESIS ETHANOGENESIS Major landmarks of bio-logical evolution on Earth 0 20 40 60 80 0 50 100 150 200 250 time [h] CH4 0 1 2 3 4 5 6 7 8 9 temperature temperature [°C] depth [cm] 300 250 200 150 100 50 0 0,00 0,02 0,04 0,06 0,5 1,5 300 250 200 150 100 50 0 acetate 0,00 0,02 0,04 0,06 0,5 1,5 hydrogen core LD-01-1 active layer CONCLUSION ONCLUSION contact: [email protected] Martian surface and terrestrial permafrost areas show similar mor-phological structures. Northern Martian hemisphere (NASA) Lena Delta, Siberia (AWI) The presented results show that methanogenic archaea are suitable key-organisms for further studies about adaptation strategies and long- term survival in extreme environments. Microbiological studies in combination with geochemical and physical analysis can give insights into early stages of life in terrestrial permafrost, which can be used as a model for exobiological processes. Studies of CH 4 production in the active layer showed methanogenesis at in situ temperatures between 0.6 and 1.2 °C as well as at –3 °C (0.1 – 11.4 nmol CH 4 h -1 g -1 ) and –6 °C (0.08 – 4.3 nmol CH 4 h -1 g -1 ). In Holocene permafrost deposits high CH 4 concentrations were proven and methanogenesis could be initiated after thawing of the sediments. The results indicated the existence of a methanogenic community , which has well adapted to the low in situ temperature of permafrost. 800 700 600 500 400 300 200 100 0 0 2500 5000 7500 0 2500 5000 7500 Samoylov (72°22N/126°29E) depth [cm] Kurungnakh (72°19N/126°13E) 1 2 1 2 3 3 In situ CH 4 production in the boundary layer to the permafrost at 1 °C CH 4 production at subzero temperatures with H 2 /CO 2 as a substrate CH 4 concentration in Holocene permafrost deposits of the Lena Delta CH 4 production potential at 5 °C with acetate or hydrogen as substrate after thawing of the Holocene sediments Aggregates of methanogenic archaea in permafrost soils detected by fluorescence in situ hybridisation. The aggregate formation could serve as protection against extreme habitate conditions. CH 4 [ppm] 0 100 200 300 400 500 0 500 1000 1500 2000 2500 3000 0 150 300 450 600 750 900 - 3 °C CH4 time [h] - 6 °C CH4 CH 4 [ppm] CH 4 [ppm] CH 4 [ppm] CH 4 production [nmol h -1 g -1 ] 4 H 4 H 2 + CO + CO 2 CH CH 4 + H + H 2 O 500 nm Methanosarcina Methanosarcina spec spec. Climate Climate history history of of early early Earth and Mars Earth and Mars Earth Earth Mars Mars Atmosphere Atmosphere Pressure Temperature Duration Hydrosphere Hydrosphere Biosphere Biosphere CO 2 , N 2 , H 2 O CO 2 , N 2 , ? ≥ 1 atm ≈ 1 atm ≥ 0 °C ≈ 0 °C until today first Ga oceans rivers, lakes ? since > 3.8 Ga ??? McKay and Davis, 1991 10 m 4,0 3,0 2,0 1,0 0,0 4,5 Origin of life Origin of modern eukaryotes Origin of metazoans Age of dinosaurs 20% 10% 1% 0,1% Chemical evolution Origin of cyanobacteria Microbial diversification Archaea Bacteria Oxygenated environment Morphological evolution of metazoans Eukarya anoxic O 2 concentration time before present [billions of years]