Tolerance limits of methanogenic life in terrestrial permafrost

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TOLERANCE LIMITS OF METHANOGENIC LIFE IN TERRESTRIAL PERMAFROSTD. Morozova and D. WagnerAlfred Wegener Institute for Polar and Marine Research, Telegrafenberg A 43, 14473 Potsdam, dwagner@awi-potsdam.deIntroduction: Prokaryotic microfossils, found in early Archaean rocks, implies that the earliest life forms on Earth probably date from between 3.5 3.8 Ga ago [1, 2], when living conditions on Mars were similar to those on early Earth. Therefore it is legitimate to assume that life on Mars emerged as well as on Earth. Accepting that first life on both planets was determined by complex microbial communities, the Martian life must have adapted to drasti-cally changing environmental conditions or be-come again extinct. One possibility for survival of Martian primitive life might be subsurface lithoautotrophic ecosystems. Comparable envi-ronments exist in permafrost regions on Earth [3, 4].The current ESA (European Space Agency) mission Mars Express determined the existence of water as ground ice on Mars, which is a fun-damental requirement for life. Furthermore, Mars Express demonstrated for the first time the presence of CH4 in the Martian atmosphere, which due to the lifetime of CH4 could be only originated from active volcanism or biological sources [5]. This finding may have important implications for the possibility that microbial life could exist on Mars.Methanogenic archaea colonising terrestrial permafrost, are highly specialized organisms from the view point of metabolism. The capa-bility of these organisms to lithoautotrophic growth under strictly anaerobic conditions [6], tolerance to low temperatures and survival un-der extreme conditions of permafrost for sev-eral millions of years [7, 8] make methanogens one of the most suitable keystone organism for the investigation of possible Martian life [9].Main Results of the 1st period of applica-tion: Within the scope of the project we study the tolerances of methanogens under unfavour-able life conditions of terrestrial or extraterres-trial permafrost (Mars simulation). The borders of growth influenced by desiccation, tempera-ture extremes, radiation and high salt concentra-tion were analyzed for the organisms in pure cultures obtained from permafrost soils as well as in their natural environment of Siberian per-mafrost.First results represent high survival poten-tial of methanogenic archaea under tested ex-treme conditions. Methanogens revealed CH4 production under in situ temperature conditions (0 to 2°C) and salt concentration up to 6 M with a rate of about 0.077 0.009 nmol CH4 h-1 g 1. Incubation of pure cultures with different salt concentration (0.1 to 6 M) showed a significant CH4 production rate even at salt concentration of 6 M (0.013 0.022 nmol CH4 h-1 ml-1). Addi-tionally, the influence of temperature on the salt tolerance of methanogens was analyzed. The organisms showed better adaptation to high salt concentration at temperatures of 4°C, with a CH4 production of 0.019-0.026 nmol CH4 h-1 ml-1 compared to the activity at 28°C (0.012-0.014 nmol CH4 h-1 ml-1) [10]. Methanogenic archaea are highly resistant to high doses of UV-C radiation (up to 5000 J m 2 for soil sam-ples and up to 800 J m-2 for pure cultures). Irra-diated cells indicated significant methane for-mation without prolonged lag-phase (up to 5.87 nmol CH4 h 1 ml-1 for pure cultures and about 0.9 nmol CH4 h-1 g-1 for soil samples). The tolerance to high intensities of UV-C radia-tion correlates well with the observed desicca-tion resistance of up to five days. Our results show that methanogenic archaea from perma-frost are more resistant against unfavourable living conditions than known methanogens from non-permafrost environments.Objectives for the 2nd period of applica-tion: Presented investigations of tolerance lim-its of methanogenic archaea indicate that the organisms from Siberian permafrost possess extraordinary high survival potential under ex-treme environmental conditions. These results provide an excellent starting point for further studies on methanogenic archaea regarding the new results obtained by Mars Express. High resistance of methanogens to defined stress fac-tors is an important requirement for long-term survival and adaptation to extreme environ-ments of terrestrial permafrost, a model of ex-traterrestrial protected niches. The existence of microorganisms like methanogenic archaea on Mars might be possible due to geothermal sources of hydrogen, carbon dioxide - which is abundant in the Martian atmosphere - and sub-surface water. Presented results support the hy-pothesis that methanogenic archaea from Sibe-rian permafrost habitats can survive also under present Martian environmental conditions (an-oxic conditions, dryness, coldness, intensive radiation and high salinity). Thus, further simu-lation experiments (Mars simulation) with methanogens as keystone organisms are of par-ticular importance for analogue extraterrestrial life investigations.The main objectives for the scheduled pro-ject phase are: physiological and phylogenetical char-acterization of methanogenic isolates from permafrost environments with re-gard to their adaptation strategies and survival potential under extreme condi-tions determination of the main methane formation pathways under permafrost conditions using 13C labelled substrates permafrost simulation experiments (thawing-freezing processes) stress experiments (preliminary tests) for the preparation of the Mars simula-tion: determination of radiation limits and the influence of pressure and low temperatures characterization of the survival poten-tial of methanogenic archaea from ter-restrial permafrost under simulated Martian conditions in cooperation with the DLR (Dr. Rettberg, RE 1574/1-1, SPP 1115)The comparative system studies will serve to understand the modern Mars cryosphere and other extraterrestrial permafrost habitats. This knowledge represents an essential basis for searching and understanding of extraterrestrial life, if present, especially concerning possible protected niches on present Mars.References: [1] Schidlowski, M. (1993) The chemistry of life origin, 389-414. [2] Schopf, J.W. (1993) Science 260, 640-646. [3] Gilichinsky et al. (1993) Origins Life Evol. Biosphere 23, 65-75. [4] Abyzov, S.S. et al. (1998) Microbiology 67: 451-458. [5] Feldman, W.C. (2003) Science 297, 75-78. [6] Deppenmeier, U. et al. (1996) Arch. Microbiol. 165, 149-163. [7] Gylichinsky et al. (2003) Astrobiology 3/2, 331-341. [8] Rivkina et al. (2004) Adv. Space Res. 33, 1215-1221. [9] Wagner et al. (2001) Astro-biologie- the quest for the conditions of life, 143-159. [10] Morozova, D. and Wagner, D. (2005) submitted.

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Conference (Invited talk)
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DFG Colloquium: Mars and the Terrestrial Plantes, BerlinAugust 2005..
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Morozova, D. and Wagner, D. (2005): Tolerance limits of methanogenic life in terrestrial permafrost , DFG Colloquium: Mars and the Terrestrial Plantes, BerlinAugust 2005. .

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