Methanogenesis under Extreme Environmental Conditions in Permafrost Soils: A Model for Exobiological Processes?

D. Wagner1, S. Kobabe1, E.-M. Pfeiffer2 and H.-W. Hubberten1

1Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany2Institute of Soil Science, University of Hamburg, Hamburg, Germany

ARC 915 + DAPIARC 915 + DAPI

ARC 915 + EUB 338 mixARC 915 + EUB 338 mix

ARC 915ARC 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 lithoautotrophicecosystems. 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.

IINTRODUCTIONNTRODUCTION

MMETHANOGENIC ETHANOGENIC AARCHAEARCHAEA

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 .

MMETHANOGENESISETHANOGENESIS

Major landmarks of bio-logical

evolution on Earth

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hydrogen

core LD-01-1

active layer

CCONCLUSIONONCLUSION

contact: dwagner@awi-potsdam.de

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 CH4 production in the active layer showed methanogenesisat in situ temperatures between 0.6 and 1.2 °C as well as at –3 °C (0.1 – 11.4 nmol CH4 h-1 g-1) and –6 °C (0.08 – 4.3 nmol CH4 h-1 g-1). In Holocene permafrost deposits high CH4 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.

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(72°22N/126°29E)

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pth

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Kurungnakh(72°19N/126°13E)

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In situ CH4 production in the boundary layer

to the permafrost at 1 °C

CH4 production at subzero temperatures with H2/CO2 as a substrate

CH4 concentration in Holocene permafrost

deposits of the Lena Delta

CH4 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.

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pm

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H4

[pp

m]

CH4 [ppm]

CH4 production [nmol h-1 g-1]

4 H4 H22 + CO+ CO22

CHCH44 + H+ H22OO

500 nm

MethanosarcinaMethanosarcina

specspec..

ClimateClimate historyhistory of of earlyearly Earth and MarsEarth and Mars

EarthEarth MarsMars

AtmosphereAtmosphere

Pressure

Temperature

Duration

HydrosphereHydrosphere

BiosphereBiosphere

CO2, N2, H2O CO2, N2, ?

≥≥≥≥ 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

Microbialdiversification

Archaea

Bacteria

Oxygenated

environment

Morphological

evolution ofmetazoans

Eukarya

anoxic

O2concentration

time before present

[billions of years]