International Journal of Astrobiology



DNA signature of thermophilic bacteria from the aged accretion ice of Lake Vostok, Antarctica: implications for searching for life in extreme icy environments


Sergey A. Bulat a1a2a3, Irina A. Alekhina a1, Michel Blot a2 1 , Jean-Robert Petit a3, Martine de Angelis a3, Dietmar Wagenbach a4, Vladimir Ya. Lipenkov a5, Lada P. Vasilyeva a1, Dominika M. Wloch a2, Dominique Raynaud a3 and Valery V. Lukin a5
a1 Division of Molecular and Radiation Biophysics, Petersburg Nuclear Physics Institute, Leningrad region, Gatchina 188300, Russia e-mail: bulat@omrb.pnpi.spb.ru
a2 Plasticité et Expression des Génomes Microbiens, UJF, CNRS, Grenoble 38041, France e-mail: sergey.bulat@ujf-grenoble.fr
a3 Laboratoire de Glaciologie et de Géophysique de l'Environnement, CNRS, BP96, Saint Martin d'Hères 38402, France
a4 Institut für Umweltphysik, INF 229 Heidelberg 69120, Germany
a5 Arctic and Antarctic Research Institute, 38 Bering Str., St. Petersburg 199397, Russia

Article author query
bulat s   [PubMed][Google Scholar] 
alekhina i   [PubMed][Google Scholar] 
blot m   [PubMed][Google Scholar] 
petit jr   [PubMed][Google Scholar] 
de angelis m   [PubMed][Google Scholar] 
wagenbach d   [PubMed][Google Scholar] 
lipenkov v   [PubMed][Google Scholar] 
vasilyeva l   [PubMed][Google Scholar] 
wloch d   [PubMed][Google Scholar] 
raynaud d   [PubMed][Google Scholar] 
lukin v   [PubMed][Google Scholar] 

Abstract

We have used 16S ribosomal genes to estimate the bacterial contents of Lake Vostok accretion ice samples at 3551 m and 3607 m, both containing sediment inclusions and formed 20000–15000 yr ago. Decontamination proved to be a critical issue, and we used stringent ice chemistry-based procedures and comprehensive biological controls in order to restrain contamination. As a result, up to now we have only recognized one 16S rDNA bacterial phylotype with confident relevance to the lake environment. It was found in one sample at 3607 m depth and represents the extant thermophilic facultative chemolithoautotroph Hydrogenophilus thermoluteolus of beta-Proteobacteria, and until now had only been found in hot springs. No confident findings were detected in the sample at 3551 m, and all other phylotypes revealed (a total of 16 phylotypes, 336 clones including controls) are presumed to be contaminants. It seems that the Lake Vostok accretion ice is actually microbe-free, indicating that the water body should also be hosting a highly sparse life. The message of thermophilic bacteria suggests that a geothermal system exists beneath the cold water body of Lake Vostok, what is supported by the geological setting, the long-term seismotectonic evidence from 4He degassing and the ‘18O shift’ of the Vostok accretion ice. The seismotectonic activity that seems to operate in deep faults beneath the lake could sustain thermophilic chemolithoautotrophic microbial communities. Such a primary production scenario for Lake Vostok may have relevance for icy planets and the approaches used for estimating microbial contents in accretion ice are clearly relevant for searching for extraterrestrial life.

(Published Online August 5 2004)
(Received November 20 2003)
(Accepted March 4 2004)


Key Words: accretion ice; Antarctica; bacteria; contamination; exobiology; geothermal environment; Lake Vostok; subglacial lake environments; thermophiles.


Footnotes

1 Deceased 8 September 2002.