International Journal of Astrobiology

Terrestrial models for extraterrestrial life: methanogens and halophiles at Martian temperatures

I.N. Reid a1a2, W.B. Sparks a1a2, S. Lubow a1a2, M. McGrath a1a2a3, M. Livio a1a2, J. Valenti a1a2, K.R. Sowers a1a4, H.D. Shukla a1a4, S. MacAuley a1a4, T. Miller a1a4, R. Suvanasuthi a1a4, R. Belas a1a4, A. Colman a1a4, F.T. Robb a1a4, P. DasSarma a1a4, J.A. Müller a1a4a5, J.A. Coker a1a4, R. Cavicchioli a1a6, F. Chen a1a4 and S. DasSarma a1a4
a1 Maryland Astrobiology Consortium, USA
a2 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail:
a3 Marshall Spaceflight Center, Huntsville, AL 35812, USA
a4 University of Maryland Biotechnology Institute, Center of Marine Biotechnology, Baltimore, MD 21202, USA e-mail:
a5 Department of Biology, Morgan State University, Baltimore, MD 21215, USA
a6 School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia

Article author query
reid in   [PubMed][Google Scholar] 
sparks wb   [PubMed][Google Scholar] 
lubow s   [PubMed][Google Scholar] 
mcgrath m   [PubMed][Google Scholar] 
livio m   [PubMed][Google Scholar] 
valenti j   [PubMed][Google Scholar] 
sowers kr   [PubMed][Google Scholar] 
shukla hd   [PubMed][Google Scholar] 
macauley s   [PubMed][Google Scholar] 
miller t   [PubMed][Google Scholar] 
suvanasuthi r   [PubMed][Google Scholar] 
belas r   [PubMed][Google Scholar] 
colman a   [PubMed][Google Scholar] 
robb ft   [PubMed][Google Scholar] 
dassarma p   [PubMed][Google Scholar] 
muller ja   [PubMed][Google Scholar] 
coker ja   [PubMed][Google Scholar] 
cavicchioli r   [PubMed][Google Scholar] 
chen f   [PubMed][Google Scholar] 
dassarma s   [PubMed][Google Scholar] 


Cold environments are common throughout the Galaxy. We are conducting a series of experiments designed to probe the low-temperature limits for growth in selected methanogenic and halophilic Archaea. This paper presents initial results for two mesophiles, a methanogen, Methanosarcina acetivorans, and a halophile, Halobacterium sp. NRC-1, and for two Antarctic cold-adapted Archaea, a methanogen, Methanococcoides burtonii, and a halophile, Halorubrum lacusprofundi. Neither mesophile is active at temperatures below 5 °C, but both cold-adapted microorganisms show significant growth at sub-zero temperatures (−2 °C and −1 °C, respectively), extending previous low-temperature limits for both species by 4–5 °C. At low temperatures, both H. lacusprofundi and M. burtonii form multicellular aggregates, which appear to be embedded in extracellular polymeric substances. This is the first detection of this phenomenon in Antarctic species of Archaea at cold temperatures. The low-temperature limits for both psychrophilic species fall within the temperature range experienced on present-day Mars and could permit survival and growth, particularly in sub-surface environments. We also discuss the results of our experiments in the context of known exoplanet systems, several of which include planets that intersect the Habitable Zone. In most cases, those planets follow orbits with significant eccentricity, leading to substantial temperature excursions. However, a handful of the known gas giant exoplanets could potentially harbour habitable terrestrial moons.

(Received May 8 2006)
(Accepted June 12 2006)
(Published Online August 8 2006)

Key Words: Astrobiology; Archaea; biofilm; extrasolar planets; Mars; psychrophiles.