Thermophile bacteria in permafrost: model for astrobiology

Details Thermophile bacteria in permafrost: model for astrobiology Thermophile bacteria in permafrost: model for astrobiology

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....12773g&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #12773

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Scientific paper

According the NASA point of view, one way to have liquid water on Mars at shallow depths would be through subglacial volcanism. Such volcano-ice interactions could be going on beneath the polar caps of Mars today, or even within the adjacent permafrost around the margins of the ice caps. This is why one of the Earth's models, close to extraterrestrial environment, represented by active volcanoes in permafrost areas and the main question is - does such econishes as volcanoes and associated environment contain recently microbial communities? The first step of this study was carried out on volcano Stromboli (Italy), using the marine water samples extracted from the borehole near the island marine coast, surrounding the volcano. According the temperatures (45^oC), this thermal water has the hydraulic connection with volcano. Microscopy analyses of studied water shown the presence of different morphological types of microorganisms: small mobile roads, coccoid and sarcina-like organisms and long fixed roads, as well as rest forms (spores and cysts). To separate this community on marine and volcano microorganisms, the common mineral media with added CO_2, acetate or glucose-peptone as a source of carbon were used for culturing, and Fe3+, S^o, SO_42- were added as a electron acceptors. We attempt to isolate thermophilic anaerobic microorganisms of different metabolic groups - methanogens, acetogens, iron-, sulfur- and sulfate-reducers, and to test each group of microorganisms on the presence of halophilic forms. After 24 hours of incubation at temperatures varied 55 to 85^o, the grow relatively the control media was observed at CO_2+H_2 and glucose-peptone media. Microscopy study of preparations showed small coccus of irregular shape that was unable to reduce S^o or SO_42-. During the subsequent re-seeding were obtained the enrichment cultures of themophilic bacteria, genetically closed to genera Thermococcus: heterotrophic, growing up to 95^oC with the growth optimum at 87^oC and acetogenic, growing up to 92^oC with the optimum at 80^oC. Both isolated bacteria were non-halophiles. Using these data, one can conclude that isolated thermophiles are associated with volcano. The next step of this study was carried out on volcano Tolbachik, south border of permafrost zone, Kamchatka peninsula (Russia). During the volcano eruption in 1975-76 the thick (12 to 16 m) layer of interstratify volcano ash, sand and scoria was accumulated on the elevation 1100 m and to the moment this horizon is complete freeze, t=(-1)-(-2)^oC. The analyses showed that frozen samples extracted from the borehole, crossing these young volcano deposits, contain viable microorganisms and among them, thermophilic anaerobic bacteria. Moreover, biogenic methane (up to 1100-1900 μlCH_4/kg soil) was also found in these samples. Thermophiles were never found before in permafrost thickness and this is why this study demonstrate that there are only one way for thermophilic bacteria to appear within frozen volcanic horizon - during the eruption, from volcano or surrounding associated subsurface geological strata. The most important conclusion is that thermophilic bacteria might survive in permafrost and even produce the biogenic gases. This is why the terrestrial volcano microbial community might serve as an exobiological model for hypothesis of existing ancient microbiocenoses, i. e. extraterrestrial habitats that probably might be found around Martian or other planet volcano in the absence of oxygen.

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