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

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.

Microbial origin of excess methane in glacial ice and implications for life on Mars

“…T he record of atmospheric methane (CH 4 ) concentration trapped in the Greenland Ice Sheet Project 2 (GISP2) ice core serves as a climate proxy, showing that climate during the last glacial period oscillated rapidly between cold and warm states that lasted for several thousand years (1). The source is believed to be wetland methane emissions that depend on temperature, precipitation, net ecosystem production, and oxidation by tropospheric OH.…”

“…Bacteria and archaea have been found in all subfreezing terrestrial environments (2)(3)(4)(5)(6). Studies of terrestrial psychrophiles and psychrotrophs have involved extraction and examination of cells from cold water, ice, or permafrost.…”

“…Price and Sowers (13) measured both CH 4 and microbial concentrations in the GISP2 basal ice and concluded that in situ metabolism at Ϫ9°C accounted quantitatively for the excess CH 4 . The silty, basal ice probably originated in flow-induced mixing of glacial ice with a frozen wetland soil (12) some 3 ϫ 10 5 yr ago (14).…”

Diffusion-controlled metabolism for long-term survival of single isolated microorganisms trapped within ice crystals

“…Numerous papers report the identification of microbes of diverse taxa, including nonextremophiles in ice (13)(14)(15)(16)(17)(18)(19)(20)(21)(22). Eukarya up to Ϸ10 2 m in size, some of which are viable, have been found in glacial ice (23)(24)(25)(26)(27).…”

The Vostok Venture: An Outcome of the Antarctic Treaty

“…Rather, they live at great depths in "hot" basement faults filled with sediments that may have been colonized soon after their formation and possibly before the onset of the Antarctic glaciation around 30 mya. According to He maximum concentration suggests contribution from a shallow-depth area upstream from Vostok (adapted from Bulat et al, 2004). a scenario built from the available geophysical and geochemical information, some niches have been suggested within deep faults or sediments close to fault mouths where chemolithoautotrophic microorganisms are likely to be protected and fed by hydrothermal fluids.…”