Microbes that Like it Cold: Antarctic Critters and Extraterrestrials
Microbes don’t always get as much attention as charismatic animals like polar bears or whales, but as we discussed previously, they impact the ocean more than any other marine organism. This is the last in a three-part series on microbes that thrive in extremely cold environments like the Arctic.
Antarctica is almost entirely covered in ice that can reach three miles thick. Some microorganisms thrive in ice, and Antarctica is no exception for such psychrophiles. Lakes deep underneath Antarctica’s ice contain liquid water, like there may be on Jupiter’s moon Europa, and make Antarctica a model for extraterrestrial life. The largest of Antarctica’s deep ice lakes is Lake Vostok. After drilling 11,800 feet, (3600 m) into the ice, and carefully extracting intact samples, scientists discovered microorganisms in the ice just above the lake in 1999 (see references below). Not only was this an impressive technical feat, but it showed that microorganisms could be found thousands of meters deep in ice, at pressures 400 times that at sea level, where temperatures can go below -40˚C (-40˚F). How microorganisms survive in the deep ice environments, and how they got into the ice at those depths is still being studied.
The discovery made a significant impact on our understanding of the potential for life elsewhere in the solar system. Research on psychrophiles in a variety of cold habitats is revealing that microbial life can exist far below what we consider the normal range of temperature and nutrients. As a result, we can anticipate other places in the solar system where microbial life might be found. The Lake Vostok habitat is remarkably similar to what is expected on Jupiter’s moon Europa. Jupiter, the largest planet in our solar system, and its 66 moons, some of which are almost as big as planets themselves, has been compared to a miniature solar system in its own right, and is referred to as the Jovian system.
Size comparison of Earth, our moon, and Europa. Photo via Wikimedia Commons.
Evidence from recent probes there suggests a thick ice sheet covering deep oceans on Europa, which is similar in size to our moon, making relative pressures under the ice there quite similar to those in Antarctica. The similarities between the subglacial lakes in Antarctica and Europa make them enticing to scientists looking for extraterrestrial microorganisms.
The icey moon Europa, with a closeup from the surface. Images courtesy of NASA.
Lake Vostok has recently been in the news because a Russian team has drilled completely through the ice layer above it and penetrated the lake for the first time. As winter begins in the harsh Antarctic, the team will wait until next year to explore the lake further. However, there are many subglacial lakes currently under investigation in Antarctica, promising many new and exciting discoveries about microbial life in the cold.
The relationships between ice, water, and rock for Europa and Subglacial Lake Vostok. Microbial metabolism in both systems can be driven by material from the surface and the bottom of both water bodies, according to Priscu. Figure courtesy of JC Priscu and KP Hand. Reprinted with permission from the American Society for Microbiology (Microbe, April 2012, p. 167-172).
References and further reading:
1. Priscu, J. C. & Hand, K. P. Microbial Habitability of Icy Worlds. Microbe 7, 167–172 (2012).
2. Price, P. B. & Sowers, T. Temperature dependence of metabolic rates for microbial growth, maintenance, and survival. Proc. Natl. Acad. Sci. U.S.A. 101, 4631–4636 (2004).
3. Price, P. B. A habitat for psychrophiles in deep Antarctic ice. Proceedings of the National Academy of Sciences 97, 1247–1251 (2000).
4. Karl, D. et al. Microorganisms in the accreted ice of Lake Vostok, Antarctica. Science 286, 2144 (1999).
5. Priscu, J. C. et al. Geomicrobiology of subglacial ice above Lake Vostok, Antarctica. Science 286, 2141–2144 (1999).
6. Carr, M. H. et al. Evidence for a subsurface ocean on Europa. Nature 391, 363–365 (1998).