Extremophiles in Antarctica: Life at low temperatures

Abstract

In this chapter, we will explore the different adaptations of extremophiles to life in the extreme cold. We generally forget that the Earth is mostly cold and that most ecosystems are exposed to temperatures that are permanently below 5°C. Such low mean temperatures mainly arise from the fact that ≈70% of the Earth’s surface is covered by oceans that have a constant temperature of 4–5°C (below a depth of 1000 m), irrespective of the latitude. The polar regions account for another 15% of the surface, to which the glacier and alpine regions must also be added. Here, we will take an illustrated look in particular at the Antarctic environment, as it is by far the coldest environment on Earth — the lowest temperature on the surface of the Earth (−89.2°C) was recorded at the Russian Vostok Station, at the centre of the East Antarctic ice sheet. Antarctica is a place where organisms are often subjected to combined stresses including desiccation, limited nutrients, high salinity, adverse solar radiation and low biochemical activity. The incredibly harsh environment of the Antarctic continent precludes life in most of its forms, and the microorganisms are therefore dominant.

Generally, conditions include air temperatures that average well below freezing all year round, strong winds that increase the effects of the cold, light which varies from months of total darkness to total sunlight and little free available water, with all but 2% of the continent covered with ice. Given this combination of extremes, it is surprising that anything lives on the continent at all, let alone thrives there. For the organisms that do manage to adapt, however, the benefits from a lack of competition in the extreme cold are enormous, and this is often seen in very large population sizes. So how do some organisms survive extreme cold, and others exploit and take advantage of it? As organisms have been subjected to these stresses over extremely long periods of time, a range of adaptations have evolved; some species have adapted to live at the limits, some produce specific compounds such as antifreeze, some remain viable but frozen in a state of suspended animation whilst higher organisms can adapt their life cycles in such a way that when conditions are harsh they die, leaving the next generation to recover as conditions improve. By looking at a range of different strategies in a wide variety of organisms, it is hoped to bring together general mechanisms of adaptation to life in the extreme cold.