The Antarctic continent is one of the most physically and chemically extreme terrestrial environments to be inhabited by microorganisms. Although most of the continent is covered by glacial ice sheets, ice-free areas comprising ~0.4% of the continental land mass are discontinuously distributed around the coastal margins, and many of these areas seem to have been ice free since at least the last glacial maximum2. The McMurdo Dry Valleys are a series of generally west-to-east-oriented, glacially carved valleys located between the Polar Plateau and the Ross Sea in Southern Victoria Land, Antarctica. Dry Valley soil ecosystems are characterized by large variations in temperature and light regimes, steep chemical gradients and a high incidence of solar radiation with an elevated ultraviolet B light component. The microorganisms inhabiting these ice-free, cold-soil environments exist under conditions of low nutrient status and low bioavailability of water, this being further compromised by high levels of salinity. The additive effects of the extreme aridity and widely fluctuating physiochemical conditions of these cold deserts are expected to have a great impact on the adaptations and life cycle strategies used by resident biota.
Recent applications of molecular methods have revealed a dramatically contrasting picture – a very wide diversity of microbial taxa, many of which are uncultured and taxonomically unique, and a community that seems to be structured solely by abiotic processes. This article reviews these extreme Antarctic terrestrial microbial communities, with particular emphasis on the factors that are involved in their development, distribution and maintenance in these cold desert environments.