Antarctic micro-organisms: coming in from the cold

During the past two decades, there has been a large increase in research on cold-adapted micro-organisms, generally known as psychrophiles, driven by the realisation that they and their enzymes have a great potential for exploitation in biotechnology1. As a consequence, many more laboratories are culturing micro-organisms at low temperatures. However, many of the most commonly used growth media were designed originally for the culture of pathogenic micro-organisms that grow best at 37°C. Such media are also generally “rich”, ie, in comparison with most natural environments they not only contain relatively high concentrations of carbon and nitrogen sources but also generous supplies of other necessary nutrients, usually in a readily assimilable form. Nutrient cornucopia is relatively rare on Earth and many habitats will be deficient in more than one important component of a micro-organism’s nutrition. In addition, most of our earthly environment is (from a human perspective) relatively cold, ie, it is more or less permanently below 5°C. Therefore, most micro-organisms are coldadapted. They have special adaptations to their enzymes, membranes and other cellular components, enabling them to grow at low temperatures at rates comparable to those of mesophiles at moderate temperatures. These molecular changes are discussed in several reviews2, 3. This short review instead considers the growth of psychrophiles, and the requirements of isolating them from natural habitats and culturing them in the laboratory. Antarctica is used as the example of a cold habitat, which is not only one of the most extreme on Earth but also has been used both as a source of psychrophiles for biotechnological use and as a model in the search for extraterrestrial life.