It is now well recognised that many environments considered by man to be extreme are colonised by micro-organisms which are specifically adapted to these ecological niches. These organisms not only survive but actively grow under such conditions. A diverse range of bacteria, cyanobacteria, algae and yeasts has now been isolated from these habitats which are extreme in terms oftemperature, pH, salinity and pressure as well as species which are resistant to radiation and toxic chemicals. Whilst originally considered to be mere 'scientific curiosities', it is now generally accepted that many...