Figure 30e.1
An extreme thermophile. Extreme thermophiles, like this Sulfolobus brierleyi, only live in habitats with extremely high temperatures.

In this enhancement chapter, written by Professor Michael Madigan of Southern Illinois University, we examine the many prokaryotic organisms that inhabit "extreme environments"–habitats in which some chemical or physical variable(s) differ significantly from that found in habitats that support plant and animal life. Great strides have been made in recent years in the isolation and characterization of extremophilic prokaryotes and many of them turn out to have fascinating metabolic properties and interesting evolutionary histories. Prokaryotes that grow at very high temperatures are perhaps the most dramatic in these regards (figure 30e.1), as all cellular components need to be made heat stable and their evolutionary position is that of the least derived of all known life forms. As our knowledge of bacterial diversity improves, primarily from the introduction of molecular tools for assessing bacterial phylogeny and diversity and from new advances in isolation and laboratory culture, it is becoming clear that the bulk of evolutionary diversity on Earth does not reside in plants and animals, but instead in the invisible prokaryotic world. There is now great interest in mining the diverse genetic resources of Earth’s smallest cells for use in biotechnology and related areas.