Archaea can be spherical, rod, spiral, lobed, rectangular or irregular in shape. An unusual flat, square-shaped species that lives in salty pools has also been discovered. Some exist as single cells, others form filaments or clusters. Until the 1970s this group of microbes was classified as bacteria.
Many archaea have been found living in extreme environments, for example at high pressures, salt concentrations or temperatures. These types of organisms are called extremophiles. Their cell wall differs in structure from that of bacteria and is thought to be more stable in extreme conditions, helping to explain why some archaea can live in many of the most hostile environments on Earth.
Examples of archaea habitats are boiling hot springs and geysers such as those found in Yellow Stone Park, USA and ice such as the Arctic and Antarctic oceans, which remain frozen for most of the year.
Learn more about archaea
From extreme temperatures and highly acidic conditions to the insides of volcanoes and the depths of the ocean, a diverse group of microbes called archaea thrive in many places that most life can't survive. This issue of Microbiology Today highlights the importance of archaea and our current understanding of them.
Are there really no archaeal pathogens? And if not, why not? Dr James Chong explores these questions in a film and article for Microbiology Today.
As part of the latest issue of Microbiology Today, called ‘What is life?’ (published online 10 May), we explore the Archaea. These are microbes that have been around since the beginnings of life on Earth, but were only discovered in the last 40 years.