What are the 5 examples of archaebacteria?

What archaea live in humans?

By Dr Tom Chivers

BBC News Online science reporter Published duration 10 May 2025.

image copyright Getty Images image caption Archaea are single-celled organisms with no clear evolutionary ancestor. When news reached me in 2025 that scientists had found bacteria in people's bloodstream it didn't take much time before I decided to get on the next plane to California to find out for myself. My wife was feeling ill - she has a sore throat and a headache - and were keen to see if the doctors were right. It was clear from my wife's side that the antibiotics weren't working and when she said she was thirsty I didn't waste time worrying about how easy it would be to find micro-organisms in her bloodstream. It was an easy answer - we just headed straight to the nearest drinking water.

As soon as I got to the source of her thirst - the local fast-food chain - I poured a cup of water into a plastic cup. When I lifted the cup to drink I thought I saw something weird moving in there but the cup was really shaking, like those jiggling plastic spoons you often see next to the kettle at petrol stations.

When I started to look again what I had previously mistaken for shaking was moving very fast between the coffee cup's lip and my mouth. "That's because you're drinking it very quickly," my wife explained. "It's called foam and it's full of bacteria."

She's right: it does explain it - the foam would contain millions of micro-organisms - most of which would be water-dwelling bacteria. All of them would be extremely easy to find.

And we did find them. The next day, on a trip back to Japan, my wife bought a straw-like drinking instrument - an "oral thermometer". When I drank from the straw a lot of foam popped out and we had another clue.

After I came back from the USA I learned that researchers have indeed found archaea in humans' bloodstream. This single-celled organism with no clear evolutionary ancestor has been found living inside people.

What are the 5 examples of archaebacteria?

The 5 examples of Archaea are: Halobacteria.

Euryarchaeota. Thaumarchaeota. Aigarchaeota. Crenarchaeota. How can I tell the 5 groups of Archaea apart? This is a great question. There are many ways to tell the difference, as you can see from this picture. The Archaea are the yellow part of the chart. The green part are the Eukarya (or Bacteria).

What are the 5 examples of Archaea? There are five main groups of Archaea: Halobacteria (blue). Euryarchaeota (red). Thaumarchaeota (green). Aigarchaeota (yellow). Crenarchaeota (purple). Halobacteria. You may not have heard of them, but they are amazing. In fact, the halophilic (salt-loving) Archaea are thought to be the oldest organisms on Earth. They live in extreme conditions (often high salt concentrations), and make up about 15% of all life on Earth. Many species can eat a lot of salt, and they are known to live in brackish water (sewage).

Euryarchaeota. This group of Archaea was discovered in 1987 by Martin J. Donat and James W. McFall-Ngai, and it is thought that they are most similar to bacteria. They live in extreme environments (some even in boiling water or molten lava) and even in the ocean. These Archaea are also found to be in the majority of cells in the human body.

Thaumarchaeota. These Archaea were discovered in 1995 by Tim Klapstine and Robert T. Shih. They are usually found in hot, acidic environments and can actually grow on metals like gold. This is a group of extremophiles, so they can eat and thrive in these conditions.

Aigarchaeota. Archaea were discovered in 2025 by Stephen Giovannoni and colleagues at the University of Michigan.