Archaea vs. Bacteria: What Are the Differences?

Microorganisms in a super-heated hot spring
Archaea are extremophiles, capable of surviving in extreme conditions (like boiling hot springs).

Anastassiya Bornstein / Getty Images

Archaea and bacteria are two different domains of cellular life. They are both prokaryotes, as they are unicellular and lack a nucleus. They also look similar (even under a microscope).

However, DNA analysis reveals that archaea are as different from bacteria as they are from human beings. Discovered during the 1970s as a unique life form, archaea play an important role in our daily lives, including as part of the human gut microbiome.

What Are Archaea?

Archaea are a domain of single-celled microorganisms. They are extremophiles, capable of surviving in extreme environments where no other organisms would survive. The domain Archaea contains a diverse set of organisms that share properties with both bacteria and eukaryotes (the two other domains).

Differences Between Archaea and Bacteria

Both bacteria and Archaea are microorganisms that live in a wide range of habitats, including the human body. They look very similar to one another, even under a microscope. Their chemical makeup and physical characteristics, however, are quite different from one another. Some of their key differences include:

  • The cell walls and membrane lipids (fatty acids) of bacteria and Archaea are made up of different chemicals;
  • Many types of bacteria can perform photosynthesis (generating oxygen from sunlight), while Archaea cannot;
  • Archaeal and bacterial flagella are constructed differently;
  • Archaea reproduce by fission while some bacteria produce spores;
  • The chemical makeup of Archaeal and bacterial DNA and RNA are quite different from one another;
  • While some bacteria are pathogenic (cause disease), no archaea are pathogenic.

Discovery of Archaea

Before the discovery of archaea, scientists believed that all prokaryotes were a single type of organism called bacteria.

In the late 1970s, a biologist named Dr. Carl Woese conducted genetic experiments on organisms believed to be bacteria. The results were startling: One group of so-called bacteria were radically different from the rest. This unique group of microorganisms lived in extremely high temperatures and produced methane.

Woese termed these microorganisms Archaea. Their genetic makeup was so different from the bacteria that he proposed a major change to the way life on Earth is organized. Instead of organizing life into two domains (prokaryotes and eukaryotes), Woese organized life into three domains: eukaryotes, bacteria, and archaea.

Role of Archaea

Archaea, like bacteria, exist in a huge range of environments, including the human body. And, like bacteria, Archaea play an important role in many biological processes. Some of those roles include:

  • Global nutrient cycling
  • Ammonia oxidation
  • Sulfur oxidation
  • Methane production, aiding in digestion
  • Removal of hydrogen as part of the carbon cycle

Archaea Are Extremophiles

Perhaps the most fascinating aspect of Archaea is their ability to live in incredibly extreme environments. They are capable of thriving where no other organism can survive.

For example, according to one study, the archaeal Methanopyrus kandleri strain can grow at 252 degrees F, while Picrophilus torridus can thrive at the incredibly acidic PH of 0.06. These are both records for extremophile environments.

Other examples of Archaea in extremophile environments include:

  • The hot springs in Yellowstone National Park, in boiling hot water
  • Near hydrothermal vents at the bottom of the ocean where temperatures are above 100 degrees Centigrade
  • In the world's most alkaline and acid water
  • In the digestive tracts of termites and many other animals where they produce methane
  • Deep underground in petroleum deposits

Additionally, archaea may be able to survive in toxic waste and heavy metals.

Archaea and the Origins and Future of Life

Scientists have found that Archaea, particularly those that thrive in extreme heat, are genetically close to the “universal ancestor” of all organisms on Earth. This finding suggests that Archaea may be the key to understanding the evolutionary origins of life on Earth.

Some scientists also believe that Archaea's ability to survive in extraordinarily harsh environments could provide insight into extraterrestrial life. The nature of extremophiles makes them a natural focus for researchers exploring the question of what, if anything, can survive in interstellar space or on planets where typical Earth-based plants and animals would quickly die. One study subjected Archaea to temperature, UV radiation, humidity, and pressure resembling conditions on Mars and on the moon Europa; not surprisingly, the microorganisms lived and thrived.

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