Introduction to Archaea: Videos & Practice Problems

Archaea, a major domain of life alongside bacteria and eukarya, are prokaryotic organisms distinct from bacteria. They possess unique ribosomal RNA sequences and lack peptidoglycan in their cell walls. Many archaea, known as extremophiles, thrive in extreme environments, such as high salinity or temperature, while others inhabit moderate environments, including human microbiota. Examples include Haloquadratum walsbyi and Pyrococcus furiosus. Understanding these differences is crucial for grasping microbial diversity and ecological roles.

Introduction to Archaea

In this video, we're going to begin our introduction to archaea. The term archaea is actually a plural term, and the singular form is archaeon. These refer to organisms in one of the three domains of life. Recall from our previous lesson videos that the three domains of life are bacteria, archaea, and eukarya. Archaea is one of the major domains of life. Like bacteria, archaea also have a prokaryotic cell structure, which makes archaea prokaryotes along with bacteria. Many students mistakenly believe that bacteria and archaea are identical because they are both prokaryotes, but that is not the case at all. It turns out that bacteria and archaea are as different from each other as they are from eukaryotes. There are still many differences between bacteria and archaea, although they are both categorized as prokaryotes. For example, archaea have unique ribosomal RNA (rRNA) sequences that significantly differ from the ribosomal RNA sequences of bacteria and eukarya. Also, archaea have cell walls that lack the molecule peptidoglycan, whereas bacteria have cell walls made of peptidoglycan, a molecule unique to bacteria.

Archaea are well known for growing in extreme environments, and those that do are known as extremophiles because they can survive in incredibly salty environments, extremely hot environments, or environments with extremely high pressures, and other challenging conditions. However, although many archaea grow in extreme environments, some archaea can grow in moderate environments as well. They can be found in soils, and they can even be part of the human microbiota. If we take a look at our image below, notice again on the left-hand side, we are showing you a snippet of our map of the lesson of the microbial world. We already talked about bacteria, and in this video, we are focusing on archaea. You can once again see that both bacteria and archaea are classified as prokaryotes. Although they are both classified as prokaryotes, meaning they are unicellular and do not have a nucleus, they have some similarities, but they still have many differences. Bacteria and archaea are not identical.

On the right-hand side, we are showing you some examples of archaea. Some are extremophiles that can grow in extremely salty environments, such as Haloquadratum walsbyi, known as the salt square. It has a square-like arrangement and is able to grow in extremely salty environments. Down below, we have some archaea that are capable of growing in extremely hot environments, such as Pyrolobus fumarii, known as the fire lobe of the chimney, Pyrococcus furiosus, known as the furious fireball, and Thermococcus gammatolerans, known as the ball of fire. These are examples of archaea that can grow in extremely hot environments.

This concludes our brief introduction to archaea. We will be able to discuss more about archaea as we move forward in our course. For now, this concludes our introduction, and we will get some practice applying these concepts as we move forward. I'll see you all in our next video.

Many species of Archaea are known to thrive in environments in which most living things would not survive. We call these Archaea…  

• A. Extremophiles.
• B. Thermophiles.
• C. Halophiles.
• D. Acidophiles.
• E. Alkaliphiles.

Answer: (A)

If you wanted to increase your chances of obtaining a member of Archaea (rather than a member of another domain), which would be the best site to obtain a sample?

• A. Inside a human intestine.
• B. On the surface of human skin.
• C. A 95°C (203°F) hot spring in Yellowstone.
• D. A 22°C (72°F) freshwater spring in Hawaii.
• E. On the surface of a raw hamburger patty.

Answer: (C)

Here’s what students ask on this topic:

What are the main differences between archaea and bacteria?

Archaea and bacteria, though both prokaryotes, have several key differences. Archaea possess unique ribosomal RNA (rRNA) sequences that are distinct from those of bacteria. Additionally, archaea lack peptidoglycan in their cell walls, a molecule that is present in bacterial cell walls. Archaea often thrive in extreme environments, such as high salinity or temperature, and are known as extremophiles. In contrast, bacteria are found in a wider range of environments. These differences highlight the distinct evolutionary paths and ecological roles of archaea and bacteria.

What environments do extremophilic archaea inhabit?

Extremophilic archaea are known for inhabiting some of the most extreme environments on Earth. These include highly saline environments, such as salt flats, where species like Haloquadratum walsbyi thrive. They also inhabit extremely hot environments, such as hydrothermal vents, where species like Pyrococcus furiosus and Pyrolobus fumarii can be found. Additionally, some extremophiles live in environments with high pressures or acidic conditions. Despite these harsh conditions, extremophilic archaea have adapted to survive and even thrive, showcasing their remarkable resilience and versatility.

How do archaea differ from eukaryotes?

Archaea differ from eukaryotes in several fundamental ways. Firstly, archaea are prokaryotic, meaning they lack a nucleus and membrane-bound organelles, whereas eukaryotes have a defined nucleus and organelles. Archaea have unique rRNA sequences and cell membranes composed of ether-linked lipids, unlike the ester-linked lipids in eukaryotic membranes. Additionally, archaea do not have peptidoglycan in their cell walls, a feature absent in eukaryotes. These differences underscore the distinct evolutionary lineage and biological characteristics of archaea compared to eukaryotes.

Can archaea be found in moderate environments?

Yes, while many archaea are known for thriving in extreme environments, some can also be found in moderate environments. These include soils, oceans, and even as part of the human microbiota. For example, methanogenic archaea are found in the digestive tracts of humans and other animals, where they play a role in breaking down organic matter. This diversity in habitat demonstrates the adaptability of archaea to a wide range of environmental conditions, from extreme to moderate.

What is the significance of archaea in the microbial world?

Archaea play a crucial role in the microbial world due to their unique metabolic pathways and ecological functions. They contribute to nutrient cycling, such as the nitrogen and carbon cycles, by breaking down complex organic compounds. Extremophilic archaea are also of interest for biotechnological applications, including the production of enzymes that function under extreme conditions. Additionally, studying archaea helps scientists understand the evolutionary history of life, as they represent a distinct domain of life alongside bacteria and eukarya. Their presence in diverse environments highlights their ecological importance and adaptability.