Archaea

Archaea are a special group of tiny living things. They are different from both plants and animals. They are one of the three main groups, or domains, of life on Earth, along with bacteria and eukaryotes. Even though they look like bacteria, archaea have unique features. For example, their cell membranes are made from special materials. They can survive in some of the most extreme places on the planet, like very hot springs and very salty lakes.

Scientists first thought archaea were a type of bacteria, but now we know they are their own group. They can get energy in many different ways. Some can even turn sunlight into energy, like plants do. These tiny organisms are very important for the environment. They help clean up the planet by recycling nutrients. They even live inside our bodies, helping us digest food.

Archaea are found almost everywhere — in soil, oceans, and even in the human gut. Because they can survive in tough conditions, scientists study them to learn about life in extreme places. They also use enzymes from archaea in many technologies, like making clean energy from waste. Even though we have only recently learned about them, archaea play an important role in keeping Earth healthy and balanced.

Discovery and classification

For much of the 20th century, tiny living things without cells were grouped together. Scientists looked at their chemistry, shapes, and the foods they could use. In 1977, scientists Carl Woese and George E. Fox studied these tiny beings. They looked at the genes inside, especially the ribosomal RNA (rRNA) genes. They found a new group they called Archaea. This helped divide all living things into three big groups: Eukarya, Bacteria, and Archaea.

Archaea were first found in very harsh places like hot springs and salty lakes. People thought they only lived in extreme conditions. But by the end of the 20th century, scientists realized archaea are found everywhere — in normal places like soil and water too. This discovery was made possible by a technique called polymerase chain reaction (PCR). Today we know archaea are a large and diverse group all around us.

Prokaryotic phyla

Archaea are very small, simple living things. Some groups of these organisms have names that scientists use. These include Methanobacteriota, Microcaldota, Nanobdellota, Promethearchaeota, and Thermoproteota.

Other groups might be archaea, but they do not have official names yet. These include "Aenigmatarchaeota", "Altarchaeota", "Augarchaeota", "Geoarchaeota", "Hadarchaeota", "Hadesarchaeota", "Huberarchaeota", "Hydrothermarchaeota", "Iainarchaeota", "Micrarchaeota", "Nanohalarchaeota", "Nezhaarchaeota", "Parvarchaeota", "Poseidoniota", and "Undinarchaeota".

Origin and evolution

Further information: Timeline of evolution

The Earth is very old, about 4.54 billion years old. Scientists think life began here at least 3.5 billion years ago. Early signs of life include tiny fossils and special rocks found in places like Western Greenland and Western Australia.

Archaea are a special group of very old tiny living things. They were once thought to be simple, but we now know they are closely related to the complex cells that make up plants and animals. Researchers learned this by studying tiny parts inside these organisms, called ribosomal RNA, which helps make proteins. This showed that archaea are different from bacteria. Some archaea can even make methane gas, which is important for nature.

Morphology

Archaea are tiny living things. They can be as small as 0.1 micrometers and as large as 15 micrometers across. They come in many shapes, like spheres, rods, spirals, or flat squares. Some archaea, like those in Haloquadratum walsbyi, live in very salty water and look like flat, square pieces.

These archaea can also form groups or chains of cells that stick together. Some connect using long, thin tubes. Others form colonies that look like strings of pearls. Their shapes help scientists learn about these ancient organisms.

Structure, composition development, and operation

Archaea and bacteria look similar in shape, but they are different in important ways. Like bacteria, archaea do not have internal membranes or organelles. They usually have a cell wall and can move using structures called flagella.

However, archaea are special because of their unique cell walls and membranes.

Archaea often have a cell wall made of special proteins arranged in a pattern called an S-layer. This protects the cell. Their flagella, called archaella, work like bacterial flagella but are made from different materials. Archaea have special membranes made from unusual fatty molecules. These molecules are different from those in bacteria, which helps archaea live in extreme places. Some archaea even have a single layer of membrane instead of a double layer, making their cells very tough.

Metabolism

Further information: Microbial metabolism

Archaea have many ways to get energy and nutrients. Some archaea get energy from simple chemicals like sulfur or ammonia. These are called chemotrophs. In these reactions, one chemical gives electrons to another, making energy that the cell uses to make adenosine triphosphate (ATP). ATP is the cell's energy source.

Other archaea use sunlight for energy, called phototrophs. But they do not make oxygen like plants do. Many archaea share steps for breaking down food, such as a changed form of glycolysis. Some archaea, called methanogens, live in places without oxygen, like swamps. They make methane as they break down materials. Others can take carbon from the air and turn it into food through a process called carbon fixation.

Genetics

Further information: Plasmid and Genome

Archaea usually have one round piece of DNA called a chromosome. Some archaea have more than one copy. The biggest archaeal chromosome found has over 5 million base pairs. The smallest has around 491,000 base pairs and contains few genes. Small pieces of DNA called plasmids can also be found in archaea. These plasmids can move between cells.

Archaea have unique genes that make them different from bacteria and eukaryotes. They share many important genes for basic cell functions with both bacteria and eukaryotes. Archaea also have special ways of organizing their genes and unique types of proteins. Their process of making proteins and copying DNA mixes methods from bacteria and eukaryotes.

Reproduction

Further information: Asexual reproduction

Archaea can make new cells without needing another organism. They split into two parts, break into pieces, or grow buds. They do not use mitosis or meiosis. This means all new cells are just like the parent cell. Before splitting, the cell copies its chromosome, then divides into two.

Some archaea, like those in the group Sulfolobus, have ways of copying DNA and dividing that are a mix of bacteria and eukaryotes. Some archaea can change shape or grow in different ways to survive, but these changes do not make new cells.

Behavior

Archaea, like many tiny living things, can talk to each other in a special way called quorum sensing. This helps them share messages when there are many of them close together. They also work well with bacteria to build groups called biofilms.

Biofilms are like sticky homes that protect Archaea from harm. They build these homes in steps: first, they stick to a surface, then they make a sticky matrix to hold together, and finally, some leave when they are done. These biofilms help them survive and share useful information.

Ecology

Archaea live in many different places, from very hot to very cold, and from salty to fresh water. They are found in oceans, swamps, soil, and even inside animals. Some archaea love very hot places, like geysers, while others can live in very salty or very acidic water.

Archaea help control important elements like carbon, nitrogen, and sulfur. They play a big role in the nitrogen cycle, helping to change nitrogen into forms that plants can use. In the sulfur cycle, they help release sulfur from rocks. In the carbon cycle, some archaea help break down dead material in places without oxygen.

Significance in technology and industry

Further information: Biotechnology

Tiny living things called archaea, especially those that love very hot or very acidic places, make special proteins called enzymes. These enzymes work in tough conditions and are very useful.

For example, they help scientists copy DNA quickly in a process called the polymerase chain reaction. They are also used in food production to make milk without lactose. They can help create chemicals that are better for the environment.

Archaea can also help clean sewage and may be used to get valuable metals from rocks. Scientists are excited about special antibiotics from archaea that could work in new ways against harmful germs.