If you’re interested in learning about microbiology, one of the topics you will need to cover is archaebacteria.
Archaebacteria constitute a kingdom of single-celled organisms that can survive some of the most inhospitable environments on Earth. That’s partly because they have been around for almost as long as the Earth itself!
When the world was still in the process of forming, the conditions were very extreme, and archaebacteria adapted to live in those conditions.
In this article, we’ll be exploring this fascinating kingdom of organisms, from their shared characteristics to different subgroups within the kingdom!
An Introduction To Archaebacteria
The organisms within the archaebacteria kingdom can be anaerobic or aerobic. This means that some bacteria under this heading require an oxygenated environment to survive, whereas others can grow and reproduce without oxygen.
This is just one example of how archaebacteria have adapted to exist in inhospitable environments, hence why they can survive at the bottom of oceans and in volcanic areas.
Until fairly recently, archaebacteria were considered a type of bacteria like any other. As such, before the year 1977, they were classified as part of the Plantae kingdom.
Eventually, it was decided that the organisms should be part of the Monera kingdom instead. However, in 1977, scientists George Fox and Carl Woese suggested that archaebacteria should be their own kingdom.
It wasn’t until around 1990 that research proved that the sequences 18S rRNA and 16S rRNA are vastly different in archaebacteria than they are in different from those found in established types of bacteria.
This was the point at which archaebacteria were taken out of the Monera kingdom and a sixth kingdom was introduced: the archaebacteria kingdom.
Archaebacteria Overview
If you’re wondering what makes an organism part of the archaebacteria kingdom, this is the basic overview of the criteria that one of these organisms must meet:
Organism Type: Unicellular
Cell Structure: Prokaryotic
Natural Habitat: Extreme environmental conditions
Cell Wall Peptidoglycan: None
Method of Reproduction: Asexual
Mode of Nutrition: Autotrophic/Heterotrophic
Basically, in order for an organism to be classified within the archaebacteria family, it must be a unicellular organism (comprised of a single cell) with a prokaryotic cell structure, meaning that the cell doesn’t have a nucleus in the traditional sense, or the other organelles you would expect from bacteria because these cells don’t have any internal membranes.
Archaebacteria are also lacking a Peptidoglycan, which is an ‘envelope’ that typically surrounds the cytoplasmic membrane found in the majority of bacteria.
In addition to this, the organism must be able to survive in extreme conditions and environments, reproduce asexually, and feed themselves either autotrophically or heterotrophically.
Autotrophic nutrition is where an organism makes its own food from a combination of water, light, and carbon dioxide, plus other chemical substances in its environment. On the other hand, heterotrophic nutrition involves feeding on plant matter or other animals.
Other Archaebacteria Characteristics
In addition to the characteristics we’ve already mentioned, archaebacteria all share the following features:
- Cell walls made of polysaccharides and glycoproteins
- Cell wall containing lytic agents and with high antibiotic resistance
- RNA polymerase similar to that found in eukaryotes
- Ribosomal proteins resembling eukaryotic ribosomal proteins
- Lipid cell membrane bi-layer differs significantly from bacteria
While archaebacteria has a structure that is similar to that of eukaryotes, it differs significantly from the structure of most bacteria, hence why these organisms are now classified in their own kingdom.
Some Archaebacteria Examples
If you’re wondering which organisms are included in the archaebacteria family, here are some examples:
- Halobacterium
- Ignicoccus
- Methanococcus
- Halococcus
- Thermoplasma
- Sulfolobus
- Nanoarchaeum equitans
- Methanococcus jannaschii
- Methanobacterium
- Methanospirillum
- Pyrolobus fumarii
Archaebacteria Sub-Groups
We’ve established that archaebacteria are able to survive in very extreme, inhospitable conditions.
This is partly because they are able to nourish themselves autotrophically, meaning that they rely on carbon dioxide in the atmosphere for carbon fixation.
Carbon fixation is where inorganic carbon is turned into carbohydrates.
Archaebacteria use different chemical processes to navigate their harsh habitats. Depending on which process each organism uses, it will be put into one of three sub-groups. These are as follows:
Halophiles
In order to be classified as a halophile, an organism must demonstrate that it can survive salt levels that are concentrated 10 times more than the salt levels found in the ocean.
Because they can survive this much salt, you’ll usually find halophiles in Utah’s Great Salt Lake and even in the Dead Sea!
Halophiles use ion pumps such as halorhodopsin and bacteriorhodopsin to generate ion gradients and distribute ions over their plasma membranes. Inside these gradients is where energy is stored.
With the help of ATP synthase, the energy is converted into ATP.
Under a microscope, halophiles can be identified by an orange or red pigment. This pigment is called bacteriorhodopsin, and it’s the same substance used by halophiles as an ion pump.
Methanogens
Another sub-group of organisms within the archaebacteria family is methanogens.
Methanogens are able to survive their tough environments by turning carbon dioxide into methane. As a result of this process, marsh gas is produced. The gas can actually be seen in the form of bubbles in bodies of water.
This sub-group of organisms make electron acceptors from carbon dioxide and use these acceptors for the process of hydrogen oxidation.
This is accomplished with the help of coenzymes such as methanofuran. It’s these co-enzymes that make methanogens unique because they don’t occur outside archaebacteria.
While some members of the archaebacteria family can exist aerobically, methanogens can’t be exposed to any oxygen or they will die. Therefore, they primarily live in the digestive systems of termites and cattle, where no oxygen is present.
If you look at methanogens under a microscope, you’ll see that they can be either spherical or long and shaped like rods. These organisms may be either gram-negative or gram-positive.
Thermoacidophiles
The third and final sub-group of archaebacteria is thermoacidophiles. This is the name given to organisms that are able to survive two extremes in their living conditions: acidity and heat.
Thermoacidophiles can be found living in environments where the temperature reaches 100 degrees Celsius and they are able to survive in conditions where the pH drops as low as 2.
As you can imagine, there is typically not a lot of oxygen in such environments, so thermoacidophiles are anaerobic.
Thermoacidophiles, like all archaea, reproduce asexually through fission, which can be multiple or binary, or by budding. There is no meiosis and spores are not formed.
Why Are Archaebacteria Important?
We’ve given you a lot of information about the different types of archaebacteria so far in this article, but you may still be wondering what exactly these organisms do and what purpose they serve.
Actually, archaebacteria are some of the most important organisms on the planet. In some situations, they are essentially indispensable, and without them, our world would look very different.
First of all, we can’t overlook the contribution that archaebacteria have made to the fields of homology and phylogeny.
The phylogenetic differences between archaebacteria and members of the Plantae kingdom, for example, have provided researchers with crucial information regarding evolutionary differentiation between organisms.
Attempts to classify archaebacteria within existing kingdoms resulted in the creation of a new and entirely separate kingdom, so without studying these organisms, we would be much less informed today.
The very existence of archaebacteria has helped scientific researchers to learn a lot about the Earth’s climate and development.
The fact that archaebacteria live in some of the most extreme environments on the planet has led to a lot of investigation into these environments and this, in turn, has informed us on the subjects of biology, geology, and geography.
Archaebacteria have also contributed to the Biotechnological field because they can be used to help produce enzymes that are active at extreme temperatures.
They have also been used to produce some of the antibiotics that the medical field uses on a daily basis all over the world.
Scientific research and experimentation have seen archaebacteria employed as biosensors and in the synthesis of restriction enzymes as well as thermophilic enzymes.
The sub-group of archaebacteria known as methanogens has been used to produce domestic gas (the kind you use for cooking). This is because these organisms have the ability to turn waste from cows into the by-product of methane when grown in biogas fermenters.
In terms of what archaebacteria do in the natural world, these organisms play a fundamental role in cycles such as the carbon cycle, the sulfur cycle, and the nitrogen cycle.
All of these chemical cycles are essential for the continuation of life on Earth as we know it. Certain animals even rely on archaebacteria for their biological functioning.
For example, animals that ruminate (like cattle and sheep) need some types of methanogens in their digestive tracts to help them digest cellulose.
Final Thoughts
Archaebacteria is a kingdom of organisms that was only recognized as such in recent years.
These organisms have some important cellular and behavioral differences that separate them from members of the Plantae and Monera kingdoms into which they were initially classified.
The archaebacteria kingdom is divided into three sub-groups: thermoacidophiles, methanogens, and halophiles. Organisms in each sub-group employ different methods of staying alive in the extreme environments that make up their natural habitats.
Archaebacteria are fundamental to some of the Earth’s most important natural cycles and are essential for the survival of some ruminating animals.
They have also been used in the production of domestic gas and certain enzymes. Most importantly, archaebacteria have taught us a lot about how our world has evolved over time and how organisms can survive in some of the most inhospitable environments on Earth.
Ever since I was a little girl, I have been fascinated by science. Every holiday I would ask for the newest science kit, and spend weeks learning with it.
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