Archaebacteria are almost as old as the Earth. They came into existence when the Earth was in its nascent stage and the conditions were extreme. Till date, these organisms live in conditions that mimic the extreme ones that were the norm, when the Earth was just beginning to take shape.The image shown alongside, is of the Grand Prismatic Spring in Yellowstone National Park. The brilliant colors observed in the spring, are attributed to archaebacteria.
Archaebacteria kingdom is a group of bacteria that are anaerobic, as well as aerobic prokaryotes. These bacteria are adapted to living in extreme environmental conditions, like near volcanic activity, deep oceans, etc, and do not need oxygen and light to survive. All living organisms are placed in the five kingdom system: plantae, animalia, fungi, protoctista
. Not so long ago, before 1977, archae
were considered to be a group of bacteria. They were thus, placed in Kingdom Plantae. Soon, they were placed under the new kingdom Monera, after the bacteria. Carl Woese and George Fox, were two scientists who proposed in 1977, that archaebacteria should have a separate kingdom of their own. By 1990, scientists found out that the 16S rRNA and 18S rRNA sequences were totally different in archea from other bacteria. Genome analysis of archaea
in 2003, confirmed that they are different from bacteria. Thus, finally they were removed from kingdom Monera and the five kingdom of living things was converted into six kingdom system, with the inclusion of the new archaebacteria kingdom. Do you want to know what is the difference between archaebacteria and bacteria? The following characteristics will help you understand the reason for this transition.
In a Nutshell
Type of Organism: Unicellular
Cellular Structure: Prokaryotic
Habitat: Extreme Environment
Peptidoglycan in Cell Wall: Absent
Reproduction Method: Asexual
Nutrition Mode: Heterotrophs/Autotrophs
Characteristics of Archaebacteria
The term achaio
is a Greek word for 'ancient'. This term aptly describes the archaebacteria who are thought to have a common ancestor like the bacteria and eukaryotes. Archaebacteria is similar in structure to eukaryotes than bacteria. There are several archaebacteria kingdom characteristics that help in distinguishing them from eubacteria. These characteristics of archaebacteria are as follows:
- Archaebacteria have no peptidoglycan in their cell walls.
- The cell wall is made up of glycoproteins and polysaccharides.
- The cell wall envelopes have a high resistance to antibiotics and lytic agents due to difference in cell wall composition.
- They have a very different lipid bi-layer making up the cell membranes.
- The RNA polymerase of archaea is very similar to that of eukaryotes.
- The ribosomal proteins in eukaryotes and archea are also similar to each other.
Archaebacteria are about 1/10th of a µ
meter to about 15 µ
meter in size. A few are flagellated and the flagella structure is different from the flagella of other bacteria. The archaebacteria are non-pathogenic bacteria that live in and around other organisms. However, they do not cause any infections or diseases.
Sub-groups of Archaebacteria
Archaebacteria are autotrophs and use CO2 in atmosphere as a source of carbon for a process called carbon fixation. Archaebacteria are able to survive in extreme conditions and therefore also known as extremophiles. They can survive in conditions that are highly acidic, alkaline, saline aquatic environment. Some are even able to survive in temperatures above 100° Celsius or 212° Fahrenheit. Few can even withstand over 200 atmosphere pressure and live really deep within the earth. They employ different chemical reactions to be able to survive in these harsh conditions. Thus, they are divided into 3 subgroups - methanogens, extreme halophines and thermoacidophiles. Let us learn more about the characteristics according to the sub-groups.
Metanogens are able to reduce CO2 into methane (CH4). They are obligately anaerobic and can die if exposed to oxygen. They produce marsh gas that can be observed as bubbles in stagnant water. They are also present in the gut of cattle and termites, since there is no oxygen there. Methanogens use carbon dioxide as an electron acceptor to oxidize hydrogen using co-enzymes like co-enzyme M and methanofuran. These co-enzymes are very unique to archaebacteria. These bacteria are rod shaped or spherical, and can be gram positive as well as negative.
Halophiles are bacteria that can survive in 10 times the concentration of salt present in sea. You can find halophilic archaebacteria in Great Salt Lake in Utah and the Dead Sea in Middle East. Halobacter uses photophosphorylation for metabolism. They use light activated ion pumps like bacteriorhodopsin and halorhodopsin for generation of ion gradients to pump out ions across the plasma membrane. The energy that is stored in the electrochemical gradients is converted to ATP by ATP synthase. They contain bacteriorhodopsin, a red or orange pigment.
The thermoacidophiles are organisms that can survive in extremely high temperatures and low pH. They can survive in 100° Celsius with a pH of 2. Most of these organisms are anaerobic in nature.
Reproduction in archaea is carried out asexually by binary or multiple fission, fragmentation or budding. They do not undergo meiosis and therefore organisms of a species that are present in more than one form share the same genetic matter. Archaebacteria do not form spores and a few species of Haloarchaea undergoes phenotypic switching. This means it can grow several different cell types that are resistant to osmotic shock. Thus, the organisms can survive in low salt concentration aquatic environment.
Importance of Archaebacteria
Archaebacteria are important, nay, almost indispensable, for the following reasons:
- They have phylogenetic importance that helps in studying their homology and establish their phylogeny.
- Their ability to tolerate extreme conditions helps researchers learn about the climatic conditions, environment and their survival on ancient earth.
- Methanogens can grow in biogas fermentors and decompose cow dung into methane gas as a by-product. Thus, they are used for production of domestic gas for cooking.
- Organisms like Methanobacterium ruminantium are present in the guts of ruminating animals, helping them digest the cellulose.
- Poor ores of molybdenum are microbial leached using Sulfolobus.
- Archaebacteria are also used to synthesize thermophilic enzymes, restriction enzymes and are also used as biosensors.
- Archaebacteria have an important role in many chemical cycles, like carbon cycle, nitrogen cycle, sulfur cycle, etc.
- Due to their extremophilic nature, archaebacteria have proven to be of great help in the field of Bioechnology, by helping in the production of enzymes that work at very high temperatures, as well as in the production of some antibiotics.
Examples of Archaebacteria
- Pyrolobus fumarii
- Methanococcus jannaschii
- Nanoarchaeum equitans
The characteristics of archaebacteria
kingdom prove that life can exist anywhere, under any condition. The mere existence of these extremophiles gives us hope. Maybe we will discover something on the other planets yet!