Embedded Files
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 µmeter to about 15 µmeter 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.
1. Methanogens
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.
2. Halophiles
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.
3. Thermoacidophiles
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.
Report abuse