Archebacteria are unicellular organisms that initially have no nucleus. According to one theory of the origin of life, it is believed that these creatures were the first to appear, and only then bacteria, viruses and other organisms came from them.
Historical perspective
Archaebacteria were first identified as a separate kingdom in 1977 by scientists C. Wese and J. Fox. It has been proven that their cell wall produces original enzymes and is not like the cell walls of other bacteria that were previously investigated. This discovery was made using comparative analysis of 16S rRNA. With traditional microscopy, it is practically impossible to detect the characteristic differences between the representatives of the kingdom of the archaebacteria from real bacteria. Presumably, they appeared on the planet about three billion years ago, being nuclear weapons.
Classification
All bacteria belong to the biological kingdom of prokaryotes. Archaebacteria are no exception. In the biosystem, the considered organisms belong to the kingdom of the same name, within which they distinguish:
- anaerobic (living without oxygen);
- sulfur-reducing microorganisms;
- bacteria that metabolize molecular sulfur and are related to extreme thermophiles;
- thermoacidophilic mycoplasmas and extremely halophilic bacteria.
Researchers classify this type of organism in different ways. Some distinguish the kingdom of prokaryotes for them, while others believe that it is more correct to attribute them to a separate class of the kingdom of prokaryotes.
What are needed and what are
Archaebacteria are distinguished by metabolism, environmental and physiological characteristics. Consider some varieties of representatives of this bioclass.
The most known methane-forming archaebacteria. These are microorganisms with the help of which methane is formed on our planet. They are obligate anaerobes, most often found in swamps, pond mud, the digestive system of cattle and other ruminants, sewage treatment plants, and flooded soils.
In addition, some representatives of sulfur bacteria are also referred to as archebacteria. They take part in the circuit of sulfur, contribute to its oxidation and the formation of acid, which has corrosive properties. These microorganisms in their cells concentrate the chemical substance, and therefore their accumulation in certain places plays a decisive role in the process of nucleation of large sources of sulfur.
Archaebacteria are not parasitic organisms, therefore, in limited quantities they are used in medicine as a tonic. They also contribute to the disposal of organic waste. This is the significance of archaebacteria.
Environmental features
Archebacteria are living organisms adapted to any living conditions, to any type of ecology. Among them there are thermophiles that can exist at a temperature exceeding 110 ° C. Bacteria living under diametrically opposite conditions in terms of acidity are acidophiles. They “love” acid and live at a pH level of 1. Alkafil prefer to live in an alkaline environment, where the pH can reach 11. In addition, among the indicated kingdom there are representatives who can:
- exist with limited moisture resources (xerophiles);
- multiply in conditions of lowered positive and negative temperatures, up to -10 (psychrophiles);
- dwell in saline solutions with a salt concentration of up to 30% (halophiles);
- withstand atmospheric pressure up to 700 atmospheres (barophiles).
From the environment, they consume only simple organic substances. Dependence on natural conditions is minimal.
Structure
For all representatives of archaebacteria, the following features are characteristic:
- There is no peptidoglycan in the cell wall. Instead, they include pseudo-murein, which does not contain muramic acid and D-amino acids in peptide bridges.
- The membranes of the representatives of the subdomain of archaebacteria contain bifinal glycerol esters instead of fatty acids with glycerin.
- In transport RNA, thymine is replaced by other bases. The genes encoding this RNA have introns characteristic of eukaryotes.
- In the genome, sequences are repeated many times, which is equivalent to chromosomal DNA in eukaryotes.
- Compared with the latter, archaebacteria have more protein of high acidity.
- In archaebacteria, mainly cylindrical and spherical cells are found. There are also flat cells, similar to pieces of broken glass.
These are the structural features of archaebacteria.
What is common with other microorganisms
All bacteria belonging to the kingdom of prokaryotes are subdivided into the kingdoms of Archebacteria and Oxyphotobacteria, as well as Real bacteria.
Colonies of some true bacteria can be seen with the naked eye. In shape, they can be very different: cocci, spirillas, sarcinomas and others. The cell wall is built on the basis of a substance that is close in composition, structure to cellulose, is covered with mucus from above. Its contents are separated from the wall by a membrane. There are no plastids and mitochondria surrounded by a membrane, which are characteristic of animal and plant organisms. The synthesis of proteins, as in eukaryotic organisms, is carried out using ribosomes.
When adverse conditions occur, most bacteria are able to form spores due to the release of part of the cytoplasm covered by the capsule. Metabolism in the cell stops, but the bacteria continue to live. They are carried by the wind, in favorable conditions, return to active life.
Unlike bacteria, archaebacteria have ribosomes comparable in size to eukaryotes. At the same time, both of them belong to heterotrophs. Some are capable of photosynthesis, but unlike plants, not due to the content of chlorophyll, but due to the presence of the so-called bacteriochlorophyll. In the process of bacterial photosynthesis, oxygen is not released here, as in plants. Representatives of these two classes often have flagella.
Comparative characteristics of arche- and oxyphytobacteria
The second type includes mainly cyanobacteria or blue-green algae. Archaebacteria and oxyphytobacteria significantly differ, despite the fact that both species belong to heterotrophs. Oxyphytobacteria have chlorophyll, which differs in structure. In addition, photosynthetic pigments may be available for this microorganism. In the sub kingdoms of archaebacteria and oxyphytobacteria, the process of photosynthesis proceeds differently. In this case, the flagella are not observed in the second. In oxyphytobacteria, unlike archaebacteria, the process of photosynthesis is accompanied by the release of oxygen.
Reproduction in all prokaryotes occurs approximately the same - by dividing the cell in half. The cell of oxyphytobacteria has a small amount of cellulose, mainly pectin and polysaccharides are there.
Methods of obtaining energy in prokaryotes
From the external environment, there can be different ways of obtaining energy for prokaryotes. Archebacteria adapt to life both with oxygen (aerobic) and without it. With anaerobic respiration, methane formation occurs. A number of archaebacteria living on the seabed, in silt sediments, carry out the so-called "sulfate respiration" (sulfate reduction), in which sulfates are converted to hydrogen sulfide.
Chemosynthesis is characteristic of the considered kingdom of living organisms. By it is meant the oxidation process of not only organic, but also inorganic compounds. So, hydrogen from the depths of our planet can be oxidized due to sulfates, forming water and hydrogen sulfide. Sulfur in the process of chemosynthesis plays the role of both an oxidizing agent and a reducing agent.
Thus, archaebacteria are capable of carrying out a chemosynthesis process in which organic substances are formed due to the occurrence of redox reactions.
In addition, some representatives of this species are able to receive energy through fermentation. Others find sources for themselves in the chain of electronic transport, in which cytochromes, quinones, ferredoxins participate. In this case, transmembrane proton transfer occurs.
Types of nutrition and metabolic reactions in archaebacteria
For the organisms that make up the sub kingdom under consideration, 4 types of nutrition are characteristic:
- chemoorganeterotrophic;
- photoheterotrophic;
- chemolithoheterotrophic;
- chemolithoautotrophic.
For the most part, metabolic reactions occur similar to those of Real bacteria.
Finally
Archaebacteria are ancient bacteria in the literal translation from the Greek language. They are microorganisms with a nuclear structure of the cell. In some properties, they differ from these bacteria. The greatest differences are observed between archaebacteria and oxyphotobacteria. The main differences from the fact that the cell walls contain pseudo-murein, a different sequence of bases is observed in the composition of tRNA. These organisms are adapted to exist in almost any environment. For some of them, a process of photosynthesis without oxygen evolution, occurring using bacteriorhodopsin (bacteriochlorophyll), is characteristic.