We explain what the monera kingdom is, the origin of the term, its characteristics and classification. What is its taxonomy and examples.
What is the monera kingdom?
The monera kingdom is one of the five biological kingdoms, which are used in biology to classify living beings, in addition to the animal kingdom, plant kingdom, protista kingdom and fungi kingdom.
this kingdom includes the simplest and most primitive forms of life known. They can be very diverse in nature, although they have common cellular characteristics: they are unicellular and prokaryotic (cells do not have a nucleus or internal organelles). Furthermore, they reproduce asexually and the type of nutrition can be autotrophic or heterotrophic, depending on the species.
Today the term monera is out of use. Other classification models are preferred, such as the one proposed by Carl Woese in the 1970s, which distinguishes three domains: Eukarya (which includes all eukaryotic organisms, within the animal, plant, fungi and protist kingdoms), Archaea (archaebacteria) and Bacterium (bacteria). The organisms of the Monera kingdom are differentiated into these last two domains.
The organisms that were grouped in the kingdom Monera are very primitive. are believed to have been the first life forms to inhabit the Earth.
One of the most accepted ideas is the call Theory of serial endosymbiosisdeveloped by the American biologist Lynn Margulis in 1967. This theory proposes that a pair of single-celled organisms belonging to the kingdom Monera would have developed a very close symbiosis, which led one to form part of the other's body and take care of some internal functions.
- See also: Biological kingdoms
Characteristics of the monera kingdom
The main characteristics that the members of the Monera kingdom share are:
- are very small in size. They are the smallest living beings that exist on the planet. They measure 3 to 5 micrometers (thousandths of a millimeter).
- are unicellular. They are organisms made up of a single cell, which functions autonomously. They do not form tissues or more complex organs.
- are prokaryotes. They are very simple cells: they lack a cell nucleus and do not have organelles of any type. The genetic information is found in a circular DNA molecule that is loose in the cytoplasm.
- reproduce asexually. They are organisms that reproduce by binary fissiona reproduction mechanism that does not involve the production of sex cells. In this process, one individual gives rise to two that are identical.
- can have heterotrophic or autotrophic nutrition. Many species within this kingdom are heterotrophic organisms (they feed on organic matter from the environment). Other species are autotrophic (they make their own food). They obtain organic matter by taking advantage of sunlight and other substances (photosynthesis) or through chemical reactions from the environment (chemosynthesis).
The organisms that were traditionally grouped in the kingdom Monera included all prokaryotic organisms, that is, bacteria and archaea. Over time, great differences were discovered between these two groups, which caused them to be considered different ways of life.
History of the Monera kingdom
The term “monera” It has its roots in the Greek word moneres (meaning “simple”) and has been used over time, with different meanings. It was initially proposed by the German naturalist and philosopher Ernst Haeckel in 1866, who proposed a classification of life based on evolutionism.
Haeckel distinguished three kingdoms: animal, plant and protist, and brought together in the last all the “simple” or “primitive” forms of life, which did not seem to have a specific relationship with animals and plants, considered “superior”. Haeckel placed the microscopic moneras at the base of the evolutionary tree and classified them within the kingdom protista.
Later, in the 1920s, the French naturalist Édouard Pierre Chatton discovered that bacteria do not have a cell nucleus and, based on this discovery, he proposed the distinction and use of the terms prokaryotes for organisms without a cell nucleus and eukaryotes for organisms with a nucleus. cell phone respectively.
As a result, in 1939, Fred Alexander Barkley used the term monera to refer to a new kingdom formed by the set of all prokaryotic organisms, and which was divided between archaeophytes or Archeophyta (current cyanobacteria) and schizophytes or Schizophyta (bacteria).
In 1956, the American biologist Herbert Copeland reorganized the kingdoms of life into four categories: animals, plants, protoctists (where the unicellular eukaryotes and those with simple organization were) and moneras (where the prokaryotes were). In 1969, the American ecologist Robert Whittaker added the kingdom of fungi (Fungi) to this classification.
Although this classification continues to be popularly used, the term monera has disappeared from technical literature, after the changes proposed by the American microbiologist Carl Woese, known as the creator of the new molecular taxonomy. In the 1970s, this scientist discovered that prokaryotes fit into two distinct groups based on their structure, composition, and molecular genetics.
Woese proposed the reorganization of this group of organisms into two distinct taxa, Archaea (or archaea) and Bacterium (also called Eubacteria), with the new category of domain. The other domain, Eukaryais made up of all eukaryotic organisms, divided into the four kingdoms that had already been described: Protista, Animalia, Fungi and Plantae.
Classification of the monera kingdom
The main groups within the Monera kingdom are:
1. Eubacteria
The name eubacteriss means “true bacteria” and represent the simplest forms of cellular life known on Earth. This group of prokaryotic organisms has a single chromosome and a rigid cell wall composed of peptidoglycan (a combination of sugars and amino acids that provides great resistance).
Some bacteria are motile and have flagella that they use to move. They can present various shapes and based on this criterion they can be classified into bacilli (rod-shaped), cocci (round-shaped), spirili (corkscrew-shaped) and vibrios (comma-shaped).
2. Archaebacteria
Archaebacteria share some characteristics with bacteria (such as the lack of a nucleus within the cell), but their differences, such as the composition of their cell wall, place them in a separate category.
are characterized by living in conditions that make the life of other living beings impossible. They are found in extreme habitats, where they survive by taking advantage of the chemical resources of the environment (such as salinity, heat, pH). They are believed to be so numerous that they make up 20% of the earth's biomass.
3. Cyanobacteria
Known as blue-green algae cyanobacteria are the only prokaryotic organisms capable of oxygenic photosynthesis, just like plants (although in a slightly different way).
They are the largest prokaryotic beings: they can reach dimensions of up to 60 micrometers. Their presence in most habitats allows them to form symbiotic relationships with other species.
- See also: Bacteria
Differences between bacteria and archaea
The difference between bacteria and archaea is that They have different evolutionary origins. Despite the morphological similarities, molecular studies revealed that archaea are actually much older and are not evolutionarily related to bacteria. For this reason, there are scientific proposals to consider that bacteria and archaea do not belong to the same kingdom.
Taxonomy of the kingdom Monera
This kingdom was initially subdivided into two: bacteria and archaea, each with its own subclassification. But after the discovery of ribosomal DNA in the 1980s, a new classification was established based on four different groups:
- Mendosicutesarchaea or archaebacteria. Archaea means “ancient”, since they were initially assumed to be a species of protobacteria. It is difficult to classify them since they are really very small, but they have metabolic routes and internal processes much more similar to eukaryotes than to other traditional prokaryotes.
- Mollicutes , Tenericutes or mycoplasmas. They are a type of mostly parasitic bacteria, whose notable feature is that they lack the cell wall present in most bacteria and that they have one of the simplest known shapes and genetic codes.
- Gracilicutes or gram negative bacteria. They are a supergroup of bacteria that make up the groups Spirochaetes, Proteobacteria, Planktobacter and Sphingobacteria. They are characterized by having a very thin cell wall (sometimes even absent) composed of murein and a double plasma membrane. The characteristics of their cell wall mean that they are not susceptible to Gram stain, and hence their name.
- Firmicutes or gram positive bacteria. Called endobacteria, they have a very thick cell wall and are shaped like a bacillus or coccus. In this group are gram positive bacteria, which respond to Gram stain by acquiring a blue or violet color.
Examples from the monera kingdom
Some examples of organisms from the monera kingdom are:
- Escherichia coli . It is a gram-negative bacillus that often lives in the human digestive tract.
- Clostridium tetani. It is a very common bacteria in the soil and in the digestive tract of some animals, which can cause a disease known as tetanus.
- Helicobacter pylori . It is a bacteria that can infect stomach cells of some mammals and cause ulcers..
- Bacillus anthracis . It is a bacteria that lives in the digestive tract of some herbivores and forms spores. It can affect human health.
- Mycobacterium tuberculosis . It is the causative agent of tuberculosis in humans. It is an intracellular pathogen, since it can live inside eukaryotic cells. Its cultivation is very difficult and slow.
- Treponema pallidum . It is an elongated bacteria with a spiral or spring shape. It is responsible for syphilis, a disease that exists only in humans..
- Anabaena variabilis . It is a cyanobacteria. It has the ability to photosynthesize and form symbiosis with plants and fungi.
- Methanococcus jannaschii . It's an archaea. It lives in environments with extreme temperatures (it is thermophilic) and eliminates methane as a waste product of its metabolism.
- Halobacterium salinarum . It's an archaea. It lives in environments with high concentrations of salt (it is halophyte).
- Thermoproteus tenax . It's an archaea. It lives in environments with extreme temperatures (it is thermophilic). It uses sulfur in its metabolism.
Importance of the monera kingdom
The members of the Monera kingdom were the first organisms that existed when life originated on the planet. Their simplicity allowed them to emerge and survive in the hostile initial conditions of the Earth and even today it is possible to find representatives of this group in habitats where other forms of life cannot adapt or survive.
From this approach, studying these organisms is trying to deepen our knowledge about the origin of life.
Within this group, many are infectious agents of human beings whose study allows us to better combat diseases and save lives. On the other hand, many microorganisms classified in this kingdom are used by humans in different industries, such as pharmaceuticals or food).
The monera kingdom is essential for the environment, above all, due to its role in food webs. Many bacteria are decomposers and, therefore, allow the carbon cycle to be completed, returning this element to its inorganic form. Nitrogen-fixing bacteria, for example, which are of great importance for plants.
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References
- Curtis H., Barnes N., Massarini A., Schnerck A., BIOLOGY. 7th Edition. Panamericana Medical Editorial (2008).
- Whittaker RH, Margulis L. Protist classification and the kingdoms of organisms. Biosystems (1978).
