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Kingdom Monera Classification, Characteristics, Microscopy Methods

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Kingdom Monera Overview

  • In essence, Monera is a biological kingdom comprised of prokaryotes (particularly bacteria). It is made up of single-celled organisms without the true nuclear nucleus.
  • Based on classifications from the past Based on previous classifications, the kingdom Monera comprises organisms classified by the name of Archaea (Archaebacteria) as well as to blue-green algaeand Schizopyta (bacteria). But further research has revealed specific features of Archaea which allowed them to be distinguished and recognized as a distinct kingdom.
  • In addition to some of the first types for classification (e.g. Linnaeus two kingdoms (1735) and the Haeckel 3 kingdoms (1866)) the kingdom of Monera is recognized in all different classification systems (e.g. two-empire kingdom system, the five-kingdom system, and the 6-kingdom model) in the form of a particular form or in different forms.
  • Archaebacteria is made up of bacteria which are known collectively as extremophiles. This is due to the fact that they can survive extreme environmental conditions.
  • The word Archaebacteria originates from Greek words which mean “ancient things/bacteria”.
  • The term “Prokaryote” comes from the Greek words “Pro” which means before and “Karyon” that means kernel/nucleus”Before a nucleus.
  • The term Monera originates by the Greek word “Moneres” that means single.

Classification and Characteristics of Kingdom Monera

Different classification systems were developed between 1866 and 1997. This includes:

  • Three kingdom classification system by Haeckel (1866)
  • Four kingdom classification system by Copeland (1956)
  • Five-kingdom classification system by Whittaker (1969)
  • Six kingdom classification system by Woese (1977)

For this section it is expected that the classification system of five kingdoms will be utilized. In 1969, it was first described from Robert H. Whittaker, the classification of the 5 kingdoms system comprises five kingdoms which comprise:

  • Kingdom Animalia
  • Kingdom Plantae
  • Kingdom Fungi
  • Kingdom Protista
  • Kingdom Monera

The majority of the time the five-kingdom classification system that was formulated by Whittaker is built upon the model of nutrition and the structure of cells as well as the thallus’s organization, method of reproduction, as and their phylogenetic connections.


The only kingdom to contain bacteria (which are prokaryotic), Monera is the sole prokaryotic kingdom of the classification system of five kingdoms.

In general, within the Whittaker (Five Kingdom Classification) system, the kingdom Monera can be divided into two main groups (subkingdoms) which are Archaebacteria as well as Eubacteria.

Archaebacteria in Kingdom Monera

When compared with eubacteria archaebacteria have a more primitive nature, as they are the oldest living organisms on Earth. They are also more rare in comparison to Eubacteria, archaebacteria is capable of withstanding extreme environmental conditions such as hot springs, extremely acidic and salty environments, etc.

Classification of Archaebacteria

Within this subkingdom, living things are classified or grouped on the basis of the of the environment in which they reside:

a. Methanogenic bacteria (methanogens)

  • Bacteria that can be found in the intestinal tract of animals as well as sewage matter. They are capable of producing methane in hypoxic conditions. 
  • Some examples of methanogenic bacteria include: Methanobrevibacter smithii, Methanococcus maripaludis, Methanobrevibacter ruminantium

b. Thermoacidophilic bacteria (thermoacidophiles)

  • These are bacteria that can be found living in hot springs. They are also capable of surviving in environmental conditions with very low pH. 
  • Thermoplasma Picrophilus is a good example of thermoacidophiles.

c. Halophilic bacteria

  • This includes bacteria that can be found living in extremely salty conditions (e.g. bacteria found in the Dead Sea). 
  • Examples of halophilic bacteria include: Halomonas, Chromohalobacter, Halomonas elongata, Halomonadaceae.

As compared to other bacteria, Archaebacteria have a unique cell wall structure which allows them to survive harsh environmental conditions. They can also be found in less extreme environments (fresh and ocean waters and soil).

Cell Structure of Archaea

1. Flagella

  • According to a variety of studies, a majority of archaeal bacteria have been shown to possess flagella used for motility. Compared to the flagella found in other bacteria, archaeal flagella have been found to be more similar to type VI pili of bacteria. In general, they have been described as rotating structures with a filament.
  • Given that a majority of archaea are either chemotactic or phototactic in nature (or both), these structures, consisting of preproteins, allow them to move from one point to another in their respective environments.
  • For a majority of archaea found in extreme environments, glycosylation has been shown to be one of the main components of flagellins. As a result, it has been suggested to contribute to protein stability that allows the organisms to survive.
  • The flagella of archaea also have the following functions: Swarming across surfaces, Formation of biofilm connecting cells to each other: This may play a role in genetic transfer.

2. Cannulae

  • Apart from flagella, some of the archaea have been shown to contain structures known as cannulae on their surface. 
  • These are hollow tubes consisting of various subunits of glycoprotein. Like several components of the flagella, these structures are also highly resistant to such extreme environmental conditions as heat.
  • For the most part, cannulae have been identified in newly formed cells. Given that no studies have found these structures to penetrate the cell cytoplasm (they have only been shown to enter the periplasmic region of cells), researchers have concluded that by connecting newly formed cells to each other, these structures allow for nutrient and, in some cases, genetic material between the cells.

3. Pili

  • Pili have been identified in many archaea species across the globe. As is the case with flagella, pili of archaea have been shown to be different from those of other bacteria. Depending on the species, they also play a number of functions ranging from aggregation to motility.
  • For instance, in a study where Sulfolobus cells were exposed to UV light treatment, pili formation allowed for aggregation of the cells before conjugation occurred (the transfer of genetic material from a donor to recipient).

4. Plasma Membrane

  • While archaea and other bacteria share various characteristics with regards to the plasma membrane, the plasma membrane of archaea has a number of unique characteristics that contribute to their general characteristics.
  • In archaea, the glycerol linkage between the phospholipid head and side-chain has been shown to be of the L-isomeric form which is different from the D-isomeric form found in other bacteria and eukaryotes.
  • Also, the ether-linkage located between the glycerol and side chain in archaea provide better chemical stability to the membrane of these organisms which also contributes to their overall ability to survive extreme environmental conditions.
  • With regards to the plasma membrane, some of the other unique characteristics include:
    • Contain isoprenoid chains that may contain branching side chains
    • Plasma membrane exist as monolayers

5. Cell Wall

  • As is the case with other bacteria, the cell wall of archaea also plays an important role in protecting the internal components of the cell from the environment. In addition, the cell wall also serves to withstand turgor pressure exerted against the plasma membrane.
  • While some archaea lack a cell wall, these structures vary from one species to another depending on their environment. Moreover, they display characteristics that are unique and different from the cell wall of other bacteria.
  • In some of the species, the cell wall has been shown to contain a proteinaceous S-layer. This, in some species, acts as the sole component of the cell wall.
  • Although they lack peptidoglycan found in bacteria, some archaea possess pseudomurein, which has a similar chemical structure. Also, they contain N-acetylalosaminuronic acid that is linked to the N-acetylglucosamine thus increasing the overall strength of the structure.
  • Some of the other components of the cell wall in archaea include:
    • Methanochondroitin – Lattice structure that forms the protein sheath
    • Plasmids – Small DNA molecules consisting of between 5 and 100 genes
    • Ribosome – spherical particles involved in protein synthesis
    • Cytoskeleton – proteins involved in cell division as well as influencing the shape of the cell

Eubacteria in Kingdom Monera

It is often called “true bacteria” or simply “bacteria”, eubacteria is the more complicated realm (described as an underkingdom in certain books) of the Monera kingdom. Monera.

In comparison to archaebacteria members of eubacteria are much more prevalent and widespread in all habitats (water soil, in as well as on other organisms and so on.) all over the world.

As part of the kingdom Monera Eubacteria are prokaryotes. They don’t have membrane bound organelles. While certain species are parasitesthat cause disease to animals and plants (including humans) However, certain organisms are healthy and can be utilized for food and drug production among other purposes.

Classification of Eubacteria

Since every single species of bacteria (except archaebacteria) are part of the domain/subkingdom eubacteria can be classified into one of the categories below:

1. Cyanobacteria

  • Also known as blue-green algae they contain chlorophyll which allows them to produce the food they consume. In this way, they like plants, are photosynthetic autotrophs..
  • In the natural world, they could exist as colonial, unicellular or filamentous in marine or fresh waters. But, they may also be in terrestrial environments, that rely on carbon dioxide, water, and solar energy to make the food they consume.
  • Although they can produce food by themselves, certain species within this group establish symbiotic relationships with the fungi which result in forming”lichens. In this relationship, bacteria provide organic nutrients that fungi require, while the fungi provide organic material and protection for the bacteria.
  • Cyanobacteria are the sole prokaryotes able of photosynthetic activity and the production of oxygen.
  • With over 2,000 species of this category, cyanobacteria are found in a variety of shapes and sizes , with various cells. Certain species cause toxic substances in water and also harmful blooms, and therefore are important for water quality management.
  • The most well-known Cyanobacteria that are most well-known include: Mat-formers, Bloom-formers, Picocyanobacteria.
  • Apart from photosynthetic and autotrophic bacteria, cyanobacteria is also autotrophic chemosynthetic bacterium which convert inorganic molecules (e.g. ammonia and nitrates for instance) into organic compounds. In this way, they get energy through the oxidation process of organic molecules.

2. Heterotrophic Bacteria

  • Heterotrophs are organisms that obtain energy by consuming organic material.
  • Contrary to photosynthetic and chemosynthetic autotrophs they are unable to produce their own food or organic material, and therefore rely on organic material or food sources within their surroundings. Heterotrophic bacteria are plentiful in the natural world, with the majority of them functioning as the decomposing agents.
  • In this way, they consume dead animals and plants in their surroundings, thereby dissolving them. This results in soil humus, which in turn aids in the proper growth of plants. These kinds that are a part of the bacteria family is referred in the field of saprophytic bacteria.
  • Apart from heterotrophic bacterial species that can be found in the natural world (terrestrial habitats, for instance) Some of these are present in the normal microflora of the human skin, and don’t typically cause harm. However, some can be pathogens and can cause illness not just in humans however, as well in animals and plants. Many of these bacteria rely on their host for nutrition and therefore are parasites.

Classification of Heterotrophic bacteria 

Heterotrophic bacteria can be classified into these groups:

  • Spirochetes
  • Chlamydias
  • Gram-positive bacteria
  • Proteobacteria
  • Gram-negative bacteria

General Characteristic of Heterotrophic Bacteria

  • While a handful of bacteria are sufficiently large to be observed through an eye (e.g. Epulopiscium fishelsoni bacteria, which can grow up to 600um long) However, the majority of microorganisms are only visible with the aid of microscopes. But, they differ in size, and range from 100-200 nanometers in size.
  • The bacteria also differ in form, which has enabled their classification based on how they appear. For instance, while certain species have rod-like shapes (bacillus) while others are more spherical (coccus). Some bacteria are more intricate in their forms, such as spirillum that are spiral-shaped as well as vibrios which look like curving rods.
  • Based upon the type of species these bacteria could exist as individual cells, in pairs, or as colonies, etc. For instance, while staphylococci are cocci bacteria that live in clusters, streptobacilli is bacilli bacteria that live in chains. The form of heterotrophic bacteria plays an important role in motility.
  • The shape of spirochaetes , as well as vibriobacteria (in combination with flagella) aid in the mobility of these bacteria in their surroundings.
  • Diverse species of heterotrophic bacteria are also dependent on specific environmental conditions to survive. Therefore, they can only thrive in specific conditions in their surroundings. These traits have also enabled the classification of bacteria based on the conditions they need to reproduce and grow.
  • While some bacteria require oxygen for normal breathing (Bacillus subtilis as well as Azotobactor) Others, such as Clostridium Tetani thrive in extremely low oxygen levels in its vegetative period.
  • Certain species can switch between aerobic and anaerobic respiration based on the oxygen content of their environments. For example, while facultative anaerobes are able to generate energy when oxygen in the environment, they also switch to anaerobic when oxygen is not present (energy is created by fermentation).
  • While real bacteria aren’t in a state of extreme, as is the situation with archaebacteria, they’re capable of producing spores that can withstand harsh environmental conditions. They can withstand under these conditions.

Cell Surface Structures of Eubacteria

As previously mentioned, there are several differences between the cell surface of archaebacteria and eubacteria. Whereas the glycerol linkage between the phospholipid head and side-chain is of D-isomeric form in eubacteria, it is of L-isomeric form in archaebacteria.

But, eubacteria contain ester-linked lipids between Glycerol and side chains, in contrast to the ether-linkage present in archaebacteria. Similar to many other cell types plasma membranes that is found in the eukaryotes (eubacteria) is distinguished by bilayers of lipids which separate the external and internal environments of cells.

The majority of eukaryotes have the cell wall. It’s a semi-rigid cellular structure used to keep the shape of cells. Typically, the cell’s wall of eubacteria can be identified through the presence of peptidoglycan, which allows for the distinction among Gram positive and Gram negative bacteria.

Microscopy Techniques

To study and observe members of the Kingdom of Monera there are many microscope techniques are available. While some of these methods are employed to study and distinguish the genetic material that is found within these organisms, other techniques are used simply to examine general morphology. This helps to distinguish between the various species within the Kingdom.

1. FISH (Fluorescent in Situ Hybridization)

In contrast to microscopy methods that are used to examine the general structure of various kinds of bacteria FISH is a method of molecular analysis that is able to identify the presence of certain genetic elements in an organism, which allows it to distinguish between different species. In general, the method is based on the hybridization process of a probe using an emitted fluorescent tag that is compatible with a specific DNA sequence.

The probe is inserted into the sample in the right conditions to permit the attachment for the sample to the area of importance. The sample is then examined in the microscope ( fluorescent microscope). This technique makes it possible to distinguish the various archaebacteria or species and eubacteria based the genetic content of their genome.

* In fluorescence microscopy fluorescence dyes can also be used to determine cells’ components. For instance, with the phalloidin color it is possible to determine the filaments of actin of bacteria.

2. Thermo-Microscope (Phase-Contrast Microscope inside a Plexiglas Housing)

This is a method that is used to examine the behavior of swimming archaea. In the beginning, cells from the sample were moved in glass capillaries (rectangular in shape). The capillaries then were sealed (both faces) and then placed onto an electro-heated stage placed on the table for the microscope. The thermo-microscope was later utilized for investigating the swimming behaviour of the archaea.

This method of heating the stage was a good way to create the ideal environment for M. thermoautotrophicus.

For bacteria that are referred to in the context of “true bacteria” a variety of microscopic techniques may be employed. They include:

  • Epifluorescence microscopy with wide-field
  • Laser scanning Confocal microscopy
  • Internal reflection microscopy with total internal reflection
  • Photoactivated localization microscopy


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