Kingdom Monera: The Classification, Microscopy Methods, And Characteristics

Monera is a unique kingdom of prokaryotic organisms that usually reproduce through fission or asexual budding. Despite their unique cellular structures, moneras are one of the most widely distributed organisms on earth. 

Want to learn more about the Monera kingdom? Keep reading to learn about its classification, characteristics, microscopy techniques for observation, and more. 

What Is Kingdom Monera?

The kingdom monera belongs to the prokaryote family, which lacks a defined nucleus. Moneras are usually found in moist environments; essentially, any living thing that is unicellular belongs to the Monera kingdom. 

To be classified into the monera kingdom, a living thing must have the following characteristics: 

• A whole organism comprised of just one cell.
• A cell that’s more basic than the cells of other microorganisms. For example, these cells won’t have exactly the same parts as the cells found in the human body. 
• Most should reproduce through fission when a single cell divides into two identical cells. 
• They may be able to withstand challenging temperatures and environments. This is why there are more monera on earth than any other organism. 
• Sap vacuoles will not occur; instead, gas vacuoles may be present. 

Organisms in the monera group can either be autotrophs (that produce their own food), or heterotrophs (consume the food in their surrounding environments). 

What Is A Kingdom? 

In biology, a kingdom is a classification type used to group organisms. Kingdoms are the second-highest taxonomic category below domain. Kingdoms are composed of smaller divisions called phyla. 

Kingdom Monera: Characteristics And Classification 

Between 1866 and 1977, multiple classification systems were suggested for Kingdom bacteria. These included: 

• Haeckel (1866): Three Kingdom Classification System
• Copeland (1956): Four Kingdom Classification System 
• Whittaker (1969): Five-Kingdom Classification System
• Woese (1977): Six Kingdom Classification System 

For the purposes of this article, we’ll be exploring the five-kingdom classification system developed by Whittaker in 1969. 

When Robert H. Whittaker developed the five-kingdom classification system in 1969, he described it as consisting of five key kingdoms. These kingdoms are: 

• Kingdom Monera: This includes all bacteria called monerans. These are single-celled prokaryotic organisms. 
• Kingdom Protista: This kingdom is composed of both single-celled and multicellular eukaryotes without specialized tissues. Examples include some types of algae and protozoa. 
• Kingdom Plantae: Members of the Plantae kingdom tend to be mostly multicellular. They’re usually autotrophic eukaryotes that can perform photosynthesis. 
• Kingdom Animalia: Members of kingdom Animalia are mostly multicellular and are heterotrophic eukaryotes. These can digest food outside of their cells and process it to absorb all of the digested nutrients. 
• Kingdom Fungi: Members of the fungi kingdom can include saprotrophic organisms, multicellular, and non-photosynthetic organisms. Most can absorb food via a solution in their cell walls and then reproduce through the spores. 

The five-kingdom classification system is based primarily on the structure of a cell, the nutrition model, the mode of reproduction, thallus organization, and the phylogenetic relationships of the kingdoms. 

Monera is the only kingdom to contain prokaryotic bacteria in the five-kingdom classification system. Under the five-kingdom classification system, Monera is separated into two groups or subkingdoms: Eubacteria and Archaebacteria.

We’ll explore these in more detail below. 

Kingdom Monera: Eubacteria

Eubacteria, sometimes just called ‘bacteria’ or ‘true bacteria’ is the most complex subkingdom of the kingdom Monera.

Those in the eubacteria domain tend to be more widely distributed and can be found in most habitats across the world. These habits include extracellular organisms, soil, and water. 

By nature, eubacteria are prokaryotes. This means that they lack membrane-bound organelles and a distinct nucleus. This is because prokaryotes do not have any internal membranes.

Some types of prokaryotes are parasites and can cause diseases in most plants and animals, including humans. However, other bacteria can be beneficial to life and are even used in the production of foods and medication. 

All bacteria, with the exception of Archaebacteria, can be classified under the subkingdom of eubacteria, and they can be divided into the categories below: 

Heterotrophic Bacteria

Heterophs, or heterotrophic bacteria, are collections of microorganisms such as bacteria, mold, and yeast, that harness organic carbon and use it as food. These organisms source their energy solely from the ingestion of organic material. 

Heterotrophic bacteria differ from chemosynthetic and photosynthetic autotrophs because they fail to create their own organic material and food.

As a result, they depend largely on food and organic material in their environments for sustenance. These bacteria are widespread and exist primarily as decomposers – organisms that can decompose organic material. 

In order to get their nutrients, heterotrophic bacteria feast on dead animals and plants in their environment and decompose them.

When they do this, the remains make up part of the soil humus, which aids plant development. Heterotrophic bacteria are also known collectively as saprophytic bacteria. 

Although the majority of these bacteria are found in terrestrial habitats, many also make up the normal flora on the human skin. When they reside here, they tend not to be harmful.

In some cases, though, heterotrophic bacteria can exist as pathogens that cause diseases in animals, plants, and humans. Therefore, a significant portion of these bacteria will depend on their host to offer them nutrition, making them parasites. 

Heterotrophic bacteria can be divided into several groups, including: 

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

Characteristics Of Heterotrophic Bacteria

The majority of bacteria are not visible to the naked eye and can only be observed using a microscope. However, some can be observed without a microscope, such as Epulopiscium fishelsoni, which grows to lengths as long as 600um. 

As well as varying in size, most bacteria will also vary in shape. Such significant variations in shape have allowed bacteria to be classified into groups depending on their appearance.

For example, some bacteria such as bacillus take on a rod-shaped appearance, while others like coccus appear to have a spherical body when observed.

Some bacteria can have even more complex shapes, such as spirillum, which, as the name suggests, takes on a spiral-shaped form. Vibrios bacteria are also complex and often have curved-rod bodies. 

Depending on the species of bacteria, heterotrophic bacteria can appear in colonies, in pairs, or as single cells. For example, staphylococci often form in clusters, and bacilli and streptobaccili appear in chain form.

Heterotrophic bacteria can form in a variety of shapes, and their shape also plays a pivotal role in motility – the ability of a bacteria to move independently using its metabolic energy. 

Like most bacteria, different species of heterotrophic bacteria will also require different environmental conditions to survive. This means that certain species can only thrive under specific environmental conditions.

As such, this has allowed heterotrophic bacteria to be classified according to the conditions they need to both develop and reproduce. For example, some bacteria such as Azotobacter and Bacillus Subtilis need oxygen for cellular respiration.

In contrast, others like Clostridium Tetani can exist in low-oxygen environments when in a dormant or vegetative state. 

Some species of heterotrophic bacteria can also switch between aerobic and aerobic respiration, depending on the levels of oxygen in their surrounding environment.

Facultative anaerobes, for example, can create energy if there’s enough oxygen, but they can also switch to anaerobic respiration if there’s little to no oxygen. 

Cyanobacteria

Cyanobacteria are photosynthetic and aquatic. This means they can manufacture their own food and live in the water. Although they’re predominantly unicellular, cyanobacteria can also grow into large colonies which can be visible to the naked eye. 

Cyanobacteria, also called blue-green algae, contain chlorophyll, which is why they’re able to create their own food.

This is also what makes them photosynthetic autotrophs, like plants. Although they can be unicellular and colonial, they can also be filamentous in marine water or fresh water.

Sometimes, cyanobacteria can also be found in terrestrial environments. It’s here that they use solar energy, carbon dioxide, and water to create their own food. 

Although they can manufacture their own energy sources, some species of cyanobacteria can also create symbiotic relationships with other fungi and form lichens.

Lichens are composite organisms that consist largely of a fungus and an alga. When this relationship is created, the bacteria (in this case, cyanobacteria) can give the fungi organic nutrients, while the fungi provide the bacteria with inorganic material and protection.

Cyanobacteria are the only prokaryotes that we know of that can produce oxygen and are photosynthetic. 

There are in excess of 2,000 species in the cyanobacteria division. These bacteria can come in various shapes and sizes and often have varying cell structures.

Many also play a significant role in water quality management because they can produce toxins in the water and noxious blooms. 

Some of the most common species of cyanobacteria include: 

• Picocyanobacteria
• Bloom-formers
• Mat-formers

Although cyanobacteria also include photosynthetic autotrophic bacteria, there are also chemosynthetic autotrophic bacteria in this division.

These bacteria can turn inorganic molecules, such as ammonia and nitrates, into organic substances. Consequently, they can create energy from the oxidation of these inorganic compounds. 

Kingdom Monera: Archaebacteria 

Archaebacteria are the oldest organisms on earth, making them more primitive than eubacteria. Archaebacteria are also not as prevalent as eubacteria; however, they are still capable of surviving in extreme environmental conditions, including acidic and salty environments.

Organisms in this subkingdom can be divided into groups depending on the environments they live in. Let’s take a look at some examples below. 

Methanogenic Bacteria (Methanogens)

These bacteria are most often found in sewage matter and in the intestinal tracts of animals. Methanogenic bacteria can produce methane when they reside in hypoxic conditions. Here are some common examples of methanogenic bacteria: 

• Methanobrevibacter ruminantium
• Methanobrevivacter Smithii
• Methanococcus Maripaludis

Halophilic Bacteria

The halophilic bacterial subgroup includes bacteria that live in challenging environments, such as salty waters. An example would be the bacteria that can be found living in the Dead Sea. Some common examples of halophilic bacteria are: 

• Halomonadaceae
• Halomonas
• Chromohalobacter
• Halomonas Elongata

Thermoacidophilic Bacteria (Thermoacidophiles)

Thermoacidophilic Bacteria are often found in hot springs. These bacteria can also survive living in conditions with an extremely low pH level. An example of a thermoacidophile is Thermoplasma Picrophilus. 

Archaea Cell Structure

When compared with other bacteria, archaebacteria have an incredibly unique cell wall structure.

This structure is what allows archaebacteria to thrive in harsh conditions, although they’re also found in calmer environments, such as soil and ocean waters. So let’s take a closer look at the cell structure of archaebacteria below. 

Flagella 

The flagella is a delicate, slender structure that resembles a whip that protrudes outward from the cell and allows the cell to move around freely. 

Several studies have confirmed that archaeal bacteria have a flagella which they use for motility.

However, when compared to the flagella structures we see in other bacteria, the flagella of archaebacteria appear to have a rotating structure and filament, resembling the structures in the Type VI Pili of bacteria. 

Most archaebacteria are either phototactic or chemotactic. These structures allow them to move from A to B in their environments. 

When archaebacteria living in extreme environments were observed, it was discovered that glycosylation was one of the primary components of their flagellins.

This is what contributes to archaebacteria protein stability, and it allows the organisms to survive and thrive. 

The flagella of the archaebacteria also perform other functions, including: 

• The formation of biofilm, which connects cells to each other. It’s thought that this may play a role in genetic transfer.
• Flagella also helps archaebacteria to swarm across surfaces. 

Cannulae

In some organisms, cells grow in a network of tubes called the cannulae. Some archaea have also been shown to house cannulae on their surface.

Cannulae are hollow tubes made up of several subunits of glycoprotein. The cannulae structures, like structures in the flagella, can also withstand extreme environmental conditions such as heat. 

In most cases, cannulae have been identified in new cells. However, there is no evidence to suggest that the cannulae structure penetrates the cytoplasm of the cell.

Which tells us that when newly formed cells are connected to each other, the structures can assist with the transfer of genetic material and nutrients between cells. 

Pili

Pili are structures of a protein that extend from the bacterial envelope of a cell. Pili have been discovered in various species of archaea throughout the world.

Like the flagella, the archaea’s pili differ from those observed in other bacteria. They can perform several functions, including motility and aggregation, depending on the species of the bacteria. 

One study exposed Sulfolobus cells to UV light treatment and discovered that the pili formation allowed cells to aggregate before the conjugation process occurred. 

Plasma Membrane

The plasma membrane (sometimes called the cell membrane) is present in all cells. It consists of proteins and lipids, and it forms an essential protective boundary around the cell and its organelles. 

The plasma membrane observed in archaea has several unique characteristics that contribute to the overall structure of this bacteria. 

In archaebacteria, the joining of glycerol between the side-chain and the phospholipid head has been found to be an L-isomeric form. This is incredibly different from the D-isometric form observed in most other bacteria and eukaryotes. 

It’s also been discovered that ether-linkage between the side change and glycerol in archaebacteria can offer improved chemical stability for the membrane of the organisms; this gives them an improved ability to withstand extreme conditions in their environments. 

Other unique characteristics of the archaebacteria plasma membrane include: 

• The presence of isoprenoid chains which may also contain branching side chains
• A plasma membrane that exists as monolayers 

Cell Wall 

The cell wall is one of the most important parts of a cell. The cell wall is a structural layer that surrounds many types of cells and sits just outside the cell membrane.

The cell wall is often tough and rigid and consists largely of polysaccharides. In algae and higher plants, it can be made up predominantly of cellulose. 

As seen in other bacteria, the cell wall of archaebacteria is responsible for protecting the internal components of the cell from its surrounding environment. The cell wall can also help the cell withstand pressure from the plasma membrane. 

Although some archaebacteria lack cell walls, these structures can vary according to the bacteria’s environment. The archaea cell wall’s primary characteristics differ from other bacteria’s cell walls.

For example, in some species, the cell wall may contain a layer of Proteinaceous S, which for some species, can make up the primary component of the cell wall. 

Archaebacteria lack the peptidoglycan found in other bacterias. However, some archaea contain pseudomurein, which has a similar chemical structure to peptidoglycan.

Archaea also contains N-Acetyltalosaminuronic acid, which is linked to N-Acetylglucosamine. This increases the general strength and rigidity of the cell’s structure. 

There are other components of the archaea cell wall, which include: 

• Plasmids – Plasmids are small DNA molecules consisting of between 5 to 100 genes. 
• Ribosome – Ribosomes are small, spherical particles that play a significant role in protein synthesis. 
• Cytoskeleton – The cytoskeleton is a collection of proteins involved in the cell division process. The cytoskeleton can also influence the overall shape and structure of a cell. 
• Methanochondroitin – The methanochondroitin is a lattice-like structure that makes up the protein sheath of the cell. 

The Cell Surface Structures Of Eubacteria

Archaebacteria and eubacteria have some significant differences in the cell surface. The glycerol linkage between the phospholipid head and the side chain in eubacteria takes on a D-isomeric form. In archaebacteria, it’s L-isomeric. 

Archaebacteria also have ether-linkage, whereas eubacteria have ester-linked lipids between their side chains and glycerol. Like other cells, the eubacteria plasma membrane consists of lipid bilayers that divide the external and internal environments of the cells. 

A large majority of eukaryotes (eubacteria) also have a cell wall. For most eubacteria, the cell wall contains peptidoglycan, making it simple to distinguish gram-positive bacteria from gram-negative bacteria. However, archaebacteria lack the presence of peptidoglycan. 

Kingdom Monera: Microscopy Techniques

If you want to observe and study the members of Kingdom Monera, you’ll need to utilize a number of microscopic techniques.

Some of these techniques can be used to differentiate the genetic material in these organisms, while other techniques are simply used to observe their morphology.

This can also be used to differentiate between the different members of the Monera kingdom. We’ll explore these microscopic techniques in more detail below. 

Thermo-Microscope (Phase-Contrast Microscope In Plexiglas Housing)

The thermo-microscope technique has been used to study the swimming behaviors of archaebacteria. To do this, cells were moved into glass capillaries that had a rectangular shape.

Then, these capillaries were sealed at both ends and placed directly onto an electrically heated stage on a microscope table. Then, the thermo microscope was used to assess the swimming behaviors of these bacteria. 

Other microscopic techniques can also be used when examining’ true bacteria’. These include: 

• Photoactivated localization microscopy: Sometimes called PALM or FPALM, this technique uses photoactivatable fluorophores in order to expose the spatial bearings of tightly compressed molecules. When they’ve been activated with lasers, the fluorophobes will emit for a short time before they eventually bleach. The laser will activate the fluorophores until they’ve all emitted. 
• Laser scanning confocal microscopy: Usually shortened to confocal microscopy, this technique uses the principle of fluorescence excitation to assess the structures of a cell and the location of certain structures of protein population in the cells. 
• Wide field epifluorescence microscopy: This imaging technique illuminates a whole sample with the light of a specific wavelength. This then excites the fluorescent molecules, and the emitted light becomes viewable through an eyepiece or can be captured using a camera. 
• Total internal reflection microscopy: Sometimes abbreviated to TIRFM, this imaging technique seeks to excite fluorescent cells in a thin optical specimen section supported on a glass slide. 

FISH (Fluorescent In Situ Hybridization)

The FISH technique can be used to find genetic elements in an organism. This makes it possible to differentiate between various species of bacteria.

This differs from other microscopy techniques which can be used to assess the general morphology of different species of bacteria. 

The FISH technique depends largely on the hybridization of a probe with a fluorescent tag on it. This probe is complementary to a specified DNA sequence. 

This technique uses the probe on the sample under favorable conditions. This allows the probe to be attached to the DNA sequence being used. Then, the sample is assessed under a fluorescent microscope.

This technique makes it possible to differentiate between various species of archaebacteria and eubacteria according to their genetic material. 

With fluorescent microscopy, fluorescent dyes can also be used to distinguish specific cellular components. For example, by using phalloidin, it’s simple to identify actin filaments in bacteria. 

Final Thoughts

Moneras are the most abundant organisms on the earth. Their unique cellular structure allows them to thrive in even the harshest of environments, and they differ greatly from most other bacteria. 

Monera includes various organisms, including archaea, blue-green algae, and even schizopyta. However, as more studies were performed, unique characteristics of archaea were identified, allowing them to be divided and identified as their own unique kingdom. 

Some of the earliest modes of classification were discovered as far back as the 1700s, but today, Whittakers 1969 classification system is the most commonly used system. 

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