Eubacteria: Definition, Types & Characteristics

What is Eubacteria?

Eubacteria are prokaryotic organisms characterized by the lack of a membrane-enclosed nucleus, predominantly unicellular with DNA in a single circular chromosome and having peptidoglycan on the cell wall when present. This includes most of the known bacteria of medicinal and economic importance such as E. coli, Staphylococcus, Salmonella, Lactobacillus, Nitrosomonas, Streptomyces, etc.

Eubacteria Definition

Eubacteria also referred to as “true bacteria”. The term eubacteria generally referred to as prokaryotic organisms, it characterized by a unicellular, lack of a membrane-enclosed nucleus, with single circular DNA in the chromosome, and have peptidoglycan on cell wall when present. eubacteria represent one of the three groups of life which are bacteria.

Characteristics of Eubacteria

Eubacteria or microorganisms that lack a defined membrane nucleus have several general characteristics. They are all surrounded by a cell wall made of peptidoglycans in a networked chain pattern. This gives the wall of bacteria the strength it needs to maintain its shape and size in changing environments.

Small molecules can diffuse through the cell wall, but often a proton gradient must first be established for the molecule exchange to take place properly. In contrast to eukaryotes, bacteria have cholesterol in the membrane to improve the membrane’s permeability properties and increase its rigidity. Similar to eukaryotes, bacteria also have a plasma membrane within the cell wall.

Some bacteria may have flagella or a protrusion of protein filaments that are used for movement. Other bacteria can have pili, small protrusions on the outside of the cell that is used to adhere to surfaces and transfer DNA. When a large number of bacteria adhere to a surface and are surrounded by a polysaccharide sac, this is called a biofilm. This complex has a high level of antibiotic resistance.

The cytoplasm or the intracellular milieu is located within the plasma membrane of the bacteria. It consists mainly of water (approx. 80%) but has a gel-like consistency. In contrast to eukaryotes, which have mitochondria and chloroplasts, bacteria have no membrane-bound organelles.

However, there are ribosomes, which are organelles made up of RNA that are used for protein synthesis. Also floating in the cytoplasm is the genome or the bacterial DNA that is in the nucleoid. Bacterial chromosomes are often circular, but they can also be linear in shape. This shape comes in handy when a bacterium is replicating.

Bacteria can reproduce asexually by binary fission or budding. Binary fission is when two of the same progeny cells are produced. Bacteria that experience binary fission must first elongate before separating. Budding is when the parent cell grows. The binary fission creates two identical daughter cells, while budding creates a new cell while the parent cell remains.

In times of extreme conditions that are not conducive to replication, such as starvation, eubacteria can become endospores. In this state, the bacteria can tolerate extremely high and low temperatures, acidic and basic conditions, and large amounts of radiation. Endospores are extremely difficult to kill.

Surprisingly, they can be boiled for hours and still survive. Endospores can only be produced by gram-positive bacteria. The bacterial DNA remains inside the endospore, but the cytoplasm has a reduced water concentration. This is to help protect against high heat. The bacteria take on a tough coating of calcium and dipicolinic acid, creating a dense and impregnable barrier to stabilize the DNA in the cell. DNA repair enzymes are also still active and support the resistance of the endospore.

Plasmids are also found in bacteria that are separated from the circular DNA of the bacteria. Plasmids are also known as “replicons” and are autonomous replicating DNA molecules. However, not all plasmids replicate in bacteria. These elements enable a horizontal gene transfer, whereby a bacterium can acquire new genes and thus characteristics.

They primarily support the rapid mutation of bacteria into various factors. Similar to the other genetic material, the plasmids can be transferred to daughter cells during replication. They are the DNA structure commonly used in research because they are relatively easy to manipulate, implant, and measure.

Types of Eubacteria

Eubacteria are typically divided into five different phylums: chlamydia, cyanobacteria (blue-green algae), gram-positive bacteria, proteobacteria, and spirochetes. Chlamydia is often parasitic bacteria. Cyanobacteria are most commonly known to be aquatic and gain energy through photosynthesis. Some, but not all, bacteria have an additional layer that encloses the cell wall called a lipopolysaccharide or LPS layer.

This extra layer cannot be stained with a Gram stain, which is often used by researchers to classify bacteria and is therefore called Gram-negative bacteria or proteobacteria. Proteobacteria form the second largest group of bacteria and can be stained by the dye. These bacteria are called gram-positive. Spirochetes are long, thin, spiral-shaped bacteria that are known to cause Lyme disease. They differ from the other types of bacteria in their helical shape and movement. They usually move by rotating along their axis.

Bacteria commonly take on one of three shapes: bacilli, cocci, and spirilla. Bacilli have a rod shape, cocci have a spherical shape, and spirilla have a spiral or wave shape. Their shape was often used as a classification system until recently. Bacteria may stay linked after division, forming other shapes such as clusters, filaments, and tight coils.

Structure of Eubacteria

Like archaeans, eubacteria are prokaryotes, meaning their cells do not have nuclei in which their DNA is stored. This distinguishes both groups from the eukaryotes, whose DNA is contained in a nucleus. Despite this structural resemblance, the Eubacteria are not closely related to the Archaea, as shown by analysis of their RNA (see below).

Eubacteria are enclosed by a cell wall. The wall is made of cross-linked chains of peptidoglycan, a polymer that combines both amino acid and sugar chains. The network structure gives the wall the strength it needs to maintain its size and shape in the face of changing chemical and osmotic differences outside the cell. Penicillin and related antibiotics prevent bacterial cell growth by inactivating an enzyme that builds the cell wall. Penicillin-resistant bacteria contain an enzyme that chemically modifies penicillin, making it ineffective.

Some types of bacteria have an additional layer outside the cell wall. This layer is made from lipopolysaccharide (LPS), a combination of lipids and sugars. There are several consequences to possessing this outer layer. Of least import to the bacteria but significant for researchers, this layer prevents them from retaining a particular dye (called Gram stain) that is used to classify bacteria. Bacteria that have this LPS layer are called Gram-negative, in contrast to Gram-positive bacteria, which do not have an outer LPS layer and which do retain the stain. Of more importance to both the bacteria and the organisms they infect is that one portion of the LPS layer, called endotoxin, is particularly toxic to humans and other mammals. Endotoxin is partly to blame for the damage done by infection from Salmonella and other Gram-negative species.

Within the cell wall is the plasma membrane, which, like the eukaryotic plasma membrane, is a phospholipid bilayer studded with proteins. Embedded in the membrane and extending to the outside may be flagella, which are whiplike protein filaments. Powered by molecular motors at their base, these spin rapidly, propelling the bacterium through its environment.

Within the plasma membrane is the bacterial cytoplasm. Unlike eukaryotes, bacteria do not have any membrane-bound organelles, such as mitochondria or chloroplasts. In fact, these two organelles are believed to have evolved from eubacteria that took up residence inside an ancestral eukaryote.

Bacterial cells take on one of several common shapes, which until recently were used as a basis of classification. Bacilli are rod-shaped; cocci are spherical, and spirilla are spiral or wavyshaped. After division, bacterial cells may remain linked, and these form a variety of other shapes, from clusters to filaments to tight coils.

Examples of Eubacteria

Eubacteria are common bacteria. You’ve probably heard several of them, like Streptococcus pneumoniae, which causes pneumonia, or Lactobacillus, which is a good bacteria in our gut.

When it comes to eubacteria, there are typically 5 different groups that these bacteria fall into proteobacteria, cyanobacteria, chlamydia and spirochetes, and gram-positive. Immerse yourself in eubacteria examples from each group.

Escherichia Coli

If you’ve ever had flu-like symptoms from lettuce on a ham sandwich or undercooked burger, you’ve met Escherichia coli, better known by the street name E. coli. These bacteria are usually innocent in your digestive tract, but the wrong strain can destroy your digestive system.

E. coli is one of the largest groups of bacteria known as proteobacteria and comprises several strains. For example, E. coli O157: H7 is a strain that causes intestinal infections. Other E. coli strains cause urinary tract infections. In fact, MedMD finds that 75-95% of UTI infections are caused by E. coli.


You may not notice this, but some bacteria use photosynthesis. Cyanobacteria, known as blue-green algae, are photosynthetic bacteria that occur in large colonies in water. So not only do they making their own food, but you can also see these bacteria without a microscope if the colony is large enough

Interestingly enough, cyanobacteria have two pretty amazing bragging rights. In addition to being the oldest fossils, Berkley University also states that cyanobacteria contributed to the evolution of plants.

Borrelia Burgdorferi

Borrelia burgdorferi, also known as B. burgdorferi, falls into a group of bacteria called spirochetes. They get this name because of their unique spiral shape under the microscope. While a spiral bacterium sounds like a good time, Borrelia burgdorferi is anything but.

B. burgdorferi causes Lyme disease in humans. As a rule, B. burgdorferi does not cause any problems with ticks in most small animals. However, when it is passed on to humans, it causes an infection with a variety of symptoms, including fever and rash.

Chlamydia Trachomatis

Chlamydia bacteria belong to the Chlamydiaceae family and are gram-negative, immobile bacteria. A special type of chlamydial bacteria is Chlamydia trachomatis

Chlamydia trachomatis is one of the “bad bacteria” and causes trachoma, a disease that causes 1.9 million people to go blind. This disease spreads through person-to-person contact and flies. Another strain of these bacteria is also known to cause the sexually transmitted disease chlamydia.

Staphylococcus Aureus

Last but not least is good old Staphylococcus aureus or Staphylococcus. Staphylococcus aureus is a gram-positive bacterium, which means that it retains its purple color in a gram stain test. Staphylococcus is a member of the Staphylococcaceae family and is a common germ that most people carry around in their noses and on their skin.

However, this example of eubacteria can cause serious infections under the right conditions. It is the culprit for the infection that is commonly known as MRSA. In healthcare, MRSA is a serious infection because it is resistant to common antibiotics.