Eubacteria: what are they, characteristics and types?

A summary of the characteristics of eubacteria and their diversity as life forms.

We do not see them, but we are surrounded by them. They come in all shapes and forms and, although very small in size, contribute greatly to our world as it is today.

Eubacteria are microorganisms present in most ecosystems on Earth and can have functions ranging from being beneficial to our species to being harmful, causing disease and organ damage.

In the following we are going to delve into the domain of eubacteriaalso known as true bacteria, and we will discover how they reproduce, what forms they can take and what groups there are.

What are eubacteria?

Eubacteria are unicellular prokaryotic organisms. These microorganisms are known as the true bacteria or simply as bacteria and their domain is one of the three domains of life proposed according to the current evolutionary modelalong with Eukarya and Archaea.

Until relatively recently, the term "bacteria" was used interchangeably to refer to all prokaryotic and unicellular organisms, but over time this domain was divided into that of eubacteria (Eubacteria) and archaebacteria (Archaebacteria), subsequently being renamed bacteria and archaea (Archaea).

Being prokaryotic organisms (without a cell nucleus), these organisms are relatively simple, having their genetic material scattered throughout their bodies.having their genetic material scattered throughout the cellular matrix. But despite their simplicity, they are also among the most abundant living organisms in nature, being found in practically any ecosystem on the planet. They inhabit all environments: soil, water, air, as well as biotic and abiotic surfaces.

More than 5,000 different species of true bacteria have been described, which is why many biologists and bacteriologists consider eubacteria to be among the most common organisms in nature. There are all kinds of eubacteria, including pathogenic species, i.e., those that cause diseases in other living beings, although the majority of eubacteria are not pathogenic.However, most eubacteria are harmless and even beneficial for the rest of life.

Characteristics of eubacteria

As we have already mentioned, eubacteria or true bacteria are very simple, unicellular and prokaryotic organisms. One of their main characteristics is the lack of a membranous nucleus in which their DNA is enclosed.or any other membranous cytosolic organelle. In addition to this, we can highlight other very interesting characteristics of eubacteria.

The first is that, apart from being prokaryotes, they have a cell membrane formed by a lipid bilayer, as happens in eukaryotic cells or cells with a nucleus. In the case of eubacteria, this lipid bilayer encloses an aqueous interior, known as the cytosol, which contains the cell's genetic material and, among them, cellular proteins. and, among them, also cellular proteins such as, for example, ribosomes for protein translation.

Eubacteria are covered by a protective wall, which consists of a polymer called peptidoglycan. This polymer is composed of repeated residues of the glycoside N-acetyl-glucosamine and N-acetylmuramic acid, linked by β-1,4-linkages. In some cases, bacteria present on their surface protein structures in the form of filaments that allow them to move known as cilia (if they are short and many) or flagella (if they are long and few).

The genetic material of prokaryotic cells is located in a specialized region of the cytosol known as nucleoid since, although it is not a well-defined nucleus, it performs more or less the same functions. Eubacteria have all their genetic material collected in a single circular chromosome. Added to this, in the cytosol we can also find other extrachromosomal DNA fragments, called plasmids, which can be shared with other bacteria through a structure called pilus and generally carry useful metabolic information.

In many cases, eubacteria are surrounded by a gelatinous capsule or matrix known as a glycocalyx.. It is a component rich in carbohydrates that protrude from the cell membrane and cell wall, which provide some resistance to adverse environmental conditions, pathogens and antibiotics.

Some eubacteria can transform into endospores in case they face extreme environmental situations. These are resistance structures that help them tolerate factors such as extreme temperatures, pH levels that are too acidic or too basic, excessive radiation... In fact, it is thanks to their ability to become endospores that they can survive almost anywhere on the planet, on any type of surface and feed on anything.

Size and shape

Bacteria have minuscule sizes but can range from 0.2 to range from about 0.2 to 50 microns, although the average size is between 1 and 3 µm.. Their shape varies greatly from species to species, with the following three being the most common.

1. Cocci

Cocci are spherical or ovoid cells.They are usually found singly or spatially arranged, depending on the plane in which they have divided, since they can sometimes remain united even after they have divided. They can be found in pairs, chains or numerous groups depending on the species.

2. Rods or bacilli

Rods or bacilli are solitary or united cells. Because of their rod-like shape, these cells resemble those of a sausage or, in the case of a sausage, a sausage, a chorizo. or a sausage if they are found in a group.

3. Spirocytes

Spirocytes are spiral-shaped bacteria as their name suggests, usually flexible.

Types of bacteria

At present, the most widely accepted classification for the domain of bacteria consists of the following 5 phyla.

1. Proteobacteria

Proteobacteria are one of the most widespread, abundant and diverse groups of microorganisms in the world.. To this phylum belong many bacteria with pathogenic capacity for humans and other species of the animal kingdom, being in this group the genera Salmonella, Helicobacter, Escherichia, Neisseria, Vibrio....

One of the characteristics that distinguish proteobacteria is that they cannot be stained by the Gram method, that is why they are known as Gram-negative bacteria. These microorganisms are divided into the following groups:

• ε-Proteobacteria
• δ-Proteobacteria
• α-Proteobacteria
• β-Proteobacteria
• γ-Proteobacteria

2. Spirochaetae

Spirochaetes are spiral-shaped bacteria that can grow to a great length, up to 500 µm long.. Many of them are free-living microorganisms present in fresh or salt water, bodies of water rich in organic matter. Some of them are pathogenic for mammals, as is the case of Leptospira bacteria.

3. Chlamydiae

Chlamydial bacteria are generally intracellular parasites and this phylum is composed of only one class (Chlamydia).. In turn, this group is divided into two orders known as Chlamydiales, with 4 families; and Parachlamydiales, with 6.

4. Cyanobacteria

Cyanobacteria were once known as blue-green algae, or rather cyan-colored as their name suggests. They are photoautotrophic, free-living or endosymbiont bacteria..

5. Gram-positive bacteria

Finally, we have the case of Gram-positive bacteria, whose name means that they can be stained by the Gram staining methodinvented by the Danish bacteriologist Hans Christian Gram (1853-1938). Within this phylum we find:

• Firmicutes: endospore-producing bacteria. Used for industrial purposes.
• Actinobacteria: used for bioremediation of contaminated water and soil.
• Mycoplasma: includes pathogenic bacteria resident in mucous membranes and epithelia.

Nutrition of eubacteria

Within the bacterial domain we can find both heterotrophic and autotrophic organisms. Heterotrophic bacteria are those that need to obtain their food from external sources, as is the case in the animal kingdom.As in the animal kingdom, while autotrophs are capable of producing their own food from inorganic compounds, as do plants.

Most heterotrophic bacteria are saprophytes, which means that they feed on dead or decaying organic matter. In other cases we find parasitic bacteria, that is, they live inside or outside another organism, causing it some kind of detriment. We also find the case of symbiont bacteria which establish a mutually supportive relationship with another organism, giving it some benefit while receiving food in return.giving it some benefit while receiving food in return.

In the case of autotrophic eubacteria we can find photosynthetic or chemosynthetic, which may or may not depend on the presence of oxygen. In the case of photosynthetic eubacteria, they produce organic substances through photosynthesis using the energy provided by the sun's rays and by making different types of pigments work. and making different types of photosynthetic pigments work, such as chlorophyll. In the case of chemosynthetic bacteria, they use inorganic compounds such as ammonium, molecular hydrogen, iron or sulfur to produce their organic molecules.

Reproduction

Generally, true bacteria reproduce by binary fission, an asexual reproduction mechanism characteristic of prokaryotes and other unicellular organisms. As the name suggests, in this process two identical cells are formed from the fission of a progenitor or parent cell. Binary fission is a very fast reproductive mechanism, although the time varies according to the species of bacteria, with some dividing in less than 20 minutes and others taking several hours.

The process begins with the duplication of the genetic material, i.e., the bacterial chromosome in a circular fashion.. The progenitor cell then begins to increase in size and, moments later, the chromosome creates a copy of itself, one migrating to one pole of the cell and the other to the other. At this point, the cell has reached almost twice its original size.

Within the bacterium, a series of proteins begin to activate, which are responsible for forming a ring of division of the two daughter cells.The two daughter cells are located more or less halfway between the mother cell and the daughter cell. In the region where this dividing ring has been formed, a new transverse cell wall begins to be synthesized, which ends up separating the two chromosomes located at each pole of the cell and causes the separation of the two identical daughter cells.

Depending on the orientation in which the duplicated chromosomes are distributed, we speak of different types of binary fission (longitudinal, transverse or irregular), but in all of them the same events that we have mentioned occur.

The importance of these microorganisms

True bacteria make it possible for the world to be as it is today, in addition to the fact that they can be used for economic benefit. they can be used for economic benefit. For example, these microorganisms participate in the cycling of nutrients such as phosphorus, sulfur, carbon and nitrogen, decomposing organic matter and producing these nutrients as a residue of their action. In the case of photosynthetic bacteria, they use solar energy to synthesize organic compounds and release oxygen into the atmosphere, just as plants do.

We have bacteria inside us, but they are good bacteria. Some species act as symbionts in the Gastrointestinal system of many animals, including humans and many ruminant herbivores, participating in digestion. Among these we can highlight the Lactobacillus acidophilus and Streptococcus thermophilus.

In the field of biomedical research, bacteria are often used as model organisms for the study of various life phenomena and are also exploited to produce various biotechnological compounds useful to mankind. Without bacteria it would not be possible to have foods such as cheese or yogurts, nor medicines such as insulin, obtained by means of a transgenic strain of the Escherichia coli.