The eubacteria, better known as true bacteria, they are unicellular prokaryotic organisms belonging to the Bacteria domain. Together with the Eukarya and Archaea domains, the Bacteria domain is one of the three proposed domains of life today..
Eubacteria, since they are prokaryotes, are relatively simple organisms that lack a membranous nucleus to enclose their genetic material. However, these living beings are extremely abundant in nature, being found in practically all the ecosystems of the planet..
They can inhabit the soil, water, air and in different types of biotic or abiotic surfaces. Some eubacteria are pathogenic, that is, they cause diseases in other living beings, but most consist of harmless and even beneficial organisms from different points of view.
More than 5,000 species of true bacteria have been described, so many authors are of the opinion that they are the most commonly found organisms in nature..
Eubacteria are single-celled prokaryotic organisms. In accordance with this, we can say that one of its main characteristics is the lack of a membranous nucleus that encloses its DNA or any other membranous cytosolic organelle. Among its other characteristics, the following stand out:
Bacteria have highly variable sizes, ranging from approximately 0.2 to 50 microns, although the average size is between 1 and 3 microns. Likewise, the shape of these cells can vary considerably depending on the species, with three being the most common:
- Coconuts: spherical or ovoid cells that are usually solitary or spatially ordered depending on the plane in which they divide, as some cells can remain united even after division. They can be found in more numerous pairs, chains or groups depending on the species.
- Canes or bacilli: rod-shaped cells solitary or united with each other, as if it were a string of sausages.
- Spirits: they are spiral-shaped bacteria, generally flexible.
In the Bacteria domain there are heterotrophic and autotrophic organisms.
Heterotrophic bacteria, as is true for animals, are those that need to obtain their food from external sources, while autotrophic bacteria are those that, like plants, produce their own food from inorganic compounds.
Most of the heterotrophic bacteria are saprophytes, that is, they feed on dead or decomposing organic matter. Others are parasites, which implies that they live inside or outside another organism to the detriment of this one, and others are symbiotes, since they provide benefits to other organisms and obtain food in return.
Autotrophic bacteria can be photosynthetic or chemosynthetic, dependent or not on oxygen. Those photosynthetic ones produce organic substances by photosynthesis, using the energy of the sun's rays (these have photosynthetic pigments such as chlorophyll).
Chemosynthetic bacteria use inorganic compounds such as ammonium, molecular hydrogen, sulfur, or iron to produce their organic molecules, but they do not do so through photosynthesis..
True bacteria generally reproduce by binary fission, which is a type of asexual reproduction typical of prokaryotes and other single-celled organisms. The process consists of the formation of two identical cells from a "progenitor" cell..
Binary fission is a very fast type of reproduction, although the time is highly variable from one species to another. Some bacteria can divide in less than 20 minutes, while others can take several hours.
Depending on the orientation in which the duplicated chromosomes are distributed, binary fission is classified as transverse, longitudinal, or irregular, but it always consists of the same events noted above..
The most accepted classification of the Bacteria domain consists of the following 5 phyla:
It is one of the most abundant and diverse groups of microbes. Many pathogenic organisms for man and other animals belong to this, including representatives of the genera Salmonella, Vibrio, Helicobacter, Escherichia, Neisseria, etc.
Because bacteria in this group cannot be stained by the Gram method, they are known as Gram Negative bacteria. It is divided into the following groups:
They are bacteria with a spiral shape and of great length (up to 500 microns long). Many are free-living organisms, generally associated with bodies of fresh or marine water rich in organic matter..
Other members of this phylum are pathogenic for some mammals, such is the case of bacteria of the genus Leptospira.
Chlamydial phylum bacteria are generally intracellular parasites. The phylum is composed of a single class (Chlamydia) that is divided into two orders known as Chlamydiales (4 families) and Parachlamydiales (6 families).
Formerly known as “blue-green algae”, the bacteria belonging to this phylum are free-living photoautotrophic organisms or endosymbionts..
Bacteria that can be stained by the Gram method are grouped into this set. The following groups are usually recognized:
There are many citable examples of eubacteria, here are some of them:
A proteobacterium residing in the human intestines, where it contributes to the digestion of food. It is a type of rod-shaped bacteria and some strains can be pathogenic, causing severe diarrhea.
It is another rod-shaped gram-negative proteobacterium that causes the disease called "cholera" in humans, characterized by acute diarrhea followed by severe dehydration..
A highly positive bacterium from the Firmicute group that naturally resides in the intestines of many animals, including humans, as well as in the mouth and female genitalia. Since it is capable of metabolizing the sugars in milk and fermenting it, it is used together with Streptococcus thermophilus for the production of foods such as yogurt.
It is a species of cyanobacteria widely distributed throughout the world, where it can inhabit both terrestrial and freshwater environments. It is used as food in some Asian countries and in some regions it is used for its anti-inflammatory properties.
Although they may seem "simple" at first glance, these cells make possible the existence of the world as we know it today:
- They participate in the cycling of nutrients such as carbon, phosphorus, sulfur and nitrogen, since many species are responsible for the decomposition and degradation of dead organic matter.
- Photosynthetic bacteria, like plants, use the energy of the sun's rays to obtain energy, synthesize organic compounds and release oxygen into the atmosphere.
- They act as symbionts in the gastrointestinal system of many animals, including humans and many ruminant herbivores..
- They are used as model organisms for the study of various aspects of cell life and are also exploited for the mass production of different biotechnological compounds of great use to humanity (food, drugs, enzymes, etc.).
Given their diversity and the importance that many of these have in relation to public health and the pharmaceutical and food industries, for example, bacteria have been extensively studied, characterized and exploited biotechnologically for more than 150 years.
There are some notable differences between eubacteria and archaebacteria:
- Eubacteria have membranes composed of lipids composed of a glycerol backbone to which fatty acids are esterified, but archaebacteria have ether-like bonds between fatty acids and glycerol.
- The composition of the cell wall of archaea is also different from that of bacteria, with a pseudopeptidoglycan being the main compound in archaea..
- While eubacteria are found almost anywhere in the biosphere, archaebacteria are often said to be restricted to "extreme" sites in terms of temperature, salinity, pH, etc..
- Although archaebacteria do not have a nucleus either, they do have circular chromosomes associated with histone-like proteins, elements absent in true bacteria..
- Bacteria are said to be sensitive to antibiotic substances, while archaebacteria are not.
- Pathogenic archaebacteria have not been reported for humans, otherwise that of bacteria.
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