Bacteria (Meaning and Explanation)

We explain what bacteria are, the types that exist and what their structure is like. Also, some examples and their differences with the virus.

Bacterium — Bacteria are the most primitive and abundant living beings on planet Earth.

What are bacteria?

Bacteria are a large group of prokaryotic microorganisms (lacking a membrane that delimits the cell nucleus) of various possible shapes and sizes. Although in the past the term “bacteria” grouped all prokaryotic organisms, currently taxonomy divides them into two categories: the domain Bacteria and the domain Archaea. Both are grouped in the superkingdom or Prokaryota empire, made up of all prokaryotic organisms, which constitute the most primitive and most abundant living beings on planet Earth adapted to practically all conditions and habitats. Some bacteria can even survive in hostile conditions, such as outer space.

Modern prokaryotes, among which are all bacteria, are immediate descendants of the first unicellular life forms on the planet, which arose in very different conditions from those of today about 4 billion years ago.

Bacteria have been implicated, perhaps due to their abundance, in most cellular evolutionary leaps. For example, it is believed that, through endosymbiosis processes, they influenced the origin of mitochondria (organelles present in all eukaryotic cells) or chloroplasts (organelles exclusive to algae and plant cells).

These living beings have relationships with practically all forms of life on the planet whether through relationships of commensalism (such as bacteria that proliferate on the skin), mutualism (such as those that collaborate with the digestion of food in the intestine) or parasitism (such as those that cause infections and diseases).

Bacterial life is essential in the decomposition processes of organic matter, necessary for the recycling of elements such as carbon or nitrogen, and constitute the basis of the trophic chains of various environments.

Types of bacteria

Coconut bacteria — Cocci bacteria have a spherical or round shape.

Bacteria are studied by bacteriology, a branch of microbiology. This discipline has classified them according to various criteria:

According to its morphology:
- Bacilli. Elongated shapes, like microscopic bars. Bacilli can also be found in groups of two or forming filaments.
- Coconuts. Of spherical or round shapes. Coccus-type bacteria can also occur in pairs (diplococci), in groups of four (tetracocci), in chains (streptococci) and in irregular groups or clusters (staphylococci).
- Helical shapes. They can be: vibrios, comma-shaped and slightly curved; spirals, rigid helical or corkscrew shape; or spirochetes, in the shape of a flexible ringlet.

It is common among bacteria of the same species to adopt different morphological types, which is called “pleomorphism”.

Depending on the composition of its cell wall:
- Gram positive bacteria. They acquire a violet or bluish color when crystal violet dye is used, due to the presence of a thickened cell wall.
- Gram negative bacteria. They take on a pink or red color when crystal violet dye is used, due to the presence of a thin cell wall.
According to your nutrition:
- Photoautotrophic bacteria. They use sunlight as a source of energy and inorganic substances (mainly CO₂) as a carbon source.
- Chemoautotrophic bacteria. They use reduced inorganic compounds as an energy source and carbon dioxide as a carbon source.
- Photoheterotrophic bacteria. They use light as a source of energy and organic molecules as a source of carbon.
- Chemoheterotrophic bacteria. They use organic molecules as a source of carbon, which they also use as a reactant in reactions to obtain energy.

structure of bacteria

The bacterial single-cell structure is usually quite simple. The bacteria are formed by a single cell without a membrane that delimits the cell nucleus and almost without defined organelles, but with a nucleoid (irregular region where the circular DNA of prokaryotes is found) and a peptidoglycan cell wall that covers the cell outside the plasma membrane. In addition, they frequently have pili (structures involved in the exchange of genetic material between bacteria) or flagella to move (if they are mobile). Some bacteria also have a capsule, a rigid protective structure that is located outside the cell wall.

Scattered throughout the bacterial cytoplasm are ribosomes (in which protein synthesis takes place) and there are also usually plasmids (small molecules of non-chromosomal DNA) and small vacuoles (which function as reservoirs for reserve substances). Some bacteria have prokaryotic compartments primitive organelles surrounded by folds of the plasma membrane towards the cytoplasm, destined for specific biochemical tasks within the cell, depending on its metabolism.

Examples of bacteria

The Escherichia coli It is common in the intestines of warm-blooded living beings.

Bacteria are the most abundant organisms on the planet and have enormous diversity. Throughout the evolution have managed to adapt to all types of environments and that is why they are found in all terrestrial and aquatic habitats, even in the most extreme ones, such as acidic water springs and ocean depths.

It is very common to think of bacteria as pathogenic organisms capable of causing infectious diseases. While some of them are harmful, there are many others that are harmless or even beneficial. For example:

Escherichia coli. It is a gram-negative bacteria common in the gastrointestinal tracts of humans and other warm-blooded animals. Some strains of this bacteria are capable, at certain times, of causing an infection.
Neisseria gonorrhoeae. It is a gonococcus that causes gonorrhea, a sexually transmitted infection in humans.
Bacillus anthracis. It is a non-motile, gram-positive bacteria that produces recognizable black lesions on the skin (carbuncles).
Sorangium cellulosum. It is a gram-negative myxobacteria that is extremely common in soils and has a harmless metabolism.
Clostridium botulinum. It is a causal agent of botulism. This bacteria secretes a neurotoxin whose growth is known in canned foods (bloated cans that release gas when opened are a clear symptom) and other preserved foods.
Lactobacillus acidophilus . It is a lactic acid bacteria, a mutualistic inhabitant of the human intestine and other mammals. As a result of its own metabolism, this bacteria provides different benefits as it collaborates in digestion, increases the bioavailability of nutrients and helps keep the digestive tract free of pathogenic microorganisms.

Differences between viruses and bacteria

Although they are the most well-known and frequent infectious forms for humans, viruses and bacteria are extremely different.

The main difference has to do with their structure and size: while bacteria are single-celled organisms whose size ranges between 0.5 and 5 micrometers in length, Viruses are acellular beings, much simpler and more elemental incapable of reproducing except by infecting other cells that function as viral replication factories, after being inoculated with the invading viral DNA.

Currently, the scientific community does not fully agree on whether viruses are really alive., because of how primitive its existence is, which is not much more than a DNA or RNA molecule wrapped in a layer of proteins. For this reason Antibiotics do not work on viruses but on bacteria ; while antivirals and antiretrovirals are exclusively used to combat virus infections.