What are bacteria? Concept, Types, Structure and Examples

What are bacteria?

We explain what bacteria are, the types that exist and how they are structured. In addition, some examples and their differences with the virus.

What are bacteria

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

Bacteria are a domain of prokaryotic microorganisms (devoid of a cell nucleus) of various possible shapes and sizes, which together with the archeas, constitute the most primitive and abundant living beings on planet Earth, adapted to practically all conditions and habitats, including parasites. Some may even subsist in hostile conditions, such as outer space.

Bacteria are immediate descendants of the planet’s first single-celled life forms, which arose in very different conditions to those of today some 4 billion years ago. It is not known whether these beings were more like archeas or bacteria, but it is known that they are their common ancestor.

However, bacteria have been involved, perhaps due to their abundance, in most cell evolutionary leaps, such as the origin of mitochondria (in eukaryotic cells) or chloroplasts (in plant cells), through endosymbiosis processes.

Likewise, these living beings have relations with practically all forms of life on the planet, be it commensalism (such as the bacteria that proliferate on the skin), mutualism (such as those that collaborate with the decomposition of food in the intestine) or parasitism (such as those that cause infections and illnesses). To combat the latter, humans created antibiotics.

On the other hand, bacterial life is indispensable in the processes of decomposition of organic matter, necessary for the recycling of elements such as carbon or nitrogen, and constitute the floor of microscopic trophic chains in various environments.

Bacteria reproduce with speed and by means of asexual procedures, which consist in the replication of the progenitor cell in two exactly equal to it (mitosis or binary fission). It is estimated that, in a propitious environment, a bacterium divides in two in just 15-20 or 20-30 minutes, depending on the species.

Types of bacteria

Coconut bacteria are spherical or round in shape.

Bacteria are studied by bacteriology, a branch of microbiology. This discipline has classified them according to various criteria, such as their form or their response to staining. In that sense, one can speak of:

  1. Bacteria by shape:
  2. Bacilli. Elongated shapes, such as microscopic rods.
  3. Coconuts. Spherical or round.
  4. Vibrios. In the shape of a corkscrew or corkscrew.
  5. Spirils. Propeller or spiral shape.
  6. Bacteria according to their response to dyeing:
  7. Gram positive. They acquire a violet or clearly violet colour when the dye is used.
  8. Gram negatives. They are clearly red when the dye is used.

There are other classifications, which take into account the habitat, its cellular metabolism or its biochemical components.

Structure of bacteria

The bacterial unicellular structure is usually quite simple, with no cell nucleus and almost no defined organelles, but with a nucleoid (irregular region where the circular DNA of the prokaryotes is found), a peptidoglycan cell wall that covers the cell outside the plasma membrane and frequently pili or flagella to move around (in case they are mobile).

Dispersed in the bacterial cytoplasm, there are usually plasmids (small, non-chromosomal DNA molecules), vacuoles (deposits of reserve substances) and ribosomes (for protein synthesis). Some bacteria present prokaryotic compartments, primitive organelles surrounded by membranes, destined to specific biochemical tasks within the cell, depending on its metabolism.

Examples of bacteria

Escherichia coli is common in the intestines of warm-blooded living things.

Some of the best known bacteria are:

  • Escherichia coli. A gram-negative bacterium common in the gastrointestinal tracts of humans and other warm-blooded animals, capable at certain times of causing an infection.
  • Neisseria gonorrhoeae. Gonococcus that causes gonorrhea, a sexually transmitted infection in humans.
  • Bacillus anthracis. Immobile, gram-positive bacteria that produce recognisable black lesions on the skin (anthrax).
  • Sorangium cellulosum. Myxobacteria gram negative extremely frequent in soils and innocuous metabolism.
  • Clostridium botulinum. Causal agent of botulism, by means of a neurotoxin secreted by these bacteria, whose growth in canned food (the filled cans that release gas when opened are a clear symptom) and other food preserves is known.

Differences between viruses and bacteria

Viruses and bacteria are extremely different, even though they are the best-known and most common infectious forms for humans.

The main difference has to do with their structure and size: while bacteria are unicellular organisms whose size oscillates between 0.5 and 5 micrometers in length, viruses are much simpler and elemental acellular beings, incapable of reproducing if not by infecting other cells that act as factories of viral replicas, after being inoculated with invading viral DNA.

Consider that viruses are not even known if they are really alive, how primitive their existence is, which is not much more than a simple molecule of DNA or RNA wrapped in a layer of proteins. For this reason, antibiotics have no effect on viruses but on bacteria, while antivirals or retrovirals are used exclusively to fight virus infections.

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