Classification of bacteria

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Bacteria are prokaryotic living beings microscopic in size, a few microns (typically 0.5–5 µm in length). Bacteria are the most abundant organisms on Earth and have been able to adapt to a large number of environments that, at first glance, seem inhospitable: hot and acidic springs, in radioactive waste, calderas from erupting volcanoes and even in space! Exterior! Therefore, it is to be expected that scientists, in order to study them more easily, have created numerous classifications of bacteria, attending to different criteria according to the interest in that moment. In this lesson from a TEACHER we will review the classification of bacteria attending to criteria such as its shape, its nutrition, the reaction to dyes, etc. If you want to know more, we invite you to continue reading!

Index

1. Classification of bacteria according to their shape
2. Classification of bacteria according to their nutrition
3. Classification of bacteria according to their staining
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4. Classification of bacteria according to the temperature in which they live

The bacteria they can be classified according to their shape seen under the microscope. The four basic forms and the modifications that bacteria can present are:

• Spherical shape: they are called coconut. These cocci can form groups of two cocci (diplococci), four (tetracocci), rows of several cocci (streptococci), or irregular or cluster-shaped groupings (staphylococci).
• Stick or bar shape: bacillus. These rods can be more rounded (coccobacillus), go in groups of two (diplobacillus), form chains (streptobacillus) or form garden fence-like structures (palisade bacilli).
• Curved filament shape: vibrio. Vibrios have a shape that is commonly described as comma, bean, peanut, or kidney-shaped.
• Screw or helical shape: spirillae and spirochetes. Spirals are shaped like a rigid corkscrew or corkscrew, while spirochetes are shaped like a flexible or spring corkscrew.

Many of the names of the microorganisms that we know have to do with their morphology. For example, species belonging to the genus of the Streptococcus, seen under a microscope, have the shape of chains while those belonging to the Staphylococcus they are arranged in the form of clusters.

Unlike higher organisms, bacteria have managed to adapt to a wide variety of environments and types of nutrition. The classification of bacteria according to their nutrition or bacterial metabolism is classified based on two main criteria: the origin of the carbon and the source of energy.

Bacteria need a carbon source to form their structures. Depending on where they get it from, they can be:

• Heterotrophs: They are bacteria that use organic compounds as a carbon source.
• Autotrophs: They are bacteria that obtain their carbon by fixing carbon dioxide in reactions more or less similar to photosynthesis.

In addition to carbon, bacteria need energy. According to power source, bacteria can be:

• Phototrophs: They are those bacteria that use light to obtain energy through photosynthesis or processes very similar to it. Depending on the habitat or environment where the bacterium is found, it develops different types of pigments, which make better use of one or another wavelength.
• Chemotrophs. Bacteria that obtain energy from chemicals are called chemotrophs. To obtain energy, chemical compounds have to be oxidized, and for this they can use oxygen (through aerobic respiration) or other alternative electron receptors (anaerobic respiration).

Thus, for example, a bacterium can be chemoheterotrophic, that is, obtain energy from chemical substances and carbon from organic compounds (in the vast majority of cases the compound from which they obtain carbon is the same from which they obtain Energy). Another possible option is chemoautotrophic bacteria, which use reduced inorganic compounds as an energy source and carbon dioxide as a carbon source (for example, Nitrobacter, Thiobacillus, etc).

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One of the most widely used bacterial classifications is that of gram stain. Gram stain is a very commonly used staining process by which add one or two substances that give color to bacteria. Normally, when gram staining is performed, two stains are used: the Gram stain and another, which is used merely to contrast cells that do not take up the gram stain and that would otherwise be colorless and very difficult to see microscope. Depending on their reaction with said dye, the bacteria can be:

• Bacteria gram positive- Stains blue or dark purple when processed with the Gram stain
• Bacteria gram negative: They do not stain with this dye, and are usually seen as pink due to the contrast dye.

Gram-positive and Gram-negative bacteria stain differently because their cell walls are different: Gram-positive bacteria have a cytoplasmic membrane and a cell wall composed of a thick layer of peptidoglycan, which surrounds the previous one while the Gram-negative cells have a double cell membrane (one external and the other cytoplasmic), between which a thin cell wall of peptidoglycan.

The classification of gram-positive and gram-negative does not only reflect a structural characteristic since it has been seen that These bacteria cause different types of infections and pathologies, and effective antibiotics against them are also very different.

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Bacteria can also be classified according to the temperature at which they can grow. According to this, bacteria can be:

• Psychrophilic. Psychrophilic bacteria thrive at low temperatures, from -10 ° C to about 20 ° C. Within this group we can find two types of microorganisms: obligate psychrophiles and pfacultative syrophiles. Obligate psychrophiles have an optimal growth temperature that is around 15-18 ° C, although they live perfectly at zero degrees and even at lower temperatures while facultative psychrophiles have the ability to resist cold, although their optimum temperature is higher, around the 20-30 ° C.
• Mesophilic. Mesophilic bacteria are those that live at a temperature similar to body temperature; that is, between 15 ° C and 40 ° C. Its most common habitats are human organisms and some animals.
• Thermophiles. Thermophilic bacteria inhabit environments at high temperatures, above 45 ° C, which are usually marine environments.
• Hyperthermophiles. Hyperthermophilic bacteria are, as their name suggests, are bacteria that grow in extremely high temperatures, above 100 ° C. They are the bacteria that live in the calderas of volcanoes, for example.

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If you want to read more articles similar to Classification of bacteria, we recommend that you enter our category of biology.

• Cabeen M, Jacobs-Wagner C (2005). "Bacterial cell shape". Nat Rev Microbiol 3 (8): 601-10.
• Wikipedia (March 27, 2020) Bacteria. Recovered from https://es.m.wikipedia.org/wiki/Bacteria
• Rodríguez, D. (s.f) Classification of Bacteria: The 16 Main Types. Recovered from https://www.lifeder.com/clasificacion-bacterias/