What are bacteria? Types, Structure, Examples, and viruses/bacteria

What are bacteria?

Bacteria are a large group of prokaryotic microorganisms (without nuclei) with various possible shapes and sizes. Although all prokaryotic organisms used to be grouped under the term “bacteria”, today they are divided into two categories in taxonomy: the bacterial domain and the archaeal domain. Both are summarized in the Prokaryota Superkingdom, which consists of all prokaryotic organisms that represent the most primitive and most common living things on planet earth and are adapted to practically all conditions and habitats. Some bacteria can even survive in hostile conditions such as space.

Modern prokaryotes, to which all bacteria belong, are immediate descendants of the first unicellular life forms on the planet that arose under conditions very different from those of about 4,000 million years ago today.

Bacteria were possibly involved in most of the cellular evolutionary jumps because of their abundance. For example, it is believed that endosymbiotic processes influenced the origin of mitochondria (organelles that are present in all eukaryotic cells) or chloroplasts (cells that are only found in plants).

These living things have relationships with virtually all life forms on the planet, either through commensal relationships (like bacteria that multiply on the skin), reciprocity (like those that work together to break down food in the intestines), or parasitism (like those that cause infections and cause disease).

The life of bacteria is essential for the decomposition processes of organic matter necessary for the recycling of elements such as carbon or nitrogen and forms the bottom of microscopic trophic chains in various environments.

Bacteria multiply quickly and through asexual processes that consist of the replication of the precursor cell in two the same cells (binary fission). It is estimated that in a favorable environment, a bacterium can divide in as little as 15 to 20 or 20 to 30 minutes, depending on the species.

Types of bacteria

What are bacteria? Types, Structure, Examples, and viruses/bacteria

Bacteriology, a branch of microbiology, studies bacteria. She has classified this discipline according to various criteria, such as B. their morphology, their metabolism, or the properties of their cell wall.

  • According to its morphology:
    • Bacilli. Elongated in shape, like microscopic rods.
    • Coconuts. Spherical or round shapes. Coconut-like bacteria can also occur in pairs (diplococci), in groups of four (tetracocci), in chains (streptococci), and irregular clusters or clusters (staphylococci).
    • Helical shapes. They can be vibrios, comma-shaped and slightly curved; spirals, rigid helical or corkscrew; or spirochetes, in the form of a flexible corkscrew.

It is common among bacteria of the same species that they adopt different morphological types, which is called pleomorphism.

  • According to the composition of its cell wall:
    • Gram-positive. Acquire a colored purple or blue when the dye due to the presence of a cell wall thickened used.
    • Gram-negative. They turn pink or red when the dye is used, due to the presence of a thin cell wall.
  • According to its nutrition:
    • Photoautotrophs. They use sunlight as a source of energy and inorganic substances (mainly CO2) as a source of carbon.
    • Chemoautotrophs. They use reduced inorganic compounds as an energy source and carbon dioxide as a carbon source.
    • Photoheterotrophs. They use light as a source of energy and organic molecules as a source of carbon.
    • Chemoheterotrophs. They use organic molecules as a carbon source, which they also use as a reagent in reactions to obtain energy.

There are other classifications of bacteria, which take into account the habitat or its biochemical component

Structure of bacteria

The unicellular bacterial structure is usually quite simple. Bacteria are made up of a single cell with no nucleus and almost no defined organelles, but with a nucleoid (an irregular region that houses the circular DNA of prokaryotes) and a peptidoglycan cell wall that covers the cell outside the plasma membrane. Besides, they often need to move pili (structures that are involved in the exchange of genetic material between bacteria) or flagella (if they are mobile). Some bacteria also have capsules, a rigid protective structure outside the cell wall.

Ribosomes (where protein synthesis takes place) are scattered throughout the bacterial cytoplasm, and there are usually also plasmids (small non-chromosomal DNA molecules) and small vacuoles (which act as reservoirs for reserve substances). Some bacteria have prokaryotic compartments, primitive organelles that are surrounded by membranes and, depending on their metabolism, are intended for certain biochemical tasks in the cell.

Examples of bacteria

Bacteria are the most abundant organisms on the planet and are extremely diverse. Throughout evolution, they have managed to adapt to all types of environments and that is why they can be found in all terrestrial and aquatic habitats, even the most extreme ones, such as B. in acidic waters and the depths of the ocean.

  • It is very common to think of bacteria as pathogenic organisms that can cause infectious diseases. While some of them are harmful, many others are harmless or even useful. For example:
  • Neisseria gonorrhoeaeIt is a gonococcus that causes gonorrhea, a sexually transmitted infection in humans.
  • Bacillus anthracisIt is an immobile, gram-positive bacterium that produces recognizable black lesions on the skin (carbuncles).
  • Sorangium cellulosumIt is a gram-negative myxobacterium that is extremely frequent in soils and of harmless metabolism.
  • Clostridium botulinumIt is a causal agent of botulism, through a neurotoxin secreted by these bacteria, whose growth is known in canned food (inflated cans that release gas when opened are a clear symptom) and other canned foods.
  • Lactobacillus acidophilus. It is a lactic acid bacterium, a mutualistic inhabitant of the human intestine and other mammals. As a result of its metabolism, this bacterium provides different benefits as it aids in digestion, increases the bioavailability of nutrients, and helps keep the digestive tract free of pathogenic microorganisms.
  • Lactobacillus acidophilus. It is a genus of bacteria that are symbiotic residents of the human digestive tract. Contributes to the production of vitamin K, vitamin B12, folate, and biotin.

Differences between viruses and bacteria

Viruses and bacteria are very different, although they are the best known and most common forms of infectivity for humans.

The main difference is related to their structure and size: while bacteria are unicellular organisms, ranging in size from 0.5 to 5 microns, viruses are much simpler and elementary acellular beings that can only reproduce when they infect other cells that act as viral replication factories after inoculation with the invading viral DNA.

At present, the scientific community disagrees on whether viruses are alive, as their existence is primitive, which is little more than a simple DNA or RNA molecule wrapped in a layer of protein. For this reason, antibiotics do not work against viruses, but bacteria. Antiviral or retroviral agents are used exclusively to fight viral infections.

What are bacteria? Types, Structure, Examples, and viruses/bacteria

What are bacteria? Types, Structure, Examples, and viruses/bacteria


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