What are microbes? Types, Bacteria, Virus, Protozoa, Fungi, and yeasts

What are microbes?

Microbes or microorganisms are the smallest known life forms, which are also most common on the entire planet earth. They cannot be visualized or identified without the aid of a microscope.

Many of them coexist with us without posing a threat to us, while others have learned over the millennia to lead a parasitic or pathogenic existence, that is, as infectious agents of other organisms, especially multicellular ones.

The term microbe comes from the Greek voices mikrós (“tiny”) and bíos (“life”) and was coined in the 19th century to give names to the invisible beings responsible for diseases.

The idea of ​​these beings had already appeared in the philosophical and pre-scientific realm of humanity in the 13th century. For this reason, we still tend to associate the word microbe with pathogenic microorganisms, that is, those that carry parasitic stocks.

It wasn’t until the 17th century that its existence was proven, and microbiology developed into an area of ​​organized scientific knowledge. In this way, the huge, microscopic fauna and flora were verified, the species of which, as initially assumed, are not directly related.

Microbes are found all over the world, both on land, in water, and the air, and both inside and outside of our bodies. In our intestines, for example, there is an entire macrobiotic ecosystem that coexists with us and helps us digest food.

Microbes are also responsible for the breakdown of organic matter outdoors, fermentation of beer, the intense taste of certain types of cheese, and even the production of certain antibiotics.

They are essential to sustain life on the planet, although from time to time some can get out of hand and cause harm to other populations of living things. But everything is part of the life processes on our planet.

Types of Microbes

As we said earlier, the types of microbes are numerous. In this case, however, we will focus on the most famous: bacteria, viruses, parasites, fungi, and yeast, which we will see separately below.


Bacteria (and to some extent archaebacteria or archaea) are prokaryotic unicellular organisms, with very few micrometers in size (between 0.5 and 5 μm). They have different but recognizable shapes, such as spheres (cocci), rods (bacilli), spirals (vibrios), or helices (spirilla).

They are the most abundant organisms across the planet and adapted to all types of habitats under virtually all conditions, both in free life (for photosynthesis, chemosynthesis, or decomposition processes) and in parasitic life (for infecting other organisms).

The existence of bacteria is essential for the ecological balance of the world as they deal with fundamental processes of recycling organic matter and intervene in various biogeochemical cycles.

Bacteria can also cause deadly diseases such as cholera, diphtheria, leprosy, syphilis, typhoid, or gonorrhea. In these cases, they are combated with various antibiotics.

What are microbes?  Microbes or microorganisms are the smallest known life forms, which are also most common on the entire planet earth.


Viruses are acellular infectious agents, which means that they are so simple that they do not even consist of a cell, but have to penetrate into foreign cells in order to multiply.

They are so simple that from some point of view it is impossible to know if they are really alive. However, they have their own genetic material that they inject into the cells they invade, forcing them to synthesize new viruses instead of their usual proteins.

If the invading cell no longer supports the number of young viruses, it explodes. Thus the viruses are released and infect other similar cells.

A virus is such a tiny and simple structure that it cannot be seen with ordinary microscopes (that is, they are submicroscopic beings). However, some species can reach exceptionally large sizes.

Their body is a DNA or RNA molecule encapsulated in relatively simple coat proteins, and a layer of lipid allows them to offer resistance in search of their host cell.

Viruses occur in almost all ecosystems in the world and can come in very different shapes and sizes and with very different methods of transmission. In humans, viruses can spread from common diseases like the flu to incurable diseases like AIDS or HPV.

What are microbes?  Microbes or microorganisms are the smallest known life forms, which are also most common on the entire planet earth.


Protozoa or Protozoa (from the Greek proto “first”, zoon, “animal”) is the name that the German naturalist Georg Goldfuss (1782-1848) coined in 1818 for the animals that were then considered to be primitive animals, which simply exist. They were then classified within the protist kingdom or as their own kingdom apart from eukaryotic and unicellular beings.

Protozoa are a very diverse group of microscopic creatures that can sometimes be as small as a few millimeters. Over 30,000 species are known.

They tend to be abundant in aqueous media and in the soil itself, and play various roles within the food chain: heterotrophs, predators, detritivores, and even mixotrophs (as some are partially autotrophs through photosynthesis).

Protozoa generally have a unicellular body equipped with a permeable membrane and vacuoles to digest their food, as well as flagella or other means of transport. Depending on the species, they can survive in encrypted form under difficult environmental conditions and reactivate at the right time.

In some cases, they can lead parasitic lives and cause infections of varying degrees of risk. This is the case with amoebas, Giardia, or Trichomonas. Other species like Paramecium live in rainwater basins and are completely harmless to humans.

Fungi and yeasts

Fungi and yeast are located in an intermediate region between plants and animals and form a whole realm of life, many of which are microscopic in size.

Fungi have cells that are equipped with chitinic cell walls that are different from those of plants, and they reproduce in humid environments and reproduce using spores, which are generally asexual. In many cases, its spores act as infectious agents and infect living things with parasitic fungi, causing disease.

Of course, microscopic mushrooms do not have the traditional hyphae shape of mushrooms or other common types of mushrooms but are unicellular, devoid of flagella and motility.

In some cases they are of great benefit to humans, for example, yeasts, which are used to make bread, to ferment certain liqueurs, or to make biochemical substances such as the antibiotic penicillin produced by the fungus Penicillium.

What are microbes? Types, Bacteria, Virus, Protozoa, Fungi, and yeasts