Ever imagined being Alice in Lewis Carroll’s book, Alice in Wonderland? Yes? Now imagine that instead of shrinking up to 25 cm, Alice shrunk to an even smaller size, for example 10 μm? (A micrometer, is one thousandth of a millimeter). Alice would have found so many different forms, classes and sizes of microorganisms that her wonderful adventure would need a longer story than the saga of the Game of Thrones, and probably more interesting (in my view: D)!
As the main focus of this blog are microorganisms, we want to begin by telling you, who are they? Where are they? How are they? Then, it would be easier to think about their existence and their functions, as well as their relationships with the living and non-living environment. Ahh and by 'non-living', we mean the chemical and physical component of the environment as water, climate, light and not the world of the Walking Dead! (Don't be scared!)
By definition, microbe (from the Greek: "micrós" = "small" and "bios" = "life") means a small living thing. Microorganisms are too small to be seen by naked eye. Therefore, we need to use microscopes to see them. They are so tiny that you could have a billion microbes in a teaspoon of soil (which is the same number of humans currently living in Africa).
Unfortunately, the fact of microorganisms not being visible by the naked eye, led us to play them down for a long time. Currently we are discovering both its functions and how they affect all aspects of life on earth. Today we know that microbes were the first life forms of the planet, being around 3,500 million years ago. Microbes possess an impressive variety of forms and can exist in one to a multitude of environments such as hot springs, Antarctic ice or inside the body of plants and animals. As they are so diverse, we can divide them into 6 groups:
They are unicellular microorganisms (complete organism is a single cell) and these cells are of the prokaryotic type, which unlike the eukaryotes (plants, animals, fungi) are simpler since they do not have a nucleus or organelles with a membrane. Bacteria can have sizes between 0.2-700 μm and very different forms, according to which they can be said to be: spherical (cocci), bar (bacilli), spiral (espirilos), comas (vibrios).
Like bacteria, they are unicellular microorganisms of the prokaryotic type but with a different evolutionary history. Initially, they were thought to be exclusive to extreme environments, as they were frequently found in environments with very high temperatures (such as hot springs) or very saline lakes (such as the Dead Sea). Currently it is known that they can be found in more environments such as in the soil, oceans, lakes and intestines of some animals. Archaeas also have very varied forms (spherical, bar, spiral, lobular, rectangular, etc).
Unlike bacteria and archaea, fungi are eukaryotic, meaning they have cells with a defined nucleus, wrapped in a membrane. Fungi can be very complex unicellular or multicellular organisms (formed by many cells). They are found in almost any habitat, but mainly in the soil or in plant material. Among the unicellular forms of fungi, we find yeasts (like Saccharomyces), which are oval microorganisms larger than bacteria (between 6 and 20 μm), very important in the production of bread and brewing. Other fungi are shaped like filaments (filamentous fungi) that may or may not form macroscopic bodies like the ones we see growing on decaying trees or the famous Amarita muscaria.
They are unicellular eukaryotic microorganisms. They have different shapes and sizes ranging from an amoeba that can change its shape to paramecium as a fixed form. The protozoa can move using pseudopodia (like in Amoeba), flagella (in Trypanosoma) or cilia (in Paramecium). Protozoa live in a wide variety of humid habitats, including freshwater, marine environments and soil. These microorganisms can also live as free-living entities or parasites (removing nutrients from other living organisms), absorbing or ingesting organic compounds from the environment.
Algae are photosynthetic eukaryotic organisms, that is, with the capacity to produce their own food from light, water and carbon dioxide. As a result of photosynthesis, algae produce oxygen and carbohydrates that are used by other organisms, including animals. Most algae live in fresh or marine water, where they can float freely or adhere to the bottom. Some algae can grow on rocks, soil or vegetation (if there is enough moisture). Some algae form associations with fungi to form lichens. The most unusual habitats of algae are the hairs of sloth bears and polar bears.
They are the smallest and different of all the microbes mentioned here. It is said that they are so small that 500 million rhinoviruses (which cause the common cold) could enter the head of a pin. They are the only acellular (not formed by cells) and are only composed of a nucleus of genetic material (DNA or RNA) surrounded by a protective layer composed of proteins. Viruses are only considered alive when they can multiply within the cells of other living beings. In this sense, viruses are parasites of other life forms.