What are microorganisms? Check the definition on this page. Note that this is not a detailed note on microorganisms but just a short lecture note.

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Microorganisms – Definition

A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells.

So, we call microorganisms all kinds of living beings that have little in common, except that they are generally so small that they cannot be seen with the naked eye and that they have to be a microscope to observe them. Among microorganisms, we also rank organisms that are not really part of the living world: viruses .[/tds_warning]

The different families of microorganisms

Microorganisms are classified according to their morphology.

They are grouped into the following families:

bacteria
protozoa
microscopic algae
microscopic fungi
viruses

Bacteria

Bacteria are made up of a cell bounded by a membrane. It is a very simple cell, in which genetic information is not protected by a nucleus (this cell is called a prokaryote )

Bacteria are larger than viruses: they are generally between 500 and 10,000 millionths of a millimeter (that is, between 0.5 and 10 thousandths of a millimeter).

Protozoa

Protozoa are small organisms, approaching a millimeter for the largest, which exist as solitary cells or colonies of cells. They do not develop the differentiated three-dimensional structures characteristic of complex multicellularity. In the form of colonies, some protozoa can nevertheless form superorganisms (eg Dictyostelium discoideum ) which exhibit high levels of cell specialization and border on multicellularity.

In biology, the term protozoan ( Protozoa ), designates protists ( eukaryotes generally unicellular and without specialized tissues ) motile heterotrophs which ingest their food by phagocytosis, unlike the two other types of protists ( protophytes and oomycetes ).

Microscopic algae

The term microalgae, sometimes called microphyte, refers to microscopic algae.

Microalgae have been consumed for thousands of years around the world. For example, traces of the consumption of various species of microalgae in Mexico during the time of the Aztecs have been found. Europe and industrialized countries use microalgae as food supplements to fight against malnutrition as well as for aquaculture.

Microscopic fungi

The group of micromycetes, microfungi, or microfungi brings together very small or microscopic eukaryotic fungi. It is an artificial category, which is likely to evolve, where we have placed organisms such as rust, but also mildew (which is not in fact a fungus ).

Viruses

Viruses are not, strictly speaking, living beings, because they are not made up of cells and do not have a life of their own. They are immobile particles, made up of a simple assembly of molecules.

However, they are capable of parasitizing (infecting) living cells and causing them to produce other viruses. Extremely small, viruses range in size from 20 to 300 millionths of a millimeter (that is, 0.02 to 0.3 thousandths of a millimeter)

THE ESSENTIAL ECOLOGICAL ROLE OF MICRO-ORGANISMS

Many microorganisms live in the soil: a single gram of good soil can contain 3 billion microorganisms! By breaking down organic matter, they allow the recycling of mineral elements essential to life.

In the aquatic environment, unicellular algae, whose total mass is greater than that of terrestrial plants, produce a very large part of the planet’s oxygen.

Other microorganisms live with plants or animals in such close association (called symbiosis) that they are absolutely essential to their survival. Man himself harbors millions of bacteria, yeasts and protozoa in his intestine!