THE MICRORGANISMS

They are invisible organisms to the naked eye. The bacteria belong to the Prokariotes' kingdom , the protozoa to  Protists, the leaven and the mildews belong to Fungi. The viruses are considered neither living neither not living things, because they live and are reproduced only inside the cells that they infect.

The bacteria

The bacteria are unicellular microorganisms. They are very important because they are responsible for the decomposition of the organic matter in mineral substances. Plants utilize the minerals for the photosynthesis and reintroduce them in the alimentary cycle.

The shape

The bacteria diameter is between 1 and 10 micrometers. The bacterial cell is encircled by a cellular membrane and by a cellular wall, a rather rigid covering that protect it. Many bacteria surfaces are provided with one or more filaments (the flagellums) that allow them to move.
If the bacterium has a round shape is called coccus, if it has a shape like a rod is called bacillum, tif it has a spiral shape is called spirillus.

Where they live

The bacteria live everywhere: in the land, in the water, in the air, on the surface or inside the body of other organisms. Often they live in colonies. If they need oxygen for living are called aerobic, if  not they are called anaerobic.

The reproduction

The bacterial multiplication happens in asexual way through  binary division:

1.      the DNA doubles itself inside the cell, forming a new chromosome, that sticks to the cellular membrane

2.      the cell divides itself forming two cells with the same genetic patrimony of the mother cell

The useful bacteria

The bacteria are very useful not only for the men but also for all the living beings. The decomposers decompose the dead organisms transforming, by means of fermentation processes, the complex substances in simple, mineral substances that are reused by the plants and  return in cycle.
This ability to transform organic substances is used for the depuration of waters.
Some bacteria improve the fertility of the soil because they live in symbiosis with the plants (Leguminosae) and transform the atmospheric nitrogen in a chemical substance that can be used by the plants.This  process is called "nitrogen fixation ".
Other useful bacteria live in the stomach of ruminants and allow the digestion of the vegetable fibers. Whitout they the cows and the sheeps couldn’t digest the grass and the hay.
Many bacteria are fundamental in the fabrication of various useful products for the men, such as foods, medicinal and other chemical products. The cheese, the butter and the yogurth derive from the fermentation of the milk made by bacteria. Thanks to the bacteria, substances of remarkable importance such as the alcohol and the antibiotics (like the streptomicina and the tetraciclina) can be produced on industrial scale.

The harmful bacteria

The harmful bacteria cause most serious diseases such as tuberculosis (supported from the Mycobacterium tuberculosis), meningitis, cholera (Vibrio comma), typhus  and tetanus. Until a century ago, the humanity was afraid for these diseases that were spreaded quickly and caused the death of thousand of people. Only at the end of the XIX century, thanks to the work of Louis Pasteur and of the German doctor Robert Koch, the bacterial origin of these diseases was discovered.

The fermentation

Fermentations are natural phenomena that the men learnt to control and to reproduce.
For example the wine and the beer are produced through the fermentation. The wine is made with the grape pressed in the vats and transformed in a mesh that after a short time begins to boil; the sugar of the grape becomes alcohol while carbon dioxide developes. The beer is produced from the barley in a similar way.Also the yogurth and the cheeses are produced by the fermentation. The flour worked with water and yeast and then cooked become bread.