Bacteria are small, mostly colorless cells without real nucleus which have different forms, need different living conditions and are spread everywhere.

As the bacteria are only 0,001 mm on an average, it has become possible to examine them more carefully only since the middle of the last century, since the microscopic technology has developed. The statement of Robert Koch (1876) that certain bacteria cause certain infection diseases was the basis for the bacteriology.

There are different morphological forms of the bacteria: spherical, rod-shaped, comma-shaped, helical and branched threads.

The cells of bacteria have a lot simplier structure than the cells of the plants and animals. They have no real nucleus, i.e., they own the substances which other living beings have in the core, however they don’t have a membrane surrounding the core. For dissimilation they have the cell parts which are substantially simplier built than the mitochondria. They have no chloroplasts. Their cell wall contains no cellulose.

In spite of the simple structure and the small size every bacterial cell can perform assimilation and dissimilation.

The big group of the heterotroph living bacteria is divided into saprophytes, parasites and symbiotes.

Saprophytes eat the organic materials of dead animals, nutrients, dead leaves, excrement. Specifically they live in the ground (25 billion bacteria per gramme). If nitrogen-containing materials are diminished by saprophytes, it is called putrefaction, which is recognised by the bad smell (e.g., H₂S).

The parasitic living bacteria live on organic materials of living organisms, they damage and cause infection illnesses.

Symbiotes live together with other kinds of organisms. Besides, they have a mutual use.

Some types of bacteria live autotrophic. To form their endogenous substances, they use the inorganic substances and light energy (photosynthesis) or chemically energy of other materials (chemosynthesis).

Different kinds of bacteria have different dissimilation. They perform respiration or fermentation. With both kinds of the dissimilation organic materials (mostly carbohydrates) are used for power production. During breathing the substances completely dissolve in carbon dioxide and water and a large amount of energy is released. During some fermentation processes the substances do not dissolve completely, and only a small amount of energy is released for vital processes of the corresponding bacteria. There are bacteria which need oxygen to the live (aerobic bacteria), and those which use no oxygen (anaerobic bacteria).

Not only different bacteria differ in the nutrients and in the use of oxygen, but also they are adapted to different temperature. Most bacteria are active with from 10 to 40 °C. They all need water for the realisation of the metabolism processes.

With favourable living conditions all bacteria increase by cell division (asexual reproduction).

5.3 Formation and germination of a hypnospore

1- old bacterial walls, 2 - capsule of the hypnospore 3 - cell contents for storage materials

Some bacterial kinds can form hypnospores. These bacteria are called bacilli. When living conditions deteriorate, they deliver water from the cell and form a capsule around the cell contents in which the cell contents are enclosed. The hypnospore are resistant to very high and very low temperatures (100 C,-250 °C), dryness and many chemical materials. The cell contents live with very slow metabolism on the accumulating substances and remain long viable. The hypnospores do not serve the increase.

If the living conditions improve, the cell contents from the capsule grow by water admission: hypnospore germinates.

Bacteria play a very big role in nature, economy and medicine.

Many bacterial kinds are useful. Saprophites located in the ground are useful, because they diminish the dead organic materials to their components materials (water, carbon dioxide, salts) on which the autotrophen plants live. The circulation of the substances takes place in nature with the help of the saprophytes.

The more there are dead organic substances in the ground, the better the plants can live. For centuries the people fertilise the ground of their fields with organic fertilizer.

Now you can read two examples of saprophytes use.

Nitrogen available in the air cannot be used by plants. Only few bacterial kinds are able to do this, one of these bacterial kinds lives in the roots on legumes, namely in the thickening of the roots which is known as nodule. These nodule bacteria use a part of carbohydrates formed by plants and produce protein, while they connect nitrogen of the air with it. These proteins are used by legumes for their growth. If there is not enough nitrogen exists for the plant nutrition in the form of salts in the ground, the legumes, nevertheless, can live with the help of the nodule bacteria. If the human leaves the roots of the legumes with the harvest in the ground, he doesn’t have to fertilise the ground with nitrogen salts. This is an economic advantage. Other bacterial kinds live as symbionts in the digestive canal on herbivores (e.g., cows). These bacteria diminish the cellulose of the herbal food for their own assimilation. The herbivores, which unlike people, are unable to diminish the cellulose, can use the contents of the herbal cells with the help of the symbionts. They also live on large amounts of the symbionts. As the human uses animals meat and milk his food, these symbionts have indirectly great importance for the human food.

5.4 Carbon circulation in the nature

The bacteria which cause the milk acid fermentation have direct use for the human food. Sour milk, cheese and bread are produced with their help. Vegetables and feed are also preserved with their help, because lactic acid originating with the fermentation prevents the increase of putrefaction bacteria. Thus, the sour vegetables and sour feed are still usable after months for food.

In last decades bacterial activity in metabolism has been increasingly used in industry. Drugs, vitamins, enzymes are produced among other things with the help of bacterial kinds.

However, many bacterial kinds are very injurious. Saprophytes can make human food or feed for domestic animals useless by fermentation or putrefaction if this process isn’t prevented by certain measures. Such measures are freezing, cooking, drying, salting or sugaring.

Other bacterial kinds are not only injurious, but even critical for people, animals and plants. The parasitic bacteria damage the living beings not only because they take away nutrients from them, but also because they eliminate poisonous toxins. Bacteria can cause diseases, such as the lung tuberculosis (cause: Bacterium tuberculosis), and dysenteria (cause: Bacterium dysenteriae).

The transference of the parasitic bacteria occurs directly from sick people to healthy ones; or indirectly through objects (food, water, cups among other things).

When agents of disease penetrate into the body, it is named infextion. The agents of disease increase and form toxins. At the same time the organism of the landlord becomes sensitive to the penetrated agents and toxins and forms the antibodies which destroy bacteria or its toxins. If the body is not resistant enough, a relevant disease appears. The time of the infection until the appearance of clinical picture is called incubation time. Its length is different depending on illness and strength of the body (examples: tuberculosis – several weeks, dysenteria – from 3 to 8 days). The clinical picture of lung tuberculosis shows in cough, fever, tiredness; the clinical picture of dysenteria appears in diarrhea with blood and fever. The ill organism can be helped with drugs and vaccination with antibodies (remedial vaccination).

After the infectious disease, the body is still able to form the antibodies for a long time.

The origin or spreading of infectious disease can be prevented by preventive measures. Such measures are cleanness, healthy food, enough sleep and protective inoculations. The body thereby becomes resistant. The control of the drinking water and food by the government, as well as the separation of sick people from healthy, are also essential measures. In the countries where the population is inoculated against all major infectious diseases, these diseases have strongly been decreased. These are mostly social causes that in many countries also even today millions people die of infectious diseases.

1. Answer the questions using the information from the text:

1. What is the most important difference in the structure of cells between the bacteria and the other organisms?

2. What is bacteriology?

3. How can the bacteria be differentiated by their shape?

4. Which two groups are the bacteria divided in after assimilation?

5. What are saprophytes and symbionts in general?

6. Which two groups are the bacteria divided into after dissimilation?

7. What is fermentation?

8. Which material is glucose diminished into without oxygen consumption by bacteria?

9. How do aerobic and anaerobic bacteria differ?

10. What is splitting by the bacteria?

11. What do hypnospores make under favourable living conditions?

12. What is an organic fertilizer?

13. Which abilities does nodule bacterium have?

14. Describe the sausage which became useless by bacteria.

15. What is the name of the toxic metabolism products formed by bacteria?

16. What is infection, incubation time, clinical picture?

17. What vaccination does a sick person receive? Why?

18. What vaccination should a healthy person receive? Why?

2. Structure of bacterial cells

1. Describe the structure of bacterial cells.

2. Compare the cells structure of plants, animals and bacteria.