Bacteria nitrifying. The importance of nitrifying bacteria

According to the type of food, all known living organisms are divided into two large species: hetero- and autotrophs. A distinctive feature of the latter is their ability to independently construct new elements from carbon dioxide and other inorganic substances.

Sources of energy that support their vital activity, cause their division into photo-fluotrophs (source-light) and chemoautotrophs (source-mineral substances). And, depending on the name of the substrate, which oxidizes chemoauthortopaths, they are divided into hydrogen and nitrifying bacteria, as well as sulfur and iron bacteria.

This article will be devoted to the most common group - nitrosating bacteria.

History of the discovery

In the middle of the 19th century, German scientists proved that the process of nitrification is biological. Experimentally, they showed that the addition of chloroform to the sewage water stopped the oxidation of ammonia. But they could not explain why this is happening.

This was accomplished several years later by the Russian scientist Vinogradsky. He singled out two groups of bacteria, which gradually took part in the process of nitrification. Thus, one group ensured the oxidation of ammonium to a nitrogenous acid, and the second group of bacteria was responsible for its conversion to nitric acid . All nitrifying bacteria involved in this process are gram-negative.

Features of the oxidation process

The process of nitrite formation by ammonium oxidation has several stages, during which nitrogen-containing compounds with different degrees of oxidation of the NH group are formed.

The first product of ammonium oxidation is hydroxylamine. Most likely, it is formed due to the inclusion of molecular oxygen in the NH ₄ group, although this process has not been finally proved and remains controversial.

Further hydroxylamine is converted to nitrite. Presumably, the process is carried out through the formation of NOH (giponitrite) with the liberation of nitrous oxide. In this case, scientists consider the production of nitrous oxide as just a by-product of the synthesis, due to the reduction of nitrite.

In addition to the production of chemical elements, during the process of denitrofication a large amount of energy is released. Similar to what happens in heterotrophic aerobic organisms, in this case the synthesis of ATP molecules is associated with oxidation-reduction processes, as a result of which electrons are transferred to oxygen.

During the oxidation of nitrite, an important role is played by the process of reverse electron transport. Inclusion of its electrons in the chain occurs directly in cytochromes (C-type and / or A-type), and this requires a fairly large expenditure of energy. As a result, chemoautotrophic nitrifying bacteria are fully provided with the necessary energy reserve, which is used for the processes of building and assimilating carbon dioxide.

Types of nitrifying bacteria

In the first phase of nitrification, four kinds of nitrobacteria take part:

• Nitrosomonas;
• Nitrocystis;
• Nitrosolus;
• Nitrospira.

By the way, on the proposed image you can see nitrifying bacteria (photo under the microscope).

Experimental way among them is quite difficult, and often it is impossible to single out one of the crops, therefore their consideration is mostly complex. All of the listed microorganisms have a size of up to 2-2.5 microns and are predominantly oval or rounded (with the exception of nitrospires, which have the appearance of a stick). They are capable of binary division and directed movement due to flagella.

The second phase of nitrification involves:

• Genus Nitrobacter;
• Genus of nitrosoin;
• Nitrococus.

The most studied strain of bacteria of the genus Nitrubacter, named after its discoverer, Vinogradsky. These nitrifying bacteria have a pear-like form of cells, multiply by budding, with the formation of a mobile (due to the flagellum) daughter cell.

Structure of bacteria

The nitrified bacteria studied have a similar cellular structure with other Gram-negative microorganisms. Some of them have a sufficiently developed system of internal membranes forming a stack in the center of the cell, while in others they are located more on the periphery or form a structure in the form of a bowl consisting of several sheets. Apparently, it is with these formations that enzymes are associated that are involved in the oxidation process of specific substrates by nitrifiers.

Type of nourishment of nitrifying bacteria

Nitrobacteria belong to obligate autotrophs because they can not use exogenous organic substances. However, the ability of some strains of nitrifying bacteria to use certain organic compounds has nevertheless been demonstrated experimentally.

It was found that a substrate containing yeast autolysates, serine and glutamate in low concentrations, stimulated the growth of nitrobacteria. This occurs both in the presence of nitrite and in its absence in the nutrient medium, although the process proceeds much more slowly. Conversely, in the presence of nitrite, the oxidation of acetate is suppressed, but the incorporation of its carbon into the protein, various amino acids and other cellular components is significantly increased.

As a result of multiple experiments, data were obtained that nitrifying bacteria can still switch to heterotrophic nutrition, but how productive and how long they can exist in such conditions remains to be seen. While the data is sufficiently contradictory to make final conclusions on this matter.

Habitat and the importance of nitrifying bacteria

Nitrifying bacteria belong to chemoautotrophs and are widely distributed in nature. They are found everywhere: in soil, various substrates, and also reservoirs. The process of their vital activity makes a great contribution to the general cycle of nitrogen in nature and can in fact reach enormous proportions.

For example, a microorganism such as the nitrocystis oceans, isolated from the Atlantic Ocean, refers to obligate halophiles. It can exist only in seawater or substrates containing it. For such microorganisms, not only the habitat is important, but also constants such as pH and temperature.

All known nitrifying bacteria are classified as obligate aerobes. In order to oxidize ammonium to nitrous acid, and nitrous acid to nitric acid, they need oxygen.

Habitat conditions

Another important point, which scientists discovered, was that the place where nitrifying bacteria live should not contain organic substances. A theory was advanced that these microorganisms can not in principle use organic compounds from outside. They were even called obligate autotrophs.

Subsequently, the harmful effects of glucose, urea, peptone, glycerol and other organics on nitrifying bacteria have repeatedly been proven, but experiments do not stop.

The importance of nitrifying bacteria for soil

Until recently, it was believed that nitrifiers favorably affect the soil, increasing its fertility by splitting ammonium to nitrates. The latter not only are well absorbed by the plants, but also in themselves increase the solubility of some minerals.

However, in recent years scientific views have undergone changes. The negative effect of the microorganisms described on the fertility of the soil was revealed. Bacteria nitrifying, forming nitrates, acidify the environment, which is not always a positive moment, and also to a greater extent provoke the saturation of the soil with ammonium ions than nitrates. Moreover, nitrates have the ability to be reduced to N ₂ (during denitrification), which in turn leads to a depletion of the soil with nitrogen.

What is the danger of nitrifying bacteria?

Some strains of nitrobacteria in the presence of an organic substrate can oxidize ammonium, forming hydroxylamine, and subsequently nitrites and nitrates. Also, as a result of such reactions, hydroxamic acids may occur. Moreover, a number of bacteria perform the process of nitrification of various compounds containing nitrogen (oximes, amines, amides, hydroxamates and other nitro compounds).

The scale of heterotrophic nitrification under certain conditions can be not only enormous, but also very detrimental. The danger lies in the fact that during such transformations, toxic substances, mutagens and carcinogens are formed. Therefore, scientists are working closely on the study of this topic.

Biological filter, which is always at hand

Nitrifying bacteria are not an abstract concept, but a very common form of life. Moreover, they are often used by man.

For example, in the biological filters for aquariums are precisely these bacteria. This type of cleaning is less expensive and not as labor-consuming as mechanical cleaning, but at the same time it requires certain conditions to be met in order to ensure the growth and vital activity of nitrifying bacteria.

The most favorable microclimate for them is the ambient temperature (in this case water) of the order of 25-26 degrees Celsius, a constant supply of oxygen and the presence of aquatic plants.

Nitrifying bacteria in agriculture

In order to increase the yield, farmers use various fertilizers containing nitrifying bacteria.

Soil nutrition in this case is provided by nitrobacteria and azotobacteria. These bacteria extract necessary substances from the soil and water, which form a sufficiently large amount of energy during the oxidation process. This is the so-called process of chemosynthesis, when the energy obtained goes to the formation of complex molecules of organic origin from carbon dioxide and water.

For these microorganisms, not necessarily the supply of nutrients from their environment - they can produce them themselves. So, if green plants, which are also autotrophs, need sunlight, then for nitrifying bacteria it is not necessary.

Self-cleaning of soil

Soil is an ideal substrate for the growth and reproduction of not only plants, but also many living organisms. Therefore, its normal state and balanced composition is extremely important.

It should be remembered that biological cleansing of the soil is provided, among other things, by nitrifying bacteria. They, while in soil, water bodies or humus, convert ammonia, which secrete other microorganisms and waste organic materials, into nitrates (to be more precise, in the salt of nitric acid). The whole process consists of two stages:

1. Oxidation of ammonia to nitrite.
2. Oxidation of nitrite to nitrate.

In this case, each stage is provided by separate types of microorganisms.

The so-called vicious circle

The cycle of energy and the maintenance of life on Earth is possible due to the observance of certain regularities in the existence of all living things. At first glance it is difficult to understand what is at issue, but in fact everything is quite simple.

Let's imagine the following picture from the school textbook:

1. Inorganic substances are processed by microorganisms and thereby create favorable conditions in the soil for plant growth and nutrition.
2. They, in turn, are an indispensable source of energy for most herbivores.
3. The next chain of this vital link are predators, whose energy is, respectively, their herbivorous counterparts.
4. People are known to belong to higher predators, which means that we can receive energy from both the plant world and the animal.
5. And already our own residues of vital activity, as well as those of plants and animals, serve as a nutrient substrate for microorganisms.

Thus, it turns out a vicious circle, continuously functioning and ensuring the life of all life on Earth. Knowing these principles, it is not difficult to imagine how multifaceted and in fact unlimited is the power of nature and all living things.

Conclusion

In this article, we attempted to answer the question of what nitrifying bacteria are in biology. As you can see, despite irrefutable evidence of the vital activity, functioning and influence of these microorganisms, there are still many controversial issues requiring further experimental research.

Nitrifying bacteria are referred to as chemotrophs. The source of energy for them are various minerals. Despite their microscopic size, these living organisms exert a tremendous influence on the world around them.

As is known, chemotrophs can not absorb organic compounds that are in the substrate (soil or water). They, on the contrary, produce building material for the creation of a living and functioning cell.