Nitrogen-fixing bacteria: habitat, functions

Bacteria - a concept that is well known to everyone. Getting cheese and yogurt, antibiotics, wastewater treatment - all this makes unicellular bacterial organisms possible. We will get to know them closer.

Who are the bacteria?

Representatives of this realm of living nature are the only group of prokaryotes - organisms whose cells lack nuclei. But this does not mean that they do not contain any hereditary information at all. DNA molecules are freely located in the cytoplasm of the cell and are not surrounded by a membrane.

Since their size is microscopic - up to 20 μm, the bacteria is studied by the science of microbiology. Scientists have found out that prokaryotes can be unicellular or unite in colonies. They have a fairly primitive structure. In addition to the nucleus, bacteria are deprived of all types of plastids, the Golgi complex, EPS, lysosomes and mitochondria. But despite this, the bacterial cell is capable of carrying out the most important processes of vital activity: anaerobic respiration without the use of oxygen, heterotrophic and autotrophic nutrition, asexual reproduction and cyst formation during the experience of unfavorable conditions.

Classes of bacteria

The classification is based on different signs. One of them is the shape of cells. So, the vibrios look like a comma, the cocci is a round shape. The spiral has spirals, and the bacillus form is bacilli.

In addition, the bacteria are grouped according to the structure of the cell. The present can form a slimy capsule around their own cells and are equipped with flagella.

Cyanobacteria, or blue-green algae, are capable of photosynthesis and, together with fungi, are part of lichens.

Many types of bacteria are capable of symbiosis - a mutually beneficial cohabitation of organisms. Azotfixers settle on the roots of legumes and other plants, forming nodules. What function is performed by nodule bacteria, it is easy to guess. They convert atmospheric nitrogen, which is so necessary for plants to develop.

Means of Nutrition

Prokaryotes are a group of organisms to which all methods of nutrition are available. So, green and purple bacteria feed autotrophically, due to solar energy. Due to the presence of plastids, they can be painted in different colors, but necessarily contain chlorophyll. Bacterial and plant photosynthesis are significantly different. In bacteria, water is not a required reagent. The electron donor can be hydrogen or hydrogen sulphide, so oxygen is not released during this process.

A large group of bacteria feeds heterotrophically, ie, ready organic substances. Such organisms use to feed the remains of dead organisms and the products of their vital functions. The bacteria of putrefaction and fermentation are capable of decomposing all known organic substances. Such organisms are also called saprotrophs.

Some plant bacteria can form a symbiosis with other organisms: they are included in the composition of lichens along with mushrooms, nitrogen-fixing nodule bacteria co-exist with the roots of leguminous bacteria.

Hemotrophs

Another group on the type of food are hemotrophs. This is a kind of autotrophic nutrition, during which energy of chemical bonds of various substances is used instead of solar energy. Nitrogen-fixing bacteria belong to such organisms. They oxidize some inorganic compounds, while providing themselves with the necessary amount of energy.

Nitrogen-fixing bacteria: habitat

Similarly, microorganisms that are capable of converting nitrogen compounds are also fed. They are called nitrogen-fixing bacteria. Despite the fact that the bacteria live everywhere, the habitat of this species is the soil. Or rather, the roots of legumes.

Structure

What is the function of nodule bacteria? It is due to their structure. Nitrogen-fixing bacteria are clearly visible to the naked eye. Settling on the roots of legumes and cereals, they penetrate into the plant. In this case, thickenings are formed, inside which a metabolism takes place.

It is worth saying that nitrogen-fixing bacteria belong to the group of mutualists. Their coexistence with other organisms is mutually beneficial. In the course of photosynthesis, the plant synthesizes the carbohydrate glucose, which is necessary for vital processes. Bacteria are not capable of such a process, so ready-made sugars are obtained from beans.

Plants for life need nitrogen. This substance in nature is large enough. For example, the nitrogen content in the air is 78%. However, in this state plants are not able to absorb this substance. Nitrogen-fixing bacteria assimilate atmospheric nitrogen and convert it into a form convenient for plants.

Performance

What function is performed by nitrogen-fixing bacteria, one can be convinced by the example of a hemotrophic bacterium azospirillum. This organism lives on the roots of cereals: barley or wheat. He is rightly called the leader among producers of nitrogen. On a hectare of land, he is able to give up to 60 kg of this element.

Nitrogen-fixing bacteria of legumes, such as rhizobites, sinorizobiums and others, are also good "workers". They are able to enrich a hectare of land with nitrogen up to 390 kg. The perennial legumes are home to the winners of nitrogen formation, whose productivity reaches up to 560 kg per hectare of arable land.

Life processes

All nitrogen-fixing bacteria according to the specific features of life processes can be combined into two groups. The first group is nitrifying. The essence of the metabolism in this case lies in the chain of chemical transformations. Ammonium, or ammonia, is converted into nitrites, salts of nitric acid. Nitrites, in turn, turn into nitrates, which are also the salts of this compound. In the form of nitrates, nitrogen is better assimilated by the root system of plants.

The second group is called denitrification. They carry out the reverse process: the nitrates contained in the soil are converted to nitrogen gas. Thus there is a cycle of nitrogen in nature.

The process of reproduction is also referred to as vital processes. It happens by dividing the cells in two. Much rarer - by budding. Characteristic for bacteria and the sexual process, which is called conjugation. At the same time, genetic information is exchanged.

Since the root system allocates many valuable substances, there are a lot of bacteria on it. They convert plant residues into substances that are capable of absorbing plants. As a result, a layer of soil around acquires certain properties. It is called the rhizosphere.

Pathways of penetration of bacteria into the root

There are several ways to introduce bacterial cells into the tissues of the root system. This can occur due to damage to the coverslips or in places where the root cells are young. The zone of the root hairs is also the path of penetration of the hemotrophs into the plant. Further, the root hairs become infected and as a result of active division of bacterial cells, nodules are formed. The introduced cells form infectious filaments, which continue the process of penetration into plant tissues. With the help of a conducting system, bacterial nodules are connected to the root. With the passage of time, a special substance appears in them - llegoglobin.

By the time of optimal activity, the nodules become pink in color (due to the pigment of the legoglobin). Only bacteria that contain leogoglobin are able to fix nitrogen.

Importance of chemotrophs

People have long noticed that if you dig up legumes with soil, the harvest at this place will be better. In fact, the essence is not in the process of plowing. Such soil is more enriched with nitrogen, which is so necessary for the growth and development of plants.

If a sheet is called an oxygen production plant, then nitrogen-fixing bacteria can rightfully be called a nitrate production plant.

Back in the 19th century, scientists drew attention to the amazing abilities of leguminous plants. Due to lack of knowledge, they were only attributed to plants and not associated with other organisms. It was suggested that the leaves can fix atmospheric nitrogen. During the experiments it was found out that the legumes that have grown in water, lose this capacity. For more than 15 years, this issue remained a mystery. Nobody guessed that all of these nitrogen-fixing bacteria are carried out, the habitat of which has not been studied. It turned out that the matter is in the symbiosis of organisms. Only together, legumes and bacteria can produce nitrates for plants.

Now scientists have identified more than 200 plants that do not belong to the family of legumes, but are able to form a symbiosis with nitrogen-fixing bacteria. Potatoes, sorghum, wheat also have valuable properties.