Bacteria is a familiar concept to everyone. Getting cheese and yogurt, antibiotics, wastewater treatment - all this makes possible single-celled bacterial organisms. Let's get to know them better.
Who are the bacteria?
Representatives of this kingdom of naturethey are the only group of prokaryotes - organisms whose cells lack a nucleus. But this does not mean that they do not contain 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 20um, bacteria is studying the science of microbiology. Scientists have found that prokaryotes can be single-celled or unite in colonies. They have a rather primitive structure. In addition to the nucleus, the bacteria lack all types of plastids, the Golgi complex, EPS, lysosomes and mitochondria. But despite this, the bacterial cell is able to carry out the most important vital processes: anaerobic respiration without the use of oxygen, heterotrophic and autotrophic nutrition, asexual reproduction and the formation of cysts during the experience of adverse conditions.
Bacteria classes
The classification is based on various signs. One of them is the shape of the cells. So, vibrios have the form of a comma, cocci - a rounded shape. Spirals have the appearance of a spiral, and bacilli have a rod-shaped form.
In addition, bacteria are grouped together depending on the structure of the cell. These are able to form a mucous capsule around their own cells and are equipped with flagella.
Cyanobacteria, or blue-green algae, are capable of photosynthesis and, along with fungi, form part of lichens.
Many types of bacteria are capable of symbiosis -mutually beneficial cohabitation of organisms. Nitrogen fixers settle on the roots of legumes and other plants, forming nodules. What function do nodule bacteria perform, it is easy to guess. They convert atmospheric nitrogen, which plants need so much for development.
Nutrition Methods
Prokaryotes are a group of organisms thatall 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 they must contain chlorophyll. Bacterial and plant photosynthesis are significantly different. In bacteria, water is not a necessary reagent. Hydrogen or hydrogen sulfide can serve as an electron donor; therefore, oxygen is not emitted during this process.
A large group of bacteria feeds heterotrophically, t.e. prepared organic substances. Such organisms use to feed the remains of dead organisms and their metabolic products. The bacteria of decay and fermentation are capable of decomposing all known organic matter. Such organisms are also called saprotrophs.
Some plant bacteria can formsymbiosis with other organisms: together with the fungi they form part of lichens, nitrogen-fixing nodule bacteria coexist mutually with the roots of legumes.
Chemotrophs
Another group by type of food arechemotrophs. This is a type of autotrophic nutrition, during which, instead of solar energy, energy of chemical bonds of various substances is used. 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
Microorganisms feed in the same way,able to convert nitrogen compounds. They are called nitrogen-fixing bacteria. Despite the fact that bacteria live everywhere, the habitat of this particular species is 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. At the same time, thickening occurs, within which the metabolism occurs.
It is worth saying that nitrogen-fixing bacteriabelong to the group of mutualists. Their coexistence with other organisms is mutually beneficial. During photosynthesis, the plant synthesizes carbohydrate glucose, which is necessary for vital processes. Bacteria are incapable of such a process, so the finished sugars are obtained from legumes.
Plants need nitrogen to live.This substance in nature is quite a large number. 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 suitable for plants.
Performance
What is the function of nitrogen-fixing bacteria,can be seen on the example of the chemotrophic bacterium azospirillum. This organism lives on the roots of cereals: barley or wheat. He is rightly called the leader among nitrogen producers. He is able to give up to 60 kg of this element per hectare of land.
Nitrogen-fixing legume bacteria, such asrhizobitums, shinorizobiums and others are also good "workers". They are able to enrich a hectare of land with nitrogen weighing up to 390 kg. The perennial legume plants, whose productivity reaches up to 560 kg per hectare of arable land, inhabit perennial leguminous plants.
Life processes
All nitrogen-fixing bacteria by featureslife processes can be combined into two groups. The first group is nitrifying. The essence of metabolism in this case lies in the chain of chemical transformations. Ammonium, or ammonia, is converted into nitrites - nitric acid salts. Nitrites, in turn, are converted to nitrates, which are also salts of this compound. In the form of nitrates, nitrogen is better absorbed by the root system of plants.
The second group is called denitrifiers. They carry out the reverse process: nitrates contained in the soil are converted into gaseous nitrogen. Thus, the nitrogen cycle occurs in nature.
The processes of life also includebreeding process. It occurs by dividing the cells in two. Much less often - by budding. Characteristic of bacteria and the sexual process, which is called conjugation. When this occurs, the exchange of genetic information.
Since the root system allocates a lot of valuableThere are a lot of bacteria on it. They convert plant residues into substances that plants can absorb. As a result, the layer of soil around acquires certain properties. It is called the rhizosphere.
Ways of penetration of bacteria in the root
There are several ways to implementbacterial cells in the tissue of the root system. This can occur due to damage to the epithelial tissues or in places where the root cells are young. The zone of root hairs is also a way for chemotrophs to penetrate the plant. Further, the root hairs are infected and as a result of the active division of bacterial cells nodules are formed. Introduced cells form infectious filaments that continue the process of penetration into plant tissue. By means of the conducting system, bacterial nodules are connected with the root. Over time, they appear a special substance - legoglobin.
By the time the optimum activity is manifested, the nodules acquire a pink color (due to the legoglobin pigment). Only bacteria that contain legoglobin can fix nitrogen.
Chemotrophic Significance
People have long noticed that if you dig up legumesplants with soil, the harvest at this place will be better. In fact, the essence is not in the process of plowing. This soil is more enriched with nitrogen, so necessary for the growth and development of plants.
If the leaf is called an oxygen factory, then the nitrogen-fixing bacteria can rightly be called a nitrate factory.
Еще в 19 веке ученые обратили внимание на amazing ability of legumes. Due to a lack of knowledge, they were attributed only to plants and were not associated with other organisms. It has been suggested that the leaves can fix atmospheric nitrogen. During the experiments, it was found that legumes, which grew in water, lose this ability. For more than 15 years, this question has remained a mystery. No one guessed that they were implementing all this nitrogen-fixing bacteria, whose habitat was not studied. It turned out that the matter is a symbiosis of organisms. Only together can legumes and bacteria produce nitrates for plants.
Now scientists have identified more than 200 plants thatdo not belong to the legume family, but are able to form a symbiosis with nitrogen-fixing bacteria. Potatoes, sorghum, wheat also have valuable properties.
