Bacteria - a concept that is familiar to everyone. Getting cheese and yogurt, antibiotics, wastewater treatment - all this make single-celled bacterial organisms possible. Get to know them better.
What are bacteria?
Representatives of this kingdom of wildlife represent 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 shell.
Since their microscopic sizes are up to 20 microns, bacteria are studied by the science of microbiology. Scientists have found 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, Golgi complex, EPS, lysosomes and mitochondria. But despite this, the bacterial cell is able to carry out the most important processes of life: anaerobic respiration without the use of oxygen, heterotrophic and autotrophic nutrition, asexual reproduction and cyst formation while experiencing adverse conditions.
Bacteria classes
The classification is based on various characteristics. 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 depending on the structural features 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, together with mushrooms, are 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 is performed by nodule bacteria is easy to guess. They transform atmospheric nitrogen, which plants need so much for development.
Nutrition Methods
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 must 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 sulfide, so oxygen is not released during this process.
A large group of bacteria feeds heterotrophically, i.e., prepared organic substances. Such organisms use the remnants of dead organisms and their metabolic products for nutrition. Bacteria of decay and fermentation are able to decompose all known organic substances. Such organisms are also called saprotrophs.
Some plant bacteria can form a symbiosis with other organisms: together with fungi they are part of lichens, nitrogen-fixing nodule bacteria coexist with the roots of legumes.
Hemotrophs
Chemotrophs are another type of diet . This is a type of autotrophic nutrition, during which, instead of solar energy, the 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 that can convert nitrogen compounds feed in a similar way. They are called nitrogen-fixing bacteria. Despite the fact that bacteria live everywhere, the habitat of this particular 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 the plant. In this case, thickenings are formed, inside of which a metabolism occurs.
It is worth saying that nitrogen-fixing bacteria belong to the group of mutualists. Their coexistence with other organisms is mutually beneficial. During photosynthesis, the plant synthesizes the glucose carbohydrate, which is necessary for vital processes. Bacteria are not capable of such a process, therefore, finished sugars are obtained from legumes.
Plants need nitrogen to live. This substance in nature is quite a large amount. 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 absorb atmospheric nitrogen and translate it into a form suitable for plants.
Performance
What function are 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.
Bean nitrogen-fixing bacteria, such as rhizobitum, sinorizobium and others, are also good workers. They are able to enrich a hectare of land with nitrogen weighing up to 390 kg. Perennial leguminous plants are home to the winners of nitrogen production, the productivity of which reaches up to 560 kg per hectare of arable land.
Life processes
All nitrogen-fixing bacteria according to the features of vital processes can be combined into two groups. The first group is nitrifying. The essence of metabolism in this case is a chain of chemical transformations. Ammonium, or ammonia, is converted to nitrites - salts of nitric acid. 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 in nature occurs.
The processes of reproduction also include the process of reproduction. It occurs by dividing cells in two. Much less often - by budding. Also characteristic of bacteria is the sexual process called conjugation. At the same time, genetic information is exchanged.
Since the root system releases a lot of valuable substances, a lot of bacteria inhabit it. They convert plant debris into substances that plants can absorb. As a result, the soil layer around it acquires certain properties. It is called the rhizosphere.
Routes of bacteria to root
There are several ways to introduce bacterial cells into the tissues of the root system. This can occur due to damage to the integumentary tissues or in places where the root cells are young. The root hair zone is also the pathway for chemotrophs to enter the plant. Further, root hairs become infected and nodules form as a result of active division of bacterial cells. Intruded cells form infectious filaments, which continue the process of penetration into plant tissues. Using a conductive system, bacterial nodules are connected to the root. Over time, a special substance appears in them - legoglobin.
By the time optimal activity is manifested, the nodules become pink (due to the pigment legoglobin). Only those bacteria that contain legoglobin can fix nitrogen.
The value of chemotrophs
People have long noticed that if digging up legumes with soil, the crop in this place will be better. Actually, the point 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 leaf is called a factory for the production of oxygen, then nitrogen-fixing bacteria can rightfully be called a factory for the production of nitrates.
Back in the 19th century, scientists drew attention to the amazing abilities of legumes. Due to lack of knowledge, they were attributed only to plants and were not associated with other organisms. It has been suggested that leaves can fix atmospheric nitrogen. During the experiments, it was found that the legumes that grew in water lose this ability. For over 15 years this question has remained a mystery. No one knew that all this is done by nitrogen-fixing bacteria, whose habitat has not been studied. It turned out that the point is the symbiosis of organisms. Only together can legumes and bacteria produce nitrates for plants.
Now scientists have identified more than 200 plants that do not belong to the legume family, but are able to form a symbiosis with nitrogen-fixing bacteria. Potatoes, sorghum, wheat also have valuable properties.