Bacteria is a concept familiar to everyone. Getting cheese and yogurt, antibiotics, sewage treatment - all this is made possible by single-celled bacterial organisms. Let's get to know them better.
Who are bacteria?
Representatives of this kingdom of wildlife 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 sizes are microscopic - up to 20 microns, bacteria are studied by 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, 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 life processes: anaerobic respiration without the use of oxygen, heterotrophic and autotrophic nutrition, asexual reproduction and cyst formation during the experience of adverse conditions.conditions.
Classes of bacteria
The classification is based on different features. One of them is the shape of the cells. So, vibrios have the form of a comma, cocci - a rounded shape. Spirals have a spiral shape, and bacilli have a rod-shaped form.
In addition, bacteria are combined into groups depending on the structural features of the cell. The real ones are able to form a slimy capsule around their own cell and are equipped with flagella.
Cyanobacteria, or blue-green algae, are capable of photosynthesis and, together with fungi, are part of lichens.
Many species of bacteria are capable of symbiosis - mutually beneficial cohabitation of organisms. Nitrogen fixers settle on the roots of legumes and other plants, forming nodules. It is easy to guess what function nodule bacteria perform. They convert atmospheric nitrogen, which is so necessary for plants to develop.
Eating Methods
Prokaryotes are a group of organisms that have access to all types of food. 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 necessarily contain chlorophyll. Bacterial and plant photosynthesis are fundamentally different. In bacteria, water is not an essential 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, that is, ready-made organic substances. Such organisms use the remains of dead organisms for food andtheir life products. Bacteria of decay and fermentation are capable of decomposing all known organic substances. Such organisms are also called saprotrophs.
Some plant bacteria can form symbiosis with other organisms: together with fungi, they are part of lichens, nitrogen-fixing nodule bacteria coexist mutually beneficially with the roots of legumes.
Chemotrophs
Chemotrophs are another food group. This is a kind of autotrophic nutrition, during which, instead of solar energy, the energy of chemical bonds of various substances is used. Nitrogen-fixing bacteria are one such organism. They oxidize some inorganic compounds, while providing themselves with the necessary amount of energy.
Nitrogen-fixing bacteria: habitat
Microorganisms capable of converting nitrogen compounds also 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 leguminous plants.
Building
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 which metabolism takes place.
It should be said that nitrogen-fixing bacteria belong to the group of mutualists. Their coexistence with other organisms is mutually beneficial. ATDuring photosynthesis, the plant synthesizes carbohydrate glucose, which is necessary for life processes. Bacteria are not capable of such a process, so ready-made sugars are obtained from legumes.
Plants need nitrogen to live. There are quite a lot of this substance in nature. 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 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. It is rightly called the leader among nitrogen producers. On a hectare of land, he is able to give up to 60 kg of this element.
Nitrogen-fixing bacteria of legumes, such as rhizobitums, sinorhizobiums 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 nitrogen-forming winners, whose productivity reaches up to 560 kg per hectare of arable land.
Life processes
All nitrogen-fixing bacteria according to the characteristics of life 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 into nitrites - s alts of nitric acid. Nitrites, in turn, are converted to nitrates,are also s alts 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: the nitrates contained in the soil are converted into gaseous nitrogen. This is how the nitrogen cycle occurs in nature.
The processes of life also include the process of reproduction. It occurs by cell division in two. Much less often - by budding. Characteristic for bacteria and the sexual process, which is called conjugation. In this case, the exchange of genetic information takes place.
Since the root system releases many valuable substances, a lot of bacteria settle 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.
Pathways for bacteria to enter 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 integumentary tissues or in places where the root cells are young. The root hair zone is also a pathway for chemotrophs to enter the plant. Further, the root hairs become infected and, as a result of the active division of bacterial cells, nodules are formed. The invading cells form infectious threads that continue the process of penetration into plant tissues. With the help of a conducting system, bacterial nodules are connected to the root. Over time, a special substance appears in them -legoglobin.
By the time of manifestation of optimal activity, the nodules acquire a pink color (due to the legoglobin pigment). Only those bacteria that contain legoglobin can fix nitrogen.
The importance of chemotrophs
People have long noticed that if you dig up leguminous plants with soil, the harvest in 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 the leaf is called an oxygen factory, then nitrogen-fixing bacteria can rightly be called a nitrate factory.
Even in the 19th century, scientists drew attention to the amazing abilities of leguminous plants. Due to lack of knowledge, they were attributed only to plants and not associated with other organisms. It has been suggested that leaves can fix atmospheric nitrogen. During the experiments, it was found that legumes that grew in water lose this ability. For more than 15 years, this question has remained a mystery. No one guessed that all this was carried out by nitrogen-fixing bacteria, the habitat of which had 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 legume family, but are able to form a symbiosis with nitrogen-fixing bacteria. Potatoes, sorghum, wheat also have valuable properties.
