Cyanobacteria combine photosynthesis and atmospheric nitrogen fixation in one cell. Bacteria and cyanobacteria

Due to the presence of unique features of the morphofunctional organization, wide distribution in the biosphere and great ecological significance, this division (type) of bacteria (Fig. 7.12) is considered separately.

Cyanobacteria are characterized by the following features.

The cell membrane is similar in structure and in relation to dyes to that of gram-negative bacteria.

Cyanobacteria are the only prokaryotes that have the ability for oxygenic photosynthesis, i.e. the synthesis of organic substances from inorganic substances using light energy. The source of carbon is CO 2 , the source of hydrogen is water, and molecular oxygen is released. The photosynthetic apparatus is represented by flattened membrane structures - thylakoids with small globular formations - phycobilisomes - located on their surface. The latter contain green (including chlorophyll) d, allowing to absorb light quanta in the near infrared part of the spectrum), blue and red (in some) pigments, due to which they capture light and transmit them to the reaction centers of the photosynthesis system. In the cytoplasm of cyanobacteria there are also special crystal-like inclusions - carboxysomes, which are the depot of one of the key enzymes of the tempo phase of photosynthesis.

Rice. 7.12.cyanobacteria. Images taken with a light-optical(a) and electronic(b) microscopes

In the cytoplasm of cyanobacteria there are trophic inclusions represented by granules of a special polymer - cyanophycin; this is a kind of nitrogen depot used in conditions of nitrogen starvation.

Forms living in plankton have gas vacuoles (aerosomes) in the cytoplasm, which give the cells better buoyancy.

Many cyanobacteria (primarily multicellular filamentous cyanobacteria), along with photosynthesis, carry out nitrogen fixation - the reduction of molecular nitrogen to ammonia and the synthesis of nitrogen-containing organic compounds on its basis. The combination of these processes (recall that the key enzyme of nitrogen fixation - nitrogenase - can function only in an oxygen-free environment) is achieved in various ways: their separation in time (photosynthesis - during the day, nitrogen fixation - at night) or through the division of functions between cells (some cells carry out photosynthesis, others are heterocysts covered with a dense membrane impermeable to oxygen - nitrogen fixation).

Cyanobacteria have a wide range of adaptive mechanisms, such as the formation of a pigment that protects them from ultraviolet radiation, the synthesis of siderophores - special substances that bind iron ions and convert them into a usable form, the synthesis of surfactants - surfactants, in the presence of which suspended particles stick together and settle to the bottom of reservoirs, making the water transparent (thanks to this, the bacteria receive the necessary amount of light), the synthesis of antibiotics that inhibit the development of other cyanobacteria, algae, fungi, etc.

These are the only prokaryotes capable of forming multicellular structures with a sufficiently high level of integration (see Fig. 7.11). Multicellular cyanobacteria are characterized by a variety of shapes (filamentous, branching, etc.), some of them can reach macroscopic sizes. Such formations exhibit some properties inherent in integral organisms: differentiation of body parts, coordinated movement in space, etc.

Cyanobacteria often enter into symbiotic relationships with fungi, mosses, ferns, sponges, sea squirts. Some species of cyanobacteria live inside algae and flagellates. It is suggested that the chloroplasts of plant cells arose from symbionts - cyanobacteria.

It is believed that it was thanks to the photosynthetic activity of cyanobacteria that the oxygen atmosphere of the Earth was formed. Their remains were found in the most ancient geological formations with an age of about 3500 million years.

In the modern biosphere, cyanobacteria are distributed almost everywhere (including in places where there are no other life forms, such as alkaline lakes and hot springs) and, being a component of terrestrial and aquatic biocenoses, significantly increase their productivity.

Practical application of bacteria. Different types of bacteria have many uses in different fields.

Lactic acid bacteria ferment milk.

Propionic acid bacteria are used in cheese making.

Some types of cyanobacteria are used as a food product in Mexico, China, India, and the Philippines. It should be noted that in terms of protein content (70% of dry weight), they have no equal among photosynthetic organisms.

Pathogenic bacteria cause many infectious diseases, such as cholera, syphilis, plague, typhoid, anthrax.

Some types of soil bacteria ( Bacillus brevis etc.) are used to obtain antibiotics.

In agriculture, lactic acid bacteria are used for ensiling green fodder. To improve soil fertility, certain types of nitrogen-fixing bacteria are introduced into them.

Some types of chemosynthetic bacteria are used in metallurgy to extract metals (iron, copper) from natural ores and their processed products (slags, etc.).

Injection of a suspension of certain types of bacteria (together with a nutrient substrate for their active reproduction) into a natural reservoir containing oil makes it possible to increase its production.

Various types of bacteria are widely used for the processing of waste from industrial enterprises and household waste.

Exotic forms of bacteria. We list some special forms of bacteria.

The largest representatives of bacteria (80-600 microns) - Epulopiscium fishelsoni(Department Firmicutes) - are symbionts of surgeon fish.

Bacteria with linear DNA Borellia burgdorferi(Department of Spirochetes), Streptomyces lividans(Department of Actinobacteria).

Bacteria that have two ring-shaped "chromosomes" (diploid genome) - Rhodobacter sphaeroides(Department of Proteobacteria).

Planctomycetes (Division Planctomycetes) are a special group of aquatic microorganisms characterized by a number of unique properties. The cell wall does not contain proteoglycan. The internal volume of the cell is subdivided into "compartments" with the help of membranes. The nucleoid is surrounded by a double membrane. Part of the genome (of one of the largest bacteria in the world - up to 9 million base pairs) shows homology not with the genes of other groups of bacteria, but with the genes of eukaryotes and archaea. Some planctomycetes are capable of anaerobic ammonium oxidation.

bacteria Deinococcus mdiodurans(Deinococcus-Termus Department) withstand exposure to ionizing radiation at a dose of 10,000 grays per bacterium (for comparison, the lethal dose for humans is 40-50 grays). (Recall that gray - a unit of measurement of the absorbed dose of ionizing radiation - is equal to one joule of energy per kilogram of mass.) The high radioresistance of these microorganisms is associated with an increased content of Mn ions in their cytoplasm, which can effectively neutralize free radical particles formed in large quantities during irradiation and that have a destructive effect on biopolymers, in particular DNA and proteins.

Purple alpha proteobacteria Rhodospirillum rub git(Department of Proteobacteria) - a unique group of microorganisms capable, depending on the habitat, of carrying out photosynthesis, fixing molecular nitrogen, reversibly switching to heterotrophic or chemoautotrophic types of nutrition, and maintaining viability under anaerobic conditions.

Heterotrophic bacteria are described that can grow using only a certain organic compound as a source of carbon and chemical energy. For example, Bacillus fastidiosus(Department Firmicutes) can only use uric acid and its degradation products, and some members of the genus Clostridium grow only in a medium containing purines. They cannot use other organic substrates for growth. The plastic metabolism of these bacteria is organized in such a way that they themselves can synthesize all the carbon compounds they need.

Chrysiogenes arsenatis - obligate anaerobic chemolithoautotrophic microorganism of the genus Chrysiogenes(Department Chrysiogenetes), the only bacterium capable of using arsenic salts (arsenates) as the final electron acceptor during the so-called "arsenate respiration". It uses acetic, pyruvic, D- and L-lactic and other organic acids as an electron donor. It was first isolated from arsenic-contaminated areas of gold mines in Ballarat (Australia).

bacteria Cupriavidus metallidurans and Delftia acidovorans(Department of Proteobacteria), found in a thin biofilm covering gold grains in rock, are capable of reducing gold ions (Au 3+) toxic to them into a chemically inert - metallic - form. At the same time, the former carry out this process inside the cell, accumulating insoluble gold in the form of cytoplasmic granules, while the latter - outside the cell. To do this, bacteria synthesize a special peptide - delftibactin (specifically reacting with gold ions) and release it into the external environment.

The position of cyanobacteria in the system of the living world

Definition 1

cyanobacteria- This is a group of prokaryotic organisms that can participate in the processes of photosynthesis.

Cyanobacteria have features characteristic of different kingdoms of living organisms. For a long time they were classified as lower plants, but as knowledge of the eukaryotic and prokaryotic cellular organization expanded, blue-green algae (cyanobacteria) began to be attributed to bacteria.

To classify cyanobacteria, use:

• patterns of development of culture;
• permanent morphological features;
• features of the cellular structure;
• nucleotide characteristics and genome size;
• features of carbon and nitrogen metabolism, etc.

Morphology, life cycle of cyanobacteria

cyanobacteria are gram-negative organisms, including unicellular, multicellular and colonial forms. In multicellular forms, the unit of structure is a specific thread - the trichome, or filament.

Trichomes can be simple, single row, or branching. Distinguish between true and false branching.

With true branching, the filament cells divide in different planes, with the formation of single-row filaments with single-row lateral branches or multi-row trichomes. With false branching, the threads are connected or attached at an angle to each other.

During the life cycle, cyanobacteria can form short filaments or single differentiated cells that perform different functions:

• necessary in the process of reproduction (hormogonium, baeocytes);
• for survival in adverse conditions (akinetes, or spores);
• for nitrogen fixation under aerobic conditions (heterocysts).

A characteristic feature of both unicellular and multicellular forms is the ability to slide.

Methods for reproduction of cyanobacteria:

• binary division;
• budding;
• multiple division;
• with scraps of trichomes;
• hormogonies

Cyanobacterial cells have a well-developed system of intracytoplasmic membranes in the form of thylakoids. They contain components of the photosynthetic apparatus (excl. the genus Gloeobacter).

Remark 1

characteristic feature of cyanobacteria- the ability to anoxic photosynthesis. The activity of photosystem I is maintained, while photosystem II is turned off. Reduced sulfur compounds, hydrogen, some sugars, and organic acids are used as exogenous electron donors.

ATP synthesis is carried out due to cyclic electron transport, which is associated with photosystem I. The ability to switch from one type of photosynthesis to another under changing conditions is proof of the flexibility of light metabolism in cyanobacteria, which is of great ecological importance.

Most cyanobacteria are obligate phototrophs. In the dark, active endogenous metabolism is observed. In this case, the previously stored glycogen acts as a substrate. It is possible to obtain energy in the dark due to glycolysis. Some cyanobacteria have been shown to be capable of chemoheterotrophic growth.

To build a cell, cyanobacteria need a minimum amount of inorganic substances:

• carbon dioxide;
• molecular nitrogen, nitrate and ammonium salts;
• mineral salts that serve as a source of magnesium, sulfur, phosphorus, iron;
• water.

Cyanobacteria exhibit nitrogen-fixing activity, which depends on the content of molecular oxygen and bound nitrogen in the medium.

Major taxonomic groups of cyanobacteria

According to the International Code of Nomenclature for Bacteria, five orders of cyanobacteria are distinguished:

• Order Chroococcales. Unicellular. They reproduce by binary fission or budding. Characterized by the formation of sheaths around the cells.
• Pleurocapsales order. Unicellular. They reproduce by multiple fission or by binary and multiple fission alternately.
• Order of Oscillatoriales. Multicellular filamentous. Trichomes consist of a number of vegetative cells, non-branching.
• Nostocales order. Multicellular filamentous. Trichomes consist of a number of vegetative cells; there are heterocysts and akinetes, non-branching.
• Order Stigoneomatales. Signs characteristic of the pores. nostocales. Vegetative cells are able to divide in several planes, resulting in the formation of filaments with true branching or multi-row trichomes.

People most often intuitively understand the world that surrounds them. But there are also microscopic creatures on Earth that are not visible to the naked eye. In the process of studying them, questions arise: what are these bacteria and cyanobacteria? How are they different from viruses?

Bacteria is a group of unicellular microorganisms that lack an enveloped cell nucleus. Bacteria come in different shapes. They are divided into types such as:

• cocci (spherical);
• bacilli (rod-shaped);
• spirochetes (spiral);
• convoluted: vibrios (in the form of a comma).

According to the methods of nutrition, heterotrophic and autotrophic organisms can be distinguished. The latter live off the inorganic substances that they produced themselves with the help of the energy of chemical reactions.

Other classifications can also be distinguished. For example, they are separated on the basis of staining or non-staining according to the Gram method. To do this, the bacteria are treated with special dyes, then it is checked whether they discolor after washing or not. If they do not discolor, then they are called gram-positive, otherwise - gram-negative. The first group includes most pathogenic bacteria. To the second - for example, cyanobacteria.

Archaebacteria (or archaea, Archaebacteria) stand out separately. These are prokaryotes (they lack a nucleus). Archaebacteria and bacteria have some similarities. For example, they are brought together by similar size and shape of cells. However, despite the outward resemblance to bacteria, in some ways (part of the genes), archaebacteria are more reminiscent of eukaryotes. There are more than 40 types of archaebacteria.

Bacteria and viruses

In everyday life, these concepts are often not distinguished. Although in reality the difference is huge:

It is important to distinguish viruses from bacteria, if only because the diseases caused by the action of these organisms are treated differently. For example, antibiotics do not work for viral infections.

Cyanobacteria and their features

Cyanobacteria are a group of gram-negative bacteria capable of photosynthesis with the release of oxygen. In Latin, the name is written as Cyanobacteria. Cyanobacteria are blue-green algae.

According to modern science, cyanobacteria arose about 3 billion years ago. They are cells with multilayered walls, consisting of insoluble polysaccharides. These cells do not have nuclei or chloroplasts. There are both solitary and colonial forms.

Cyanobacteria are photoautotrophs, they are capable of synthesizing carbohydrates. Like green plants, they can break down water molecules using light energy. In the process, hydrogen and free oxygen are formed. In addition, a sufficiently large number of cyanobacteria are able to fix atmospheric nitrogen, which is subsequently consumed by animals and plants, that is, they are capable of chemosynthesis.

The color of cyanobacteria is determined by the pigments in the cells:

• chlorophyll - green;
• phycocyanin - blue;
• phycoerythrin - red;
• carotenoids are yellow.

The color can vary from blue-green to brownish.

The main difference from bacteria is photosynthesis with the release of oxygen.

Reproduction and sporulation

In most cases, cyanobacteria reproduce by simple cell division. The life cycle of unicellular forms under favorable conditions is about 6-12 hours.

If adverse environmental conditions occur, some types of cyanobacteria can form spores. At the same time, the amount of water in the cell decreases, the shell becomes thicker. Spores can stay in unfavorable conditions for a long time and without water due to reserve substances. When favorable conditions occur, a dormant cell emerges from the spore.

habitats

Most often, cyanobacteria can be found in water bodies rich in organic matter. Some species also live in highly saline lakes. They are also found on the soil, as participants in symbioses (for example, in lichens)

Notable Representatives

• Oscillatoria. Lives in fresh water.
• Nostoc. The colonial form also lives in fresh water. In China and Japan it is eaten.

Harm and benefit

1. Cyanobacteria are capable of releasing toxins, especially when massively overdeveloped. As a result, various types of fish die.
2. Cyanobacteria are one of the causes of water blooms.

1. They are an important part of oceanic plankton.
2. Participate in a large number of food chains.
3. They produce a lot of oxygen.
4. Some of their species are edible.

Thus, both bacteria in general and cyanobacteria in particular are important elements of biocenoses necessary for the life of many animals and plants. This is due, in particular, to their ability to autotrophic nutrition and release of oxygen.

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Department Gracilicutes

Class Oxyphotobacteria

OrderCyanobacteriales

Unicellular, colonial, filamentous organisms, live in water and on land in damp places (Fig. 16) . Contains blue-green pigment Phycocyanin and in connection with the habitat they used to be called blue-green algae . However, cytologically cyanobacteria are typical prokaryotes. Covered with mucus, capable of sliding movement. Sometimes a group of cells is united by a common mucosal capsule and is called Zooglea. The cell wall is layered, contains some peptidoglycan murein, Gram-negative. Has a nucleoid Chromatophores (platy-type mesosome system), bearing photopigments: Chlorophyll, Phycocyanin, Allophycocyanin responsible for the blue-green color. They feed photoautotrophically through photosynthesis. Cyanobacteria reproduce by binary fission, filament fragmentation, hormogonia - short mobile chains of cells. During the passage of the life cycle, they form specialized cells or threads: hormogonies (use for reproduction) heterocysts - Thick-walled cells capable of absorbing nitrogen from the air and Akinetes (stages of rest for experiencing adverse conditions) . Oscillatory does not form heterocysts and is capable of assimilation of atmospheric nitrogen only under anaerobic conditions. In the presence of oxygen in the environment, nitrogen fixation stops. At Anabens there are heterocysts that protect the nitrogen fixation system from oxidation, so it absorbs nitrogen and carbon dioxide from the air at the same time in the light. Cyanobacteria are highly resistant to antibiotics and ultraviolet rays.

Meaning of cyanobacteria:

1). They are the primary producers of organic matter in water and soil.

2). Saturate water and atmosphere with oxygen.

3). Participate in soil formation, in the fixation of atmospheric nitrogen.

4).Used as environmentally friendly fertilizer in rice fields (anabena).

5). They form a lot of protein and biologically active substances (vitamins), therefore they are used for the manufacture of medicines (spirulina).

6). Cause the flowering of reservoirs, produce strong neurotoxic poisons, as a result of which the water becomes undrinkable.

Rice. 16 . Morphology of cyanobacteria: 1) Gloeocapsa ; 2) Nostoc ; 3) Anabaena ; 4) Oscillatoria , 5) Lyngbya ; SpecializedCells: A) hormony; b) heterocysts

The subkingdom of oxyphotobacteria - Oxyphotobacteria, or Oxyphotobacteriobionta - are autotrophic prokaryotes capable of aerobic photosynthesis. These include cyanobacteria and chloroxybacteria. The type of autotrophic prokaryotic organisms is "bacteria rather than algae." Solitary and colonial forms. Colonies create organogenic calcareous structures (stromatolites).

Cyanobacteria, surprisingly unpretentious microorganisms that need only sunlight, water and air. Their role in the evolution and existence of the biosphere of our planet is especially significant [Gromov B.V. 2000]. By the nature of their cellular organization, they correspond to gram-negative bacteria and represent their independent evolutionary branch. In the botanical literature, cyanobacteria are still sometimes referred to as blue-green algae, where they are considered as a taxon of high rank - a department or type in the system of lower plants. Blue-green - the most ancient organisms of the Earth (Archea - now). Known from deposits of at least 2.8 billion years old, they still play an important role in the cycles of matter and energy.

In their cells there is not only a nucleus, but also chromatophores - cell formations containing pigments and taking part in photosynthesis, there are no vacuoles. In the central dense part of blue-green cells, nucleoproteins are concentrated - compounds of nucleic acids with protein. Blue-greens are remarkable in that they are able to use atmospheric nitrogen and convert it into organic forms of nitrogen. During photosynthesis, they can use carbon dioxide as the only source of carbon. Unlike photosynthetic bacteria, blue-green bacteria release molecular oxygen during photosynthesis.

Cyanobacteria that live among plankton have gas vesicles that contain gas and give the cells better buoyancy. Some cyanobacteria are capable of cell differentiation. One of the types of specialized cells are akinetes (or spores) - these are large resting cells with a thickened membrane. They serve for the survival of the organism in adverse conditions. When optimal conditions occur, akinetes germinate. Another type of differentiated cells are heterocysts - specialized cells in which the process of atmospheric nitrogen fixation is carried out. Some filamentous cyanobacteria (Anabaena, Nostoc) can form them.

It has already been said above that blue-greens are represented not only by unicellular, but also by colonial, filamentous and multicellular forms. But multicellular nuclear organisms did not evolve from multicellular blue-green, but from single-celled nuclear forms. Thus, for the first time, the blue-greens have an attempt to break through to the next stage - to the level of multicellularity. However, this attempt did not have any special consequences for evolution.

Cyanobacteria are the only example of a prokaryotic multicellular organism in which functional cell specialization occurs.

Understanding the potential of cyanobacteria is expanding with the availability of developed genetic methods and data on genomic nucleotide sequences. Cyanobacteria are intensively used as model organisms for studying fundamental biological processes, including: photosynthesis and its genetic control [