In the name of the department (from Greek. cyanos – blue) reflects a characteristic feature of these algae – the color of the thallus, associated with a relatively high content of the blue pigment phycocyanin. Cyanophytes usually have a specific blue-green color. However, their color can vary greatly depending on the combination of pigments - be almost green, olive, yellowish-green, red, etc. In recent years, another name is increasingly being used for blue-green algae - “cyanobacteria”. This name better reflects the two most important characteristic features of these organisms - the prokaryotic nature of the cells and the close relationship with eubacteria. On the other hand, the traditional name refers to traits such as the ability for oxygenic photosynthesis and the similarity between the structure of blue-green algae and the structure of eukaryotic chloroplasts.
About 2 thousand species of cyanophytes are known, widely distributed in marine and fresh waters and in terrestrial habitats.
Cell blue green algae prokaryotic. It consists of cell covers (cell wall) and internal contents - protoplast, which includes plasmalemma and cytoplasm with various structures: photosynthetic apparatus, nuclear equivalent, ribosomes, granules, etc. (Fig. 12).
Blue-green algae lack organelles surrounded by membranes: nucleus, chloroplasts, etc., as well as non-membrane structures: microtubules, centrioles, microfilaments.
The most characteristic features of the cell structure of blue-green algae are:
Absence of typical nuclei surrounded by nuclear membranes; The DNA lies loose in the center of the cell.
Localization of photosynthetic pigments in thylakoids in the absence of chloroplasts; thylakoids contain chlorophyll A.
Masking of green chlorophylls with red - phycoerythrin and blue pigments - phycocyanin and allophycocyanin.
DNA is located in the fibrillar granular nucleoplasmic region and is not surrounded by a membrane.
Rice. 12. Cell structure of blue-green algae (according to: C.Hoek van den et al., 1995): A – Synechocystis; B – Prochloron; IN - Pseudoanabena; 1 – cell wall; 2 – plasmalemma; 3 – thylakoid; 4 – phycobilisome; 5 – gas vesicles; 6 – carboxysome; 7 – DNA fibrils; 8 – cyanophycin granule; 9 – ribosomes; 10 – polysaccharide cover; 11 – stack of thylakoids; 12 – swollen thylakoid; 13 – pores; 14 – cyanophycin starch granules; 15 – lipid drop; 16 – transverse partition; 17 – young transverse septum; 18 – invagination of the plasmalemma
The presence of rigid (inflexible) layered cell membranes.
Formation in most cases of mucous membranes.
The presence of various inclusions: gas vacuoles (providing buoyancy), cyanophycin granules (nitrogen fixation), polyphosphate bodies (phosphorus fixation).
general characteristics
Unicellular blue-green algae are characterized by coccoid body type . In multicellular individuals, filamentous (trichomal) is found , less commonly, heterotrichous (heterotrichal) form of thallus structure . Very rarely there is a definite tendency towards a lamellar or volumetric arrangement of cells. In filamentous colonies, there is no plasmatic interconnection between cells.
They can be attached or unattached to the substrate, immobile or capable of gliding movement. However, flagella and cilia are never formed. The movement of cyanophytes is affected in various ways by lighting. Firstly, light determines the directions of movement. Movement towards the light source is called “positive phototaxis”, in the opposite direction – “negative phototaxis”. Secondly, the intensity of light changes the speed of movement - "photokinesis". Thirdly, a sharp increase or decrease in light intensity quickly changes the direction of movement - “photophobia”.
The cells of blue-green algae are most often spherical, barrel-shaped or ellipsoid in shape, less often elongated to cylindrical and spindle-shaped, straight or bent. Sometimes the cells are pear-shaped. In attached unicellular individuals, and sometimes in unicellular cyanoids, cell heteropolarity is often observed. In this case, mucous legs and discs are formed, with which they are attached to the substrate.
Individuals very often form various compounds - colonies of individuals, sometimes occupying large spaces, and produce a significant amount of mucus, which often noticeably affects the shape and general appearance of the colonies.
Cyanophyta individuals are usually microscopic, but colonial individuals in a number of species can measure centimeters.
The main pigments of blue-green algae are chlorophyll A, carotenoids (carotene, xanthophyll) and phycobiliproteins (allophycocyanin, phycocyanin, phycoerythrin). The latter are found in the form of special structures - phycobilis, which are located on the surface of the thylakoids.
Blue-green algae are capable of various types of photosynthesis: oxygenic and anoxygenic. Oxygen Photosynthesis is the process of fixing carbon dioxide using water as an electron donor, accompanied by the release of oxygen. Occurs under aerobic conditions. Anoxygenic photosynthesis is the process of fixing carbon dioxide using hydrogen sulfide or sulfide as an electron donor, accompanied by the release of sulfur. Occurs under anaerobic conditions. In the hyperhaline lakes of Israel, where highly anaerobic conditions are created in winter, the use of a combination of oxygenic and anoxygenic photosynthesis allows algae of the genus Oscillatorium dominate the lake year-round. In oxygen-free conditions, photosynthesis occurs in the sands of the tidal zone of the seas with the release of sulfur or thiosulfate. Many cyanophytes in the light under anaerobic conditions can fix carbon dioxide using hydrogen, but this process occurs at a low speed and quickly stops.
Blue-green algae have several types of nutrition:
Obligate photoautotrophic. They can only grow in light on an inorganic carbon source.
Facultative chemoheterotrophic. Capable of heterotrophic growth in the dark using organic matter, and phototrophic growth in the light.
Photoheterotrophic. Organic compounds are used in light as a source of carbon.
Mixotrophic. Organic compounds are used as an additional source of carbon. They are also capable of autotrophic carbon dioxide fixation.
The product of photosynthesis of cyanobacteria is cyanophycin starch. It is deposited in small granules located between the thylakoids. Cyanobacteria are able to quickly absorb and accumulate nitrogen in the form of cyanophycin granules, usually located near the transverse partitions of the cells. Phosphates in blue-green algae are stored in polyphosphate granules, and lipids are stored in the form of droplets in the cytoplasm at the periphery of the cell.
Reproduction. All living cells of blue-green algae are capable of division. Cell division of metazoans and colonial representatives usually results in growth. Cell division is possible in one, two, three or many planes. In multicellular forms, during longitudinal division, filamentous forms appear in one plane, lamellar forms in two planes, and cubic forms in three planes. When single-celled individuals divide, reproduction occurs simultaneously. Single-celled cyanophytes reproduce by equal, or less often unequal, division. In this case, the inner layers of the cell membrane grow inside the cell. In some cases, multiple content divisions are observed. Mitosis and meiosis are absent. Reproduction of individuals is vegetative, less often asexual. A number of representatives of cyanobacteria form resting spores (akinetes) . There is no typical sexual process.
Vegetative propagation in coccoid forms, it is carried out by simple division of the cell in two in all possible directions, depending on the random influences of the environment. As a result, two equal, but not equivalent, parts are formed, giving rise to two new organisms. Cell division in two occurs in one or more planes. In the latter case, colonies are most often formed.
Multiple cell division occurs when the division of the cell and its nuclear region is inconsistent. As a result of increased division of the “nucleus,” the cell becomes multinucleated, then the areas of protoplasm around the “nuclei” are isolated and many isolated embryonic cells are formed. The main factors leading to repeated and multiple cell division of cyanobacteria are excess nutrition, causing its hypertrophied growth, as well as changes in the physicochemical conditions of existence. Hypertrophied growth causes a delay in cell maturation, and then repeated or multiple divisions.
One of the ways of vegetative propagation of cyanophytes is fragmentation (disintegration) of their thalli. The cause of fragmentation may be mechanical factors, the death of some cells, or disruption of the close connections that exist between them. In hormogonium blue-green algae, fragmentation occurs by disintegration of the thread on the hormogonium due to the death of some trichome cells - necroids. Each hormogonium consists of 2-3 or more cells, which, with the help of the mucus they secrete, slip out of the vaginal mucosa and, making oscillatory movements, move in water or along the substrate. Each hormogonium can give rise to a new individual. If a group of cells similar to hormogonium is covered with a thick membrane, it is called hormocystos. It performs the functions of reproduction and tolerating unfavorable conditions. In some species, single-celled fragments called gonidia, cocci or planococci separate from the thallus. Gonidia retain a mucous membrane; cocci and planococci lack distinct membranes. Like hormogonies, they are capable of active movement.
Asexual reproduction carried out using special cells that do not have thickened membranes: “exospores” and “endospores”. Exospores are formed by unequal cell division, when a smaller one buds from the mother cell.
When unfavorable conditions occur (drying, cold, nutrient deficiency), cyanobacteria form akinetes. These large, thick-walled, resting spores, filled with reserve products, serve to survive these unfavorable conditions. Akinetes can remain viable for decades, for example, in lake sediments in the absence of oxygen.
Taxonomy
All modern forms of the division Cyanophuta can be grouped into one, two or three classes. If we accept the idea of 3 main paths of evolutionary development of blue-green algae from the original coccoid unicellular forms, then we can agree with the identification of three classes within Cyanophyta: Chroococcophyceae - chroococcal algae, Chamaesiphonophyceae - chamesiphon algae and Hormogoniophyceae - hormogonian algae.
Class Hormogonium–Hormogoniophyceae
(Orders Oscillatoryaceae, Nostocaceae, Stigonemus -
Oscillatoriales, Nostocales, Stigonematales)
The species are characterized by a trichal form of the body structure of individuals, as well as the ability to form hormogonies, i.e. special fragments of threads capable of active voluntary movement and germination into new individuals. Individuals are multicellular, "simple" or colonial (with multicellular cyanoids). Threads can be branched or unbranched, branching can be real or false. In true branching, trichome branching occurs. With false branching, only the vaginas branch. Trichomes can be single-rowed or multirowed, unbranched or branched, homocytic or heterocytic. Homocyte trichomes consist of similar cells that are not differentiated in shape and function. Heterocyte trichomes consist of cells that are unequal in shape, function and location. Cells that are similar in appearance to homocytic trichome cells are called vegetative; sharply different from them - special. The latter include heterocysts and akinetes.
Development cycles are often complex, during which a number of morphologically different stages are observed. In addition, hormogonium algae are characterized by multivariate development.
Genus Oscillatorium(Fig. 13, A). There is no differentiation of cells according to shape, function and localization. The threads are unbranched, uniseriate, homocytic. Vaginas are absent or present.
Rice. 13. Morphological diversity of blue-green algae (according to:): A – Oscillatorium; B – Nostok; IN - Anabena; G - Lingbia; D – Rivularia; E – Gleocapsa; AND - Chroococcus: 1 – general view, 2 – low magnification view, 4 – heterocyst
Genus Nostok(Fig. 13, B). Cells are differentiated by form and function. Exclusively colonial organisms, with well-developed mucus that affects the shape of the colonies. Trichomes are heterocytic, uniseriate, unbranched, with or without sheaths.
Genus Rivularia(Fig. 13, D). Thallus in the form of unbranched or branched filaments, with or without sheaths. Individuals are solitary or form compounds. trichomes are heterocytic, asymmetrical in maturity, narrowing from the base to the apex, often ending in a hair consisting of vacuolated cells.
Genus Stigonema(Fig. 14, A). Cells are differentiated by form and function. Species of the genus are characterized by true lateral branching. Trichomes are heterocytic, uniseriate or multiseriate, forming plexuses and bundles. Threads with sheaths or, less commonly, without them. There is no clear dimorphism of the branches. The main threads are usually creeping. In the old parts of the filaments, the cells are often in a gleocapsoid state: they are united in groups and surrounded by developed mucous membranes.
Rice. 14. Stygonema blue-green algae (according to: R.E. Lee, 1999; M.M. Gollerbach et al., 1953): A – Stigonema; B – Mastigocladus: 1 – heterocyst, 2 – sheath
Genus Mastigocladus(Fig. 14, B). The thallus has complex branching and is heterocytic. Branching true and false. The cells of the main filaments are more or less spherical, the cells of the branches are elongated and cylindrical. The sheaths of the threads are narrow, strong or slimy. Heterocysts are intercalary, no spores are known. Species of the genus are widely distributed in thermal springs.
Class Chroococcus –Chroococcophyceae
Order– Chroococcales
They occur as single-celled “simple” individuals or more often form mucous colonies. When cells divide in two planes, single-layer lamellar colonies appear. Division in three planes leads to the formation of cube-shaped colonies. When cells divide in many planes, the cells are randomly located throughout the entire thickness of the mucus, and the shape of the colonies is varied. Colonial mucus combines simple and complex cyanoids of colonies. Mucus can be homogeneous or differentiated, in the form of mucous blisters sequentially inserted into one another (genus Gleocapsa) or tubes and cords (birth Voronikhinia, Gomphospheria). Mucus can be colorless or colored in blue-green, grayish, olive, brown, reddish, purple, and black tones.
The cells are mostly spherical or ellipsoidal, less often elongated, sometimes variably bent, cylindrical or spindle-shaped, in some species ovoid, pear-shaped or heart-shaped. Chroococcal algae are characterized by vegetative reproduction. Single-celled individuals divide into two in one, two, three or many planes. Colonial individuals reproduce by dividing colonies and forming endogenous colonies. Most often, reproduction occurs by dividing colonies. Within this method, there is fragmentation of colonies, or breaking them into several parts, or re-lacing of the mother colony; and budding of colonies, that is, the formation of protrusions on the mother colony that eventually separate from it. Colonial individuals also reproduce using regular vegetative cells and spores.
Genus Gleocapsa forms “simple” or complex colonies (Fig. 13, E). Cells are spherical, ellipsoidal, cylindrical. Each cell is covered with a mucous sheath. During division, the walls of the mother cells are preserved. Colonies are round or cubic, consisting of mucous bubbles sequentially included one within the other.
Genus Microcystis - colonies are spherical or irregular in shape, spherical cells are immersed in mucus and can divide in any direction (Fig. 15). Cells of many species contain gas vacuoles. The genus is widespread in freshwater plankton. Developing in masses, it can cause algae in water. Some species are toxic.
Rice. 15. Chroococcal blue-green algae Microcystis(after: M. M. Gollerbach et al., 1953)
Class Chamesiphonaceae -Chamaesiphonophyceae
(Order Pleurocapsaceae -Pleurocapsales)
Unicellular, often differentiated into base and apex, and colonial (with unicellular cyanoids), usually attached to the substrate, individuals. The formation of endospores (beocytes) is characteristic. Cells of various shapes, often with well-defined colorless or yellowish or brown mucous membranes. Cell division occurs in one, two or three planes. Cells in colonies are often very compressed and form false parenchyma, sometimes arranged in several layers. Many species are characterized by the formation of relatively clear rows of cells that resemble threads. But there is no plasmatic connection between the cells of such “threads”. The “threads” crawl along the substrate, go deeper into it or rise above it, and the threads often branch.
Endospores (beocytes) arise inside a mother cell (sporangium), similar to or different from ordinary cells in size and shape. Beocytes are released by rupture, licking of the sporangium shell, or by throwing off part of the sporangium wall as a cap; the entire contents of the sporangium or only part of it are used for their formation.
Genus Dermocarpa. Individuals are unicellular, differentiated into base and apex, attached to the substrate. They usually live alone, in small groups. They usually reproduce by beocytes.
Rice. 16. Chamesiphon blue-green algae Dermocarpa(after: M. M. Gollerbach et al., 1953)
Ecology and significance
Blue-green algae are ubiquitous. They can be found both in hot springs and artesian wells, and on the surface of snow and wet rocks, on the surface and in the thickness of soils, in symbiosis with other organisms: protozoa, fungi, sea sponges, echiurids, mosses, ferns, gymnosperms. Species of blue-greens are common in plankton and benthos of standing and slowly flowing fresh waters, in brackish and salt water bodies. They - important components of marine phytoplankton. Blue-green algae play a key role in oceanic ecosystems, where the majority of total photosynthetic production comes from picoplankton. Picoplankton consists mainly of single-celled coccoid cyanophytes. It is estimated that 20% of the oceans' photosynthetic production comes from planktonic blue-green algae. The benthos contains epiphytic, epilithic and endolithic forms. Cyanobacteria usually have special attachment organs in the form of a sole, foot, and mucous cords. Species of blue-green algae, which attach to underwater objects using mucus, are also abundant.
Cyanobacteria are typical inhabitants of hot waters. They vegetate at temperatures of 35–52°C, and in some cases up to 84°C and higher, often with an increased content of mineral salts or organic substances (heavily polluted hot wastewater from factories, factories, power plants or nuclear plants).
The bottom of hyperhaline reservoirs is sometimes completely covered with blue-green algae, among which species of the genera predominate Phormidium, Oscillatoria, Spirulina etc. Blue-green algae live on the bark of trees (species of genera Synechococcus, Afanotheke, Nostoc). They often epiphyte on mosses, where, for example, one can observe blackish-blue tufts of species of the genus Schizotrix.
Representatives of Cyanophyta are the most common among algae living on the surface of exposed rocks. Cyanophytes and accompanying bacteria form “mountain tan” (rock films and crusts) on crystalline rocks of various mountain ranges. Algae growths are especially abundant on the surface of wet rocks. They form films and growths of various colors. As a rule, species equipped with thick mucous membranes live here. The growths come in different colors: bright green, golden, brown, ocher, purple or dark blue-green, brown, almost black, depending on the species that form them. The types of genera that are especially characteristic of irrigated rocks are: Gleocapsa, Gleoteke, Hamesiphon, Calothrix, Tolipothrix, Scytonema.
Representatives of Cyanophyta make up the vast majority of soil algae. They live in deep and surface layers of the soil and are resistant to ultraviolet and radioactive radiation. In the soils of the steppe zone Nostoc vulgare forms thick films of dark green or, in the dry season, slate-black crusts on the surface. The massive development of microalgae causes greening of the slopes of ravines, roadsides, and arable soils.
Blue-green algae are components of the thallus of many lichens and coexist with higher plants, for example, Azolla aquatic fern and others. How symbionts they protect their partner from high light intensity, supply him with organic substances, and provide nitrogen compounds. At the same time, they receive protection from unfavorable external factors from the host, as well as the organic substances necessary for growth. Only a few symbiotic associations of cyanophytes with various organisms are obligate. Most cyanophytes are able to grow independently, although worse than in symbiosis. They form two types of associations with other organisms - extracellular: with fungi and intracellular: with sponges, diatoms, etc.
Blue-green algae are among the most ancient organisms; their fossil remains and waste products were found in rocks formed 3–3.5 billion years ago, in the Archean era. It is believed that the first ecosystems on Earth (Precambrian) consisted only of prokaryotic organisms, including cyanobacteria. The intensive development of cyanophytes was of enormous importance for the development of life on Earth, and not only because of their accumulation of organic matter, but also due to the enrichment of the primary atmosphere with oxygen. Blue-green algae also played a significant role in creating limestone rocks.
Nitrogen fixation. The Earth's atmosphere consists of 78% nitrogen, but the ability to fix it is found only in prokaryotes, and among algae exclusively in cyanophytes. Blue-green algae are unique organisms that are capable of fixing both carbon dioxide and atmospheric nitrogen. When nitrogen is fixed, ammonia and hydrogen are released. This process usually occurs in special thick-walled cells with mucous sheaths - heterocysts. Conditions with low oxygen content are created inside the heterocysts. Nitrogen fixation occurs faster during the day than at night, since during photosynthesis the ATP necessary for this process is formed - adenosine triphosphoric acid. By fixing atmospheric nitrogen, blue-green algae obtain the nitrogen they need to synthesize their proteins and continue to grow. Other algae depend entirely on nitrates and ammonium dissolved in water.
Biological fixation of atmospheric nitrogen is one of the important factors increasing soil fertility. The leading role in this process belongs to cyanophytes, which do not require ready-made organic matter to assimilate molecular nitrogen, but themselves bring it to the soil. For example, for temperate zone soils, the annual production of nitrogen-fixing blue-green algae is estimated at 20-577 kg/ha (dry weight). Only heterocyst forms of cyanophytes (species of the genera Nostok, Anabena, Calothrix, Tolipothrix And Cylindrospermum).
Some representatives of blue-green algae are edible (Nostok, Spirulina). In special biological ponds, communities of blue-green algae and bacteria used to decompose and detoxify herbicides. Some cyanobacteria decompose phenylcarbamate herbicides into aniline and chlorine derivatives. Wastewater, purified using the most advanced methods, still remains toxic to aquatic organisms. Only algobacterial communities, which are used for wastewater tertiary treatment, make it possible to obtain water that complies with GOST "Drinking Water".
"Blooming" of water. By “blooming” of water we mean the intensive development of algae in the water column, as a result of which it acquires different colors, depending on the color and number of organisms causing the “bloom”. The massive development of algae up to the point of “blooming” of water is facilitated by the increase in eutrophication of water bodies, which occurs both under the influence of natural factors (over thousands and tens of thousands of years), and to a much greater extent under the influence of anthropogenic factors (over years, tens of years). "Blooming" of water is observed both in continental reservoirs (fresh, brackish and saline), and in the seas and oceans (mainly in coastal areas). The Red Sea got its name due to the abundant development of blue-green algae in it. Oscillatoria erythraea. The puddle-shaped freshwater bodies of Central Europe are often colored red Haematococcus pluvialis. Of the freshwater bodies of water, large lowland rivers and their reservoirs, as well as ponds for various purposes, lakes, and cooling ponds are primarily susceptible to blooming.
Moderate vegetation of cyanophytes has a positive effect on the ecosystem of the reservoir. With a significant increase in algae biomass (up to 500 g/m3 and above), biological pollution begins to appear, as a result of which the quality of water significantly deteriorates. In particular, its color, pH, viscosity changes, transparency decreases, and the spectral composition of solar radiation penetrating into the water column changes as a result of the scattering and absorption of light rays by algae. Toxic compounds and large amounts of organic substances appear in water, serving as a breeding ground for bacteria, including pathogenic ones. The water usually acquires a musty, unpleasant odor. Hypoxia, or deficiency of dissolved oxygen, occurs; it is spent on the respiration of algae and the decomposition of dead organic matter. Hypoxia leads to summer death of aquatic organisms and slows down the processes of self-purification and mineralization of organic matter.
Among cyanophytes there are pathogenic species (about 30) that cause diseases and death of reef corals; when water blooms, diseases of domestic animals and humans, mass death of aquatic organisms, waterfowl and domestic animals, especially in the hot summer months. Poisoning of people is much less common. Children and people with liver and kidney disease are most at risk. Based on their mode of action, cyanobacterial toxins are divided into 4 groups: hepatotoxins, neurotoxins, cytotoxins and dermatotoxins. They cause food intoxication, allergies, conjunctivitis, damage to the central nervous system, etc. In their action, cyanotoxins are several times superior to such poisons as curare and botulin. Preventing the cleanliness of water bodies involves preventing the accumulation of algae near water intakes and resting places or watering places for domestic animals.
"Solar reactors" and algae. Recently, humanity has faced an acute problem of rational use of natural energy resources and the search for unconventional energy sources. Such sources include solar energy conserved in plant biomass (biopreservation of solar energy). Unlike nuclear energy, this energy source is absolutely safe; its use does not disrupt the ecological balance and does not lead to radioactive or thermal pollution of the environment.
The most promising is the use of blue-green algae to produce biofuels by methanization of algae biomass grown in wastewater. Installations for producing methane from algae have been created in the USA and Japan. Their productivity is respectively 50 and 80 t/ha (dry mass) per year, and 50-60 t of dry algae biomass can provide 74 thousand kW/h of electricity.
Control questions
Name the characteristic features of the cell structure of cyanobacteria.
What pigments and nutritional types are known in cyanophytes?
How do blue-green algae reproduce? What are hormogoniums, exospores, akinetes?
What groups of organisms are blue-green algae most similar to and when did they arise?
Name the characteristic features and typical representatives of blue-green algae of the Chroococcal class.
Name the characteristic features and typical representatives of blue-green algae of the Hormogonium class.
Name the characteristic features and typical representatives of blue-green algae of the Chamesiphonaceae class.
In what habitats are blue-green algae found? Their meaning in nature.
The role of cyanophytes in the biological fixation of atmospheric nitrogen.
Economic importance of cyanophyte. Water quality assessment.
What are algal blooms and cyanotoxins?
Blue-green algae as non-traditional energy sources.
Bacteria appeared on Earth about three and a half billion years ago and for a billion years they were the only form of life on our planet. Their structure is one of the most primitive, however, there are species that have a number of significant improvements in their structure. For example, the photosynthesis of bacteria, also called blue-green algae, is similar to that of higher plants. Mushrooms are not capable of photosynthesis.
The simplest in structure are those bacteria that inhabit hydrogen sulfide-containing hot springs and deep bottom sediments of silt. The pinnacle of evolution is considered to be the appearance of blue-green algae, or cyanobacteria.
The question of which prokaryotes are capable of synthesis has long been studied by biochemists. It was they who discovered that some of them are capable of independent nutrition. Photosynthesis in bacteria is similar to that which occurs in plants, but has a number of features.
Autotrophic prokaryotes are capable of nutrition through photosynthesis, since they contain the structures necessary for this. Photosynthesis of such bacteria is an ability that provides the possibility of the existence of modern heterotrophs, such as fungi, animals, and microorganisms.
Interestingly, synthesis in autotrophic prokaryotes occurs in a longer wavelength range than in plants. Green bacteria are capable of synthesizing organic substances by absorbing light with a wavelength of up to 850 nm; in purple bacteria, containing bacteriochlorophyll A, this occurs at a wavelength of up to 900 nm, and in those containing bacteriochlorophyll B, up to 1100 nm. If we analyze light absorption in vivo, it turns out that there are several peaks, and they are in the infrared region of the spectrum. This feature of green and purple bacteria allows them to exist in conditions of the presence of only invisible infrared rays.
One of the unusual types of autotrophic nutrition is chemosynthesis. This is a process in which the body receives energy for the formation of organic substances from the oxidative transformation of inorganic compounds. Photo- and chemosynthesis in autotrophic bacteria are similar in that the energy from the chemical oxidation reaction is first accumulated in the form of ATP and only then transferred to the assimilation process. The species whose vital activity is ensured by chemosynthesis include the following:
- Iron bacteria. They exist due to the oxidation of iron.
- Nitrifying. The chemosynthesis of these microorganisms is tuned to process ammonia. Many are plant symbionts.
- Sulfur bacteria and thionobacteria. Process sulfur compounds.
- Hydrogen bacteria whose chemosynthesis allows them to oxidize molecular hydrogen at high temperatures.
Bacteria, whose nutrition is provided by chemosynthesis, are not capable of photosynthesis because they cannot use sunlight as an energy source.
Blue-green algae - the pinnacle of bacterial evolution
Photosynthesis of cyanides occurs in the same way as in plants, which distinguishes them from other prokaryotes, as well as fungi, raising them to the highest degree of evolutionary development. They are obligate phototrophs, as they cannot exist without light. However, some have the ability to fix nitrogen and form symbioses with higher plants (like some fungi), while maintaining the ability to photosynthesize. It has recently been discovered that these prokaryotes have thylakoids that are separate from the folds of the cell wall, like eukaryotes, which makes it possible to draw conclusions about the direction of evolution of photosynthetic systems.
Other known symbionts of cyanides are fungi. In order to survive together in harsh climatic conditions, they enter into a symbiotic relationship. Fungi in this pair play the role of roots, receiving mineral salts and water from the external environment, and algae carry out photosynthesis, supplying organic substances. The algae and fungi that make up lichens could not survive separately in such conditions. In addition to symbionts such as mushrooms, cyanians also have friends among sponges.
A little about photosynthesis
Photosynthesis in green plants and prokaryotes is the basis of organic life on our planet. This is the process of formation of sugars from water and carbon dioxide, which occurs with the help of special pigments. It is thanks to them that bacteria whose colonies are colored are capable of photosynthesis. The oxygen released as a result, without which animals cannot exist, is a by-product in this process. All fungi and many prokaryotes are not capable of synthesis, because during the process of evolution they were unable to acquire the pigments necessary for this.
In plants, photosynthesis occurs in chloroplasts. In green, purple and cyanobacterial cells, pigments are also attached to the membrane. That is, the synthesis of prokaryotes also occurs in special vesicles called thylakoids. Systems that transfer electrons and enzymes are also located here.
Comparing the photosynthesis of prokaryotes and higher plants, some scientists have come to the conclusion that plant chloroplasts are nothing more than descendants of green bacteria. These are symbionts that have adapted to life inside more developed eukaryotes (the cells of such organisms, unlike bacterial ones, have a real nucleus).
There are two types of photosynthesis - oxygenic and anoxygenic. The first is most common in plants, cyanobacteria and prochlorophytes. The second occurs in purple, some green and heliobacteria.
Anoxygenic synthesis
Occurs without releasing oxygen into the environment. It is characteristic of green and purple bacteria, which are peculiar relics that have survived to this day from ancient times. The photosynthesis of all purple bacteria has one feature. They cannot use water as a hydrogen donor (this is more typical for plants) and need substances with higher degrees of reduction (organics, hydrogen sulfide or molecular hydrogen). The synthesis provides nutrition for green and purple bacteria and allows them to colonize fresh and salt water bodies.
Oxygen synthesis
Occurs with the release of oxygen. It is characteristic of cyanobacteria. In these microorganisms, the process is similar to photosynthesis in plants. The pigments of cyanobacteria include chlorophyll A, phycobilins and carotenoids.
Stages of photosynthesis
Synthesis occurs in three stages.
- Photophysical. Light is absorbed with the excitation of pigments and the transfer of energy to other molecules of the photosynthetic system.
- Photochemical. At this stage of photosynthesis in green or purple bacteria, the resulting charges are separated and electrons are transferred along a chain that ends with the formation of ATP and NADP.
- Chemical. Happens without light. Includes the biochemical processes of synthesis of organic substances in purple, green and cyanobacteria using energy accumulated in previous stages. For example, these are processes such as the Calvin cycle, glucogenesis, culminating in the formation of sugars and starch.
Pigments
Bacterial photosynthesis has a number of features. For example, chlorophylls in this case are their own, special (although some have also been found to have pigments similar to those that work in green plants).
Chlorophylls, which take part in photosynthesis in green and purple bacteria, are similar in structure to those found in plants. The most common chlorophylls are A1, C and D, AG, A, B are also found. The main framework of these pigments has the same structure, the differences lie in the side branches.
From the point of view of physical properties, chlorophylls of plants, purple, green and cyanobacteria are amorphous substances, highly soluble in alcohol, ethyl ether, benzene and insoluble in water. They have two absorption maxima (one in the red and the other in the blue regions of the spectrum) and provide maximum efficiency of photosynthesis in ordinary bacteria and cyanobacteria.
The chlorophyll molecule consists of two parts. The magnesium porphyrin ring forms a hydrophilic plate placed on the surface of the membrane, and phytol is located at an angle to this plane. It forms a hydrophobic pole and is immersed in the membrane.
Also found in blue-green algae phycocyanobilins- yellow pigments that allow cyanobacterial molecules to absorb the light that is not used by green microorganisms and plant chloroplasts. That is why their absorption maxima are in the green, yellow and orange parts of the spectrum.
All types of purple, green and cyanobacteria also contain yellow pigments - carotenoids. Their composition is unique for each type of prokaryote, and light absorption peaks are in the blue and violet parts of the spectrum. They allow bacteria to photosynthesize using light of intermediate length, which improves their productivity, can be channels for electron transfer, and also protect the cell from destruction by active oxygen. In addition, they provide phototaxis - the movement of bacteria towards a light source.
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The only energy-transforming membrane of Gloeobacter is the cytoplasmic one, where the processes of photosynthesis and respiration are localized.
Cyanobacteria are interesting because they contain a variety of physiological capabilities. In the depths of this group, photosynthesis probably formed and took shape as a whole, based on the functioning of two photosystems, characterized by the use of H2O as an exogenous electron donor and accompanied by the release of O2.
Cyanobacteria have been shown to have the ability to oxygen-free photosynthesis associated with shutdown II photosystem while remaining active I photosystems (rice. 75, IN). Under these conditions, they have a need for exogenous electron donors other than H2O. As the latter, cyanobacteria can use some reduced sulfur compounds (H2S, Na2S2O3), H2, and a number of organic compounds (sugars, acids). Since the flow of electrons between the two photosystems is interrupted, synthesis ATP paired only with cyclic electron transport, associated with photosystem I. The ability for oxygen-free photosynthesis has been found in many cyanobacteria from different groups, but the activity of CO2 fixation due to this process is low, usually amounting to several percent of the rate of CO2 assimilation under the operating conditions of both photosystems. Only some cyanobacteria can grow by anoxic photosynthesis, e.g. Oscillatoria limnetica, isolated from a lake with a high content of hydrogen sulfide. The ability of cyanobacteria to switch from one type of photosynthesis to another when conditions change illustrates the flexibility of their light metabolism, which has important ecological significance.
Although the vast majority of cyanobacteria are obligate phototrophs, in nature they often spend a long time in darkness. In the dark, cyanobacteria have discovered active endogenous metabolism, the energy substrate of which is glycogen stored in the light, catabolized by oxidative pentose phosphate cycle, ensuring complete oxidation of the glucose molecule. At two stages of this path with NADP*H2 hydrogen enters the respiratory chain, in which O2 serves as the final electron acceptor.
O. limnetica, which carries out active oxygen-free photosynthesis, also turned out to be capable of transferring electrons to molecular sulfur in the dark under anaerobic conditions in the presence of sulfur in the environment, reducing it to sulfide. Thus, anaerobic respiration can also supply energy to cyanobacteria in the dark. However, how widespread this ability is among cyanobacteria is unknown. It is possible that it is characteristic of crops that carry out oxygen-free photosynthesis.
Another possible way for cyanobacteria to obtain energy in the dark is glycolysis. In some species, all the enzymes necessary for the fermentation of glucose to lactic acid are found, but the formation of the latter, as well as the activity of glycolytic enzymes, are low. In addition, the content ATP in a cell under anaerobic conditions drops sharply, so that, probably, the vital activity of cyanobacteria cannot be maintained solely through substrate phosphorylation.
In all studied cyanobacteria CTK due to the absence of alpha-ketoglutarate dehydrogenase, it is “not closed” ( rice. 85). In this form, it does not function as a pathway leading to energy production, but only performs biosynthetic functions. The ability, to one degree or another, to use organic compounds for biosynthetic purposes is inherent in all cyanobacteria, but only some sugars can ensure the synthesis of all cellular components, being the only or additional carbon source to CO2.
Cyanobacteria can assimilate some organic acids, primarily acetate And pyruvate, but always only as an additional source of carbon. Their metabolization is associated with the functioning of the “broken” CTK and leads to inclusion in a very limited number of cellular components ( rice. 85). According to the features constructive metabolism In cyanobacteria, the ability to photoheterotrophy or obligate attachment to photoautotrophy is noted. Under natural conditions, cyanobacteria often carry out constructive metabolism of the mixed (mixotrophic) type.
Some cyanobacteria are capable of chemoheterotrophic growth. The set of organic substances supporting chemoheterotrophic growth is limited to a few sugars. This is associated with the functioning of cyanobacteria as the main catabolic pathway oxidative pentose phosphate cycle, the initial substrate of which is glucose. Therefore, only the latter or sugars that are easily converted enzymatically into glucose can be metabolized along this pathway.
One of the mysteries of cyanobacteria metabolism is the inability of most of them to grow in the dark using organic compounds. Inability to grow due to substrates metabolized in CTK, is associated with the “brokenness” of this cycle. But the main pathway of glucose catabolism is oxidative pentose phosphate cycle- functions in all studied cyanobacteria. The reasons cited are the inactivity of the transport systems of exogenous sugars into the cell, as well as the low rate of synthesis ATP, coupled with respiratory electron transport, as a result of which the amount of energy generated in the dark is only sufficient to maintain cellular activity, but not culture growth.
Cyanobacteria, in the group of which it was probably formed oxygenic photosynthesis, for the first time encountered the release of O2 inside the cell. In addition to creating a variety of defense systems against toxic forms of oxygen, manifested in resistance to high concentrations of O2, cyanobacteria have adapted to an aerobic mode of existence by using molecular oxygen to obtain energy.
At the same time, a number of cyanobacteria have been shown to grow in light under strictly anaerobic conditions. This applies to species that carry out oxygen-free photosynthesis, which, in accordance with the accepted classification, should be classified as facultative anaerobes. (Photosynthesis of any type is an anaerobic process by its nature. This is clearly visible in the case of oxygen-free photosynthesis and is less obvious for oxygenic photosynthesis.) For some cyanobacteria, the fundamental possibility of dark anaerobic processes has been shown ( anaerobic respiration , lactic acid fermentation), however, their low activity casts doubt on their role in the energy metabolism of cyanobacteria. O2-dependent and -independent modes of energy production found in the group of cyanobacteria are summarized in
1. Autotrophic nutrition. Photosynthesis, its meaning.
Autotrophic nutrition when the body itself synthesizes organic substances from inorganic ones, it includes photosynthesis and chemosynthesis (in some bacteria).
Photosynthesis occurs in plants and cyanobacteria. Photosynthesis is the formation of organic substances from carbon dioxide and water, in the light, with the release of oxygen. In higher plants, photosynthesis occurs in chloroplasts - oval-shaped plastids containing chlorophyll, which determines the color of the green parts of the plant. In algae, chlorophyll is contained in chromatophores that have different shapes. Brown and red algae, which live at considerable depths where access to sunlight is difficult, have other pigments.
Photosynthesis provides organic matter not only to plants, but also to the animals that feed on them. That is, it is a source of food for all life on the planet.
Oxygen released during photosynthesis enters the atmosphere. Ozone is formed from oxygen in the upper atmosphere. The ozone shield protects the Earth's surface from hard ultraviolet radiation, which made it possible for living organisms to reach land.
Oxygen is necessary for the respiration of plants and animals. When glucose is oxidized with the participation of oxygen, mitochondria store almost 20 times more energy than in its absence. Which makes the use of food much more efficient, has led to high metabolic rates in birds and mammals.
All this allows us to talk about the planetary role of photosynthesis and the need to protect forests, which are called “the lungs of our planet.”
2. Characteristics of the animal kingdom. The role of animals in nature. Among the ready-made microspecimens of protozoa, find green euglena. Explain why green euglena is classified by botanists as a plant, and by zoologists as an animal.
To the animal kingdom include heterotrophic organisms that are phagotrophs, i.e. absorbing food in more or less large parts, “pieces”. Unlike mushrooms, which absorb nutrients in the form of solutions (osmotrophs).
Animals are characterized by mobility, although some coelenterates lead a sedentary lifestyle as adults. Also, most animals have a nervous system that provides a response to stimuli. Animals can be herbivores, carnivores (predators, scavengers) and omnivores. In nature, animals are consumers, consume ready-made organic matter and significantly accelerate the circulation of substances in ecosystems and the biosphere as a whole. Animals help many plant species thrive by being pollinators, dispersing seeds, loosening the soil, and enriching it with excrement. We owe the formation of reserves of chalk and limestone to marine animals with a calcareous skeleton, which contribute to a constant concentration of carbon dioxide in the atmosphere.
Euglena green, a single-celled living creature, occupies an intermediate position in the taxonomy, possessing features inherent in different kingdoms. It has chloroplasts and feeds on light through photosynthesis. If there are dissolved organic substances in the water, especially in the dark, it absorbs them, switching to heterotrophic nutrition. The presence of a flagellum ensures mobility, which also makes it similar to animals.
3. Explain the biological significance of unconditioned and conditioned reflexes. Draw a diagram of the reflex arc (unconditioned reflex) and explain what parts it consists of. Give examples of unconditioned human reflexes.
The doctrine of reflexes associated with the works of the Russian physiologist Ivan Mikhailovich Sechenov.
A reflex is the body's response to stimulation, carried out with the participation of the nervous system. Reflexes are unconditioned - congenital and conditioned - acquired during life.
Unconditioned reflexes ensure the survival of the organism and species under constant environmental conditions and in the early stages of life. These include protective (blinking when a speck gets into the eye), indicative (study of the surrounding world), nutritional (sucking in children, saliva production). Instincts are also innate in nature; they are sometimes considered as a complex sequence of unconditioned reflexes. The most important instinct is procreation.
Conditioned reflexes are used to adapt to new conditions. They are formed under certain conditions and provide the best response. An example of a conditioned reflex is the arrival of birds to a familiar feeder, the recognition of edible and inedible (at first the chick pecks at everything), and teaching the dog commands.
The reflex arc of the unconditioned knee reflex includes: a receptor - the end of a sensitive neuron, nerve pathways along which the signal is transmitted to the central nervous system - a sensory neuron that transmits a signal to the spinal cord, an executive neuron in the anterior roots of the spinal cord that transmits a response command, an organ that produces response - muscle.
Most arcs of other reflexes include additional interneurons.
