Cyanobacteria are also called cyanobacteria or blue-green algae. Like higher green plants and higher algae, it contains chlorophyll a, a photosynthetic pigment, and was also a group of algae plants before the 1960 s of oxygen-producing photosynthesis. The application of modern technology shows that its nucleus has no nuclear membrane and mitotic apparatus, and its cell wall is similar to bacteria. It is composed of a mucus complex (peptidoglycan), which contains diaminopimelanic acid and is gram-negative, so it tends to be classified as a prokaryotic microorganism now.
Cyanobacteria are widely distributed, from the tropics to the poles, from the ocean to the mountains, everywhere. Soil, rocks and even bark or other objects can grow in pieces; Many cyanobacteria grow in ponds and lakes, forming micelles floating on the water. Some are dominant or unique photosynthetic organisms in hot springs, salt lakes or other extreme environments above 80℃.
The morphology of cyanobacteria is very different. Spherical or rod-shaped single cells and filaments are known, and the cell diameter varies from the size of ordinary bacteria (0.5- 1 micron) to 60 microns. Such a large cell may be rare in prokaryotic microorganisms. But the diameter or width of cyanobacteria is generally 3- 10 micron. When many individuals gather together, they can form a large group visible to the naked eye. If it grows vigorously, the color of water can change with the color of bacteria.
Compared with other prokaryotes, the most unique feature of cyanobacteria in chemical composition is that they contain unsaturated fatty acids composed of two or more double bonds, while almost all bacteria contain saturated fatty acids and single unsaturated fatty acids (one double bond).
The fine structure of the cell wall of cyanobacteria is similar to that of gram-negative bacteria. Many of them can continuously secrete sticky substances outside the cell wall, similar to the envelope of bacteria, and combine with groups of cells or filaments to form micelles or sheaths. Most of them can "slide" without flagella. The gliding motion of some cyanobacteria is not a simple transfer, but the rotation, inversion and bending of filaments. Some can also do light-avoiding exercises.
The photosynthetic mechanism of cyanobacteria has a primitive layered structure, which is composed of multiple membranes and distributed in cytoplasm. The layered structure contains photosynthetic pigments, such as chlorophyll a, phycobiliprotein and carotenoids. Phycobilitin plays the role of accessory pigments in photosynthesis and is unique to cyanobacteria. Phycobilitin also includes phycocyanin and phycocyanin. In most cyanobacteria cells, phycocyanin is dominant and mixed with other pigments to make the cells appear special blue, so it is called cyanobacteria.
Many cyanobacteria cells have bubbles in the south. Its function may be to float bacteria and keep them in the place where photosynthesis is the most abundant. Cyanobacteria can fix nitrogen by themselves or by themselves. Some species have round heteromorphic cells, which are generally distributed along filaments or in a single place at one end (see 2-7 1). Experiments show that it is the place where cyanobacteria carry out nitrogen fixation. Idioblast has cell-to-cell contact with adjacent vegetative cells and exchanges substances between these cells. For example, the products of photosynthesis move from vegetative cells to heterotypic cells, while the products of nitrogen fixation can move from heterotypic cells to vegetative cells. Idioblast contains a small amount of phycobiliprotein, which has photosynthetic system I and can carry out anaerobic photosynthesis to produce ATP high-energy bonds and reducing substances. Nitrogen-fixing enzyme system exists in idioblast. When it grows under anaerobic conditions, they produce nitrogenase and fix nitrogen in normal vegetative cells. However, some algae that do not form heteromorphic cells, such as several unicellular algae of Myxococcus (Cyanophyta) that can produce tunica vaginalis, can fix nitrogen even under aerobic conditions. It is conceivable that a different mechanism has been developed in cyanobacteria to maintain the anoxic state of its nitrogenase.
The nutrition of cyanobacteria is very simple. No vitamins are needed, and nitrate or ammonia is used as nitrogen source. Species that can fix nitrogen are common. Most of them are obligate photobiotics, some are obligate photoautotrophs, and some are chemotactic heterotrophs.
Because cyanobacteria are photoautotrophs, they can produce oxygen and photosynthesis like green plants, assimilate CO2 into organic matter, and many species also have nitrogen fixation. So their living conditions and nutritional requirements are not high. As long as there is air, sunlight, water and a small amount of inorganic salts, it can grow in large quantities. In addition, the surface of bacteria is covered with a colloidal layer to keep moisture, which has strong drying resistance. Even the dried Nostoc commune (also known as Nostoc commune) preserved for 87 years can continue to grow after being transplanted into a suitable medium. The above physiological characteristics may be the main reason for the widespread distribution of cyanobacteria.
Cyanobacteria have no sexual reproduction, mainly fission, and few species have spores.
There are more than 20 kinds of cyanobacteria with nitrogen fixation, so agriculture, especially enthusiasm, has become the main factor to maintain the nitrogen nutrition level in soil. Cultivating cyanobacteria in rice fields as a bio-fertilizer source can improve soil fertility. In recent years, it has been reported that some scholars regard cyanobacteria as human food or auxiliary nutrients, and all of them have achieved ideal experimental results. Clinically, it can be used to treat liver cirrhosis, anemia, cataract, glaucoma, pancreatitis and other diseases, and also has a certain curative effect on diabetes and hepatitis. In addition, cyanobacteria may be the first photosynthetic organism to produce oxygen, which is the first reason why the air changes from anaerobic to aerobic. Because of its significance, practical function and structural characteristics, it is a microorganism with great economic benefits and theoretical value, which has aroused great interest of biologists and done a lot of research work.
Biological characteristics of photosynthetic bacteria
Photosynthetic bacteria are widely distributed in natural soil, paddy fields, swamps, lakes, rivers and oceans. , mainly distributed in the anoxic area with light transmission in aquatic environment. The optimum water temperature of photosynthetic bacteria is 15-400℃, and the optimum water temperature is 28-360℃. PSB is rich in nutrients, and the cell dry matter contains more than 65% protein. The amino acid composition of protein is relatively complete. Cells also contain a variety of vitamins, especially B vitamins, Vb2, folic acid, pantothenic acid and biotin, as well as a large number of carotenoids, coenzyme Q and other physiologically active substances. Therefore, photosynthetic bacteria have high nutritional value, which is the material basis for their use as hydroponic bait and feed additive in aquaculture.
Photosynthetic bacteria can carry out photosynthesis in the environment with light and hypoxia, use light energy to carry out photosynthesis, and use light energy to assimilate carbon dioxide. Unlike green plants, their photosynthesis does not produce oxygen. There is only one photosystem PSI in photosynthetic bacteria cells. The initial hydrogen donor for photosynthesis is H2S (or some organic matter), not water. As a result of photosynthesis, it produces H2, decomposes organic matter, and fixes molecular nitrogen in the air to produce ammonia. In the process of its own assimilation and metabolism, photosynthetic bacteria have completed three extremely important chemical processes in the natural material cycle: hydrogen production, nitrogen fixation and decomposition of organic matter. These unique physiological characteristics make them extremely important in the ecosystem.
Photosynthetic bacteria used in aquaculture are mainly some species of Rhodosporidae, such as Rhodopseudomonas palustris;
In nature, fresh seawater usually contains nearly 100 PSB bacteria per milliliter. The cells of photosynthetic bacteria use organic acids, amino acids, ammonia, sugars and hydrogen sulfide as oxygen supply, and obtain energy through photosynthetic phosphorylation. Under the illumination of water, they can directly degrade organic matter and oxygen sulfide and self-multiply, thus purifying water.