Among the living organisms there are those whose belonging to any kingdom of living nature is constantly disputed. So it is with creatures called cyanobacteria. Although they don't even have a proper name. Too many synonyms:
- blue-green algae;
- cyanobionts;
- phycochrome pellets;
- cyanides;
- mucus algae and others.
So it turns out that a cyanobacterium is a completely small, but at the same time such a complex and controversial organism that requires careful study and consideration of its structure in order to determine the exact taxonomic affiliation.
History of existence and discovery
Judging by the fossil remains, the history of the existence of blue-green algae goes back far into the past, several (3.5) billion years ago. Such conclusions made it possible to make studies by paleontologists who analyzed the rocks (their sections) of those distant times.
On the surface of the samples werecyanobacteria were found, the structure of which did not differ from that of modern forms. This indicates a high degree of adaptability of these creatures to various habitat conditions, to their extreme endurance and survival. It is obvious that over millions of years there have been many changes in the temperature and gas composition of the planet. However, nothing affected the viability of the cyan.
In modern times, cyanobacteria is a single-celled organism that was discovered simultaneously with other forms of bacterial cells. That is, Antonio Van Leeuwenhoek, Louis Pasteur and other researchers in the XVIII-XIX centuries.
They were more thoroughly studied later, with the development of electron microscopy and modernized methods and methods of research. Features that cyanobacteria possess have been identified. The structure of the cell includes a number of new structures not found in other creatures.
Classification
The question of determining their taxonomic affiliation remains open. So far, only one thing is known: cyanobacteria are prokaryotes. This is confirmed by features such as:
- lack of nucleus, mitochondria, chloroplasts;
- presence of murein in the cell wall;
- S-ribosome molecules in the cell.
Nevertheless, cyanobacteria are prokaryotes with about 1500 thousand varieties. All of them were classified and combined into 5 large morphological groupings.
- Chroococcal. A sufficiently large group, uniting single orcolonial forms. High concentrations of organisms are held together by the common mucus secreted by the cell wall of each individual. In terms of shape, this group includes rod-shaped and spherical structures.
- Pleurocapsal. Very similar to the previous forms, however, a feature appears in the form of the formation of beocytes (more on this phenomenon later). The cyanobacteria included here belong to three main classes: Pleurocaps, Dermocaps, Myxosarcins.
- Oxillatories. The main feature of this group is that all cells are combined into a common mucous structure called trichomes. The division occurs without going beyond this thread, inside. Oscillatoria include exclusively vegetative cells that divide asexually in half.
- Nostock. Interesting for their cryophilicity. Able to live in open icy deserts, forming colored raids on them. The so-called phenomenon of "blooming ice deserts". The forms of these organisms are also filamentous in the form of trichomes, however, sexual reproduction, with the help of specialized cells - heterocysts. The following representatives can be attributed here: Anabens, Nostocs, Calotrix.
- Stigonem. Very similar to the previous group. The main difference in the method of reproduction is that they are able to divide multiplely within the same cell. The most popular representative of this association is the Fisherells.
Thus, cyanide is classified according to the morphological criterion, since for the rest there are many questions and confusion. Botanists and microbiologists to a common denominator insystematics of cyanobacteria cannot yet come.
Habitats
Due to the presence of special adaptations (heterocysts, beocytes, unusual tillakoids, gas vacuoles, the ability to fix molecular nitrogen, and others), these organisms settled everywhere. They are able to survive even in the most extreme conditions in which no living organism can exist at all. For example, hot thermophilic springs, anaerobic conditions with hydrogen sulfide atmosphere, acidic environment with pH less than 4.
Cyanobacteria is an organism that quietly survives on sea sand and rocky ledges, ice blocks and hot deserts. You can recognize and determine the presence of cyanides by the characteristic colored plaque that their colonies form. Color can vary from blue-black to pink and purple.
They are called blue-green because they often form a blue-green slimy film on the surface of ordinary fresh or s alt water. This phenomenon is called "water bloom". It can be seen on almost any lake that begins to overgrow and swamp.
Features of cell structure
Cyanobacteria have the usual structure for prokaryotic organisms, but there are some features.
The general plan of the cell structure is as follows:
- cell wall made of polysaccharides and murein;
- plasma membrane bilipid structure;
- cytoplasm with freely distributed genetic material in the form of a moleculeDNA;
- tillacoids that perform the function of photosynthesis and contain pigments (chlorophylls, xanthophylls, carotenoids).
Special parts of the cell will be discussed further.
Types of specialized structures
First of all, these are heterocysts. These structures are not parts, but the cells themselves as part of a trichome (a common colonial thread united by mucus). They differ when viewed through a microscope in their composition, since their main function is the production of an enzyme that allows the fixation of molecular nitrogen from the air. Therefore, there are practically no pigments in heterocysts, but there is a lot of nitrogen.
Secondly, these are hormogonies - areas torn out of the trichomes. Serve as breeding grounds.
Beocytes are a kind of daughter cells, in the mass endowed from one mother. Sometimes their number reaches a thousand in one division period. Dermocaps and other Pleurocapsodiaceae are capable of such a feature.
Akinets are special cells that are at rest and are included in the trichomes. Differ in a more massive, polysaccharide-rich cell wall. Their role is similar to heterocysts.
Gas vacuoles - all cyanobacteria have them. The structure of the cell initially implies their presence. Their role is to take part in the processes of water blooming. Another name for such structures is carboxysomes.
Cell inclusions. They certainly exist in plant, animal, and bacterial cells. However, in blue-green algae, these inclusions are somewhat different. These include:
- glycogen;
- polyphosphate granules;
- cyanophycin is a special substance consisting of aspartate, arginine. Serves for the accumulation of nitrogen, since these inclusions are in heterocysts.
This is what the cyanobacterium has. The main parts and specialized cells and organelles are what allow cyanideans to carry out photosynthesis, but at the same time belong to bacteria.
Reproduction
This process is not particularly difficult, as it is the same as that of ordinary bacteria. Cyanobacteria can divide vegetatively, parts of trichomes, a normal cell in two, or perform a sexual process.
Often specialized cells of heterocysts, akinetes, beocytes are involved in these processes.
Methods of transportation
The cyanobacteria cell is covered on the outside with a cell wall, and sometimes also with a layer of a special polysaccharide that can form a mucus capsule around it. It is thanks to this feature that the movement of cyan is carried out.
There are no flagella or special outgrowths. Movement can only be carried out on a hard surface with the help of mucus, in short contractions. Some Oscillatoriums have a very unusual way of moving - they spin around their axis and at the same time cause the entire trichome to rotate. This is how the surface moves.
Nitrogen fixation capacity
This feature has almost every cyanobacteria. This is possible due to the presence of the enzyme nitrogenase, which is able to fix molecular nitrogen andconvert it into a digestible form of compounds. This happens in the structures of heterocysts. Therefore, those species that do not have them are not able to fix nitrogen from the air.
In general, this process makes cyanobacteria very important creatures for plant life. Settling in the soil, cyanes help flora to assimilate bound nitrogen and lead a normal life.
Anaerobic species
Some forms of blue-green algae (for example, Oscillatoria) are able to live in completely anaerobic conditions and an atmosphere of hydrogen sulfide. In this case, the compound is processed inside the body and as a result, molecular sulfur is formed, which is released into the environment.
