Cyanobacteria: Definition, Characteristics, Occurrence, Cell Structure, Reproduction, and, Importance

Cyanobacteria: Definition, Characteristics, Occurrence, Cell Structure, Reproduction, and, Importance

Cyanobacteria: Definition

The name cyanobacteria come from their color, giving them their other name, “Blue-Green Algae“, The cyanobacteria are also known as Cyanophyceae because of their blue color. they are also called Micro-Alga, Blue-Green Algae. It is the largest gram-negative bacteria. The cyanobacteria are also called Oxy–Photo–Bacteria because it contains PS1 and PS2. The PS2 which is present is involved in the water broke down means there is the release of oxygen. When it performs photosynthesis it releases oxygen so we can say it is oxygenic photosynthesis, due to this oxygenic photosynthesis was performed by cyanobacteria, a primitive earth atmosphere that was anaerobic that was changed to present-day earth atmosphere i.e aerobic. this is the only bacterial group that shows Oxygenic Photosynthesis. The present-day oxygen which is present today is due to the presence of their activity i.e Cyanobacteria.



Some important characteristics of cyanobacteria are as follows

1. The blue-green alga is the only known oxygen-producing prokaryote, comprising about 2500 species placed under 150 genera in a single class Cyanophyceae or Myxophyceae.

2. The blue-green alga is considered the simplest living autotrophic plants

3. the cells constituting the thallus are prokaryotic

4. The nuclear membrane, nucleolus, and membrane-bound plastids are absent in cyanobacteria.

5. the unique food storage compounds are Myxophycean starch and the proteinaceous material cyanophycin.

6. the blue-green alga has a mucilaginous sheath outside the cell wall.

7. the blue-green alga is sensitive to antibiotics

8. sexual reproduction is completely absent in blue-green alga however genetic recombination is known to occur in many blue-green algae.


Cyanobacteria are a diverse group of bacteria. they are present in frozen lakes, hot water springs, etc It implies that they are also present in stressful situations. this is the only organism that shows the association with every eukaryotic group. E,g it shows association with aquatic fern i.e Azolla, in Azolla, it shows an association with the leaves and the cyanobacteria which are associated with leaves is Anabaena. the cyanobacteria also show an association with Gymnosperms i.e Cycas. In the cycas, the association of cyanobacteria is in the roots they are known as coralloid roots. A notable example of marine blue greens is Trichodesmium erythrueum in which the red pigment predominates. this species flourishes in the Red sea and is responsible for the red color of its water.

Organization of The Thallus

Blue-green algae are among the most basic photosynthetic plants on the planet today. The thallus can be a single cell or a colony in structure.

1. Unicellular forms: Some species have a single-celled thallus that is spherical or oval. After cell division, the daughter cells are immediately separated from each other. E,g Chroococcus, Anacystis

2. Colonial Forms:  In most Blue-greens, the cells are held together by their cell walls following division. A gelatinous matrix links cells together to form a colony, which is a loose cell structure. Of course, the colony’s cells frequently aggregate into irregular, palmelliod forms with a wide range of variety,g Gloeothece, Aphanocapsa, The colonies might be filamentous or non-filamentous.  Each colony is wrapped in a gelatinous sheath general.

A.Non-filamentous colonies: Non-filamentous colonies are of many forms. They’ll probably be divided into cubicles. Depending on the planes and orientations in which the cells split, they can be spherical, square, or irregular.  E,g Microcystis, Gamphophaera.

B.Filamentous colonies: The filamentous colonies are the result of repeated cell divisions in a single plane and a single direction forming a chain or a thread. It is known as Trichome. Separation barriers or a shared viscous sheath encircling the trichome may hold the cells together. E,g Spirulina, Rivular

Cell structure

The body of the cyanobacteria is covered by a mucilaginous covering or slimy covering. The sheath is a thick and dense mucilaginous coating that surrounds the cell. Behind this slimy covering is a cell wall. cell wall in cyanobacteria is made up of four layers. below the cell, there is a cell membrane, The cell membrane is made up of phospholipid bilayers. It has lamellose ingrowths on it. The most common type of ingrowth is plates/lamellae. the function of lamellae is just like mesosomes. they have enzymes that are helpful in respiration. to the lamellose, there is an attachment of the Nucleoid i.e primitive nucleus. there is central cytoplasm and peripheral cytoplasm. the cytoplasm which is present at the periphery contains pigments. Because of the presence of pigments, peripheral cytoplasm is referred to as chromoplasm. Thylakoids are sac-like structures that form in the peripheral cytoplasm. the membrane of the thylakoid contains photosynthetic pigments i.e chlorophyll A. There are carotenoids present, including carotene and myxoxanthin, in addition to chlorophyll. Some complexes are found on the surface of the thylakoids. these complexes are known as Phycobilisomes. Pigments can be found in these compounds. The type of pigment which is present is proteinaceous, water-soluble pigments called phycobilins. There are three types of phycobilins Phycoerythrin, Phycocyanin, and Allophycocyanin. Allophycocyanin is light blue, Phycoerythrin is red, and Phycocyanin is blue. Among the three pigments, the main pigment is phycocyanin because it is involved in the trapping of light. the color of phycocyanin is blue which is why it is known as cyanobacteria or blue-green algae. It also contains cytoplasmic inclusions, they have reserved food. the Alpha granule contains reserve food in the form of myxophycean starch. β-granule contains reserve food in the form of fats, volutin granule stores phosphate while cyanophycin granule has storage of protein. polyhedral granule contains one enzyme which is involved in CO2 fixation RUBISCO, which results in food synthesis.

Nitrogen Fixation

Cyanobacteria are a group of photosynthetic bacteria, some of which are nitrogen-fixing. Nitrogen fixation is performed by cyanobacteria with the help of the enzyme nitrogenase. This enzyme will work out only in anaerobic conditions. Special nitrogen-fixing cells called Heterocysts are used to create anaerobic conditions inside cyanobacteria. it is larger and is surrounded by a cell wall which is why it is known as a Cyst. Phycobilins are not present in this cyanobacteria cell. It signifies that the cell will appear pale yellow rather than red or blue in hue. One of the most frequent types of cyanobacteria i.e Nostoc in which there are specialized nitrogen cells. this is a filament of nostoc. In nostoc, large-sized cells are nitrogen-fixing cells called Heterocysts. mucilage around the heterocyst is absent. the heterocyst will work like an anaerobic device. due to this reason, nitrogenase is active and it will perform nitrogen fixation. now, how will it work like an anaerobic device, around the heterocyst there is the presence of a thick wall due to this reason the oxygen which is present in the environment will not penetrate inside the cell. in the cyanobacteria, there is the presence of PS1 and PS2.the PS2 is involved in the breakdown of water. when water breaks down there is the release of oxygen but in heterocyst cells PS2is absent and only PS1 is present. this will prevent the release of oxygen thus condition is anaerobic and nitrogenase is active. Now nitrogenase enzyme fixes nitrogen and converts nitrogen into Ammonia. This Ammonia can easily be utilized for the synthesis of amino acids, as amino acids are involved in protein synthesis.

 After polymerization N2——-NH3——– Amino acids.

This nitrogen-fixing ability is not present in every organism but present in a few prokaryotic organisms e,g Cyanobacteria and the Enzyme involved in Nitrogenase.

 N2 fixation—-Nitrogenase—Anaerobic condition—Heterocyst


There are several methods of asexual reproduction which are present in Cyanobacteria, some important ones are as follows

1. Binary Fission: the most common method of multiplication is binary fission. The rate of cell division is quite rapid, with some forms undergoing as many as 12 doublings per day. As a result of this rapid growth, dense water blooms emerge. many bloom-forming species are buoyant and may rise to the surface forming scum or mat.

2. Fragmentation: In filamentous cyanobacteria, reproduction occurs through fragmentation. the filament of cyanobacteria due to some mechanical injuries breaks into fragments and each fragment shows growth after the growth, each fragment results in the formation of cyanobacteria.

3. Heterocyst: It is also a reproductive structure, Heterocyst can separate from the main filament after germination. It results in the formation of a new filament.

4. Akinete: During unfavorable conditions, some of the cells of the filament are surrounded with the help of a thick wall and along with that they will store abundant reserve food material. these thick wall cells are known as Akinetes. these cells will be separated till the time the conditions are unfavorable. this Akinete will act as a resting structure when the conditions are favorable, the akinete wall will dissolve, and the cell will germinate and generate a new filament after the fracture.

5. Harmogonia: In the filament of harmogonia some of the cells in the filament become dead. these dead cells are known as Necridia. The cells become dead due to the presence of abundant mucilage, these dead cells will disintegrate or break. the separated part will show growth and result in the formation of a new body of cyanobacteria. The part between two dead cells which grow is known as Harmogonia.

Ecological importance

Some useful aspects of cyanobacteria are as under

1. Nitrogen fixation is carried by cyanobacteria. Due to this activity cyanobacteria are used as cyanobacteria. Bio-fertilizers are biological agents which can increase soil fertility.

2. Some of the cyanobacteria are rich in proteins and are used as SCP (single-cell protein). SCP is obtained from cyanobacteria called Spirullina

3. It can also be involved in CO2 fixation in symbiotic conditions. It can fix nitrogen in terrestrial as well as aquatic plants.

Frequently Asked Questions about Cyanobacteria

Question 1. Why are cyanobacteria so important?

ANS:  Cyanobacteria play a critical role in the health and growth of many plants. They are one of the few species capable of converting inert air nitrogen into an organic form like nitrate or ammonia.

Question 2. Can cyanobacteria produce oxygen?

ANS: The Blue-Green Alga is the only known oxygen-producing bacteria. yes, cyanobacteria can produce oxygen.

Question 3. Are cyanobacteria bad for an aquarium?

ANS: While Cyanobacteria in aquariums usually do not harm fish, they can kill your plants if it covers their leaves and prevents them from photosynthesizing light. Blue-green alga is a type of photosynthetic bacterium that can be blue, green, brown, black, or red.

Question 4. Does UV light kill Blue-Green Algae?

ANS: UV light has no long-term impact on creatures attached to fish (such as adult ich) or rocks (e.g., algae).

Question 5. Can drinking water with algae make you sick?

ANS: Gastroenteritis can be caused by drinking algae-affected water or eating food (such as fish or shellfish) that contains toxins, which can cause vomiting, diarrhea, fevers, and headaches. The liver and neurological system may be harmed by these poisons.

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