Cyanobacteria, are a wide range of photosynthetic bacteria that can perform oxygenic photosynthesis. Cyanobacteria are also known as blue-green algae. These are prokaryotic cells that lack membrane-bound organelles and belong to the domain of bacteria. Cyanobacteria structure is filamentous, colonial, or unicellular, and Cyanobacteria function as primary producers, nitrogen fixers, and oxygen producers. In this article, we will learn about cyanobacteria, its functions, structure, and examples.
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What is Cyanobacteria?
Definition of Cyanobacteria: Cyanobacteria are oxygenic photosynthetic bacteria that develop on the surface of newly exposed rocks, causing organic matter deposition as their cells accumulate.
Cyanobacteria is also known as blue-green algae. They are microscopic organisms that exist naturally in all types of water. These single-celled organisms can exist in fresh, brackish, and marine waters. These organisms use sunlight to produce their food. Cyanobacteria thrive in warm, nutrient-rich settings, forming blooms on the water's surface.
Cyanobacteria are larger than bacteria and possess chlorophyll-A. Some kinds contain specialized terminal structures known as heterocysts. Heterocyst-bearing cyanobacteria are all aerobic photo diazotrophic. Blue-green algae are sensitive to light, salinity, temperature, and nutritional changes.
Cyanobacteria Structure
The famous scientists pankratz and Bowen (1963) described the cellular structure of cyanobacteria. The cyanobacteria is prokaryotic. To understand the formation of cyanobacteria, we have to know about their cellular and specialized structure.
Cyanobacteria Cell Structure
- Mucilagenous sheath: It is present all round outside the cells and filament.
- Cell wall: It is a four layered rigid and complex structure. Its outer layer contains muramic acid and inner layers contain analine and glutamic acid. The plasma membrane of lipoprotein is present within the cell wall.
- Protoplasm: It is divided in 2 parts- Chromoplasm and Centroplasm
- Chromoplasm: Chromoplasm refers to the coloured component of protoplasm that surrounds the cell. This section contains multiple lamellae or thylakoids, which are typically distributed in two or more parallel rows or irregularly. These lamellae contain photosynthetic pigments and other pigments such as phycocyanin, phycoerythrin, chlorophyll 'a', and carotene. The cyanobacterial cell lacks organelles such as mitochondria, and the endoplasmic reticulum, but it have ribosomes, cyanophycean granules, and gas vacuoles or pseudovacules.
- Centroplasm: It is the core component of protoplasm. It mostly consists of genetic material. It lacks the nuclear membrane and nucleolus. This section comprises dispersed strands of DNA and a minor amount of RNA. It therefore lacks a genuine nucleus. This type of nucleus is known as a nucleoid or incipient nucleus.
- Thylakoid Membranes: The inner membrane is also known as the cytoplasmic or plasma membrane. Thylakoid membranes are found in the cytoplasm and are thought to connect to the plasma membrane in "thylakoid centres."
Cyanobacteria Specialized structure
- Gas Vaculoes: In cyanobacteria, gas vaculoes are protein-bound structures that is surrounded by a protein membrane. Gas vacuoles allow cyanobacteria to orient themselves optimally for light and nutritional circumstances by providing them buoyancy. The vesicle's inside component is hydrophobic, which prevents water from entering. The diameter of gas vesicles is approximately 75 nm, and their length spans from 200 to 1000 nm.
- Akinete: A vegetative cell is developed into akinete by-
- The gradual disappearance of gas vacuoles.
- An increase in cell size.
- An increase in cytoplasmic density and number of ribosomes.
- An increase in storage products-
- High concentration of glycogen
- High concentration of cyanophycin
- The are greater resistance to cold compared with vegetative cells.
- lose their photosynthetic and respiratory capabilities.
- Heterocysts: A vegetative cell can also differentiate into a heterocyst, which has the following characteristics.
- They're larger than vegetative cells.
- In the light microscope, they appear to be empty and inactive in terms of photosynthesis.
- They neither fix CO2 nor create O2.
- They are enclosed by a thick laminated cell wall that restricts the entry of ambient gases, including O2.
- The inside environment of heterocysts is almost completely anoxic (perfect for nitrogenase, an O2 sensing enzyme).
Cyanobacteria Examples
Cyanobacteria are aquatic and photosynthetic bacteria that use oxygen to make food.
- Blue-green algae
- They are classified into a few genera, including Aulosira, Nostoc, Stigonema, Anabaena, Spirulina, Oscillatoria, Syctonema, Gloeocapsa, and Chrococcus.
- Nostoc
- It is an aquatic cyanobacterium that produces food.
- Anabaena
- It is a water-dwelling cyanobacterium that can photosynthesis.
- Spirulina
- It is a cyanobacterium that is useful in both the food sector and medicine.
- Nostoc sphaericum
- It is a cyanobacterium of the Nostoc genus that is popular in the cuisine of various Latin American countries, where it is known as cushuro.
- It has a spherical shape, gelatinous consistency, and antioxidant and antiviral activities, making it pharmacologically interesting.
Cyanobacteria Characteristics
Cyanobacteria are photosynthetic prokaryotes. These form small groups or multicellular colonies forming long filamentous chains of cells. These are without flagella and pilli. The characteristics of cyanobacteria cell consist following details-
- Structure: These are prokaryotic algae as Gram negative bacteria.
- Cell wall: Amino sugars and amino acids.
- Color: Bluish-green due to the presence of blue, green, and red pigment.
- Pigments: Chlorophyll (a and f) and phycobilin proteins (phycocyanin, allophycocyanin, and phycoerythrin) are present.
- Halomicronema hongdechloris was the first cyanobacterium discovered to synthesize chlorophyll f.
- Storage product: glycogen
- Environment: These are single-celled and adapt different environment like-
- Aquatic: Fresh, brackish, and marine water. They can also withstand harsh conditions such as hot springs.
- Terrestrial: Soil, deserts, glaciers, and Antarctic rocks are all examples of terrestrial environments. They can also survive on moist soil and temporarily moistened rocks in deserts.
- Symbiotic: exist among plants, lichens, and primitive mammals.
- Toxicity: They produce cyanotoxin that can cause Abdominal pain, nausea, vomiting, headache, diarrhea, sore throat, blistering around the mouth, and pneumonia. Microcystins can also affect the liver, kidneys, and reproductive system.
- Nitrogen fixation: The enzyme nitrogenase fixes nitrogen, although it is sensitive to oxygen and requires a virtually anoxic environment. Cyanobacteria possess distinct ways for protecting nitrogenase from oxygen and controlling the development of the N2-fixing machinery.
What is the Importance of Cyanobacteria?
The importance of cyanobacteria are as follows:
- They help in the reclamation of alkaline soil like barren soil, or soil that is water-logged
- They help in Nitrogen fixation.
- They help in releasing O2.
- They are pollution indicators like oscillitoria dying in contaminated water which is a sign of polluted water.
- They form a symbiotic relationship with plants.
- They form the pond scum which forms more than 60% protein and is used by factories and industries that form food. They are a good source of protein for diet.
Function of Cyanobacteria
Cyanobacteria have several function that can help us in many ways. Some of them are discussed below-
- Crop Production:
- Cyanobacteria improve crop production by acting as biofertilizers, improving soil conditions, mineralizing organic molecules, stimulating plant growth, and acting as a biological pest control agent.
- Nitrogen fixation:
- Terrestrial Cyanobacteria species improve soil fertility by fixing atmospheric nitrogen (N), binding soil particles, retaining moisture, and avoiding erosion.
- Blue-green algae (Cyanobacteria) fix atmospheric nitrogen through biological nitrogen fixation. As photosynthetic organisms, they do not compete with agricultural plants or soil microflora for carbon and energy.
- Soil fertility:
- Nitrogen-fixing plants like Anabaena, which grows in rice fields with the floating water fern Azolla, improve soil fertility and enhance rice output.
- Plant growth:
- Cyanobacteria-based biofertilizer promotes plant growth by improving soil chemical and biological characteristics, synthesising growth-promoting substances, restoring the soil's natural nutrient cycle, building soil organic matter, converting complex nutrients into simple nutrients, reducing soil salinity, preventing weed growth, and increasing pH.
- Cyanobacteria produce growth-promoting regulators (similar to gibberellins and auxins), vitamins, amino acids, polypeptides, antibacterial and antifungal substances, and polymers, such as exopolysaccharides, to improve soil structure and enzyme activity.
- Binding agent:
- Decomposed Cyanobacteria's organic matter works as a binding mucilaginous agent in soil, increasing humus content and promoting plant growth.
- Cyanobacteria excrete polysaccharides, peptides, and lipids while growing in soil. These chemicals bind soil particles into microaggregates. Polysaccharides include fibres that can entangle clay particles and create clusters, in addition to other substances.
Conclusion: Cyanobacteria - Structure, Examples, Characteristics
Cyanobacteria are probably the most successful group of microbes on the planet. Cyanobacteria are crucial to understand because they are seen in our daily lives and contribute significantly to ocean primary production. Their primary job is to fix nitrogen in tropical marine habitats. Marine environments are distinguished by a distinct cyanobacterial flora, and nature appears to have provided every imaginable combination of photosynthetic pigment. This is the most unknown biodiversity, particularly in the less accessible infralittoral, could become an important replenishment resource in the future.
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