Cyanobacteria are photosynthetic bacteria that are also referred to as blue-green algae. Here, let’s learn the characteristic features of cyanobacteria in detail.
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Cyanobacteria
The cyanobacteria are commonly called blue-green algae. They are photosynthetic autotrophs that have chlorophyll pigments just like that of green plants. A significant portion of the plankton found in the oceans and seas are cyanobacteria. They also serve as food for fish and produce a major fraction of the oxygen in the atmosphere.
Cyanobacteria – Habitat
A family of photosynthetic bacteria known as cyanobacteria are widely dispersed in both aquatic (such as oceans, rivers, seas and lakes) and terrestrial settings (e.g. moist soils). They can reside alone or in colonies (by establishing spheres or filaments with other cyanobacteria).
Features of Cyanobacteria
Cyanobacteria is a diverse phylum of photoautotrophs that exhibit typical prokaryotic organisation. The following are some salient features of cyanobacteria:
- The cyanobacteria are freshwater/marine, unicellular, filamentous or terrestrial algae. Their members are blue-green in colour because of the presence of phycocyanin pigment. They also contain chlorophyll-a, carotene and phycoerythrin. These pigments are well-dispersed in the cytoplasm.
- The components of a typical blue-green algal cell are the outer cellular layer, cytoplasm and nuclear material. These prokaryotes lack a true nucleus, plastids, endoplasmic reticulum, vacuoles, Golgi bodies and mitochondria.
- The outer or peripheral pigmented area of the cytoplasm comprises photosynthetic lamellae or thylakoids in a space called chromoplasm. The centroplasm, also known as the inner or central colourless region, comprises DNA and crystalline granules.
- The cell wall of each individual cell (or cyanobacterium) is thick and gelatinous. This gelatinous coating typically surrounds the colonies.
- In polluted water bodies, they frequently develop blooms. Some of these organisms, such as Nostoc and Anabaena, have the ability to fix atmospheric nitrogen in specific cells referred to as heterocysts.
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Reproduction in Cyanobacteria
Transverse binary fission is the most prevalent form of asexual reproduction in cyanobacteria. Additionally, there are a few specialised structures that play a role in reproduction, including akinetes, hormogonia, hormocysts and spores.
- Akinetes – After storing food supplies, the vegetative cell of some cyanobacteria develops into yellow-brown cells known as akinetes. It has a strong wall covering it, and when the conditions are favourable, it sprouts to create a new thallus.
- Hormogonia – Some cyanobacteria in the order Stingonematales and Nostocales produce movable filaments of cells called hormogonia. They are short filaments that exhibit gliding motion and grow into new, fully developed filaments in the later stages.
- Hormocysts – They are hormogonia with dense sheath. They can be intercalary or terminal in position and can produce new filaments through germination at either or both ends.
- Spores – When unfavourable conditions have passed, non-filamentous cyanobacteria typically produce spores like endospores, exospores and nanocysts that contribute by germinating and giving rise to new vegetative cells.
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