Cyanobacteria: occurrence, morphology, structure, reproduction

Cyanobacteria: occurrence, morphology, structure, reproduction


  • The cyanobacteria are the most important and most diverse group of photosynthetic bacteria.
  • Cyanobacteria are Gram negative bacteria.
  • They are obligate photolithoautotrophs and oxygenic photosynthetic.
  • The only organism that can do nitrogen fixation and are able to perform oxygenic photosynthesis.
  • Cyanobacteria also referred as blue green algae.
  • Photosynthetic pigments present in cyanobacteria are chl a (in very few cases chl b and chl d), carotenoids and phycobilins (phycocyanin and phycoerythrin).


  • Cyanobacteria are ubiquitous, and are often found in all types of environment-freshwater, salt marshes, hot springes, tree trunks, sea water, moist rock, frozen water, moist soil.


  • Cyanobacteria are varying greatly in shape and appearance.
  • They range in diameter from 1 to 10 micrometres.
  • Both unicellular and filamentous (termed trichomes), forms of cyanobacteria occur in nature.
  • Filamentous form may be branched or unbranched.
  • Trichomes is a row of bacterial cells that are in close contact with one another over a large area.

Morphology of cynobacteria

Single trichome filamentous may be of two types:

    • Homocystous- Undifferentiated e.g. oscillatoria.
    • Hetrocystous- Differentiated and having hetrocyst. E.g. Nostoc.
  • Spirulina has a spirally coiled filament.
  • Gliding movement is used by number of known cyanobacteria because flagella are absent.

Cell structure of cyanobacteria

  • All cyanobacteria except Gleobacter violaceus, have an internal system of thylakoid membrane in which the light reaction of photosynthesis and respiration occur.
  • Besides the thylakoid membrane the cyanobacteria cytosol contains components such as carboxysomes, glycogen granules, cyanophycin granules, lipid bodies, polyphosphate bodies.
  • Cyanobacterial cells are more elaborate and larger than bacteria.

Cell structure of cyanobacteria

  • Cyanobacteria have typically prokaryotic cell structure naked DNA, 70s ribosome, one envelope organization with peptidoglycan.
  • Membrane bound structure like endoplasmic reticulum, mitochondria, Golgi bodies, SAP vacuoles, plastids are absent in cyanobacteria.
  • Cyanobacteria cell wall is four layered with peptidoglycan is present in the second layer.


Cyanobacteria employee’s variety of mechanism with respect to reproduction:

  1. Binary fission.
  2. Budding.
  3. Fragmentation.
  4. Multiple fission.
  • Fragmentation of filamentous cyanobacteria form small, motile filaments called hormogonia.
  • Some cyanobacterial species develop akinetes, specialised, thick- walled dormant resting cells that protect the organism in unfavourable conditions.
  • Cyanobacteria lack the enzyme alpha ketoglutarate dehydrogenase, thus they do not have a fully functional citric acid cycle.


  • Many nitrogen fixing, filamentous cyanobacteria have specialised cells in which nitrogen fixation occurs known as heterocyst.
  • It has enzyme nitrogenase.
  • Heterocyst depends on adjacent vegetative cells for its nourishment.
  • Photosystem II is absent.
  • Thick walls present which is impermeable to oxygen but permeable to nitrogen.

heterocyst of cynobacteria

Economic importance of cyanobacteria

  • Nitrogen fixing cyanobacteria are often used for reclaiming user soils. E.g. Nostoc, Anabena.
  • Blue-green algae used as food for several aquatic animals.
  • In Africa, spirulina is regularly collected for human consumption. Nostoc is similarly used in China as a food.
  • From extract of, Lyngbia several antibiotic can be manufactured.
  • Several species of cyanobacteria are used to prevent the growth of mosquitoes Larvae Nearby E.g. Anabena, Aulosira.
  • Some cyanobacteria produces some toxins which may be very harmful to most of the  aquatic animals. The important toxins producing cyanobacteria are: Microcytic aeruginosa, Anabena flosaquae.

Reference and Sources

  • 1% –
  • 1% – _Proteins_ of_the_cyanobacterial_ photosystem_I
  • 2% –

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Cyanobacteria: occurrence, morphology, structure, reproduction

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