Class: Cyanophyceae

Class: Cyanophyceae

General Characteristics

  • Cyanophycea exhibits a prokaryotic cell organisation.
  • It is the oldest oxygenic photoautotrophs on the earth
  • It is commonly known as blue-green algae as their principle pigment is bluish-green ie. C- phycocyanin
  • It consists of photosynthetic pigments including chlorophyll a, chlorophyll b or d (some may have), accessory pigments phycobiliprotein.
  • They may be unicellular or multicellular, free-living or colonial unbranched filamentous or branched filamentous, heterocystous or non-heterocystous, aquatic or terrestrial
  • They don’t have well-organized cell organelle and their pigments throughout the peripheral cytoplasm.
  • They have the primitive type of nucleus ie. they lack nuclear membrane and nucleolus.
  • Also, they do not have flagella and their movement is by gliding movement
  • They also lack sexual reproduction
  • Cyanophyceae can also contaminate surface water supplies mostly during warm summer months. The toxic component is microcystin, which gives the water a moldy, musty, grassy, or septic-tank odour.

Class: Cyanophyceae

Blue Green Algae

Cell structure


  • It is covered by a hygroscopic mucilaginous sheath which provides protection to the cell
  • The nature and consistency of the sheath is influenced by the environment
  • it protects cells from drying

Cell wall

  • A double-layered rigid cell wall is present under the sheath providing shape to the cell.
  • The inner layer is made of mucopeptide and muramic acid.
  • It consists of 4 layers (LI, LII, LIII, LIV)
  • The second (L-II) layer has mainly peptidoglycan and first (L-I) lie next to plasmalemma. The cell wall in both is composed of mucopeptide together with carbohydrates, amino acids and fatty acids.
  • The cell wall is quite similar to gram-negative bacteria

Class: Cyanophyceae

Plasma Membrane

  • The bilayer plasma- membrane is present beneath the cell wall and is called plasmalemma
  • It is selectively permeable and encloses the cytoplasm

Photosynthetic Apparatus

  • Pigments are present which are embedded within the lamella known as thylakoids (double-membrane structure)
  • They appear as elongated, flattened sacs consisting of two unit membranes
  • Adjacent thylakoids are separated from each other by a space of 50 nm, occupied by contiguous rows of discoidal phycobilisomes that transfer light energy to photosystem II reaction centers like chlorophyll b, c, d.
  • The basic subunit of a phycobilisome consists of apoproteins α and β, each of which is attached to a chromophore
  • α and β are attached to phycocyanin in the outer rods whereas the core of the phycobilisome α and β are attached to allophycocyanins
  • Phycobilins are major light-harvesting pigments present in Cyanophyceae
  • they have 4 phycobiliproteins
  1. c- phycocyanin (λmax- 620nm)
  2. allophycocyanin (λmax- 650nm)
  3. c- phycoerythrin (λmax- 565nm)
  4. phycoerythrocyanin (λmax- 568nm)
  • All cyanobacteria contain the first two pigments whereas the last occurs only in few species.

Class: Cyanophyceae

Cytoplasmic Inclusions

  • Plasma-membrane surrounds various inclusions like the cynophycian granules, Polyhedral bodies, Polyphosphate bodies, Polyglucoside bodies, Poly – beta-hydroxybutyric acid
  • Cyanophycin is consisting of a restricted number of amino acids, that is synthesized by a nonribosomal synthetase and it serves as a nitrogen reservoir.
  • Carboxysomes (polyhedral bodies) contain the carbon dioxide-fixing enzyme (RUBISCO)
  • Polyphosphate granules are synthesised for both energy and phosphate storage and are degraded to produce nucleotide triphosphate or phosphate.
  • Polyglucoside bodies – These are known to function in blasting the cell and play a role in buoyancy regulation.
  • Poly – beta-hydroxybutyric acid is biopolymer found exclusively in prokaryotes in which it acts as a storage and is also used as proplastic e.g., Spirulina and Nostoc muscorum

Gas Vacuoles

  • They are made of protein  cylinders which are hollow packets cylinders consisting of metabolic gases and function as gas vesicles
  • Gas vacuoles appear as bright, refractile areas in the cells.
  •  Cyanobacteria gas vacuoles are found most commonly in the truly planktonic forms that grow freely suspended in lakes and are responsible for buoying them to the water surface
  • This it helps cells moving upward, towards the light, where which helps in photosynthesis


  • Nucleolus and nuclear envelope are absent
  • DNA present inside the cytosol made up of lots of threadlike fibres or filaments and is in the centre of the cell


  • Cyanobacteria are highly diverse and are found almost everywhere including ponds, lakes, rivers, oceans, temperate soils, geothermal waters, desert soils, rocks, polar regions, brackish habitats and hypersaline waters.
  • The freshwater cyanobacterial species can grow from 0 °C under the ice to 26–35 °C in the tropical zone.
  • The thermophilic cyanobacteria may resist up to 45 °C or more
  • The soil is the best terrestrial cyanobacterial habitat as light, humidity, temperature; nutrient and pH are easily available for their growth.
  • Cyanobacteria are capable of independent existence in various environments but they also form a symbiotic association with an extensive variety of plants and animals e.g., with algae (diatoms), fungi (lichens), bryophytes ( Anthroceros ), pteridophytes ( Azolla fonds ) etc.

Special Cells

  1. Aknites
  2. Heterocysts
  3. Hormogonia


  • Akinetes function as an asexual resting state that is capable of resisting harsh environments
    and later can germinate to form new cells when conditions improve.
  • This consist of storage compound such as glycogen & proteins


  • These are modified vegetative cells
  • This helps in nitrogen fixation
  • It is multilayered and present outside the cell wall


  • This consists of gliding motility and many hormogonia also produce gas vacuoles which provide buoyancy to the cell

Class: Cyanophyceae


  • Cyanophyceae follows the vegetative and asexual mode of reproduction. Vegetative reproduction includes cell division, fragmentation and hormogonia formation.
  • Unicellular cynophyceae follow binary fission, while filamentous multicellular forms and colonial forms exhibit disintegrate and later mature into new individuals

Economic Importance

  • Cyanobacteria are used in photoproduction of biofuels, NH 3 scrubbing of excess atmospheric greenhouse gases including CO 2, production of various secondary metabolites, vitamins, toxins, cosmetics, dairy products, food-grade dyes and other therapeutic substances.

Hazards of blue-green algae

  • A few species of blue-green algae, such as MicrocystisAphanizomenon, and Anabaena, produce toxins capable of causing illness in humans and animals.
  • These toxins can cause gastroenteritis, neurological disorders, and possibly cancer.
  • Occasionally, the rapid increase in their production may lead to cyanobacterial blooms which lead to destruction of many marine species
  • Toxins like Cyanotoxins are produced by BGA.