Cyanobacteria are arguably the most successful group of microorganisms on Earth. Formerly called blue-green algae, they belong to a group oxygenic photosynthetic bacteria comprised of unicellular to multicellular bacteria possessing chlorophyll a and carrying out oxygenic photosynthesis. Cyanobacteria are the only known organisms capable of fixing both carbon dioxide (in the presence of light) and nitrogen. Their photosynthesis was the basis of the "oxygen revolution" that transformed Earth's atmosphere.

Cyanobacteria carry out the same type of photosynthesis that is characteristic of eukaryotic cells. They contain elaborate and highly organized internal membrane system called photosynthetic lamellae.

One of the distinguishing features of cyanobacteria is the presence of particular photosynthetic pigments: the phycocianins (blue) and the phycoerythrins (red), which do not occur in eukaryotic algae or higher plants. These pigments absorb lights at shorter wavelengths than chlorophyll and thus increase the ability of the cells to utilize solar radiation in the green-yellow region. As a consequence, the cyanobacteria can grow at low light intensity and in clear waters at considerable depths.1


Cyanobacteria may live free or form colonies. Depending on the species and growth conditions, colonies may range from flat sheets one cell thick to filaments to spherical balls of cells. Some filamentous colonies of cyanobacteria differentiate into three cell types: vegetative cells, spores, and heterocysts.

Some cyanobacteria species produce carcinogenic toxins. Most reports of acute animal and human cyanobacteria-related poisoning arise from consumption of contaminated drinking water.2

Cyanobacteria genera include:

  • Anabaena
  • Aphanizomenon
  • Cyanothece
  • Cylindrospermopsis
  • Microcystis causes deadly infection in dogs and liver cancers in humans.
  • Nodularia
  • Nostoc
  • Oscillatoria
  • Plectonema
  • Spirulina
  • Synechococcus
  • Synechocystis


  1. Oceans and human health: risks and remedies from the seas By Patrick J. Walsh
  2. Life: The Science of Biology by David Sadava, H. Craig Heller, David M. Hillis



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