Bacterie-fylum Cyanobacteria

Cyanobacteria are widespread oxygenic phototrophic bacteria found in aquatic and terrestrial ecosystems. Based on morphology, they are divided into Chroococcales, Pleurocapsales, Oscillatoriales, Nostocales, and Stigonematales.

Chroococcales, like Gloeothece, are unicellular and divide by binary fission.

Pleurocapsales such as Pleurocapsa are also unicellular but divide by multiple fission, forming colonies.

Nostocales, such as Nodularia, are filamentous, divide along a single axis, and form differentiated cells called heterocysts.

Oscillatoriales include Lyngbya species that are filamentous and non-heterocystous.

Stigonematales like Fischerella are able to divide along multiple planes, forming branching filaments.

The photosynthesis in cyanobacteria occurs in their thylakoid membranes, which are rich in photopigments and photosynthetic proteins.

Cyanobacteria are also capable of nitrogen fixation. Cyanothece species fix nitrogen only at night, whereas Trichodesmium species fix nitrogen only during the day.

These species introduce new nitrogen in oligotrophic environments of tropical and subtropical regions, aiding in ocean productivity.