Cyanobacteria produce the waste product oxygen that can be toxic to them.
Cyanobacteria are also known by the name blue-green algae. These are the photosynthetic bacteria. They are also involved in the process of nitrogen fixation. Cyanobacteria are one of the earliest organism's that emerged in the world.
Since cyanobacteria are also involved in nitrogen -fixation activity. Hence they possess the enzymes for nitrogen fixation, which are sensitive towards oxygen. In the presence of oxygen, the nitrogen-fixing enzymes get inactivated. This is the reason why oxygen proves to be toxic to cyanobacteria. However, cyanobacteria do have a mechanism to carry out nitrogen-fixation separately in the chamber called heterocyst.
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