Summary
Photosynthetic bacteria that oxygenated Earth's atmosphere billions of years ago.
In depth
They invented oxygenic photosynthesis about 2.4 billion years ago, causing the Great Oxidation Event. Stromatolites are layered structures built by them. Some fix nitrogen in heterocysts. Chloroplasts evolved from them.
Blooms can produce toxins.
Cyanobacteria include unicellular and filamentous forms. Heterocysts protect nitrogenase. Toxic blooms in warm, nutrient-rich waters harm animals.
Example: Prochlorococcus is among the smallest and most abundant photosynthesisers.
Cyanobacteria contain chlorophyll a and phycobilins, which give the blue-green colour, and perform oxygenic photosynthesis in thylakoid membranes. Some form filaments with specialised nitrogen-fixing cells (heterocysts), and others move by gliding. Prochlorococcus is the smallest and most abundant photosynthesiser in the ocean.
The Great Oxidation Event raised oxygen levels, killing many anaerobes and enabling aerobic respiration. Chloroplasts descend from a cyanobacterium by endosymbiosis. Blooms in lakes can produce toxins (microcystin, anatoxin) and cause water problems. Spirulina is eaten as a supplement.
Example: the oldest widely accepted fossils, 3.4 to 3.5 billion year old stromatolites, are thought to have been formed by microbial mats.
Frequently asked questions
What is Cyanobacteria?
Photosynthetic bacteria that oxygenated Earth's atmosphere billions of years ago.
Which area of biology covers Cyanobacteria, and how advanced is it?
Cyanobacteria is one of the 54 topics in Microbiology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Algae, Microorganisms, Nitrogen-Fixing Bacteria.
Can you give an example of Cyanobacteria?
Spirulina is a cyanobacterium eaten as a supplement.
What should I learn before Cyanobacteria?
Work through the Beginner topics in Microbiology first, such as Microorganisms, Bacteria, Archaea, then return to Cyanobacteria. Intermediate topics assume the Beginner vocabulary.
What topics are related to Cyanobacteria?
The closest topics to Cyanobacteria are Algae, Microorganisms, Nitrogen-Fixing Bacteria, Bacteria. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Cyanobacteria?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Cyanobacteria. To practise the whole of Microbiology, use the Microbiology quiz.
How is Cyanobacteria different from Algae?
Cyanobacteria: Photosynthetic bacteria that oxygenated Earth's atmosphere billions of years ago. Algae: Photosynthetic protists and plant-like organisms that produce a large share of the world's oxygen. Read both side by side and note what each one explains.
How should I study Cyanobacteria step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Algae and explain the difference aloud. Finally, take the Microbiology quiz and come back to this page for any question you miss.