Cyanobacteria (saɪˌænoʊbækˈtɪəriə), also known as
blue-green bacteria,
blue-green algae, and
Cyanophyta, is a
phylum of
bacteria that obtain their energy through
photosynthesis. The name "cyanobacteria" comes from the color of the bacteria (
κυανός (kyanós) = blue).
The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early
reducing atmosphere into an oxidizing one, which
dramatically changed the composition of life forms on Earth by stimulating
biodiversity and leading to the near-extinction of
oxygen-intolerant organisms. According to
endosymbiotic theory, the
chloroplasts found in
plants and
eukaryotic algae evolved from cyanobacterial ancestors via
endosymbiosis.