cyanobacterium

syanobakteeri puhekieltä Any of very many photosynthetic prokaryotic microorganisms, of phylum Cyanobacteria, once known as blue-green algae.
2003, (w), A Short History of Nearly Everything, BCA 2003, p. 262:

At some point in the first billion years of life, cyanobacteria, or blue-green algae, learned to tap into a freely available resource – the hydrogen that exists in spectacular abundance in water.

Photosynthesis was established some billion years ago by ancient bacterial precursors of modern cyanobacteria.