cyanobacterium

noun

1. Any of very many photosynthetic prokaryotic microorganisms, of phylum Cyanobacteria.

   “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.”