General Information: UCYN-A cyanobacteria are species of nitrogen-fixing marine cyanobacteria that lack the oxygen producing photosystem II complex of the photosynthetic apparatus, the enzymes of the Calvin and tricarboxylic acid cycles, as well as several enzymes involved in amino acid synthesis. The cyanobacteria live in symbiosis with photosynthetic eukaryotic cells, specifically those of a single-celled species of algae.